Fixed stars, part I
A star is coming very close to the Sun very soon, as distance and time go in astronomy.
If you look at the sky from night to night, even if you watch closely and attentively, the stars don’t seem to change. Yes, different ones appear at different times and seasons, and a few bright ones (the planets) move around in kind-of-predictable patterns, but the background “fixed” stars all seem to stay the same with respect to each other. Many constellations are thousands of years old, after all, and the shapes we see are the same as our remote ancestors named.
We know that this is an illusion, caused by the fact that stars are (by our measure) very far away and very far between. Even though they may be moving a dozen kilometers per second with respect to the average (and most are doing at least that), kilometers are tiny compared to the distances between them and seconds an impossibly short time to show any movement. It’s extremely rare for the patterns in the sky to show changes that a single human can detect, using only the naked eye. But one is coming up.
A recent paper, using data from the Gaia space mission (about which we’ll post more later), recalculates the path of the star Gliese 710. The name-and-number designation is a clue that it’s not one of the important stars known to the ancients; in fact you can’t see it at all without a good pair of binoculars and a dark sky. Its significance lies in the fact that it is moving almost directly toward us. It is now almost twenty parsecs away; the computed path brings it possibly a thousand times closer.
Some back-of-the-envelope calculations by our astronomer (we keep several old envelopes on hand, just in case) show that, at its closest, the star will be about twice as bright as Venus ever gets, much brighter than any fixed star in our current sky. It will compete with aircraft landing lights from a nearby airport. And it will be moving across the sky at an amazing pace: at its fastest, in a decade it will change position by almost the width of the Moon, altering star patterns in a way obvious to any observer. For someone used to today’s sky, it will be quite a show. Alas, it will remain among the brightest stars in the sky for a cosmic eyeblink, maybe thirty thousand years.
Even if it passes at its most probable distance, it will still reach a place among the dozen or so brightest stars in the sky, and any attentive observer will see its constellation (whichever one it’s assigned to) alter shape drastically over time.
When we talk about observers, though, we run into the hardest part of the prediction. The time of closest approach is something like 1.3 million years in the future. 1.3 million years ago there were none of our species around to see things. It seems highly improbable that our evolution will simply stop where it is and that whoever watches Gliese 710 pass by will be just like us. The most uncertain part of the prediction is who will see it come true.
