by Ann » Sat Sep 26, 2015 6:15 am
What a fine picture!
M31 and M33 are certainly "equidistant" from bright star Mirach as seen from the Earth.
This is a picture full of the letter "M". There is M31, M33 and Mirach, which is an M-type star.
As a color commentator I find the colors very interesting. The bright yellow color of Mirach is very striking. We are often told that M-type stars are very red, but when I looked at M-type stars through a telescope, I often thought they looked this sort of yellow.
But while Mirach doesn't look red (very far from it), its yellow brilliance makes the color of the galaxies pale to a faded white in comparison. The picture clearly shows us that while Andromeda and M33 are different sort of galaxies - just look at the large bulge, long straight dust lane and disky flatness of Andromeda compared with the somewhat messy spiral nature of small M33 - the color difference between these two galaxies is visible but by no means striking.
Mirach, an M-type star, is neither fusing hydrogen nor helium in its core.
Jim Kaler wrote:
It is difficult to say just what state the star is in. It is clearly massive, having three or four times the mass of the Sun, but it may have a core made of helium or one made of carbon.
If MIrach has a helium core, it is fusing hydrogen in a shell around its core, and if it has a carbon core, it is fusing helium in a shell around its core.
But as an M-type star, Mirach is redder - make that yellower - than a galaxy will ever be. Not even "red and dead" galaxies have integrated colors as red as an M-type star. Even the light of galaxies without any star formation at all is dominated by stars less red (or yellow) than M-type stars.
For comparison, the B-V index of Mirach is 1.576 ± 0.010. The overall integrated B-V index of Andromeda is 0.920, and the B-V of M33 is 0.550. Even though M31 is dominated by cool stars (and its large bulge is completely made up of cool stars) while M33 is dominated by hot stars, the "odd man out" when it comes to color of the threesome in today's APOD is the cool star, not one of the two galaxies.
Ann
What a fine picture! :D
M31 and M33 are certainly "equidistant" from bright star Mirach as seen from the Earth.
This is a picture full of the letter "M". There is M31, M33 and Mirach, which is an M-type star.
As a color commentator I find the colors very interesting. The bright yellow color of Mirach is very striking. We are often told that M-type stars are very red, but when I looked at M-type stars through a telescope, I often thought they looked this sort of yellow.
But while Mirach doesn't look red (very far from it), its yellow brilliance makes the color of the galaxies pale to a faded white in comparison. The picture clearly shows us that while Andromeda and M33 are different sort of galaxies - just look at the large bulge, long straight dust lane and disky flatness of Andromeda compared with the somewhat messy spiral nature of small M33 - the color difference between these two galaxies is visible but by no means striking.
Mirach, an M-type star, is neither fusing hydrogen nor helium in its core.
[quote][url=http://stars.astro.illinois.edu/sow/mirach.html]Jim Kaler wrote[/url]:
It is difficult to say just what state the star is in. It is clearly massive, having three or four times the mass of the Sun, but it may have a core made of helium or one made of carbon.[/quote]
If MIrach has a helium core, it is fusing hydrogen in a shell around its core, and if it has a carbon core, it is fusing helium in a shell around its core.
But as an M-type star, Mirach is redder - make that yellower - than a galaxy will ever be. Not even "red and dead" galaxies have integrated colors as red as an M-type star. Even the light of galaxies without any star formation at all is dominated by stars less red (or yellow) than M-type stars.
For comparison, the B-V index of Mirach is 1.576 ± 0.010. The overall integrated B-V index of Andromeda is 0.920, and the B-V of M33 is 0.550. Even though M31 is dominated by cool stars (and its large bulge is completely made up of cool stars) while M33 is dominated by hot stars, the "odd man out" when it comes to color of the threesome in today's APOD is the cool star, not one of the two galaxies.
Ann