Reply To: Theta Aurigae – A Double Star?

Forums Deep Sky Theta Aurigae – A Double Star? Reply To: Theta Aurigae – A Double Star?

Dr Paul Leyland

Thank you, that is very helpful. Now take a little time to think about some elementary geometry.

The definition of a parsec is the distance at which one astronomical unit subtends one second of arc. A parsec is about 3.2 light years, and Jupiter orbits the sun at a distance of 5AU in 12 years. Seen from a parsec away, Jupiter would be at most 5″ from the sun. A more massive object would orbit more quickly at the same distance, or be further away for the same period, ’tis true, but we’re talking order of magnitude estimates here.

The nearest star, alpha Centauri, is 1.3 parsecs away and although it is a multiple system the separations are many AU and the orbital periods are much more than a decade.

The only one which stands a chance of meeting your requirement is Sirius which is 2.7 parsecs away and where the companion is at most 11″ from the primary; the orbital period is about 50 years. A fair number of people have imaged Sirius B, myself included (see the gallery), but it is far from being an easy object.

Good luck!

If you want to measure stellar movements over a short period of time I would suggest that you start with stars of high proper motion. Barnard’s star is the easiest target and its movement can be measured within a week or two if you are careful. It moves around 11″ per annum, or 1″ per month. Careful astrometry should be good to around 0.3″ with amateur equipment. Again, see the gallery for my animated GIF which shows the movement from one summer to the next.