Twinkles

[caerus_sam]

I've often wondered what causes a couple of stars to twinkle to the extent that the light varies and changes colour and I hope you guys can tell me why.

I only ask after a little view earlier. I see 2 stars low on the horizon (the first is N/NNE and the second is very nearly NE) and the colours I see change from white to blue to red. Is this the colour ranges omitted from the star during it's life.?

I hope that's clear enough.

[Hobbes]

Hi Sam

Stars twinkle due to something called Stellar Scintillation. This is caused by the light from the star being refracted by the earths atmosphere on the way down to the earth's surface. The atmosphere has many layers and these act like prisms bending and refracting the light as it passes through them. the closer to the Horizon a star is the more atmosphere it has to pass through and the greater the refraction hence the wider variation in colours. Also as it has been a warm day the surface of the earth has a lot more heat to get rid off and this increases the air turbulance which creates more scintillation.

Hope this helps

Rgds

Rob

[caerus_sam]

Can't get a more comprehensive answer than that. Thanks Rob.

[yeti monster]

You get the same effect with Venus and Mercury, as they are usually so bright and low.

[Vega]

Well...what happends is...... uh oh.. Rob answered it better than I could

Not sure about Venus and Mercury though, most planets dont twinkle as they are not points of light like stars. I cant remember seeing either of them emit colours of the rainbow. (Mind you, I've only ever seen Mercury once naked eye)

Matt

[FraserClarke]

Not sure about Venus and Mercury though, most planets dont twinkle as they are not points of light like stars.

Both right I think Most planets don't twinkle because they are not point-like; but Mercury and Venus get a lot smaller than most planets because they have crescent phases, which makes them effectively like a long line of point sources.

So if they are in a crescent phase, then you can see some twinkling from Mercury/Venus.

[caerus_sam]

Thanks for further explanation's on Venus & Mercury. My thought's would have echoed Matt's until that was explained too.

[dph1nm]

I think this subject is trickier than it sounds! It is not entirely clear to me why the stars change colour when they twinkle, but apparently it i something to do with the change in path length through the atmosphere causing gaps in the arrival times of photons which are wavelength dependent.

NigelM

[caerus_sam]

So that would explain the difference in a stars 'twinkle' depending on wether it's directly above you or low on the horizon, I assume.