Change. It’s relentless. In our lives, our families, neighbors, towns, cities, on and on. Time is the culprit, time is change. If we could stop time, we could stop change. Well, good luck with that.
The constellations have seemed constant in our experience. Everything else changes and we can see it, measure it, but constellations just seem to be there, never changing. Of course, you might think, well, it’s because stars are so far away, and you would be correct. Stars are at immense distances, so distant that their own movements are not apparent, except by astronomers using exquisitely sensitive equipment. From the first cave drawings of star patterns to today they appear the same. But they are changing and someday will not look at all as they appear today.
Someday is a long time off. We’re talking tens to hundreds of thousands of years.
A familiar grouping of stars, given a name, is called a constellation. There are 88 constellations officially on record, covering the northern and southern hemispheres. The current official listing of constellations has taken a few thousand years to develop. From ancient middle eastern, Chinese, Greek, Roman, and other cultures the current International Astronomical Union (IAU) constellations list evolved. It’s the official list professional and amateur astronomers worldwide refer to when studying the heavens.
Take the Big Dipper. Oops, it’s not a constellation, it’s part of a constellation so another term to learn. A familiar grouping of stars, given a name, but not a constellation itself, is called an asterism. The Big Dipper is part of the constellation Ursa Major, the great bear. The cup is part of the bear’s body, and the handle is the bear’s tail. There is a lot more to Ursa Major, but the Big Dipper stands out.
Most of the patterns we call constellations and asterisms are made up of stars that are not associated with each other. The Big Dipper, and Ursa Major for that matter are exceptions. Many of the stars in Ursa Major belong to the Ursa Major Moving Group and are heading the same direction at the same rate. They appear to be heading toward Sagittarius. Just bear in mind, the stars of Sagittarius are moving too. All the stars in all the universe are moving.
With all this moving you can expect things to change, and it will, but so slowly you need to speed up the video to notice. This can be done in planetarium applications for your computer or phone. Or just do a search for how constellations change shape and watch on youtube. The Big Dipper will be unrecognizable in 100,000 years.
The Big Dipper will be gone.
What’s in the Sky?
July 25; before sunrise; southwest: The Moon is positioned between Jupiter and Saturn.
July 28-30; late night to early morning; south: The Southern Delta Aquariid meteor shower peaks. A bright Moon interferes.