Diffraction rings around multiple stars?

[JamesF]

I was playing at splitting multiple stars with the ST102 last night and whilst viewing Castor noticed that there definitely what appeared to be diffraction rings around the two main stars (which I could definitely split, but only just).

Is that just to be expected because of the interference of light between the two stars, or is it more likely to be an artefact of the optics?

James

[themos]

optics.

[John]

A typical refractor shows a single diffraction ring around the star disk at focus. With really close doubles the diffraction ring can appear to enclose both star disks in a sort of "peanut" shape.

What can be awkward is if one of the components of a multiple star is sitting right on the diffraction ring of another, brighter component - I find this the case with Iota in Casseopeia when viewed with a 102mm refractor.

[Ben Ritchie]

The diffraction rings are a good way of judging the seeing, too

Courses in Astrophotography

[Merlin66]

If you're interested in double stars..have you considered using your webcam and the software by Florent Losse - Reduc.

http://www.google.co.uk/url?sa=t&source=web&cd=1&sqi=2&ved=0CBgQFjAA&url=http%3A%2F%2Fwww.jdso.org%2Fvolume3%2Fnumber3%2FSchlimmer.pdf&ei=fWd2TeWjN9GLhQfLqJj-Bg&usg=AFQjCNE63omAEsUxIUKnS9TXn10j1wzR6Q&sig2=j8EOIFhDJ6hzMmWWou-ZMQ

This allows you to measure close double stars much easier than the ol' filar micrometer!!