Early March evenings provide some great opportunities to observe double stars of various levels of difficulty. This work is based on a single night’s observations, which took place on the late evening of March 4 and shortly after midnight on March 5 2019.
The instrument used was a 130mm f/5 Newtonian reflector. The cork-lined optical tube assembly provides excellent thermal stability and when it is perfectly collimated and acclimated to the night time air, it produces beautiful images of double stars under good seeing conditions.
The reader can also enjoy these doubles stars with other types of telescopes. For the most difficult systems I would recommend at least a 120mm refractor, a C5 or C6 Schmidt Cassegrain, a 6″ Classical Cassegrain or a 127mm Maksutov Cassegrain.
The evening on which the observations were made proved very good, with a brisk southwesterly wind and good steady seeing conditions (Antoniadi II). As I explained in a few previous blogs, I point the 130mm Newtonian straight into the wind, where it acts as a natural boundary layer scrubber. No fan was used.
I started with Theta Aurigae, now well past meridian passage but still quite high in the western sky. The system always provides a good challenge for the medium aperture backyard ‘scope. I used a power of 260x (Parks Gold 7.5mm coupled to a Meade 3x Barlow) to obtain a wonderful view of the faint companion.The challenge here is the large brightness difference between the pair (magnitudes 2.6 & 7.2) That said, the 130mm reflector will always resolve this tough system in good seeing conditions.
Our next target presents an altogther different type of challenge to the double star observer. Wasat (Delta Geminorum) is a creamy white star shining with a magnitude of +3.5 but it has a much fainter companion; an orange dwarf star shining feebly at magnitude +8.2. The challege here is to pick it off from the primary as it is very close in. Good transparency is a necessity for glimpsing it. I used a power of 118x (Meade 5.5mm Series 5000 UWA) to bag it. These form a true binary system with a period of about 1000 years.
Iota Cassiopeiae: a much easier system to resolve, and contrary to erroneous literature claiming otherwise (a nefarious meme promulgated by refractor nuts in paticular), presents little in the way of a serious challenge. This is a lovely triple system, with all three components observed at 260X (Parks Gold 7.5mm coupled to 3x achromatic Meade Barlow).
Our next port of call is Alula Australis (Xi UMa) in Ursa Major. Being very high in the sky at this time of year, it is ripe for exploration with a decent backyard ‘scope. The near equal magnitude creamy white components shine with magnitudes +4.3 and +4.8 are are rapidly widening, being accessible to the smallest telescopes after 2020. As a keen student of this system for over a decade, I have watched it slowly widening from season to season and now is a great time to see this wondrous apparition of nature. The changing aspect of the pair is easily explained by virtue of its short orbital period; just 60 years. Easily resolved in the 130mm f/5 at 260x, I enjoyed an even better view at 354x (Meade 5.5mm UWA coupled to a Meade 3x Barlow).
Our next target is right next door; look through your finder and move the telescope to the other bright star in the field of view. I speak of course of Alula Borealis. The 130mm f/5 presents the system beautifully; an orange primary(magnitude +3.5) and just 7.4″ away, the exceedingly faint companion shining with a magnitude of +10.1. Well seen at 118x and 135x (Meade UWA 5.5mm & 4.8mm T1 Nagler, respectively) roughly due west of the primary, observing the tiny, faint spark is a sight for sore eyes!
Back into Gemini now for our next target, which will present a much greater challenge:Propus (Eta Geminorum).The primary is a red giant star, which fluctuates in magnitude, varying in glory from + 3.1 and + 3.9 over a period of about eight months. The challenge is to see the very close-in companion, which shines much more feebly at magnitude +6.2, but it’s located just 1.6″ away, making this an exceedingly difficult system, requiring great patience and perseverance to crack. That said, I was able to successfully resolve the companion for the third time this season, on the evening of March 4, using a power of 354x (Meade UWA 5.5mm coupled to a 3x Meade Barlow) in my 130mm f/5 roughly northwest of the primary. If you don’t bag it on a good night, don’t fret, the unstable, geriatric primary probably plays a role in making it difficult to see. But repeated observations over a period of a few weeks should yield success! The stars orbit their barycentre every five centuries.
My final offering is also very challenging; much more so than many observing guide books would have you believe. I speak of Iota Leonis, a creamy white star shining at magnitude +4.1. The challenge is to resolve the secondary; shining more feebly at magnitude + 6.7. Separated by just 2.1″, I usually wait until the fairly low lying system in my far northern skies, reaches the meridian, which it did at about 00:40UT on March 5 2019. I used a power of 354x(Meade 5.5mm UWA and 3x Barlow) to resolve the tricky pair. The secondary lies roughly due east of the primary and orbits its brighter luminary every 186 years. My guide book suggests a 76mm telescope and high power is about the minimum necessary. I think this is a pipe dream though. What do you think?
Well, that’s your lot folks. I hope these systems will give readers a good challenge on cool March evenings and keep you busy and active.
Neil English recounts the history of many celebrated double star observers over four centuries of time, using both refractors and reflectors, in his latest work, Chronicling the Golden Age of Astronomy.