More Nebulae! Flames and Horseheads.

Today I have Yet Another Nebula Picture (YANP), this time of two nebulae close enough on the sky to share a field of view. One of the them, the Horsehead Nebula, is probably one of the more distinctive and well-known nebulae out there, while the lesser-known Flame Nebula is a visual treat.

Also, these nebulae are nice because they lie near a prominent feature in the night sky, one that many (if not most) people are familiar with. Take a look at the picture below:

The Flame and Horsehead Nebulae in Orion. Click for a larger version.

See that bright star there? That is Alnitak, and you probably know it better as the left (or eastern) star in Orion's belt. The large bright region to its left is the Flame Nebula. Its bright red glow comes from the hydrogen atoms in the cloud being ionized by Alnitak's intense ultraviolet radiation. Alnitak itself is an O-class star, the hottest and most luminous class of stars, and puts out nearly a million times more light across the electromagnetic spectrum than the Sun does.

Just below Alnitak you can see the prominent outline of the Horsehead Nebula silhouetted against a backdrop of glowing hydrogen. In fact, there's a very nice, nearly straight line where a large dusty cloud blocks the light of the nebula behind it that extends for over half a degree below Alnitak.

What's cool is that this cloud of dust is also responsible for the Flame Nebula's dramatic shape, because the same dust cloud that causes the Horsehead Nebula is also in view in front of the Flame Nebula's backdrop of glowing hydrogen. So in a way, these two nebulae are intimately linked.

Another way to illustrate just how dark and dusty the molecular cloud that's producing these nebulae is, is to note that there is no inherent difference in the density of stars across the picture. The left side of the picture has just as many stars as the right side (you're looking through the plane of the Galaxy, after all); it's only the presence of the dust cloud that's blocking out the light from the ones behind it. (The ones you see on the left are either stars in front of the cloud, or ones seen where it is thinner.) All in all, a very beautiful section of the sky, one with a lot of very young, hot, and luminous stars.