ST80 Club (Reprise)

[Nightspore]

Well, I managed another Moonless ST80 Club session. This one was not quite a disaster, although not totally without incident. It all started off maybe around 03:00 GMT, 19/1/24. It’s difficult to tell now as my Swiss watch is basically Swiss cheese.

 

 

I could see a lot of stars but the jet stream was not as favourable as I’d have liked. As a consequence there was a fair amount in the sky, but the seeing was only average. Leo was magnificent in the south, so my first sweeps with the 30mm GSO SuperView (13.3x) were in the big lion which was at 48°,12’,01.7” altitude. This is one of the original Sumerian/Babylonian astrological constellations. I can actually ‘see’ the ‘lion’. 

 

 

Although I was really more interested in the tail of the lion, now usually called Coma Berenices. Apparently because when Ptolemy III Euergetes ruled Egypt, with his queen Berenice II, who was the daughter of the King of Cyrene, Euergetes got into a bit of a scrap with the Assyrians. Berenice promised to sacrifice her beautiful blonde hair (not sure if she was a peroxide blonde or not) if Euergetes survived the rumble in the jungle with the Assyrians. When he returned unharmed Berenice cut her Debbie Harry barnet off and placed it in the temple of Aphrodite. Of course, over night, it got half-inched, much to the consternation of the king and queen, who were not amused. Luckily, Conon, the quick thinking court astronomer/astrologer, claimed that Aphrodite was so impressed by baldy Berenice’s detached barnet fair that the Goddess had placed it into the sky for all to admire. Luckily Euergetes and Berenice were gullible enough to fall for this. Meanwhile a certain wigmaker received a bit of a windfall. Either way, Coma Berenices needs a low power to really enjoy the heavenly golden locks. M44 aka ‘The Beehive’ (Cancer) was the next logical target. I could see it with the naked eye and at 13.3x. It was best at about 27x (15mm GSO SuperView). Well, I got a bit of a buzz out of it anyway.

 

 

The open clusters M37 and M35 were very nice. I’ve always had a soft spot for M37 (Auriga) ever since I discovered it by accident years ago in the southwest one autumn evening with my 130mm Newtonian. Many consider it to be the finest open cluster in the night sky. Apparently it was originally discovered by some cat called Giovanni Batista Hodierna before 1654. Although Messier claimed it in 1764. It is nearly as big (24 arc minutes) as the Full Moon in diameter, with perhaps 500 stars.

Eventually, as I was starting to freeze, I turned my attention to Cassiopeia, wife of King Cepheus of Ethiopia. Cassie upset the Nereids (don’t ask) who sent a whale to ravage the coast of the kingdom. Luckily for their daughter (and potential sacrifice) Andromeda, whales mostly eat plankton. Anyway Perseus took the credit for saving Andromeda. I’m guessing he also stole Berenice’s hair as well. The Owl Cluster was very nice at both 13.3x and 27x. Its head pointing to around the 5 o’clock region. I tried to split Achird at around 100x but it was not very successful. Iota Cass was equally difficult. I’m guessing anything much smaller than around a 2mm exit pupil isn’t handled well by an achromat. The CA might not be obvious but it takes its toll at higher magnifications. At least the Polaris ‘Engagement Ring’ was engaging enough. It was then that I noticed the huge constellation of Draco, well at least its head.

 

 

Draco is one of the only constellations that actually look like their name IMO. Draco supposedly guarded the Golden Fleece until Jason turned him into toast. I managed to split the double star Kuma (5th magnitude) in the Dragon’s Head, although it is fairly easy. A good pair of binoculars should do it without problem.

 

 

Finally, I noticed Corvus in the south. It looks nothing like a crow if you ask me. It consists of four stars: Algorab, Gienah Corvi, Kraz and Minkar. The ST80 failed to split Gienah Corvi, which I think is the easiest of the four (it’s been a while so I’m not sure). I did split Algieba (Leo) and Castor (Gemini) earlier at about 60x without any real problems though. I was so cold by now that I decided to pack up. I stood most of the session due to frosty seat syndrome. I then discovered my Vixen TL-130 tripod had frozen open. It’s done this before in cold weather. I have two of these tripods, only one sticks in the cold. Guess which one I took out? After two gruelling and slippery journeys back (thank the Goddess for the trolley lol) I managed to sit down indoors in the warm at about 05:00. It was a tiring night for me, and I realised the limitations of the ST80, but it was enjoyable. 

 

 

At about 05:45 I got to see a naked eye rising Venus/Ishtar again.

 

 

[Nightspore]

 

I've been thinking about the ST80 (and ST102) as doublet refractors. The objective itself is perfectly good for up to around a 1mm exit pupil (80x). Although anything above that and CA will start to cut in.

 

 

This morning I spent some time at 13.3x with a GSO 30mm SuperView. It is fairly well edge corrected at f/5.

 

 

The GSO reversed Kellner (below left) shows a fair amount of edge of field distortion with my StarTravel achromats. The Baader Hyperion Aspheric (below right) can show a small amount of edge distortion in fast refractors.

 

 

However, on-axis viewing with both the Kellner and the Aspheric are fine. The ST80 is great at low power (4-6mm exit pupil) but at higher magnifications can be problematic. Chromatic aberration is not always a problem when lunar/planetary viewing around a 1mm exit pupil. Yellow filters will take much of the fringing.

 

 

Stacks can be useful, even a Wratten #8 light yellow stacked with a 'skyglow' type takes out a lot of the cyan fringing. The LP filter tends to naturalise the colour somewhat I find. I'm not convinced that this really helps with definition when splitting double stars.

 

 

Hence why I invested in the Evostar 72ED DS PRO five years ago. It's still a doublet, but the crown is Schott glass and the flint is a very high quality. My guess is that it's possibly H-FK61 glass made by CDGM in China, which reputedly has a similar Abbe number to Japanese made Ohara FPL-51 glass. Sky-Watcher are staying mute on the actual glass type.

 

 

Just a few musings ....

[Graeme]

20 hours ago, Nightspore said:

Well, I managed another Moonless ST80 Club session.

 

 

That was a good read Nightspore. And an excellent history lesson too!

 

Graeme

[Nightspore]

23 minutes ago, Graeme said:

 

That was a good read Nightspore. And an excellent history lesson too!

 

Graeme

 

Thanks, I'm glad you enjoyed it. More a mythology lesson than anything else lol.