Westward shift of Orion and all the stars
We always get this question at this time of year:
Orion seems to have moved and turned considerably in the last two weeks. Will Orion disappear before summer?
The answer is yes, it’ll soon disappear into the sun’s glare. And – although you might notice it more easily with this particularly bright and noticeable constellation – the fact is that, like Orion, all the stars and constellations shift westward as the seasons pass. Unless they’re in the far northern or southern sky – and so circumpolar – all stars and constellations spend some portion of each year hidden in the sun’s glare. In other words, like blooms on trees or certain flowers or even specific animals in your locale, stars have their own seasons of visibility.
Why does Orion go into the sun’s glare each year at this same time? Only because – each year, as we orbit continually around the sun – our motion in orbit brings the sun between us and Orion at this same time each year.
Of course, stars and their constellations also move westward in the course of a single night, due to Earth’s spin. Orion is no exception.
Exactly when Orion will disappear from your evening sky – into the sunset – depends on your latitude. The farther south you are, the longer you can see Orion. But for the central U.S., Orion is lost in the sun’s glare by early to mid-May (depending on how carefully you look for it).
And for all of us in the U.S., Orion is gone by the time of the summer solstice in June.
If you want to notice the westward shift of the constellations due to the passage of the seasons, be sure to watch at the same time every night. If you want to watch their westward shift throughout the night, just pull up a lawn chair and watch.
Either way, you can easily notice Orion moving steadily westward.
Bottom line: Why the constellation Orion – and all the stars – shift westward as the seasons pass.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.
Published on EarthSky