While the title of this post would make a fine name for my next punk band, I’ll skip past any personal interest in the term and make this post about astronomy stuff, as always.
The term “Nebula” was first used (so far as I can tell) by William Herschel in the first half of the 18th century to describe the fuzzy stuff in the night sky, as opposed to the single points of light we see from stars and planets. Some of these things are whole galaxies, like M31, which was (and sometimes is still) called “The Andromeda Nebula” and M83, which is the name of a band, the Southern Pinwheel galaxy. The “M#” designation refers to the Messier catalog, which is a list of astronomical items with nebulosity, btw. The others are BIG clouds of gas and dust within our own galaxy. The term seems to stem from the Greek words for “cloud or fog”, nephele or nephos, which seems sensible.
Of course, the reason we see these at all is primarily because of the stars within these pockets of gas and dust, some of which are forming stars and planets , even as I write this. Our sun and planet were born in a nebula, long ago, from the scattered remains of a big star that met a violent end. But what if there aren’t any (or enough) stars around to light everything up? If we’re talking about visible light, this would mean it remains dark. If you’ve ever wondered why you can’t easily see the center of our own galaxy, it’s because there’s so much of this stuff in the way. You have to leave the visible spectrum of light and delve into the longer wavelengths of infra-red to see through it.
Here’s a picture of LDN 1622 that illustrates this very well.
Even with better known nebulae, like the famous one in Orion, the stuff you see is only part of the picture, they have expanses beyond what’s normally illuminated that block the light of other stars. Or, even the center of a galaxy that’s less than 30K light years away when they team up.
So, if it weren’t for these things, we’d see many more stars than we do now. Of course, it was stars that made them (the parts that aren’t just hydrogen anyway) and if it weren’t for nebulae like them our sun wouldn’t be here, so neither would we. Seems like a fair deal to me.