Sky Definition and 265 Threads

Would you please tell me how long a starlight can reach my eyes ? I have heard that a star might have already gone dead[/color] although I can still see it shining bright above...That is correct, right ? And another question is as to why I see the star shine with different colors, while it...

Simple question...always wondered why it's blue. :rolleyes:

What does light refraction have to do with the sky being blue (or any color for that matter)? Thanks for any replies.

This is a new launch plaform idea to assist Nasa in meeting it's extra-planetary goals. It seems that a large helium-supported platform in the upper atmosphere could save a lot of launch energy and pollution. The platform might be quite large, perhaps 0.5 to 2 km in diameter, and could be...

http://news.bbc.co.uk/1/hi/sci/tech/3394461.stm

I was reading some article about some scientists who were able to 'read' some sort of cosmic background radiation and determine the size, shape, and age of the universe or whatever. How do they take these radiation readings and create an 'image' or understanding of the universe?

I woke up at 4:30 PST (San Diego) and couldn't go back to sleep so I decided to take my telescope out and finally check out Saturn, the Orion Nebula, and Mars again. They looked awesome through the 8" telescope and I wish I was able to take pictures. Then around 5:30 I saw a really bright object...

OK, how many PFers think Nicool was behind the blackout?

On a clear day, the sky appears to be more blue toward zenith than it does towards the horizon. why? I thought it was because the atmosphere is denser higher up than it is at the Earth's surface but a friend told me "the temp of the upper atmosphere is higher than its at the Earth's urface and...

"In addition to the usual fare that comes with a thunderstorm, many on the city’s Northeast Side witnessed an unusual dark circle in the sky, which turned out to be a ring of smoke that a weather official said emanated from an 'explosion caused by lightning'"...

Not quite sure where this post should go so I'm putting it here. My wife and I were walking the dog the other night and looking toward scorpio we saw a flash of light and then a very broad "vapor trail" like a glowing stripe crossed upwards across the sky. We walked on further and about five...

[SOLVED] Why is the sky blue using avogardo's number? This question was brought up in a physics class, and was never answered for me. I was wondering if anyone here can tell me, given avogadro's number, why is the sky blue? (including all the messy equations if possible). I believe...

Saturn sets before it gets dark and Jupiter right after. I've already seen the cluster in Hercules and the Andromeda galaxy. What else can I look for? Light pollution in my area is moderate, but nothing horrible. I'm using an 8" Meade Starfinder. Thanks!

Einstein proved wrong about blue sky! In 1911 Einstein published an explanation of why the sky is blue based on analysis of Rayleigh scattering by nitrogen and oxygen molecules. His analysis was sufficiently detailed and accurate that it was used to provide an independent measurement of the...

This spring was a good time to spot the direction that our little fleet of galaxies---the Local Group---is traveling in the sky. I calculated this for myself about 10 years back and recently had it confirmed when someone gave an arXiv reference http://www.arxiv.org/abs/astro-ph/0210165 in...