Astronomers have a pretty solid idea of how stars are born. They begin within the dense, cold dust of an interstellar cloud such as this one. They heat up and get more luminous as they contract, and then drop in luminosity as they continue to contract steadily toward the main sequence.
I’m going to spend at least the next ten or so posts talking about the main-sequence portion of a star’s life cycle. Basically, we’re talking about a star’s adulthood.
You know what, while we’re at it, why don’t I draw up an analogy between a star’s life cycle and that of a human:
When a human is a mere fetus developing within its mother, a star is a protostar.
We say a star has been “born” when it crosses the birth line—basically, satisfies certain expectations for its temperature and luminosity for its specific mass—and becomes visible.
After that, a star steadily approaches adulthood. A “child” star is referred to as a Young Stellar Object (YSO) or a pre-main-sequence star.
Yeah…we’re talking about the Orion Nebula again. I know, we already took a tour through the Orion constellation in my last post…but there’s still more to cover about how stars come to life, and Orion is still the best case study I know.
So…hold up a second. Contagious star formation? What’s that supposed to mean? I mean, usually, when you think about “contagion,” you think of catching diseases from others around you. So…can stars get sick?
Well, no. Stars are pretty good at maintaining their own homeostasis, something I’ll explain in a later post. By “contagious” star formation, I mean that star formation can trigger more star formation.
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One of my favorite objects to show people at astronomy outreach events is the Orion Nebula. Not only does it reside within a fairly well-known constellation, but it’s a gorgeous sight to see with a good telescope.
There’s no time like the present up here in the northern hemisphere. Orion is a winter constellation and rises high in the sky this time of year. Not to mention, as a stellar nursery, talking about the Orion Nebula follows on perfectly from my last couple posts on star formation.
If you’ve ever seen the Orion Nebula through a small telescope, you’re probably wondering what all the rage is about. It mostly just looks like a bluish haze around a star—like the telescope operator didn’t tune the focus quite right.
Can you find a horse in this image of the night sky?
Yeah, me neither. I’m lost. I see the Great Square of Pegasus because I know what to look for, but I still don’t see a horse.
Okay, so now I see half a horse. Where’s the rest?
Your guess is as good as mine, guys. Truth is, constellations very rarely look like what they’re named after. Constellations are more like relics of our ancient past than actual descriptors of what we see up there in the sky. But they do serve a purpose, even if that horse up there is missing his back legs.
I really find myself wondering if whoever made up Pegasus was concerned with animal rights… No animals were harmed in the making of this sky map…
Okay, yeah, never mind.
Where was I? Ah, that’s right. The purpose of the constellations, and the reason why it really doesn’t matter if they don’t look like their names say they do.