M17, the Call-It-Anything-You-Want Nebula

M17 is usually called the Omega Nebula, except by people who call it the Swan Nebula. Or the Horseshoe Nebula. Or the Lobster Nebula, or the Checkmark Nebula. The names reflect a tendency our eye has to add pattern where we want to see it, even if there isn't any there. Early sketches of this object can look like any of the above names, and almost never look much like photos. Herschel gave it the name Omega in the early 19th century, so that is most commonly used now. I think Charles Messier came up with the best name for it-17.

Starting from M8 and scanning north with binoculars, this will be the third or fourth obvious patch of cloudy brightness you would find, depending on the size of your binoculars. It lies north of the Triffid, and just below the Eagle Nebula. There is a bright open cluster of a few dozen very young and hot stars in the center, which in turn are heating up the hydrogen gas in the area, which in turn emits the reddish light. The blueish bits are dust, which just reflects the natural starlight.

The main section of the nebula is roughly 15 light years across, and has a total mass of about 800 times as much as our sun. That sounds heavy, but that is still spread over a huge area...except in the very densest knots of gas and dust, that is still close to being a total vacuum.

Toward the right of the picture is another emission region; in this part of the sky, as you increase the size of the telescope and the length of the exposure, more and more stuff keeps appearing. If you are able to see the Milky Way from your location, this is all spread along the very bright patch around and above the Teapot. I keep saying it, but this is the perfect time of year to just point some cheap binoculars that direction-the night sky is anything but just a bunch of blackness, and you don't need a scope to enjoy it.