For the Record: My Telescope & Binocular Collection.

Duodecim:

Duodecim: 12″ f/5 Newtonian.

12″ f/5 Revelation Dobsonian with ultra-high reflectivity coatings on original mirrors, 23 per cent central obstruction. Used regularly.

 

Octavius:

Octavius; optimus.

8″ f/6 Skywtacher Dobsonian wth ultra-high reflectivity coatings on both mirrors. Original Skywacher primary mirror, original secondary replaced by a 44mm semi-major diameter unit from Orion Optics, UK. 22 per cent central obstruction. Now retired to garden.

 

Plotina:

Plotina: 130mm f/5 Newtonian reflector.

130mm f/5 Newtonian reflector, with ultra-high reflectivity coatings, secondary mirror replaced by a slightly smaller (26.9 per cent central obstruction) by Orion Optics UK. Most frequently used grab ‘n’ go telescope.

 

Tiberius:

Tiberius: 5″ f/12 neoclassical achromat refractor.

5″ f/12 IStar sourced neo-classical refractor with R 30 objective. Subject of much former work. Now retired to garden.

 

Gaius:

Gaius, my 80mm f/5 short tube achromat.

80mm f/5 ShortTube achromatic refractor. Skywatcher objective in Opticstar tube assembly. This is the subject telescope of a new book dedicated to the ShortTube 80.

 

The Traveler:

The AstroPhysics Traveler; 80mm f/11 doublet achromat.

80mm f/11 Astrophysics labelled achromatic refractor. Orginally donated to local school but returned to me after it was found in a sad state of neglected use. School instrument replaced by a smaller, shockproof instrument. Now seeking a new home.

 

Achromatic Binoculars:

9 x 28mm roof prism Pentax DCF LV pocket binocular (2009 vintage).

The Pentax DCF 9 x 28mm LV pocket binocular.

 

8 x 42mm Barr & Stroud Savannah roof prism  super wide angle. Most used, general purpose binocular.

The Barr & Stroud 8 x 42 wide-angle binocular

 

10 x 50mm Barr & Stroud Sierra roof prism. General purpose, astronomy binocular.

The Barr & Stroud 10 x 50 roof prism binocular.

 

Pentax PCF 20 x 60 WP II: Large porro prism instrument, used on a monopod for specialised deep sky observing/solar viewing.

Pentax 20 x 60 PCF WP II porro prism binocular.

 

Future plans: converting my two Newtonian telescopes in active use to binoviewing mode. Currently investigating options.

 

De Fideli.

The Lockyer Sequence

New year’s Day 2019: Plotina starting well on a trail first blazed by Sir Norman Lockyer(1836-1920).

On the evening of January 1 2019, I set up my 130mm f/5 Newtonian astride its Vixen Porta II mount. Conditions were cold, still, and frosty, with temperatures between 0 C and -2C. Seeing was judged to be very good (Antoniadi II).

My purpose this evening was to examine a half dozen double and multiple stars in Orion, as suggested by the distinguished Romanian observer, Mircea Pteancu, who kindly alerted me to a reference made by Norman Lockyer et al in their book, Stargazing: past and present (1878). On page 164 of that book, the authors describe a sequence of double and muliple stars in Orion, which present systems of varying degrees of difficulty for the curious telescopist. After careful collimation and adequate acclimation, the 5.1″ reflector was turned toward the Celestial Hunter, beginning at about 22:00UT and the following systems examined at magnifications ranging from 118x to 566x. The results are shown below:

The Lockyer Sequence.

 

Notes:

The times and magnifications employed are displayed beside the drawings, which depict their orientation in the Newtonian reflector. For all sketches, south is up and west is to the left.

Teasing the close companion to Zeta Orionis apart from its brilliant primary did prove quite tricky, but with a concentrated gaze during the stiller moments, it did yield to the 130mm telescope. The reader will also note the much fainter(10th magnitude) shown at the lower right of the sketch.

The most challenging proved to be 52 Orionis(1″ separation), but with its decent altitude at 22: 43UT, I was able to resolve this classic Dawes pair ( twin 6th magnitude components)  using very high powers. Intriguingly, I first attempted this system by coupling a Meade 3x Barlow lens to a 4.8mm T1 Nagler yielding 405 diameters but without much success. The image was quite dim and very difficult to see the components distinctly. As an experiment, I switched to a Meade Series 5000 5.5mm ultra-wide angle ocular, coupling it to the same 3x Barlow but I also screwed in a 1.6x Astroengineering 1.6x amplifier yielding a power of 566x. To my great surprise, I found the image of the system to be significantly brighter than with the old Nagler and it was much easier to prize the components apart. I can only suggest that the better (read more modern) coatings on the Meade 5.5mm ultra-wide angle allowed greater light throughput, despite the higher powers employed.

566x represents a power of 111x per inch of aperture.

The 130mm f/5 Newtonian continues to surprise and delight me. It’s small, high-quality optics, thermally stable (cork-lined) closed-tube design, and ease of attaining perfect collimation all contribute to its efficacy as a medium-aperture double star instrument.

I would encourage others who have similar equipment to give these beautiful systems a visit. What better way to entertain and challenge a dedicated observer on a cold winter’s evening!

 

 

De Fideli.

A Visual Extravaganza Under Dark Scottish Skies.

Looking east: sunrise over Wigtownshire.

 

The heavens proclaim the glory of God.
The skies display his craftsmanship.

                                                                              Psalm 19:1

 

Contrary to what you may have heard in the past, the British Isles offer many outstanding places to observe the heavens. Sure, we don’t have vast deserts or majestic mountain ranges that ascend for miles into the sky, but we are truly blessed with many sparsely populated regions, where the activities of human civilisation are minimal. Having lived in Scotland for more than half of my life, I have been fortunate enough to discover many fine locations that offer both very dark skies and good seeing conditions. One such region lies in Wigtownshire, in the extreme southwest of Scotland, in the district known as Dumfries & Galloway.

Not far as the crow flies from the Scottish Dark Sky Observatory, situated to the north of the Galloway Forest Park, the site offers nearly unobstructed views of the heavens from zenith to horizon in all cardinal directions. The gardens are decorated with beautiful beech and cherry trees, the leaves of which vibrantly radiate the rich colours of autumn during sunny spells. By day, there are many places to visit nearby, including the little town itself, famous for having more bookshops than any other in Scotland, as well as rugged country walkways and picturesque seaside villages that adorn the coastline all around the peninsula.

The nearby fishing village of Portpatrick on the west coast of the Rhins of Galloway.

 

During the four nights we spent there in mid-October 2018, we were fortunate enough to encounter long clear spells every night, and with a low-lying harvest Moon setting early, the skies became wonderfully dark, allowing the full glory of the northern heavens to manifest itself. Owing to its location near the sea, the skies here are regularly swept clear of particulates, which makes for exceptionally transparent conditions, ideal for astronomy.

The shores of Loch Ken, near Castle Douglas.

I took along my best travel ‘scope; a modified 130mm f/5 Newtonian, which has proven superior to a string of other, more traditional, travel ‘scopes I have enjoyed in the past, including a TeleVue 76 & 102, a classic TeleVue Genesis Fluorite F/5,  a PrimaLuceLab ED 90 and a variety of smaller Maksutovs in the 90 to 102mm aperture class. With very generous light grasp and resolution, the 5.1” Newtonian has proven to be an enormously versatile instrument for exploring the landscape by day and by night. I also brought along my recently acquired Barr & Stroud 8 x 42 roof prism binocular to soak up ultra-wide field vistas of the northern heavens that perfectly complement the more restricted field offered up by the telescope.

Plotina: the 130mm f/5 Newtonian travel ‘scope used to explore the northern heavens.

 

To get an idea of how good the skies are here, 8 members of the Pleaides are clearly visible to my average eyes once it rises to a decent altitude, as is the North American Nebula in Cygnus. In addition, a string of Messier objects in Auriga, Perseus, Cassiopeia and Pegasus are much more easily discerned visually than at home. The glory of the Milky Way, snaking its way roughly from east to west, is intensely bright here, so much so that at times I considered it a form of light pollution lol.

The patch of land where most of the observations were conducted, looking northeastward.

 

Clear skies come and go here all the time. For a few hours, they remain resolutely clear, then the clouds roll in off the Irish Sea, occluding the celestial realm for a spell before being swept away to the east. Although many calm spells occur at this site, watching the direction of smoke billowing upwards from the chimney of the cottage’s wood-burning stove, indicates that the prevailing winds are gentle and southwesterly in direction. In addition, the site is very quiet and peaceful, naturally arousing deep spritual feelings from within. In the wee small hours, only the sound of gentle breezes whistling through the trees breaks the silence.

The first night proved profitable for outreach. Although this was our third trip to the cottage, a change of ownership occurred earlier in the Summer, when a married couple with a young family underwent a home-coming of sorts, returning to the land of their youth. Their two boys instantly struck up a friendship with our lads, and so the evening started by showing them the rugged beauty of the Moon, now at first quarter phase, through the little telescope. Nearby Mars proved a little underwhelming though, as by this time it had receded greatly from the Earth in comparison to how it looked in August last, but they were still thrilled to see its little pink disk broiling in the low altitude air close to the southern horizon.

After enjoying some supper, I ventured out later in the evening when the Moon had set to show our guests, which now included the boys’ father, some of the showpieces of the deep sky with the 8 x 42 binocular and the telescope. The Andromeda Galaxy and its spooky satellite systems – M32 and M101 – made a big impression on them. For these objects I used the 25mm Celestron X-Cel LX eyepiece delivering a clean 2.3 degree true field at 26x. The dad was deeply moved with the Perseus Double Cluster, as were his sons, but I also gave them an opportunity to see M57 in Lyra and the beautiful colour-contrast double star, Albireo, well positioned high in the northwest sky in Cygnus. The owner was very surprised to learn that the telescope I had brought was quite inexpensive and seemed genuinely interested in acquiring one for himself.

The telescopic views were complemented by carefree scanning of the heavens with the 8 x 42 binocular. Showing them where to point the instrument, they gasped with sheer delight as they beheld the riot of stars centred on Alpha Persei, now high in the southeast, as well the way the binocular broke up the frothy Milky Way into myriad pinpoint stars against a coal-black sky. I don’t think the father had realised just how good the skies over his farmstead could be. I made it clear to him that he was very fortunate indeed to have such outstanding natural beauty on his doorstep!

The second day of our trip (October 16) started cloudy with some light drizzle, but as the day progressed the rain ceased and the clouds began to break up to leave a fine evening. I waited until the Moon was out of the sky before setting up the 130mm f/5 to observe M 15 in Pegasus. Having the 8 x 42 binocular hanging around my neck at all times, I was able to quickly zoom in on this fairly bright Messier object, first with the binocular, which presented the structure as a reasonably bright fuzzy star. By using averted vision, the size of M15 nearly doubled in size to more than half the size of the full Moon. Using averted vision with binoculars is a new activity for me but it certainly pays dividends! The great darkness and transparency of the air at our observing site enabled the decent light grasp of the telescope to be used productively and I was able to resolve a few dozen of its outlying stars using a 4.8mm T1 Nagler yielding 135x; a very tiny eyepiece by modern standards but a true marvel of optical engineering. Much more compact than M 13, the core of M 15 remained very bright and highly condensed, but as it floated through the huge field of view of the eyepiece with its fairly tight eye relief, I brought to mind its prodigious distance; 34,000 light years, far out in the halo of our galaxy.

From there I sped eastwards into Perseus to see how an improved sky would present the large open cluster M 34. Again, the binocular was used to locate the cluster first before centring it in the field low power (26x) field of view of the telescope. Even at 26x, the view was very impressive, with a sprinkling of 60 or so stars haphazardly strewn across a field of view roughly the same as the full Moon. The view was immeasurably improved using my trusty Parks Gold 7.5mm eyepiece (87x) which framed the entire cluster with just a little room to spare.

At 22:36UT I recorded an extraordinarily bright fireball, which was extremely long-lived, darting across the sky from north to south. At its brightest it was maybe twice the size of the full Moon and took approximately 4 seconds to fizzle out.

The 8 x 42s also made light work of tracking down the rather elusive face-on spiral galaxy, M 33 in Triangulum. At 26x in the 5.1″ the galaxy took on a ghostly cast in an interesting field of mostly 8th and 9th magnitude stars. To my eye, it looked for all the world like a planetary nebula more than a galaxy, with a slight greenish hue. Still, the extra darkness and improved transparency of the Wigtwonshire sky certainly added to the enjoyment of the view. I was particularly delighted by how well the little roof prism binocular could pick it up, as this object has a notoriously large size and low surface brightness.

With the time rapidly approaching local midnight, it was time to have a closer look at the magnificent Pleiades asterism in Taurus. For this target, the binocular proved the superior instrument, with its low power and generously wide field of view (7.33 angular degrees). Riding high in the eastern sky, it was quite simply stunning! Much of the cluster appeared to be enveiled in a fog-like nebulosity which gave it a rather life-like translucent appearance to my eye. No words come close to describiing the full glory of this extraordinary natural beauty and I spent several silent minutes just enjoying the spectacle.

I ended the vigil that evening by examining just a few double stars in the telescope. My notes from earlier years showed how good the site is for conducting high-resolution double star observing during the Summer months, but I wasn’t out to break any records. Suffice it to say that systems that have traditionally been described as ‘difficult’ in more conventional grab ‘n’ go telescopes are beautiful and easily rendered in this instrument. For example, I achieved a most excellent split of the triple system, Iota Cassiopeiae, now very high overhead, using my favourite tools in this telescope for carrying out such work; a 7.5mm Parks Gold coupled to a Meade 3x achromatic Barlow yielding 260x. The three stars were pinpoint sharp (a result of precise collimation using my Cheshire) and the subtle colour differences easily discerned to my eye. Almach (Gamma Andromedae) was gorgeous too at the same power, as was Polaris A & B and  Delta Cygni A & B.

Simply superb for tight double stars; the author’s 7.5mm  Parks Gold eyepiece coupled to a 3x Meade achromatic Barlow lens.

 

Newtonian telescopes are excellent diviners of double stars, an attribute that still appears to be lost on many contemporary amateurs. I have cultivated a theory to explain this anomaly. I suspect that many refractor enthusiasts (onlyists?), accustomed to the hassle-free observing with small refractors, never properly learn how to collimate Newtonians(it does take a while to fully learn the skill!) and, as a result, they attribute their mediocre performance in this regard to other factors and not to badly aligned optics. It’s just a hunch, but I have good reasons to believe it!

With the Moon setting later in the evening of October 17, I gave the telescope a rest and just enjoyed the 8 x 42 binocular. Up until fairly recently, I had forgotten just how wonderful it is to use such a small and lightweight instrument on its own terms. My first target was the magnificent Double Cluster (Caldwell 14) now very high in the eastern sky, as well as the less well-known open clusters surrounding it including the fairly large Stock 2(~1 degree), found by following a curvy chain of stars northwards, away from the twin clusters, and the small and compact (~10’) NGC 957. The binocular view provides a unique perspective that just can’t be replicated in even the smallest rich field telescope.

From there I sought out Kemble’s Cascade, tucked away under Perseus in neighbouring Camelopardalis. A steady hand is a great virtue when deriving the most out of this remarkable linear arrangement of mostly 8th and 9th magnitude suns. Though the cluster is well seen from my home further north, the darker and more transparent skies here made it all the more thrilling to study. For me, binoculars are almost always about hand-held instruments, but I found it beneficial to steady the view on the wooden farm gate on the grounds, where I was able to distinctly make out the small foggy patch denoting the open cluster NGC 1502, where the cascade abruptly terminates.

A little achromatic pair.

 

Though not the best season to explore M 81 and M82 in Ursa Major (they are much higher in the sky in the Spring as seen from the UK), they were very easy to locate in the 8 x 42 binocular despite the constellation’s fairly low altitude in the northern sky at this time of year.  Considerably more challenging though was M51, the famous Whirlpool Galaxy, across the border in Canes Venatici, and even lower down in the sky, which presented in the binocular as a slightly elongated fuzzy patch.

Over in the west, about 8 degrees due south of golden Albireo and on the border with Sagitta, the Coathanger (Collinder 399) asterism was also a joy to observe with the 8 x 42, albeit ‘upside down’ in comparison with the low-power view in the 5.1” reflector. The sense of unity among the stars which comprise the asterism is a pleasant illusion however, as they are actually situated at varying distances from our Solar System. Also nearby, the binocular made light work of tracking down the large planetary nebula M27, which looked like a tiny, incandescent cloudlet against a sable background sky.

Later in the evening, the large and prominent constellation Auriga, represented by a great pentagon traced out on the sky, gained altitude in the east. At its heart, the 8 x 42 presented the three open clusters M 36, M 38 and NGC 1893 very well indeed as foggy patches in a beautiful, rich field glistening with myriad, faint Milky Way stars. M 37 was easy too, just east of the pentagon. About one third of the way in a line from M38 to brilliant yellow Capella, the binocular also swept up the small and faint open cluster, NGC 1857.

As local midnight approached, Taurus had risen to a decent height and it was the ideal time to examine it with the binocular. The generous 7.33-degree field of the 8 x 42 presented the Hyades asterism in all its wondrous detail. Brilliant orange Aldebaran(not a true member however) proved to be a mesmerizing sight, as did the many binocular doubles the instrument picked up immediately to its west. Again, telescopes can’t really do justice to this asterism, as its full glory is hopelessly lost in their much smaller field of view.

As a test, I tried my hand at locating the rather elusive M1 (Crab Nebula) centred on a spot roughly 1 degree to the northwest of the bright blue-white star, Zeta Tauri. I was unable to see anything of this Messier object just hand-holding the binocular, but I believe I achieved success by steadying the view a little on the wooden fence post. Considering that M 1 is a rather lacklustre telescopic object in small and medium aperture ‘scopes, just glimpsing the tiny, roughly 6’ x 4’ smudge was considered a notable visual achievement by this author!

I ended the binocular vigil by welcoming Gemini over the eastern horizon. Though not quite visible to the naked eye owing to its very low altitude at the time of observation, my tiny 42mm ‘double achromat’ made light work of picking up the lovely telescopic open cluster, M35, at the northwestern-most foot of the constellation, together with the fainter open cluster NGC 2158 just next door. This ‘double cluster’ of sorts will look far more impressive when the constellation gains altitude in the coming months.

By half past midnight local time, and with more of the lights from the small, sleepy town nearby having been extinguished, the sky became maximally dark. “The constellations look just like they do in my observing guide!“ I wrote in my logbook.  At the zenith stood majestic Cassiopeia, and ahead of it, Cygnus, now sinking low into the west. Behind it, as if in some kind of grand procession, came Perseus, Auriga, Taurus and mighty Orion looming large in the southeast. The view was so awe-inspiring that I set my binocular aside and just sat in silent contemplation of the lightshow presented to my weary eyes. This, I thought to myself, is the view of the heavens that was accessible to the vast majority of people who ever lived. It had a singular beauty all of its own; just the way the Creator intended it!

And that’s where it all ended on the penultimate night of our stay.

After spending our last day out at Portpatrick(October 18) and a nice family dinner at Bladnoch, we returned to the cottage after dark and to rather more overcast skies. I did venture out to have a look at the waxing gibbous Moon which culminated in the south about 20:00UT when the clouds began to break up once again. Though not a dedicated lunar observer by any measure,  the telescope delivered lovely high contrast images at low and medium powers (up to about 135x). The Moon would not be setting until much later this evening however, so I set the telescope up for work that would not in the least be affected by the encroach of lunar light; double stars.

Plotina; ready for a night of casual double star observing.

 

For this work, I charged the instrument with my Parks Gold 7.5mm eyepiece coupled to a good 3x achromatic Barlow lens yielding 260x and off I went to assess how well the telescope would do this evening. After obtaining lovely splits of Delta Cygni, Iota Cassiopeiae and Epsilon 1& 2 Lyrae, I knew conditions were very good indeed; as they are in many other places in the British Isles. The 1.5″ pair, Pi Aquilae, was a little bit more suspect though, owing to its much decreased altitude in the western sky at this time of year.

A little later, I enjoyed text-book perfect images of Gamma Andromedae, its beautiful colour contrast never faiing to bring a smile to my face. The stellar images in this telescope hardly ever fail to impress. It’s a combination of perfect collimation, modest aperture, good thermal management, adequate light baffling and high-quality optics, but it also requires clear and steady skies, which are accessible to far more observers than has been reported in the recent forum literature.

Two systems in Perseus also proved profitable; Epsilon Persei, with its very faint close-in companion which, of itself, acted as an excellent test of telescopic contrast, and Eta Persei, a lovely wide open, colour contrast double, with a magnitide +3.5 orange supergiant primary and turquoise secondary shining much more feebly at magnitude +8.5.

Finally, this was the evening that I also obtained my first clean split of the tricky system, Theta Aurigae, which was perfectly resolved in the 5.1″ reflector at 260x; my first such splitting of the new season! The difficulty with such a system is the great brightness differential between the components (+2.6/ +7.5) and close angular separation, but the 5.1″ f/5 Newtonian managed it perfectly well as it has done in previous seasons.

I made a quick sketch of how it appeared in the telescope at 22:25 UT (shown below).

An old friend: Theta Aurigae.

 

Note added in proof: On the frigid evening of October 29 at 22:15 UT, in an ambient temperature of -2C, this author took advantage of excellent seeing (Ant I) to obtain his second perfect split of Theta Aurigae of the season using the 130mm f/5 reflector at 260x from his home in rural central Scotland. The Airy disks were round as buttons with a single faint Fraunhofer diffraction ring. Almach (Gamma Andromedae) was spell-bindingly beautiful and calm in the same telescope when examined just a few minutes later.

………………………………………………………………………………………………………………………………

Concluding Comments:

The intensely curious & friendly little hens on the farmstead that cannot help but entertain the visitors!

 

It was good to get away.

The weather was settled and mild throughout, with only the occasional spot of rain. All four nights proved to be good and clear for long spells and the days were filled with worthwhile family activities out and about. This is a great place to observe the preternatural beauty of the night sky, tucked away as it is far from the cities and their horrendous light pollution.

We will certainly be visiting again!

We packed up the car early next morning with the intention of getting a good head start on the road back north. Inevitably on such trips, we always leave stuff behind. Sure enough, the owner emailed us later the same evening informing us that he had found a ” telescope cover” aka my flexi dew shield, and a set of earrings belonging to my wife. The boys were not immune to absent mindedness either, as a pair of ankle socks were found inside one of their beds. He kindly offered to post the items back in the week ahead. On Wednesday, October 24, a large yellow package arrived at our home with the said items inside. I emailed him back later the same evening, thanking him for his prompt attention to this matter but also with the offer to reimburse him fully for his efforts. He replied that there was no need:

“The astronomy lesson with the boys and myself was payment enough!”

Fair is fair I suppose lol!

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Appendix: Olber’s Paradox Redux: A Brief Mathematical Treatment of the Consequences of a Dark Sky at Night.

 

In 1823, the German physician and astronomer, Heinrich Wilhelm Olbers (1758-1840) considered an interesting question; why is the night sky dark? At the time, many scientists considered the Universe to be either infinitely old or large, or both. But Olbers considered the logical consequences of this pre-supposition. In an infinite Universe, Olbers reasoned, every line of sight should eventually meet up with the surface of a star. So, the night sky should actually look like the surface of a star. Indeed, the whole sky would appear the same; uniformly bright as a consequence of an infinitely large number of stars. This interesting conundrum is known as Olbers’ Paradox.

A system of stars (or galaxies) arranged in concentric shells with the Earth at the centre.

 

Words can only go so far though, so let us consider the problem from a simple, quantitative point of view.

Suppose we start dividing up the Universe into an infinite number of concentric shells, illustrated in the sketch I’ve made above(apologies for the crudeness of the sketch, as I’m no artist lol), centred on the Earth, with each shell having a uniform thickness, dr. Thus, the volume of each shell (dV) would be the surface area of a sphere of any considered radius r multiplied by its thickness(dr);

So dV = 4πr^2dr.

Now, if there are n stars per unit volume (denoted by asterisks in my sketch), then the total number of stars, N, in each shell will be:

N = 4nπr^2dr.

It is easy to see that the number of stars per shell will scale as r^2. However, the irradiance of each star will fall inversely as r^2, which has a cancelling effect on the overall brightness of each shell and so each shell ought to be uniformly bright.

We must slightly amend the above conclusion, as each star actually has a finite size, with the result that the nearer stars will eventually occlude the light from the more distant stellar members. Still, this would not happen until the entire sky looks as though it is covered with stars. And that returns us to the original conclusion.

Nota bene: The reader will note that each star in the diagram could be replaced by a galaxy with precisely the same consequences!

Let’s now look at possible ways to reconcile Olbers’ Paradox with what we actually witness when the Sun falls out of the sky.  For example, we might consider if the absorption of distant starlight by interstellar (or intergalactic) dust might provide a means of escaping the paradox. Unfortunately, if the Universe is infinitely old, or even existing for just a very long time (say for argument several orders of magnitude older than 13.87 Gyr), then we would expect that such dust particles would have absorbed enough radiant energy to raise their temperature to the same temperature as the surface of a star. And even if it became hotter than the surface of a star, it would merely radiate the excess energy, which the stars would absorb. The consequences are the same though; the sky would look uniformly bright in all directions.

Now consider an expanding Universe, where light is redshifted. In such a case, the energy of each photon of light would decrease as a function of radius, r, so this would help attenuate the brightness of each shell considered above. What happens when we add up individual contributions from each shell? At any fixed radius, the brightness would scale as ∫dr/r, which computes as the natural logarithm of r, i.e. ln(r). But one can readily see that if we choose an arbitrarily large radius, even the quantity ln(r) can become very large indeed, so not ultimately helping us to resolve the problem.

One way out is to consider a Universe that is not infinite in extent, so we can cut off our integral at that finite radius. But there is one other way to achieve the same result, by considering a Universe that has a finite age. Let this age be denoted by t. In this scheme of events, we will only observe stars that are close enough for their light to have traversed the Universe at the speed of light, c. Thus, the radius of that Universe is simply ct. In either scheme; a finite age or finite size, there will exist a limit to the number of concentric shells that could contribute to the brightness of the sky and so the paradox can be resolved!

I find it amazing that from the simple observation that the sky is dark at night, we can arrive at a rather profound conclusion. That said, this analysis cannot, by itself, distinguish which of those scenarios, finite size or finite age (or even both), is the ultimate reason for the darkness of the night sky, but its consequences raise other philosophic/theological questions; if the Universe had a beginning, which has long remained the consensus amongst cosmologists, who or what brought it into existence?

You can’t have an uncaused cause!

To my mind, there is little doubt that the God of the Bible provides the best and most complete answer.

 

In the beginning God created the heavens and the earth.

Genesis 1:1

 

Thus says the Lord who stretches out the heavens, lays the foundation of the earth, and forms the spirit of man within him.

Zechariah 12:1

 

Neil English discusses the work of hundreds of astronomers from the annals of history in his new book, Chronicling the Golden Age of Astronomy.

 

De Fideli.

The Venerable ShortTube 80 Refractor.

The author’s versatile ShortTube 80mm f/5 achromatic telescope.

Update: January 2 2020

In my latest literary project, I’ll be dedicating my time to discussing the venerable ShortTube 80 f/5 achromatic refractor; an affordable, ubiquitous telescope that enjoys a 30 year + pedigree.

 

Now available everywhere where books are sold!

 

De Fideli.

Chronicling the Golden Age of Astronomy: A History of Visual Observing from Harriot to Moore.

 

This is an excellent book and will complement Ashbrook’s Astronomical Scrapbook and therefore have wide appeal to both amateur and professional astronomers.

Wayne Orchiston, Professor of Astrophysics, University of Southern Queensland, Australia.

 

Book Content:

Introduction & Acknowledgements

  1. Thomas Harriot, England’s First Telescopist
  2. The Legacy of Galileo
  3. The Chequered Career of Simon Marius
  4. The Era of Long Telescopes
  5. Workers of Speculum
  6. Charles Messier; the Ferret of Comets
  7. Thomas Jefferson and his Telescopic Forays
  8. The Herschel Legacy
  9. Thinking Big: The Pioneers of Parsonstown
  10. The Astronomical Adventures of William Lassell
  11. Friedrich W. Bessel: The Man who Dared to Measure
  12. W.H Smyth: The Admirable Admiral
  13. The Stellar Contributions of Wilhelm von Struve
  14. The Eagle-Eyed Reverend William Rutter Dawes
  15. The Telescopes of the Reverend Thomas William Webb
  16. The Astronomical Adventures of the Artistic Nathaniel Everett Green
  17. Edward Emerson Barnard, the Early Years
  18. William F. Denning; a Biographical Sketch
  19. A Modern Commentary on W.F. Denning’s “Telescopic Work for Starlight Evenings (1891)”
  20. The Astronomical Legacy of Asaph Hall
  21. The Life and Work of Charles Grover(1842-1921)
  22. Angelo Secchi; Father of Modern Astrophysics
  23. John Birmingham, T.H.E.C Espin and the Search for Red Stars
  24. A Historic Clark Receives a New Lease of Life
  25. A Short Commentary on Percival Lowell’s “Mars as the Abode of Life”
  26. The Great Meudon Refractor
  27. A Short Commentary of R.G. Aitken’s “The Binary Stars”
  28. S.W. Burnham; a Life Behind the Eyepiece
  29. Voyage to the Panets: The Astronomical Forays of Arthur Stanley Williams( 1861-1938)
  30. Explorer of the Planets: The Contributions of the Reverend T.E.R. Philips
  31. Highlights from the Life of Leslie C. Peltier
  32. Clyde W. Tombaugh; Discoverer of Pluto
  33. A Short Commentary on Walter Scott Houston’s “Deep Sky Wonders”
  34. A Short Commentary on David H. Levy’s  “The Quest for Comets”
  35. George Alcock and the Historic Ross Refractor
  36. What Happened to Robert Burnham Junior?
  37. The Impact of Mount Wilson’s 60-inch Reflector.
  38. Seeing Saturnian Spots
  39. John Dobson and His Revolution
  40. The Telescopes of Sir Patrick Moore (1923-2012)
  41. A Gift of a Telescope: The Japan 400 Project

Appendix:

Achievements of the Classical Refractor: A Timeline

Index

 

Available now for pre-order!

 

Thankyou for waiting!

 

De Fideli.

5-inch Shootout: 5″ f/12 Refractor vs a 5.1″ f/5 Reflector

Battle o’ the 5-inchers. Tiberius (laevo); a 127mm f/12 achromatic refractor versus Plotina; a 130mm f/5 Newtonian reflector.

 

Introduction: Many telescope reviews conducted on forums or in magazines only assess a single instrument, namely the one under consideration, entirely on its own terms. But while such informaton can be useful, particularly if a fault is discovered, it can be somewhat misleading if no other instruments are compared with it. Take for example, a top drawer 60mm refractor, which produces excellent images within the remit of its aperture, but when it’s compared to a slightly larger telescope of average quality, it begins to show its limitations and the tester gains a much more balanced view of its strengths and weaknesses.

I find myself thinking this way when evlauating all the telescopes that pass through these parts. Such tests are very important and completely warranted. For example, I was once very much enamoured by an expensive 4-inch F/5 Televue Genesis fluorite refractor but quickly fell out of love with it once I compared it to an even more expensive Televue 102 apochromat. In turn, the latter telescope was found to be slightly inferior to a SkyWatcher ED 100 f/9 refractor costing far less than either of the Televue refractors, which left a very bad taste in my mouth, making me deeply suspicious of the claims proferred by those who market so-called ‘premium’ telescopes, as well as the forum fanboys who apparently cannot see beyond them.

But sometimes it pays dividends to compare good telescopes from different genres too, such as my discovery that an 8-inch f/6 Dobsonian proved superior to a 7-inch f/15 Maksutov Cassegrain, even though the former was less expensive. Clearly, you don’t always get what you pay for! You need to find the truth for yourself.

In this capacity, I decided to compare and contrast the capabilities of two very different telescopes of similar aperture; a 127mm f/12 achromatic refractor and a 130mm f/5 Newtonian reflector costing many times less.  I have described the capabilities of this refractor in many previous blogs (now archived by the author). I have retained it as an excellent example of a historically important class of telescope that allowed amateur and professional astronomers to make great strides in understanding the Universe around them and which continues to provide excellent insights into their considerable capabilities. Interested readers will find a veritable treasure trove of classical achromat ‘culture’ in the author’s up-and-coming book, Chronicling the Golden Age of Astronomy, due out in late 2018.

But having said all of this, the Newtonian reflector has been terribly neglected by a generation of amateurs that seem to know the price of everything and the value of nothing. Unwilling to take their cue from the professional community, who have long left the refracting telescope behind in favour of the enormous advantages offered by modern reflective optics, they continue to disseminate misleading or downright false information to unsuspecting newcomers to the hobby, who are subsequently led astray in such a way that their progress as observers becomes severely stunted. That’s why it’s important to continue to question received opinion. If we stop questioning, we quickly become part of the herd culture that so typifies contemperary amateur astronomy.

The instruments compared: The refracting telescope is a high-quality neo-classical instrument (doublet objective) with an aperture of 127mm and focal length of 1524mm (so f/12). The optical tube assembly is about 1.8m long and weighs in at 40 pounds. It sports a fully multi-coated object glass which passes virtually all the light that passes through it. It has a state-of-the art,  dual speed Moonlite focuser, which is fully rotatable and extremely robust.

The beautiful objective lens on the Istar Asteria 127mm f/12 refractor..

 

The wonderful two-speed Moonlite focuser on the Istar refractor.

Such a bulky instrument requires a substantial mount and even when provision is made for its mounting (with its various counterweights)  it can prove very awkward to use in the field, particularly when the instrument is pointed high in the sky.

The Newtonian, in contrast, even with its dovetail plate and finder attached, is featherweight in comparison. Both primary and secondary mirrors possess quality, high-reflectvity coatings, reflecting 97 of the light incident upon them and with a small 27 per cent central obstruction with its upgraded optical flat, it loses very little light to deliver tack-sharp, colour free images with high contrast. It’s focuser, however, is of the simple, single speed, rack & pinion variety. It needs to be accurately collimated for such testing but this requires just a minute of one’s time to attain perfect results.

The innards of the 130mm F/5 Newtonian reflector.

The simple rack & pinion focuser on the 130mm Newtonian.

 

Test 1: Comparison of the high magnification images in daylight; conducted August 21 2018.

Both telescopes were set up on their mounts (the reflector was mounted on a simple Vixen Porta II alt-azimuth) during a warm, overcast day and the instruments charged with a high magnification (~ 50x per inch). The refractor delivered a power of 277x, while the reflector yielded a magnification of 283x. Both telescopes were aimed at the topmost bough of a Horse Chestnut tree some 80 yards distant and the instruments carefully focused.

Results: Both instruments served up sharp, detailed images of the well-developed foliage. The Newtonian was much harder to focus accurately owing to its fast f ratio(5), in comparison to the refractor (f/12). They were very comparable in terms of image brightness but the reflector showed a consistently better image. It was a shade sharper and completely devoid of chromatic aberration (CA). The refractor did show some CA in comparison, which manifested a faint chromatic fog, lowering image contrast and sharpness.

I called two other visual testers to the telescope; my wife and a next-door neighbour. Teaching them how to focus the telescopes finely, I let them examine the images in both telescopes for a few minutes, eventually enquiring of them which instrument delivered the better high power daylight views.

Their verdict was the same as my own, namely, that the reflector delivered the better image of the tree-top foliage.

Comments: It might have been anticipated that the refractor would offer the brighter image, but CA takes some of the unfocused light and spreads it around the field, slightly lowering the overall brightness of the focused image, especially at these very high magnifications.

Test 2: Double Star Performance: August 22 2018

Tiberius (laevo) et Plotina; fratrem certamen accendebant.

Wide field performance tests aborted until the Moon was out of the sky. Some double stars were critically examined instead.

Conditions: Brisk southwesterly winds, partially clear, visibility rather poor except near zenith. Temperature + 10C, rather cooler than of late.

Both telescopes were set out to cool from the late evening (19:00 UT) onwards, so completely acclimated to their environments.

4 systems examined at high powers (260x  and 277x on the 130mm f/5 and 127mm f/12, respectively):

Epsilon Lyrae 1 & 2

Delta Cygni

Pi Aquilae

Mu Cygni

Results: Only a brief observing spell possible with by telescopes this evening between 21:00  and 21:25UT as low cloud moved in and made the sky increasingly difficult to navigate. By 22:00 it had all but competely clouded over again.

Both telescopes resolved all four systems well at the powers mentioned above. The breezy conditions and the high altitude of three of the test systems made it very challenging to observe in the refractor owing to its long tube and positioning of the eyepiece very near the ground (a Televue 2-inch EverBrite dielectric diagonal being employed to make observations easier). The same systems proved far more comfortable to observe in the Newtonian, for obvious reasons. The long refractor really needs a massive equatorial mount to do it justice; something I am not interested in pursuing.

The refractor definitely pulled ahead though in terms of ease of focus of the subjects (at f/12 you’d expect that), while using the reflector with its simple rack & pinion focus and f/5 relative aperture was always much more challenging. Indeed, I had forgotten the considerable advantages the classical refractor has over faster systems in this regard. The refractor images showed little in the way of diffraction artifacts, the stellar Airy disks being very tight and round as buttons. Contrast was a tad better in the unobstructed refractor and the images were marginally more stable as judged by their reduced tendency to morph out of perfect focus as they moved across the field. That said, I was very pleased at how well the reflector held its own; the more prominent diffraction rings having no discernible effects on the resolution of these point sources. And while contrast was a shade better in the refractor, I did not judge it superior enough to warrant a discontinuation of my double star adventures with the 130mm Newtonian. Its wonderful comfort is a huge virtue in this regard.

Comments: The CA described in the daylight tests had no effect on the resolution of these test doubles (an observation well borne out by an enormous body of historical literature), although their colours were slightly distorted (yellowed) compared with the Newtonian(which by nature always delivers true colour images). Indeed, the secondary spectrum was only slightly apparent on Delta Cygni A, being quite a bright star. What is more, I felt it added slightly to the aesthetic appeal of the refractor image over the reflector, but this is a completely subjective judgement.

Test 3: Deep Sky Capability: September 6 2018.

The sloth discovers heehaw….ken.

 

Although the last three nights have been excellent for deep sky observing, I decided to leave this test until the evening of September 6 2018, to make sure no moonlight interfered with the observations. Still, the effort was very rewarding and insightful. As you can imagine, these instruments are very different beasts in regard to their demands on eyepieces. At f/12 even cheap wide angle oculars behave like champs from the centre to the edge of the field and this means that one does not need to splash out relatively large sums of money for well corrected deep sky views using heavy 2-inch oculars. The maximum true field that can be achieved with this refractor from my eyepiece arsenal is 1.79 angular degrees, power 38x. In contrast, the much faster f/5 optical system in the Newtonian requires better eyepieces that can correct for the significant off axis aberrations including coma, astigmatism and field curvature etc. But it is able to deliver a considerably larger true field than the refractor (2.3 degrees with a Celestron X-Cel LX 25mm and 2.5 degrees with a standard 32mm Plossl, though with inferior correction towards the edge of the field).

The closest match I could make to the 38x of the refractor was to couple a 1.6x Barlow to the Celestron X-Cel LX 25mm yielding a 1.44 degree true field and a power of 42x.

Low power, wide-field oculars used in the tests; a 40mm ES Maxvision and a 25mm Celestron X-Cel LX coupled to a 1.6x Barlow. The oculars yield 38x and 42x in the 5″ f/12 glass and 130mm f/5 Newtonian, respectively.

 

For higher power, deep sky comparisons, I employed a 11mm ES 82 ocular in the f/12 refractor and a 4.8mm T1 Nagler (also 82 degree AFOV) in the 130mm reflector, delivering very comparable powers of 139x and 135x, respectively.

The 4.8mm T1 Televue Nagler ( left) and the 11mm Explore Scientific 82 degree ocular delivering 135x and 139x in the Newtonian and refractor, respectively.

 

Results: Just two targets were examined: M13 in Hercules and The Double Cluster in Perseus. In the low power setting, the refractor offered a slightly punchier image of M13, with slightly greater contrast (darker sky background) than the reflector. The faintest stars in the field were just a tad easier to discern in the big glass than in the Newtonian, but otherwise they were very comparable. At high powers, the results were broadly the same; with the nod going to the refractor, but I was very impressed at how well the little reflector did. If I were to quantify the difference I’d estimate that the 5″ f/12 delivered maybe a 5 to 10% improvement over the reflector on this remote target.

Turning next to the Double Cluster, I returned to lower power. Going back and forth between the images, the views were more comparable than they were different. Contrast was a little better in the refractor, with beautiful pinpoint stars strewn all across the field. The reflector gave almost the same results, with slightly less contrast and colour saturation. The refractor did however pull significantly further ahead at the edge of the field with tighter, better corrected stars, quite in keeping with its f/12 native focal ratio.

Conclusions: This series of tests, comparing two very different instruments of broadly similar aperture is almost never done by amateur astronomers. Doubtless, part of the reason for this is that no one wants to be told that a very expensive refractor could be rivalled by a far less expensive reflector on the same targets. And yet, apart from the clear superiority of the reflector during daylight use, this is very much the conclusion I was forced to draw; the views are very comparable. I believe the results are attributed to the superior coatings on the mirrors which collect very similar amounts of light as well as the relatively small central obstruction in the reflector which tends to keep image contrast high. Had the Newtonian possessed standard coatings, I believe I would have reported a larger difference in their performance on deep sky objects. This, together with very close attention to attaining perfect collimation in the Newtonian readily explains why it performed so well  in comparison with the refractor on high resolution point sources, such as double and multiple stars. At the very high powers employed in test 2, the coma free field is much reduced in the reflector, allowing good images to be maintained from the centre of the field to its periphery.

But in all such comparisons, it pays to also consider the comfort factor; that is, how easy the instruments are to transport, mount and manoeuvre in field use. This is where the Newtonian rocks in comparison to the refractor. It is quite simply a joy to use; no hunching behind an eyepiece very low to the ground, no need to re-balance the telescope when it’s pointed to targets of greatly different altitude etc. The small advantages the refractor has over the reflector pale into insignificance when these considerations are accommodated.

Newtonians have clearly come a long way; with modern high reflectivity coatings, quality primary and secondary mirrors and careful attention to collimation and cooling, they compete very favourably with refractors, at a fraction of the cost. I hope you can appreciate why I almost always reach for the little 130mm reflector in comparsion to the refractor. Granted, the latter may look more majestic in the cold light of day, but all this is quickly forgotten under a clear, dark country sky.

 

 

Neil English explores four centuries of telescopic astronomy in his ambitious new work (660 pages), Chronicling the Golden Age of Astronomy, due out in October 2018.

 

 

De Fideli.

Living without Lasers

Collimation tools; from left right: a SkyWatcher Next Generation laser collimator, a collimation cap, a well made Cheshire eyepiece and a Baader lasercolli Mark III.

 

It is undoubtedly true that by far the most prevalent reason why so many amateurs have dissed Newtonian reflectors in the past boils down to poorly collimated ‘scopes which lead to less than inspiring images. The amateur who pays close attention to accurate collimation will however discover the solid virtues of these marvellous telescopes and will soon forget the bad experiences of the past.

I’ve noticed a trend over the last few decades, where more and more amateurs have become lazy and impatient. They want instant gratification. This is one of the main reasons why many have turned to hassle-free instruments such as small refractors and Maksutov Cassegrains. It’s an entirely understandable trend, but in other ways it is lamentable. One of the downsides of this trend is that amateurs have become less concerned with learning practical optics, deferring instead to higher tech ways of obtaining optimal results in the field. One such technology is the laser collimator; a very useful device that has made accurate collimation far less of a chore than it was just a few decades ago. But while many have defaulted to using such tools as labour-saving devices, they have, at best, become less familiar, or at worst, all but forgotten the traditional tools used in the alignment of  telescope optics; tools such as the collimation cap and the Cheshire eyepiece, and in so doing have less and less understanding of how their telescopes actually work.

The desire for super-accurate collimation has undoutedly been fuelled by the advent of faster optical systems; often supporting sub-f/5 primaries. Once, the traditional Newtonian was almost invariably made with higher f ratios:- F/7 to f/10 and beyond, and requiring very little in the way of maintenance. This is abundantly evidenced by the scant attention astronomy authors of the past gave to such pursuits. In contrast, modern Newtonians are usually f/6 or faster, necessitating much greater attention to accurate optical collimation if excellent results are to be consistently attained during field use.

In my chosen passtime of double star observing, I have acknowledged the need for accurate collimation. Such work often requires very high magnifications; up to and in excess of 50x per inch of aperture, to prize apart close double stars, some of which are below 1 arc second in angular separation. At such high powers, sub-standard collimation results in distorted images of stellar Airy disks, and that’s something that I’m not willing to put up with. In this capacity, I have tested a number of collimaton techniques using a few different laser collimating devices but have also spent quite a lot of time comparing such methods to more traditional techniques involviing the tried and trusted collimation cap and Cheshire eyepiece.

To begin with, it is important to stress that the methods covered in this blog can be achieved easily with a little practice, and I will gladly defer to recognised authorities in the art of Newtonian collimation, such as the late Nils Olif Carlin and Gary Seronik, who have done much to dispel the potentially stressful aspects of telescope collimation. Nothing I will reveal here goes beyond or challenges anything they have already said. My goal is to reassure amateurs that one can happily live without lasers, especially if your Netwonians are of the f/5 or f/6 variety.

Many of the entry-level laser collimators often manifest some issues; partcularly if they are not collimated prior to use. Thankfully, the inexpensive SkyWatcher Next Generation that I have used for a few years did come reasonably well collimated, but others have not been so fortunate. One easy way to see if your laser collimator needs collimating is to place it in the focuser of the telescope and rotate it, examining the behaviour of the beam on the primary. If the beam does not stay in place, but traces out a large annulus, you will have issues and will need to properly collimate the laser. This is not particularly difficult to do and many resources are available on line to help you grapple with this problem. See here and here, for examples.

Of course, you can pay extra for better made laser collimators that are precisely collimated at the factory. Units that have received very good feedback from customers include systems manufactured by Hotech, AstroSystems and Howie Glatter. Some of these are quite expensive in relative terms but many amateurs are willing to shell out for them because they deliver consistently good results. My own journey took me in a different direction though. Instead of investing in a top-class laser collimator, I re-discovered the virtues of traditional techniques involving the collimation cap and Cheshire eyepiece.

My personal motivation to return to traditional, low-tech tools was stoked more from a desire to understand Newtonian telescopes more than anything else. Any ole eejit can use a laser collimator but it deprives you of attaining a deep understanding of how Newtonians operate. In addition, I have frequently found myself dismantling whole ‘scopes in order to get at the mirrors to give them a good clean and this meant I had to learn how to put them back together from scratch. The simpe collimation cap has been found to be an indispensable tool in this regard, allowing one to rapidly centre the secondary mirror in the shadow of the primary.

Singing the virtues of simple tools, such as the tried and trsuted collimation cap.

 

Using just this tool, I’ve been able to set up all my Newtonians rapidly to achieve good results from the get go, at both low amd medium powers more or less routinely.

For the highest power applications  more accuracy is required and I have personally found that a quality Cheshire eyepiece to be more than sufficient to accurately align the optics in just a few minutes. Not all Cheshires are created equal though; some are less accurate than others. For my own use, I have settled on a beautifully machined product marketed by First Light Optics here in the UK ( be sure to check out the reviews while you’re at it). For the modest cost of £37, I have acquired a precision tool to take the hassle out of fine adjustment. The unit features a long sight tube with precisely fitted cross hairs that are accurately aligned with the peep hole. It needs no batteries and comes with no instructions but with a little practice, it works brilliantly!

The beautifully machined and adonised Cheshire eyepiece by First Light Optics, UK.

A nicely finished peep hole.

The precisely positioned cross hairs on the under side of the Cheshire.

 

Because all of my Newtonians are of the closed-tube variety, they are robust enough to only require very slight tweaks to the collimation. I would estimate that 80 per cent of the time, it is only the primary mirror that requires adjusting in field use. I have found this overview by AstroBaby to be very useful in regard to using the Cheshire and would recommend it to others.

The Cheshire eyepiece is a joy to use when collimating my 130mm f/5. Because the tube is short, I can access both the primary and secondary Bob’s Knobs screws to whip the whole system into alignment faster than with my laser. With my longer instruments; partcularly my 8″ f/6 and 12″ f/5, collimation using the Cheshire is decidely more challenging as they both have longer tubes. That said, by familiarising one’s self with the directions of motion executed with the three knobs on the primary, one can very quickly achieve precise collimation. One useful tip is to number the knobs individually so that you can dispense with the guesswork of which knob to reach for to get the requisite adjustment. At dusk, with the telescopes sitting pretty in their lazy suzan cradles, and with the Chesire eyepiece in place in the focuser, I swing the instrument back and forth to alternately view the position of the primary in the eyepiece and the knob(s) I need to turn. Doing this, I get perfect results in just a few minutes; a little longer than can be achieved with a laser, admittedly, but not long enough to render the process exhausting or boring. It’s time well spent.

Know thy Knobs: by spending some time getting to know which directions each of the collimation knobs move the primary mirror, it makes collimation with a Cheshire eyepiece hassle free.

The proof the pudding, of course, is in the eating, and in this capacity, I have found the Cheshire to achieve very accurate results each time, every time. Indeed, it has made my laser collimator blush on more than a few occasions, where high power star tests and images of close double stars reveal that the laser was out a little, requiring a collimation tweak under the stars. Indeed, the Chesire is so accurate that it has become my reference method to assess the efficacy of all the laser collimators I’ve had the pleasure of testing.

While I fully acknowledge the utility of good laser collimators, I get much more of a kick out of seeing, with my own eyes, how all the optical components of the Newtonian fall into place using the Cheshire. Furthermore, the fact that it requires no batteries (and so no issues with the unit failing in the field for lack of power, as has happened to me on more than a few occasions), deeply appeals to my longing for low-tech simplicity in all things astronomical. The fact that the aforementioned amateurs also recommend the Cheshire as an accurate tool for collimating a Newtonian makes it all the more appealing.

Having said all this, the utility of a Cheshire eyepiece lessens as the f ratio of your telescope gets smaller, so much so that for f/4 ‘scopes ar faster, the laser technique will, almost certainly, yield more accurate results. But that’s OK. We are blessed in this day and age with many good tools that can make Newtonian optics shine!

 

Note added in proof: August 14 2018

A really good laser collimator: the Hotech SCA, which can be used with both 1.25″ and 2″ focusers and comes in a very attractive little box with straightforward instructions on how to use it. You will still need the collimation cap to centre the secondary though.

 

If you do decide that you don’t like using a good Chesire eyepiece for precise collimation of your Newtonian reflectors, then I would highly recommend the Hotech SCA laser collimator. It’s an ingenious device (but costs significantly more than a regular laser collimator), but in this case you really do get what you pay for. I have tested the device on all three of my Newtonians and it gives accurate and reproducible results that agree perfectly with the Chesire. It yields perfect star tests at appropriately high powers (I’d recommend a magnification roughly equal to the diameter of your mirror in millimetres for such field tests) both in focus and defocused. I’d go for it if you can afford it. You will still need the collimation cap to centre the secondary before use however. See here and here for more details.

Neil English is author of Choosing and Using a Dobsonian Telescope.

 

 

De Fideli.

Focusing on Focusers.

How to adapt the Skywatcher 200P focuser to attain better collimation, as well as easier inter-change between 1.25″ and 2″ eyepieces.

 

Newtonians are tinkerers’ telescopes; they appeal to amateurs who want to learn about optics and above all other designs, they respond well to a bit of TLC. Such is the case with my modified Skywatcher 8″ f/6 Newtonian, which I have steadily improved over the last few years to transform it into my dream telescope; a modest instrument that can do all things well, from ultra-high power double star observing, through lunar and planetary studies and onwards into wide-field, deep sky observing. If I had to own only one telescope from all the varieties that now exist, I’d choose this one in a heartbeat.

The best way to improve a telescope is to spend as much time with it in the field. How else can one even begin to understand whether or not an alteration is warranted?  In this capacity, I have clocked up hundreds of hours under the starry heaven inter-changing two inch, long focal length eyepieces for their shorter focal length counterparts, which are invariably in the 1.25″ format. But doing this in the usual way is frankly a bit of a chore. On my telescope, one has to remove the 1.25″ focuser housing, insert a two inch tube adaptor and then plonk in the big 2″ eyepiece. As you can imagine, this can get a bit fiddly on a dark night and cause needless interruptions to one’s observing schedule. Can this interchange be speeded up? Thankfully, the answer is yes!

The standard 1.25″ eyepiece adaptor that comes with every Skywatcher 200P Dob.

 

The first thing I did was to remove the standard 1.25″ eyepiece adaptor that comes with the telescope and replace it with an inexpensive 35mm extension tube, such as the one featured in the first image of this blog.

Next, I inserted an old Orion precision centring adapter into the 35mm extension tube, as illustrated below:

A very useful adapter: the Orion precision Centering Adapter seen inserted onto the top of the 35mm extension tube.

 

The precision centring adapter features a helical tightening mechanism that precisely centres any 1.25″ eyepiece in the focuser draw tube. This has immediate benefits to attaining ultra-precise collimation, as it removes the remaining wiggle room that would normally attend the insertion of a laser collimator in the standard 1.25″ eyepiece adapter.

Using the precision centring adapter improves the accuracy of collimation using a laser collimator or Cheshire eyepiece.

 

Once collimated, one can insert a 1.25″ eyepiece as shown below:

The centring adapter keeps 1.25″ oculars snug and precisely centred in the focuser drawtube.

 

To use 2″ eyepieces all one needs do is remove the centring adaptor, and insert the eyepiece into the 35mm extension tube as shown below:

Removing the centring tool is child’s play and allows for rapid interchnage with a 2″ ocular.

 

Testing this new system out during the day, I can report that it allows all my eyepieces; orthoscopics, Plossls, super-wide, ultra-wide angles and even Kellners to reach sharp and precise focus at infinity, as well as targets located as close as approximately 50 yards in the distance. It greatly facilitates the inter-change between 1.25″ oculars and their 2″ counterparts in the field because it always has the 2″ eyepiece adapter in the focuser drawtube. No more fumbling about in the dark.

So, if you’ve got these adapters lying about in your ole box of tricks, I’d encourage you to give it a go. It can only serve to increase your enjoyment of a very fine telescope. You know it’s worth it!

Octavius: working more efficiently for its master.

 

Note added in proof (August 2 2018):  I’ve managed to get out on a few nights before the weather turned and test the new configuration on both my 8″ f/6 and 12″ f/5 instruments (both of which are endowed with 2-inch focusers) under rapidly darkening skies. I can report that the alteration was definitely worthwhile!. The centring adapter is very easy to remove or insert at will, allowing me to go from wide-field scanning at low power, using heavy, 2-inch eyepieces covering a couple of angular degrees of sky or more, and then zoom in at inceasingly high powers, sometimes much beyond 50x per inch of aperture, to look at high resolution stuff.

All in a jiffy!

One downside noted: some(but not all) Barlowed oculars can’t come to focus with this modus operandi.

No’ bad ken.

Neil English is author of Choosing and Using a Dobsonian Telescope.

 

De Fideli.

 

Observing in Twilight.

A great ‘scope to use in twilight; the author’s 130mm f/5 Newtonian which combines light weight with good optical power.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

At my northerly latitude (56 degrees north) every year from about the middle of May to the first week in August, the sky fails to get properly dark and twilight dominates the northern horizon. As a result, the glory of the summer night sky greatly diminishes, with only the brightest luminaries being visible to the naked eye. But despite these setbacks, one can still enjoy a great deal of observing. In this article, I wish to outline some of the activities I get up to during this season.

Observing in twilight makes observing faint deep sky objects very difficult, so my attention is drawn to the Moon, brighter stars and the planets. Although a telescope of any size can be used during twilight observing, I find it most productive to field a telescope that has decent aperture and so I generally reach for my larger telescopes. Arguably my most used instrument during these times is a simple 130mm f/5 Newtonian, which offers good light grasp and resolution but I am also very much at home with my larger 8 and 12 inch reflectors for more specialised work. The 130mm has the advantage of being light and ultraportable and so I can move the instrument around to get better views of low lying targets.

The bright planets are very accessible during twilight and I find it fun to observe them with a variety of instruments. Venus is generally uninspiring, showing only an intensely white partial disk, but I find Jupiter much more exciting owing to its constantly changing atmospheric features and satellite configurations. But because of its low altitude in my sky, I employ colour filters to bring out the most details on the planetary disk. This is where larger apertures have their advantages, as some filters can absorb a significant amount of light and dim the images too much. The sketch below was made during twilight using my 130mm f/5 and a Tele Vue Bandmate planetary filter, power 108x, which imparts a lively colour tone to the planet, enhancing the colour differences between the dark belts and light zones. It’s also an ideal filter for enhancing the visibility of the Great Red Spot(GRS).

Jupiter as observed durng twilight at 22:55 to 23:05 UT on the evening of May 28 2018 using a 130mm f/5 Newtonian, magnification 108x and a Televue BPL filter.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Twilight nights are also excellent for double star work and summer often brings prolonged periods of excellent seeing at my location. Larger apertures allow higher magnifications to be pressed into service, which also helps to darken the sky making the views more aesthetically pleasing. As in all other aspects of amateur astronomy, you can be as ambitious as you want. The most demanding systems are difficult, sub arc second pairs. As a case in point, I recently trained my 8 inch f/6 Newtonian on 78 Ursae Majoris (78UMa), conveniently located near the bright star, Alioth, in the handle of the Ploughshare. Conditions were near ideal on this evening (details provided in the sketch below) and I was able to push the magnification to 600x to splice the very faint and tight secondary star from the brighter primary.

The sub arc second pair 78 Ursae Majoris 78 as seen in twilight on the morning of May 30 2018 at 23:20UT using an 8″ f/6 Newtonian reflector (no fan).

Another system that I like to re–visit in summer twilight is Lambda Cygni (0.9″), which is easier to resolve than 78UMa, as the components are more closely matched in terms of their brightness and are slightly farther apart. Because it rises very high in my summer sky, it is ideally placed for high magnification work.

Conducting sub–arcsecond work with an undriven Dob mount is certainly not for the faint hearted but does bring its unique challenges, and I for one get a buzz out of doing this kind of work. But there are many easy and visually stunning systems that can be enjoyed at lower powers and it is to some of these that I will turn my attention to in the coming nights.

Last night (the early hours of June 2 2018) my wonderful little 130mm f/5 Newtonian was used to visit a number of easy to find and visually engaging binary and multiple star systems. During warm, settled weather, and with high pressure in charge, the twilight conditions proved near ideal for studying these fascinating objects;

Some binary systems visited in twilight using a 5.1″ f/5 Newtonian.

 

 

 

 

The celebrated Double Double in Lyra as seen through the 5.1 inch reflector at 260x.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The very fetching Epsilon Bootis as seen in the 130mm f/5 Newtonian at 260x.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

These observations were conducted between 23:00UT and 00:00 UT.

Indeed, of all my Newtonians, it is the 130mm f/5 that provides the most aesthetically pleasing views of double stars. Colours are always faithful and images are invariably calm owing to its moderate aperture and rapid acclimation. Contrast is excellent too. It just delivers time after time after time…..

The sky as experienced 15 minutes before local midnight on the evening of June 12 2018.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As May turns to June, the twilight becomes ever brighter, with more and more stars becoming invisible to the naked eye. But this greater sky brightness should never deter a determined observer. On the evening of June 12 2018, I set about visiting a score of  double and multiple stars with my 130mm f/5 Newtonian, as is my custom. I turned the telescope toward Polaris at 22:45 UT  and was deligted to be able to pick up the faint 8th magnitude companion to the 2nd magnitude Cepheid primary. Looking for something more challenging, I waited another half an hour to allow the sky to darken maximally but also to allow a summer favourite to gain a little altitude but still several hours away from culmination in the south. I speak of that wonderful binary system, Pi Aquilae( Aql), a pair of yellow white stars of near equal brightness and separated by about 1.5 seconds of arc.

From extensive, previous experience, I know it is possible to split this pair in smaller telescopes than the 5.1 inch reflector, particularly a suite of refractors ranging in aperture from 80mm to 102mm. But under these June conditions, the advantages of decent aperture become readily apparent; smaller telescopes simpy run out of light too quickly when the high powers needed to splice this pair are pressed into action. Locating the 6th magnitude pair at a fairly low altitude under bright June twilight  is even a challenge for the 6 x 30mm finder astride the main instrument. To my delight though, I was able to track it down and once centred, I cranked up the power to 325x ( using a 2mm Vixen HR ocular) to obtain a marvellous view of this close binary system, the components aligned roughly east to west with clear dark space between them. Adopting these powers with smaller apertures is problematical to say the least. Why strain one’s eyes when one can view it in much greater comfort using the generous aperture of this trusty 130mm grab ‘n’ go ‘scope?

I made sketeches of both Polaris A & B and Pi Aql as I recorded them at the eyepiece (see below).

Polaris A & B and the tricky, near equal magnitude pair, Pi Aql, as seen in the 130mm f/5 Newtonian reflector on the evening of June 12 2018.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As the June solstice approaches, the twilight continues to brghten the sky, but there’s still lots to see. Beginning about 10pm local time, I began observing a pretty crescent Moon sinking into the western sky. The instrument I chose this evening was a very inexpensive but optically excellent 76mm f/9.3 Newtonian reflector, which I described at length in previous blogs such as this one. Because our natural satellite is so big and bright, a small telescope like this one is ideal for casual observing. Because the sky is still quite bright at this time, I found it helpful to employ either a neutral density or variable polarising filter to increase the contrast between the lunar regolith and the background sky.

An amazing performer in June twilight: the Orion Space Probe 3 altazimuth reflector.

Observing the Moon in June twilight is fun at all magnifications, but I have discovered this little telescope can provide razor sharp images up to about 210x. You’ll not get this information from the telescope forums though; it still seems beneath them to test it and spread the word, but I digress!

On the evening of June 18 2018, I visited a suite of summer double and multiple stars with the same instrument.

At about 11.30pm local time, the sky was dark enough to track down some pretty tight double stars, as well as a variety of easier but just as comely systems. Conditions were good enough for the little Spaceprobe reflector to nicely resolve Epsilon Bootis, Epsilon 1 & 2 Lyrae and Delta Cygni (210x in each case). My study of the Lyra Double Double in particular with this telescope shows that it is significantly better than any 60mm refractor in terms of raw resolving power. As I have reported earlier this year, the same telescope was able to resolve Xi Ursae Majoris, Porrima, Eta Orionis, and the wonderful triple system, Iota Cassiopeiae. Sadly, the latter system, which is still present low in the northern sky in June, was hopelessly lost in the summer twilight. Bootes always presents a nice playground for easy and pretty double stars, including Kappa, Pi, Xi and Nu 1 & 2 Bootis, which were all easily split at 116x.

June is also high season for the beautiful, ghostly whisps that meteorologists refer to as noctilucent clouds. These thin, high altitude formations are lit up by the Sun while still below the northern horizon, creating quite surreal visual delights to the naked eye. I took a couple of low resolution images with my iphone (shown below).

Noctilucent clouds captured outside my house at local midnight on the evening of June 18 2018.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Another view captured at local midnight on the evening of June 18 2018.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I shall endeavour to capture some higher resolution shots of these wonderful meteorological structures in due course.

Plotina, the author’s amazing 130mm f/5 Newtonian reflector as seen at 11.10pm on the evening of June 21 2018.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

On the June Solstice of 2018, I  walked through the garden in the cool of the evening, fetching my trusty Vixen Porta II mount to field my 130mm f/5 Newtonian. A gentle westerly breeze was blowing and the sky was resolutely clear, but I have learned on many past occasions that these conditions often bring very good seeing conditions for high resolution double star work. And my efforts were rewarded with text book perfect images of a suite of difficult double stars, some of which I have mentioned earlier in this report. I also ended my year long evaluation of a variety of eyepieces and Barlow lenses,varying quite considerably in price range. These studies have led to some firm conclusions regarding the effects of moving air upon Newtonian optics, as well as some very surprising results concerning the efficacy of certain oculars in regard to resolving double stars. Do you always get what you pay for? Most certainly not!

Insofar as artificiallly blowing air on a Newtonian mirror has been shown to scrub off the so-called boundary layer immediately above the reflective surface, my field testing over many nights shows that natural wind can also improve the images in exactly the same way. For this reason, I invariably point the telescope into any prevailing wind while the telescope cools and this works especially well for my larger Newtonian reflectors (8- and 12 inches). Furthermore, I am not aware of any historical precedent for this; the work of some notable telescopic ancestors of the ilk of W.F. Denning, T.H.E.C. Espin, T.E.R. Philips, A.S. Williams, T.W Webb and N.E. Green ( the selected work of which I will feature in my up-and-coming historical work) all of whom used Newtonian reflectors to great effect do not explicitly give mention to this result, though there is no doubt it is generally true.

The Vixen HR series of oculars; nice but totally overkill for high resolution double star work in medium and large aperture aperture Newtonian reflectors.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

On many fine evenings using a variety of Newtonian telescopes, I have compared the views through top-of-the-range eyepieces, such as the new Vixen HR series of ultra-short focal length oculars(1.4mm, 2.0mm and 2.4mm) and those derived from much more modest (but still very good) Plossls and orthoscopics coupled to decent Barlow lenses and my conclusions are that the much more expensive eyepieces do not confer any real advantages over the latter.

Ordinary eyepieces and Barlows work perfectly well with Newtonian reflectors for high-resolution double star work. Left to right; a 3x Meade achromatic Barlow, a 7.5mm Parks Gold and Baader 6mm classic orthoscopic.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Yes, the HR series do display slighly better contrast and reduced light scatter compared to Plossls and orthoscopics but the differences were never enough to count. i.e. There was never an occasion where I could not see a tight companion in one over the other at comparable magnifications. Indeed, the HR series of eyepieces have very restrictive fields (42 degrees), even compared with the modest 50 degree fields offered up by a Plossl and/or the Baader classics (which have a larger 50 degree field) when Barlowed allow for significantly larger fields to be exploited. There is thus a distinct advantage to the using the far less expensive Plossl and orthoscopic type eyepieces over the HR series (the three of which will set the consumer back a hefty £750 UK), especially when employing a non-motorised altazimuth mount such as my Vixen Porta II.

Don’t believe the hype; binary stars are very simple, just tight little Airy disks. Save your money and use it more productively on other things.

Well, I hope you enjoyed this blog and that you don’t become discouraged observing throughout the twilight season wherever you live.

Thanks for reading.

 

Neil English’s new book, Tales from the Golden Age, uses history to debunk a few myths that have crept into modern amateur astronomy. Available in late 2018.

 

 

De Rerum Natura

Hubble deep Field Image. Credit: Wiki Commons.

 

However, the Most High does not dwell in temples made with hands, as the prophet says:

 ‘Heaven is My throne,
And earth is My footstool.
What house will you build for Me? says the Lord,
Or what is the place of My rest?
Has My hand not made all these things?’

                                                                                         Acts 7:48-50

 

A new paper by a team of Oxford University scientists, submitted to the Royal Society, London:

Dissolving the Fermi Paradox

(Submitted on 6 Jun 2018)

The Fermi paradox is the conflict between an expectation of a high {\em ex ante} probability of intelligent life elsewhere in the universe and the apparently lifeless universe we in fact observe. The expectation that the universe should be teeming with intelligent life is linked to models like the Drake equation, which suggest that even if the probability of intelligent life developing at a given site is small, the sheer multitude of possible sites should nonetheless yield a large number of potentially observable civilizations. We show that this conflict arises from the use of Drake-like equations, which implicitly assume certainty regarding highly uncertain parameters. We examine these parameters, incorporating models of chemical and genetic transitions on paths to the origin of life, and show that extant scientific knowledge corresponds to uncertainties that span multiple orders of magnitude. This makes a stark difference. When the model is recast to represent realistic distributions of uncertainty, we find a substantial {\em ex ante} probability of there being no other intelligent life in our observable universe, and thus that there should be little surprise when we fail to detect any signs of it. This result dissolves the Fermi paradox, and in doing so removes any need to invoke speculative mechanisms by which civilizations would inevitably fail to have observable effects upon the universe.

Full Paper here

 

 

De Fideli.