Capella query

[Sully]

This has probably been asked 100's of times, but why does Capella flicker different colours more so than other stars, to the extent it looks like like a plane??

[Atlas]

I've wondered this myself. I wonder if it has multiple gas giants zooming around it at incredible speed.

[Sully]

at 42 light years, it's not the nearest or farthest by a long way so why's it so different???

[Atlas]

looks like I need to point the scope at it tonight.

[Ags]

The atmosphere lenses the starlight, causing it to split into a rainbow. You only see a part of the rainbow at any instant, and the part you see changes with the twinkling. The effect is most obvious with Sirius. you can see the effect of atmospheric lensing on Venus with a telescope, where the planets often shows prominent blue and red fringes - when I first saw it I thought my scope was broken.

[Qualia]

I think as light goes through the atmosphere it gets bullied about (by air, for example) and if the atmosphere is turbulent enough the light gets refracted in different directions. This causes the star image you see to 'twinkle', change in brightness and even to move and change colour.

As an observer, it is handy to recognise that a night of twinklers rather than sparklers means your 'seeing' is going to be not so good. On such nights, I usually don't bother. I'd even go so far to say that general LP is one thing but it can be kind-of punched through (lowering one's expectations on finding DSOs, concentrating on Jupiter, the Moon, doubles, open clusters etc) but if it is a night of twinkle-twinkle, everything is kind of bad.

Hope that helps.

[Sully]

Thanks for the advice Qualia, would this just be applicable for low level ob's or a general thing for the night?

[Dave S]

I've wondered this myself. I wonder if it has multiple gas giants zooming around it at incredible speed.

Nice Guess. Nearly on the mark.

Cappella is actually four stars consisting of two binary systems. Two cooling G-type which are thought to be expanding to red giants and two red dwarfs.

Dave...

[Qualia]

I hope others get involved in this, Sully, so that they can give their own - probably more informed - opinion. So with that said, take my words lightly and only grounded on my own sloppy experience.

I use the twinkle of the sparklers - scintillation - to estimate how good will be my general seeing for the evening. If the stars twinkle, it's not a great sign for me on all objects apart from the moon and maybe Jupiter, Venus and Saturn. To be honest, these don't twinkle but can get mushed up and soft and blury with ground heat rising.

I live in a city, so you can imagine the LP is bad, if I put on top of this a nasty case of scintillation, I'm grounded. On the other hand, at weekends when the weather isn't bad, I try to get out to a large desert near where I live and here I have never experienced scintillation, but for one reason and another, seeing can vary.

[Atlas]

Nice Guess. Nearly on the mark.

Cappella is actually four stars consisting of two binary systems. Two cooling G-type which are thought to be expanding to red giants and two red dwarfs.

Dave...

Thanks Dave...This makes the most sense to me, especially since only a couple other stars act the same way. And it does it consistently in my region regardless of seeing conditions. multiple stars makes better sense, since if it were Gas giant planets, the orbiting rate would be too great to keep them together I would think. I've heard of really fast planetary orbits (example a few days). But every few seconds would surely rip any type of planet apart at those speeds.

What convinced me is the wobble, the fact of light wavelengths from the star turning red due to stretching as it moves away, and then white to blue from compression as it gets closer. I've seen the technique used to find large planets orbiting stars, and not sure why I didn't think to apply it to binary systems. (I must be getting slow in my old age.)

[Ags]

Thanks Dave...This makes the most sense to me, especially since only a couple other stars act the same way. And it does it consistently in my region regardless of seeing conditions. multiple stars makes better sense, since if it were Gas giant planets, the orbiting rate would be too great to keep them together I would think. I've heard of really fast planetary orbits (example a few days). But every few seconds would surely rip any type of planet apart at those speeds.

What convinced me is the wobble, the fact of light wavelengths from the star turning red due to stretching as it moves away, and then white to blue from compression as it gets closer. I've seen the technique used to find large planets orbiting stars, and not sure why I didn't think to apply it to binary systems. (I must be getting slow in my old age.)

It is just atmospheric lensing, nothing to do with multiple stars.

[Dave S]

It is just atmospheric lensing, nothing to do with multiple stars.

To re-iterate AGS It is just atmospheric lensing, nothing to do with multiple stars.

The Capella info was supposed to be background info on an amazing star (system)

Sorry if I caused any confusion.

Cheers

Dave...

[Atlas]

No worries, I knew he was right after noticing the blinking stopped when it approached zenith this morning, and the disturbance moved a set of stars lower on the horizon.

[BSIA Ralph]

This effect can be captured really nicely by photographing Capella (more pronounced on Sirius but any really bright star will do) and tapping your scope as you take one second exposures. It makes a large looping star trail with rainbow effects.

Astronomically useless but aesthetically pleasing!