The curious case of Struve 2021

[Knighty2112]

After doing a brief session on Thursday evening with the only thing worth looking at been double stars due to the light nights, on the Friday evening I sat down to chart some interesting doubles to look at for next time. I was looking at doubles in Hercules with it been in a good position for me to observe with the street lamps near me. So looking in the Cambridge Double Star Atlas one of the first ones I jotted down was listed as Struve 2021, a 7.4/7.5 magnitude double with a separation of 4.1 seconds of arc. My list didn’t grow much longer as I was too tired to only note one other double to check out been Struve 2052.

So this afternoon I decided to check out and make a list in Skysafari for my Hercules doubles list taking shape to look at the next time I get my 102mm ED f11 ‘frac out under the skies. Looking at CDSA again at Struve 2021 it was also listed as 49 with what I assumed to mean 49 Herculis. Typing this in as a search on Skysafari it listed 49 Herculis as a 6.5 mag variable star, not a double, and not in the same location in Hercules either but further to the east. Typing in Struve 2021 in Skysafari did bring up the correct double I wanted, but was not listed as under 49 Herculis. Thinking that CDSA has made an error in listings it as 49 Herculis I checked in Sissy Hass’ book on double stars, where it is listed under Hercules, but listed as 49 Serpentis! Confused, I checked Burnham’s but it was listed only under Struve 2021. Finally checking also in my Deep Sky Atlas it has it listed in the chart also as 49, so as can be seen in the image below there are two items listed in the Hercules chart as number 49. Digging deeper it seems that Struve 2021 prior to re-defining the constellation boundaries before 1930 did used to lie in Serpens where it was listed as 49 Serpentis. So today it seems that it still retains this number in some charts still, with Hass listing it as 49 Serpentis even when in the list of doubles under Hercules! 

 

 

Edited June 17, 2023 by Knighty2112

[Spile]

There is a reference to STF 2021 on CN https://www.cloudynights.com/topic/595742-49-serp-that-actually-in-hercules-stf-2021/

[NGC 1502]

What edition CDSA do you have?   Edition 1 is very different from edition 2.   Edition 1 definitely had mistakes.  Edition 2 was not just an update but a complete rewrite, and much the better for that.

Just checked my CDSA edition 2, chart 10.  The star you have red circled and is designated Struve 2021 / 49 is just designated Struve 2021 in edition 2.  It’s close to the Serpens Caput border. Perhaps precession has shifted it from Serpens Caput into Hercules. Also on your chart the 49 designation must be a mistake. 49 is a Flamsteed number and is way too high a number for the west side of Hercules.

Also in my edition 49 Herculis agrees with the other star you have red circled and is designated 49.

BTW, cannot recall if precession has shifted constellation borders east or west. Anyone remember?

The above is astronomy when it’s cloudy😊

 

[NGC 1502]

With reference to the star you have red circled and is designated Struve 2021 / 49. On my S&T sky atlas it’s just marked as 49 Ser.  Therefore it’s definitely not 49 Herculis!   On your chart it’s a bit confusing to have 2 stars with the same Flamsteed number in the same constellation!

 

Edited June 17, 2023 by NGC 1502
Correction

[Knighty2112]

Just found in my Atlas of the Heavens also that it is listed in Hercules, but noted on the chart as 49 Ser. The variable star with the same number 49 is shown also to the left. This was a chart drawn up circa 1950 by Becval.

 

[Knighty2112]

15 hours ago, Spile said:

There is a reference to STF 2021 on CN https://www.cloudynights.com/topic/595742-49-serp-that-actually-in-hercules-stf-2021/

Yeah, confusing to call it 49 Serpentis still when not in that constellation no more. Astronomy certainly has some odd things with it!  

[Knighty2112]

15 hours ago, NGC 1502 said:

What edition CDSA do you have?   Edition 1 is very different from edition 2.   Edition 1 definitely had mistakes.  Edition 2 was not just an update but a complete rewrite, and much the better for that.

Just checked my CDSA edition 2, chart 10.  The star you have red circled and is designated Struve 2021 / 49 is just designated Struve 2021 in edition 2.  It’s close to the Serpens Caput border. Perhaps precession has shifted it from Serpens Caput into Hercules. Also on your chart the 49 designation must be a mistake. 49 is a Flamsteed number and is way too high a number for the west side of Hercules.

Also in my edition 49 Herculis agrees with the other star you have red circled and is designated 49.

BTW, cannot recall if precession has shifted constellation borders east or west. Anyone remember?

The above is astronomy when it’s cloudy😊

 

It’s the second edition. It also lists it a a showpiece double in the list for Hercules in the lists after the charts. Definitely confusing for sure.
 

[Knighty2112]

14 hours ago, NGC 1502 said:

With reference to the star you have red circled and is designated Struve 2021 / 49. On my S&T sky atlas it’s just marked as 49 Ser.  Therefore it’s definitely not 49 Herculis!   On your chart it’s a bit confusing to have 2 stars with the same Flamsteed number in the same constellation!

 

Yep, confusing it is. Where are the chart police when you need ‘em?  

[Knighty2112]

I’m guessing that people making the later more modern charts are referencing this double from much earlier charts. So is this a case of them just copy and pasting here and not noticing this confusion with its designation here? 🤔

[Franklin]

I guess it's just what happens when you move the goal posts. A bit like 10 UMa being in the constellation Lynx and not Ursa Major, the sky is full of indiscrepancies.

[Knighty2112]

37 minutes ago, Franklin said:

I guess it's just what happens when you move the goal posts. A bit like 10 UMa being in the constellation Lynx and not Ursa Major, the sky is full of indiscrepancies.

Yep, exactly. Anachronisms abound in a few places in the heavens.

[Franklin]

If you're unsure on a designation just check the co-ordinates to confirm identity, surely they can't get the Ra and Dec mixed up.

Edited June 18, 2023 by Franklin

[lunator]

Here is the information from Herchel's double star catalogue from the Cambridge University Archive.

H I 82 49 Ser 16133+1332 STF 2021 AB 3/7/1783 1783 2009 402 292 356 64 2.5 4.1 1.6 7.43 7.48 0.05 16 13 18.45 + 13 31 37.2

Data from WDS2010

Herchel Notes

Double. The most north and following of two stars. A little unequal. Both pr.

Bruce MacEvoy Note

Precessing Flamsteed's 1690 coordinates places 49 Ser just inside Hercules: it is labeled in MSA (Millennium Star Atlas) 

My note

It appears it was considered part of Serpens but when the boundaries were officially agreed in the 1930's it was in Hercules.

It has quite high proper motion and is heading towards Ophiuchus but it won't get there for another 90,000 years or so

Cheers

Ian

[lunator]

I have just checked my Uranometria 2000 star Atlas and STF 2021 is marked as a double but no other designation is given.

Cheers

Ian

[Mr Spock]

Snippet from CdC...