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SYFY WIRE Bad Astronomy

Crash Course Astronomy: Star Clusters

By Phil Plait

Last week’s episode of Crash Course dealt with stars in multiple systems: binaries, triples, quadruples, and more. Most stars in the sky are multiples!

It turns out that stars can be in even bigger, more complex systems. Most stars may be born by the thousands in clusters. Maybe even the Sun was.

Clusters are gorgeous astronomical objects, but they’re more than that: They’re astrophysical laboratories, allowing us to puzzle out a lot of very cool information about the starry denizens that live there.

Want to know more? Let this guy in a fabulous shirt tell you more in Crash Course Astronomy: Star Clusters.

A caveat: At 7:30, I say that the stars in globular clusters were all born at the same time, and therefore are the same age. That’s not actually precisely really true, so much. It may be true for most globulars, but we do know of examples where star formation happened in two, separate events. This tends to happen in more massive clusters; perhaps they were so massive their gravity could draw in gas around them, triggering a second wave of star formation.

As sometimes happens in CCA, I wanted to talk about this, but it’s hard to introduce a topic like that and cover it well enough to be understood in the allotted time for the episode. I had to agonize over what to leave in and take out in practically every episode. There’s just too much astronomy!

I’ve written about globular clusters dozens of times over the years. If you’re curious, some of my favorite ones are M15, 47 Tuc, and Omega Cen.

Not to downplay open clusters! I like them too. A few of my choices are the Pleiades (duh), NGC 3603, M67 (mostly because it’s incredibly old, which is unusual for an open cluster), and the Double Cluster (h and χ Persei) in Perseus—it’s visible to the naked eye from very dark sites, shows up as a double in binoculars, and then reveals its true nature as two separate clusters when you look through a telescope. Very very cool.

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