Why is the sky blue? (APOD 03 Sep 2007)

SmartAZ · Post by **SmartAZ** » Mon Sep 03, 2007 6:15 am

"The blue regions shine primarily by reflected light. Blue light from the star Rho Ophiuchi and nearby stars reflects more efficiently off this portion of the nebula than red light. The Earth's daytime sky appears blue for the same reason."

http://antwrp.gsfc.nasa.gov/apod/ap070903.html

What a muddled explanation! Every essay I have read says the sky is blue because of refraction, not reflection. And the link http://www.why-is-the-sky-blue.org/ goes to a site that is for sale!

Andy Wade · Post by **Andy Wade** » Mon Sep 03, 2007 6:35 am

Spammer! Mods please note!

Don't click on any of the links on that website!

SmartAZ · Post by **SmartAZ** » Mon Sep 03, 2007 6:43 am

Excuse me? Did I say something I shouldn't?

Qev · Post by **Qev** » Mon Sep 03, 2007 8:23 am

The process is called Raleigh scattering. The molecules that make up the atmosphere are approximately the same scale as the wavelength of blue light, so it scatters blue light more efficiently than other colours. Thus, the sky (and reflection nebulae) appear blue.

NoelC · Post by **NoelC** » Mon Sep 03, 2007 1:19 pm

SmartAZ, you did fine. I suspect the APOD guys reused an old link to a blue sky explanation that they've used before, and the site that was once there, which very likely contained legitimate science, is now defunct.

-Noel

Case · Post by **Case** » Mon Sep 03, 2007 1:34 pm

NoelC wrote:I suspect [they] reused an old link

Not only an old link, the APOD is practically the same as the one for June 2, 2004.

Andy Wade · Post by **Andy Wade** » Mon Sep 03, 2007 3:52 pm

SmartAZ wrote:Excuse me? Did I say something I shouldn't?

Hmmmm.... Sorry about that, it's just that I saw what was your first post on here with a link to another website that had advertising on it and I put two and two together and came up with spam. That's a pattern I've seen before many times and the links from some of these websites just load up spyware on your computer. No offence intended.

Can't be too careful out there.

SmartAZ · Post by **SmartAZ** » Mon Sep 03, 2007 9:30 pm

With a name like mine I have to be careful all the time. I've tried using other names but people still know who I am. The tell me, "Oh you're such a SmartAZ!"

bystander · Post by **bystander** » Wed Sep 05, 2007 1:41 pm

It is my understanding that the light from reflection nebula is light reflected from nearby stars. The color of reflection nebula is caused by Raleigh scattering (refraction) in the same way our skies are colored blue. Emission nebula create their own light, mostly excited H-alpha ions which have a distinctly red glow.

emc · Post by **emc** » Wed Sep 05, 2007 4:46 pm

Leonardo Da Vinci had interesting insight and did some clever experimentation on why the sky is blue. You can find info from his notebook on the web if anyone's curious.

Starship Asterisk*

Why is the sky blue? (APOD 03 Sep 2007)

Why is the sky blue? (APOD 03 Sep 2007)

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