but test everything; hold fast what is good.
1 Thessalonians 5:21
Introduction: One of the statements that is oft quoted by observers, particularly in the UK, is that the meteorological phenomenon known as the Jet Stream seriously affects the quality of high resolution telescopic targets. I have decided to investigate these claims to determine to what extent they are true or not, as the case may be. These data will also provide the reader with an idea of the frequency of nights that are available for this kind of testing over the time period the study is to be conducted.
Method: For simplicity, I shall confine my studies to just four double stars that have long been considered reasonably tricky targets for telescopists. To begin with, my targets will include systems of varying difficulty, ranging from 2.5″ to 1.5″ separation, and the aim is to establish whether or not I can resolve the components at high magnification. These systems include *:
Epsilon 1 & 2 Lyrae
Epsilon Bootis
Delta Cygni
Pi Aquilae
* These systems were chosen for their easy location in my current skies, but may be subject to change as the season(s) progress.
Viewers are warmy welcomed to conduct their own set of observations to compare and contrast results in due course.
Instrument Choice & Magnifications Employed:
The 130mm f/5 Newtonian telescope used in the present investigation.
A high-performance 130mm (5.1″) f/5 Newtonian reflector was employed to investigate the effects of this phenomenon, as this is an aperture regularly quoted as being sensitive to the vagaries of the atmosphere. Magnifications employed were 260x or 354x (they can however be resolved with less power). The instrument at all times was adequately acclimated to ambient temperatures and care was taken to ensure good collimation of the optical train. No cooling fans used on any of my instruments.
Results;
Date: August 17 2018
Time: 21:20 to 21:35 UT
Location of Jet Stream: Currently over Scotland
Conditions: Mild, 14C, very breezy, mostly cloudy with occasional clear spells, frequent light drizzle.
Observations: Power employed at the telescope 354x
Epsilon 1 & 2 Lyrae: all four components cleanly resolved.
Delta Cygni: Faint companion clearly observed during calmer moments
Epsilon Bootis: Both components clearly resolved during calmer moments.
Pi Aquilae: Slightly mushier view, but both components resolved momentarily during calmer spells.
Truth seeking.
Date: August 19 2018
Time: 20:30 – 21:50 UT
Location of Jet Stream: Currently over Scotland.
Conditions: Mild, 13C, mostly cloudy and damp all day but a clear spell occurred during the times stated above, no wind, heavy dew at end of vigil.
Observations: Seeing excellent this evening (Antoniadi I-II); textbook perfect images of all four test systems at 354x and 260x.
Nota bene: A 12″ f/5 Newtonian was also fielded to test collimation techniques and I was greeted with a magnificent split of Lambda Cygni (0.94″) at 663X. Little in the way of turbulence experienced even at these ultra-high powers. Did not test this system on the 130mm f/5.
Clouded up again shortly before 11pm local time, when the vigil was ended.
Date: August 22 2018
Time: 23:30-40 UT
Location of Jet Stream: Currently over Scotland
Conditions: Very mild (15C), breezy, predominantly cloudy with some heavy rain showers interspersed by some brief, patchy clearings.
Observations: Just two test systems examined tonight owing to extremely limited accessibility; Epsilon 1 & 2 Lyrae and Delta Cygni. Both resolved well at 260x.
Date: August 22 2018
Time: 21:00-21:25UT
Location of Jet Stream: Currently over Scotland
Conditions; partially cloudy, brisk southwesterly wind, bright Gibbous Moon culminating in the south, +10C, rather cool, transparency poor away from zenith.
Observations: The telescope was uncapped and aimed straight into the prevailing SW wind, as is my custom.
All four systems well resolved at 354x, although visibility of Pi Aql was poor owing to thin cloud covering.
Date: August 23 2018
Time: 20:30-45 UT
Location of Jet Stream: Moved well south of Scotland
Conditions: Mostly clear this evening, after enduring heavy showers all day; cool, 10C, fresh westerly breeze, good transparency.
Observations: All four test systems beautifully resolved this evening (seeing Ant II) at 354x. Just slightly more turbulent than the excellent night of August 19 last.
Date: August 24 2018
Time: 20:30-45 UT
Location of Jet Stream: Just west of my observing site.
Conditions: Almost a carbon copy of last night, light westerly winds, cool (9C), good transparency and almost no cloud cover. Very low full Moon in south-southeast.
Observations: All four system resolved at 260x, but less well at 354x owing to slightly deteriorated seeing ( II-III). Delta Cygni seems especially sensitive to seeing.
Nota bene: Epsilon Bootis now sinking fast into the western sky. This test system will soon be replaced by a tougher target, located higher up in my skies; Mu Cygni.
A capital telescope.
Date: August 25 2018
Time: 20:20-21:00 UT
Location of Jet Stream: Right over Scotland.
Conditions: Very hazy, calm, poor transparency, cool (9C), seeing excellent (I-II)
Observations: Just three of the four systems examined tonight owing to very poor transparency. Only Pi Aquilae could not be examined. All three were beautifully resolved at 354x.
Date: August 26 2018
Time: 22:30-23:05 UT
Location of Jet Stream: Well south of Scotland.
Conditions: After a day of heavy rain, the skies cleared partially around 11pm local time. Fresh westerly breeze, fairly mild (12C), bright full Moon low in the south.
Observations: Mu Cygni observed instead of Epsilon Bootis owing to the latter’s sinking low into the western sky at the rather late time the observations were made.
Three systems well resolved ( Mu Cygni, Pi Aquliae and Epsilon 1 & 2 Lyrae) in only fair seeing, with Delta Cygni B only spotted sporadically in moments of better seeing. This system is very sensitive to atmospheric turbulence due to a large magnitude difference between components, as opposed to their angular separation. 260x used throughout.
Nota bene: Readers will take note of the frequency of observations thus far made.
Date: August 27 2018
Time: 20:30-21:05 UT
Location of Jet Stream: West of the Scottish mainland.
Conditions: Mostly cloudy, mild, 13C, light westerly breeze.
Observations: I took advantage of a few brief clear spells this evening to target my systems(including Epsilon Bootis). Seeing very good despite the cloud cover (II). All four systems easily resolved tonight at both 354x and 260x.
Date: August 29 2018
Time: 20:25-40UT
Location of Jet Stream: Not over Scotland.
Conditions: Mostly clear, occasional light shower, cool (11C), light westerly breeze, seeing and transparencyvery good (II).
Observations: Mu Cygni now replaces Epsilon Bootis.
All systems very cleanly resolved at 354x and 260x.
Nb. All systems also beautifully resolved in a 12″ f/5 Newtonian at 277x, set up alongside the 130mm f/5.
Date: August 30 2018
Time: 20:45- 21:00 UT
Location of the Jet Stream: Not over Scotland.
Conditions: Partially cloudy with some good clear spells, cool (9C), very little breeze.
Observations: Seeing good tonight (II). All four systems nicely resolved at 260x and 354x.
Note added in proof: Local seeing deteriorated (III-IV) somewhat between 21:00 and 22:00 UT, so much so that Delta Cygni B could no longer be seen.
Date: 31 August 2018
Time: 20:30-22:00UT
Location of Jet Stream: North of the British Isles
Conditions: Partly cloudy and becoming progressively more hazy as the vigil progressed. Mild, 12C, very light westerly breeze.
Observations: Seeing only fair this evning (II-III), all four systems resolved at 260x and 354x, though Delta Cygni B visibility was variable.
Date: September 1 2018
Time: 20:30-50UT
Location of Jet Stream: to the northwest of the Scottish Mainland.
Conditions: Partially clear, very mild (16C), light southerly breeze, good transparency.
Observations: Seeing quite good (II). All four systems resolved at 260x and even better delineated at 354x under these clement conditions.
Date: September 4 2018
Time: 19:55-20:20UT
Location of Jet Stream: Not over Scotland.
Conditions: Cool (10C), mostly clear, light westerly breeze, good transparency.
Observations: Seeing very good (II). All four test systems well resolved at 260x and 354x this evening.
Date: September 5 2018
Time: 20:35-20:55UT
Location of Jet Stream: Not over Scotland.
Conditions: Very unsettled with frequent squally rain showers driven in by fresh westerly winds. Good clear spells appearing between showers. Transparency very good. 12C
Observations: All four test systems resolved under good seeing conditions (II) at 260x and 354x.
Date: September 6 2018
Time: 20:00-25 UT
Location of Jet Stream: Not over Scotland.
Conditions: Cool (8C), little in the way of a breeze, mostly clear, excellent transparency.
Observations: Seeing good (II). All four test systems well resolved at 260x and 354x.
Date: September 7 2018
Time: 20:25-40UT
Location of Jet Stream: Not over Scotland.
Conditions: A capital evening in the glen; 11C, good clear sky, brisk westerly breeze, excellent transparency.
Observations: Seeing very good (I-II). All four test systems beautifully resolved in the 130mm f/5 using powers of 260x and 354x
Nota bene:
Know thine history!
Any serious student of the history of astronomy will likely be acquainted with the early work of Sir William Herschel (Bath, southwest England), who employed extremely high powers (up to 2000x usually but actually he went as high as 6,000x on occasion) productively in his fine 6.3-inch Newtonian reflector with its speculum metal mirrors. The high powers employed by this author are thus fairly modest in comparison to those used by his great predecessor. Check out the author’s new book; Chronicling the Golden Age of Astronomy, due out in October/November 2018, for more details.
Note added in proof:
With the excellent conditions maintained well after midnight, I ventured out at about 00:00 UT, September 8, and noted Andromeda had attained a decent altitude in the eastern sky. At 00:10UT I trained the 130mm f/5 Newtonian on 36 Andromedae for the first time this season and charged the instrument with a power of 406x. Carefully focusing, I was treated to a textbook-perfect split of the 6th magnitude Dawes classic pair that are ~1.0″ apart. It was very easy on this clement night. The pair look decidely yellow in the little Newtonian reflector. I made a sketch of their orientation relative to the drift of the field; shown below.
36 Andromedae as seen in the wee small hours of September 8 2018 through the author’s 130mm f/5 Newtonian reflector, power 406x.
If you have a well collimated 130P kicking about why not give this system a try over the coming weeks?
Date: September 9 2018
Time: 21:10-25UT
Location of Jet Stream: Currently over Scotland
Conditions: Frequent heavy showers driven in from the Atlantic with strong gusts, 11C, some intermittent clear spells.
Observations: Seeing III. 3 systems fairly well resolved this evening. Delta Cygni B only seen intermittently. Magnification held at 260x owing to blustery conditions.
Date: September 12 2018
Time: 00:10-20UT
Location of Jet Stream: Currently over Scotland
Conditions: Very wet, windy with some sporadic clear spells, good transparency once the clouds move out of the way. 10C.
Observations: Seeing (II-III). Just three systems examined tonight; the exception being Pi Aquliae, which was not in a suitable position to observe. All three were well resolved at 260x. Did not attempt 354x owing to prevailing blustery conditions.
Date: September 12 2018
Time: 21:40-55 UT
Location of Jet Stream: Not over Scotland
Conditions: Still unsettled, blustery light drizzle and mostly cloudy with some clear spells. 10C.
Observations: Seeing (III), three systems resolved well, Delta Cygni B not seen cleanly at 260x under these conditions.
Date: September 14 2018
Time: 19:30-50UT
Location of Jet Stream: Currently over Scotland.
Conditions: Rather cool, (9C), very little breeze, rain cleared to give a calm, clear sky.
Observations: Seeing II. All four systems cleanly resolved at 260x and 354x
Date: September 16 2018
Time: 19:20-40UT
Location of Jet Stream: Currently over Scotland
Conditions: Mild (12C), fresh south-westerly breeze, some occasional clear spells.
Observations: Seeing very good (II), all four systems cleanly resolved at 260x and 354x.
Overall Results & Conclusions:
This study was conducted over the course of one month, from mid-August to mid-September 2018, a period covering 31 days.
The number of days where observations could be conducted was 21, or ~68% of the available nights.
No link was found between the presence of the Jet Stream and the inability to resolve four double star systems with angular separations ranging from ~2.5-1.5″. Indeed, many good nights of seeing were reported whilst the Jet Stream was over my observing location. In contrast, some of the worst conditions of seeing occurred on evenings when the Jet Stream was not situated over my observing site.
There is, however, a very strong correlation between the number of nights available for these observations and the efforts of the observer.
Many of the nights the Jet Stream was located over my observing site were windy, but this was not found to affect seeing. While the wind certainly makes observations more challenging, it is not an indicator of astronomical seeing per se. That said, no east or northeast airflows were experienced during the spell these observations were conducted. At my observing site, such airflows often bring poor seeing.
The archived data (from January 16 2014) on the Jet Sream site linked to above provide many more data points which affirm the above conclusions.
I have no reason to believe that my site is especially favoured to conduct such observations. What occurred here must be generally true at many other locations.
These results are wholly consistent with the available archives from keen observers observing from the UK in the historical past. This author knows of at least two (or possibly three) historically significant visual observers who enjoyed and documented a very high frequency of suitable observing evenings in the UK.
Contemporary observers are best advised to take Jet Stream data with a pinch of salt. It ought not deter a determined individual to carry out astronomical obervations. Perpetuating such myths does the hobby no good.
Post Scriptum:
June 18 2019: Irish imager, Kevin Breen, used his C11 to obtain decent images of Jupiter under a very active Jet Stream. Details here.
July 2 2019: Another testimony of “good seeing” under Jet Stream here
Neil English debunks many more observing myths using historical data in his new book, Chronicling the Golden Age of Astronomy.