by Ann » Thu Apr 07, 2011 1:04 am
To return to M74, what makes it so graceful is not only its face-on orientation, but also that its two major arms are so regular, that the red HII regions mostly follow the arms, and that the irregularity in the arm above the center in today's APOD doesn't affect the overall shape of the galaxy, but is a local phenomenon. Another thing that adds to the grace of M74 is that its center is so small, and that the elegant spiral structure dominates the galaxy so completely.
Two things should be noted in the Spitzer infrared image of the galaxy that neufer included in its post. First that the importance of the two major arms is played down in the infrared, and the galaxy looks more like a multi-armed spiral than a grand design elegant two-armed spiral. Second, that the blue color in the infrared image, which represents starlight, is hardly seen at all outside the very small galactic bulge of M74. Doesn't this galaxy have stars outside its bulge? Of course it does, and we can see those stars clearly in optical images. But stars that are blue, hot and not very large don't show up in infrared images of galaxies.
Ann
To return to M74, what makes it so graceful is not only its face-on orientation, but also that its two major arms are so regular, that the red HII regions mostly follow the arms, and that the irregularity in the arm above the center in today's APOD doesn't affect the overall shape of the galaxy, but is a local phenomenon. Another thing that adds to the grace of M74 is that its center is so small, and that the elegant spiral structure dominates the galaxy so completely.
Two things should be noted in the Spitzer infrared image of the galaxy that neufer included in its post. First that the importance of the two major arms is played down in the infrared, and the galaxy looks more like a multi-armed spiral than a grand design elegant two-armed spiral. Second, that the blue color in the infrared image, which represents starlight, is hardly seen at all outside the very small galactic bulge of M74. Doesn't this galaxy have stars outside its bulge? Of course it does, and we can see those stars clearly in optical images. But stars that are blue, hot and not very large don't show up in infrared images of galaxies.
Ann