Page 1 of 1
Why is the sky blue? (APOD 03 Sep 2007)
Posted: Mon Sep 03, 2007 6:15 am
by SmartAZ
"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!
Re: Why is the sky blue?
Posted: Mon Sep 03, 2007 6:35 am
by Andy Wade
Spammer! Mods please note!
Don't click on any of the links on that website!
Posted: Mon Sep 03, 2007 6:43 am
by SmartAZ
Excuse me? Did I say something I shouldn't?
Posted: Mon Sep 03, 2007 8:23 am
by Qev
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.
Posted: Mon Sep 03, 2007 1:19 pm
by NoelC
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
Re: Why is the sky blue?
Posted: Mon Sep 03, 2007 1:34 pm
by Case
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.
Posted: Mon Sep 03, 2007 3:52 pm
by Andy Wade
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.
Posted: Mon Sep 03, 2007 9:30 pm
by SmartAZ
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!"
Posted: Wed Sep 05, 2007 1:41 pm
by bystander
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.
Posted: Wed Sep 05, 2007 4:46 pm
by emc
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.