If you’ve ever found the constellation Orion, there’s a good chance you looked right through this complex cloud of dust and gas without realizing it. The brightest star that you see in this photo is named Alnitak, and it’s the left-most star of Orion’s belt. That belt is probably the most recognizable and famous of all belts. A closer look at the area makes it even more interesting.
There are some nebulae that are well known, and easily seen in a telescope. The Horsehead Nebula, shown here, is well known but not at all easily seen, especially with a small telescope. It’s hard to see even with 12”-16” telescopes. A light pollution filter helps to tease out the faint horsehead-shaped silhouette. The Horsehead itself is actually a dark nebula named Barnard 33. It’s a pillar of nearly-opaque dust rising up in front of the glowing hydrogen gas background. It’s probably one of the biggest things you’ll ever see—that you just about can’t see. It’s about seven light years in length, or about 41 trillion miles.
I used a 10” telescope to get this photo, and, after that, a 16” telescope to see it through an eyepiece. After attaching a light pollution filter and locating the stars just above and in front of the horsehead, I was able to make out the subtle silhouette. It was so dim and indistinct that it was more like a dark blob rather than anything that looked like it belonged to a horse.
There’s one thing to keep in mind when an amateur astronomer says you “can see a nebula.” That might mean you can see it only if your eyes are perfectly dark-adapted, you jiggle the telescope, and you use peripheral vision and maybe even a little imagination! So always temper your expectations when looking through a telescope.
The Flame Nebula is the bright region just to the lower left of the bright star Alnitak in this photo. It is brighter than the Horsehead and should be easier to see, but the bright glare from Alnitak makes it hard to pick out too.
Admittedly, these clouds are hard to see, and usually don’t show color if you do happen to see them. However, that doesn’t mean there’s almost nothing there. Long-exposure photography allows us to see far beyond the limitations of our eyes. This photo consists of 178 four-minute exposures for a total exposure time of more than 11 hours. That’s about the equivalent of letting the telescope and camera stare at it for a full night. Lots of photons can strike the sensor over that time period, allowing us a striking view of what’s really there. Now instead of seeing through it, it can be hard to get through seeing it.
