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.
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.