Did I get the Pup star?

[Nikolai De Silva]

Hello, 

Got some focusing on Sirius day before yesterday night. Took some photos of Sirius and I'm not sure whether I got the pup. These are some pictures of Sirius.

Can the star down be the pup star?

[John]

I have replied to your query on this in the other thread but I think it is unlikely.

Some information on the true field of view covered, the imaging equipment used and the orientation of the images (eg: where N, S, E and W are) would help a lot.

The key thing is assessing the extent, on the image, of the glare around Sirius and the orientation of the other star shown. The Pup star is usually within the glare surrounding Sirius A - it lies around 11 arc seconds from Sirius to the NE. 

Sorry to be picky, but if you want to be sure, some precision is needed. There are a number of other stars around Sirius which I would expect also to show on the image.

[josefk]

Hi @Nikolai De Silva - do you know how to identify West in your eyepiece field of view? ...and do you know how to roughly estimate angular "size" or, for double stars,  separation between them in arc minutes or arc seconds? if yes sorry for being patronising - tell me to butt out :-).

If no then its worth having a look here for some general principles: https://www.handprint.com/ASTRO/bineye1.html#standard. This was my online tutor when getting into the hobby.

Long story short -

• as long as your mount isn't moving then stars exit your eyepiece view to the west and in your newtonian scope north will be 90-degrees anti-clockwise from that point. With North and West identified you can work out everything else in degrees (North is 0-degrees, West 270-degrees, and so on)
• your eyepiece apparent field of view [AFOV] divided by the magnification it is generating will give you your true field of view [TFOV] in degrees (roughly - there is a more complex formula for slightly greater accuracy but roughly will almost certainly do). Divide this degrees value by 60 to arrive at arc minutes and by 60 again for arc seconds.

With these two "tools" or skills you get a world of wonder for quantifying the size and spatial relationships of what you are seeing through the scope. 

Good luck.

Edited January 17 by josefk

[bosun21]

1 hour ago, josefk said:

north will be 90-degrees anti-clockwise from that point

It will actually be 180 degrees ie upside down (north at the bottom).

[josefk]

1 hour ago, bosun21 said:

It will actually be 180 degrees ie upside down (north at the bottom).

Hi @bosun21 - North is always 90-degrees from West (though if it isn't that would explain some of my terrestrial navigation errors).

I find that 'find West first" concept a bit more reliable than "top" or "bottom" because they are relative depending on your heads position towards the EP or with a star diagonal the rotation of the diagonal to the objective (actually to the horizon???). West is absolute (where the stars exit) and 90-degrees anti-clockwise from West (Newtonian) or clockwise from West (star diagonal) is also absolute. I hope so otherwise i have an absolute pile of incorrectly marked up sketches! 😉 

Edited January 17 by josefk

[bosun21]

2 hours ago, josefk said:

Hi @bosun21 - North is always 90-degrees from West (though if it isn't that would explain some of my terrestrial navigation errors).

I find that 'find West first" concept a bit more reliable than "top" or "bottom" because they are relative depending on your heads position towards the EP or with a star diagonal the rotation of the diagonal to the objective (actually to the horizon???). West is absolute (where the stars exit) and 90-degrees anti-clockwise from West (Newtonian) or clockwise from West (star diagonal) is also absolute. I hope so otherwise i have an absolute pile of incorrectly marked up sketches! 😉 

I was referring to the OP as he has a reflector which will show north on the bottom. ie upside down. I actually read your explanation wrongly and can now see that you said north will be 90° anticlockwise from west which is indeed correct. My apologies.

[Nikolai De Silva]

Thank you very much for the explanations @josefk and @bosun21! They are very helpful. We didn't get get clear skies yesterday. Will surely try today for the pup star. 👍🙂

[John]

5 hours ago, Nikolai De Silva said:

Thank you very much for the explanations @josefk and @bosun21! They are very helpful. We didn't get get clear skies yesterday. Will surely try today for the pup star. 👍🙂

If you have a clear night, before you try Sirius, have a look at Rigel (bottom right of Orion) and see if you can see it's companion star. That is a useful test of the seeing conditions and also gives you a guide to how far away from Sirius the Pup star is in the eyepiece. Rigel's fainter companion star is on the other side of Rigel than the Pup is from Sirius but it's separation from Rigel is very similar.

 

[Mr Spock]

Rigel looked good last night - Sirius was not so good though with lots of flare. That's due to it being quite low here. You should do a lot better from where you are.