What's this effect I'm seeing?

[YabiYabi]

Being a bit of a noob this is not something ive seen before but i assume it is "normal". Just wondering if someone can explain it.

I was out tonight and pointed my telescope at Sirius. I still had a high power ep in and noted that I was unable to resolve it into a point and noted that it seemed to be split into two colours - one half blue and the other yellow. I'm guessing this is an effect of the atmosphere/instability?

[brantuk]

It's chromatic abberration (CA) - try a lower power eyepiece and you may just see a yellow fringe round the edge. This sort of effect is most noticeable e.g. on the moon with an achromatic refractor

[Peter Drew]

Probably a combination of chromatic aberration, atmospheric refraction and poor seeing, a colourfull result.

[John]

Sirius is difficult enough to get sharply resolved at the best of times - add those other factors in and it's going to look a bit of a mess !.

[YabiYabi]

Thanks chaps. Colourful it certainly was, though sort of pretty in a fuzzy sort of way. Thanks for the explanation - have done a bit of reading now on CA so hopefully know what to look for next time.

[rory]

i also looked at sirius for the first time last night. as it was quite low i put it down to atmosphere effecting the view,as it was like a traffic light flashing colours at me,quite mesmirising.

[Stu]

Fortunately, Sirius is probably one of the worst stars for this, others shouldn't be so bad. It is very bright, and often low down to so is very twinkly due to the depth of atmosphere the light has to travel through

Stu