Most importantly, we’ve looked at the H-R diagram, the diagram that classifies stars by their color, temperature, composition, and luminosity…and relates those properties with many other features stars have.
We know what kinds of stars are out there. We know they range from thousands of times smaller than the sun to thousands of times larger. We know they range from desperately faint to incredibly luminous. We know they come in all the colors of the rainbow.
But how many blue stars are there? How many small stars are there? Are most of them small, or are there about the same number of small stars as large ones?
Here’s a visual binary that just about stretches the limits of the definition. It’s a star, though you’ll never see it like this with the naked eye. Specifically, this is Sirius, the brightest star in the sky.
But if you look closely on the top left, you’ll see a tiny dot just peeking out from behind Sirius’s brilliance. That’s Sirius B, this bright star’s faint companion. Together, they’re known as Sirius A and Sirius B.
It’s tradition for astronomers to name all the stars in a system the same thing, but it also makes sense. Most of them aren’t obvious. You might look at some ordinary-looking star in the sky, say…Antares. But as it turns out, Antares has a barely-visible companion.
The visibility of visual binaries has a wide range. Consider the famous double star in the Big Dipper, Mizar.
They look like billions of little pinpricks of light, right? It’s hard to imagine that each one of these is probably the size of the sun…or much larger. And the sun, by the way, is about 109 times Earth’s diameter.
So if you thought those stars were small…not so.
It makes sense that they would be very large. Their light reaches us from many light years away, with the nearest star 4.3 light years away and the most distant one likely trillions.
In order to radiate that far out and stay bright enough to speckle the night, they would have to be very luminous, and that means having a large surface area, even if they’re not particularly hot.
Have you ever looked up at the night sky and noticed that while relatively bright stars outline the constellations, there are numerous other stars that are almost too faint to see with the naked eye?
If you ever noticed this, you probably guessed that the brighter stars are literally brighter, and the fainter stars truly are fainter. Or maybe you guessed that they don’t vary in brightness that much, but fainter stars are much farther away.
But that’s not really true…or, at least, it’s not the whole answer.
So what’s the real reason why some stars appear to be brighter than others—and how can we tell how bright they really are?
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.