by Ann » Mon Jan 07, 2013 4:36 pm
ababila wrote:Hi,
Another beautiful APOD!
I am following APOD for a number of years now, I think it must be at least 6 years - I forget.
Close to 100% of the pictures I find beautifull, fascinating or (just) interesting.
This is a tribute to the work you do and of course the work of all astronomers, amateur or professional.
Keep it up
A question:
Often there is a reference to 'the surrounding emission nebula' and I always accepted this without questioning what was meant.
But in this picture I see a dark blueish haze around AE Aurigae. Is this the emission nebula or is it something else
(I do not mean the clear sky-blue streams here, but maybe you did?)
Greetings from ababila, the Netherlands.
What makes this nebula special is that the star ionizing it, AE Aurigae, was not born inside it. Instead, AE Aurigae is speeding through space and making its way though this cloud by pure chance. As it does so, it "plows" much of the dust in the cloud in front of it like a snowplow. The dust grains are the right size to reflect AE Aurigae's blue color. Take a look at
this very large (2.8 MB) true-color image to clearly see the dusty blue reflection nebula which is particularly bright in the direction where it is being compressed by AE Aurigae's motion. AE Aurigae is moving to the right as seen in the picture in the link.
Normally, however, stars as hot as AE Aurigae are not surrounded by a blue reflection nebula. That's because these very hot stars have very strong winds, which simply blow the dust grains away. Why hasn't that happened to the nebula around AE Aurigae? It is precisely because the star is just passing through at a fast clip. It hasn't been in that dust cloud for a very long time, and it hasn't had time to really dissipate the dust.
AE Aurigae isn't just making a blue reflection nebula, it's making a red emission nebula, too. The red glow of the emission nebula doesn't come from dust but from hydrogen gas. For some reason, possibly because it is easier to compress dust grains than hydrogen atoms and ions, the dust is not distributed in the same way as the gas IC 405, the nebula surrounding AE Aurigae.
Ann
[quote="ababila"]Hi,
Another beautiful APOD!
I am following APOD for a number of years now, I think it must be at least 6 years - I forget.
Close to 100% of the pictures I find beautifull, fascinating or (just) interesting.
This is a tribute to the work you do and of course the work of all astronomers, amateur or professional.
Keep it up :!:
A question:
Often there is a reference to 'the surrounding emission nebula' and I always accepted this without questioning what was meant.
But in this picture I see a dark blueish haze around AE Aurigae. Is this the emission nebula or is it something else :?:
(I do not mean the clear sky-blue streams here, but maybe you did?)
Greetings from ababila, the Netherlands.[/quote]
What makes this nebula special is that the star ionizing it, AE Aurigae, was not born inside it. Instead, AE Aurigae is speeding through space and making its way though this cloud by pure chance. As it does so, it "plows" much of the dust in the cloud in front of it like a snowplow. The dust grains are the right size to reflect AE Aurigae's blue color. Take a look at [url=http://www.azdeepskies.com/_Media/ic405-12-29crp.jpeg]this very large (2.8 MB) true-color image[/url] to clearly see the dusty blue reflection nebula which is particularly bright in the direction where it is being compressed by AE Aurigae's motion. AE Aurigae is moving to the right as seen in the picture in the link.
Normally, however, stars as hot as AE Aurigae are not surrounded by a blue reflection nebula. That's because these very hot stars have very strong winds, which simply blow the dust grains away. Why hasn't that happened to the nebula around AE Aurigae? It is precisely because the star is just passing through at a fast clip. It hasn't been in that dust cloud for a very long time, and it hasn't had time to really dissipate the dust.
AE Aurigae isn't just making a blue reflection nebula, it's making a red emission nebula, too. The red glow of the emission nebula doesn't come from dust but from hydrogen gas. For some reason, possibly because it is easier to compress dust grains than hydrogen atoms and ions, the dust is not distributed in the same way as the gas IC 405, the nebula surrounding AE Aurigae.
Ann