Twinkle, twinkle, little star

[Andy Resnick]

Not sure if this is the best subforum, but here goes:

I tried to photograph YU55 when it flew by, and have been combing through a pair of photos, looking for a dot in one and a blank spot in the other. So far there have been at least 5 instances where something appeared in one photo only, but checking the locations with google sky and SIMBAD, each location indeed has a faint (magnitude 10+) star present.

Each photo was taken with a 1.3 second exposure time, which I had thought was sufficiently long to average out any atmospheric turbulence (the twinkle). My reference text, Roggemann and Welsh "Imaging through turbulence", has a long chapter devoted to atmospheric turbulence in this specific context, and while they have a detailed discussion about the spatial extent- the correlation length as compared to the entrance pupil- there does not appear to be a similar discussion about timescales: short-time imaging gives speckle, long-time imaging gives uniform blur, but I can't find a derivation about the correlation time (which divides the two regimes).

I'd appreciate any pointers, references, etc. on this, thanks.

 

[bahamagreen]

If atmospheric turbulance is why stars twinkle, why don't planets twinkle? Why don't artificial Earth satellites twinkle?

 

[Andy Resnick]

They aren't point sources. Plus, satellites move pretty fast (I've not looked for a geosynchronous satellite).

 

[bahamagreen]

Here is an interesting re-examination of star twinkle. It discusses some photography aspects as well. He is not an official authoritative source, but his insights may give you some means to work on the photo problem... http://milesmathis.com/twink.html"

 

[Andy Resnick]

That site is rather poor, unfortunately. The referenced NASA site is better. As I mentioned, the problem is well understood (I recommend reading the reference I provided).

Edit: I found this, which appears to have all the information I need in chapter 4:

http://www.google.com/url?sa=t&rct=...sg=AFQjCNFUNLv0Lq32L73kmxBlwhRbfjZgeg&cad=rja