A question concerning Alpha Centauri

[shelltree (Shelley)]

So, here's a silly question I've been wanting to know the answer to. Now, Alpha Centauri is a binary star system of two stars so I wanted to take a look and see if I could see it. Looked through a 10" Dob at twilight just as it had become visible after the sun set and saw it as clear as day (so to speak)! But when viewed later it was a lot harder to see in the night sky.

Now, my question is this. Is it easier to see Alpha Centauri at twilight because it's comparative brightness to the twilight sky is less than the night sky making it easier to view? I've also heard the same thing about Venus and the quality of seeing with its phases. I could be spouting a load of drivel but it really interested me and I wasn't sure of the answer and wanted to put my assumptions to rest with a proper answer.

Thanks and I'm sure I'll be adding other silly questions here as I continue to learn more and more

[Barrykgerdes]

Hi
I think that is just an optical illusion brought on by relativity of brightness. You are quite right many stars are more visible at dusk than later in real darkness particularly the brightest ones. A lot depends on how dark your skies can get. However they are not brighter just easier to pick out because of the relative brightness of the sky at that time masking other less bright stars.

When I look at the stars in my local light polluted area I can pick out star patterns and easily identify the bright stars but when I go to a dark site I have greater difficulty in identifying the same stars in the clouds of other quite bright stars.

Barry

[Robh (Rob)]

There is some truth to this. The glare off bright objects like Venus is less apparent at twilight than in a dark sky. Glare would also be reduced for objects that are lower in the sky due to the increasing relative thickness of the atmosphere. However, seeing conditions are worse nearer the horizon.
The alpha Centauri bright pair are separated by about 9 arcseconds so there should not be any problem separating the two at any time.

Regards, Rob.

[shelltree (Shelley)]

Thanks both Rob and Barry for your insights, they've helped a lot! I think as well when we viewed them again a different night the seeing conditions may not have been as good with passing cloud so this may have had something to do with the difficulty we had making out the binary.