Many bright stars highlight the sky this evening: Sirius, the brightest of them all; Regulus, the heart of the lion; several sparklers in Orion, and more. Astronomers know a lot about these stars. But most of what they know is a bit uncertain. So when they pin numbers to a star, they give themselves some wiggle room to compensate.

Consider Sirius, which is in the south at nightfall. It’s one of the Sun’s closest neighbors, at a distance of about 8.6 light-years. But that could be off by up to a few percent of a light-year either way. That’s a total variation of perhaps half a trillion miles.

There’s a similar uncertainty in the distance to Regulus, the brightest star of Leo, which is in the east at nightfall. It’s measured at 79 light-years away — give or take that same half a trillion miles.

And the uncertainty is much greater for stars like Betelgeuse — an orange supergiant at the shoulder of Orion. It puffs in and out, and its outer layers are so thin that it’s hard to tell just where its surface is. That makes it harder to get a fix on its position, so it’s harder to measure the distance. Betelgeuse is thought to be roughly 550 light-years away. But it could be perhaps a hundred light-years farther, or 50 light-years closer.

Without an exact distance, it’s hard to determine a star’s size, its true brightness, and more. So the stars are pretty well known — but with sometimes big uncertainties.

Script by Damond Benningfield