So, when you look up at the stars it’s a nice, steady backdrop. An airplane might pass by, or you might be treated to an occasional meteor blazing its way across the sky, but it’s pretty much unchanging, right? Well, not really. Most of us don’t spend enough time looking at the stars to be aware of what is going on, unlike in ancient times when sailors didn’t simply stop sailing at night and go to bed, but used the stars to navigate and stay on course.
Ancient people also knew how far along into the night they were, but didn’t have watches or even clocks. They simply knew that this star or that constellation rose at a particular time of the night and that it was eight or five or three hours until dawn. They were much more acquainted with the sky than we are nowadays. They could all find Polaris with ease and could tell the time by noting the position of Ursa Major as it swept around the North Star like the hand on an analog clock.
A Matter Of Perspective
Of course you realize that the sky isn’t turning any more than the entire Universe is spinning around you when you twirl to make yourself dizzy. It’s all perspective. We’re on a planet that is so big that it seems still to us – we share its motion and don’t experience any acceleration. The Ancients thought that the Universe turned around us; that the Sun actually moved across the sky – they even created “gods” like Hermes who was responsible for dragging the Sun across the sky every day.
What Direction Do Stars Move In The Sky?
The Sun, Moon and stars all appear to rise in the East and set in the West, because the Earth revolves on its axis in the opposite direction from West to East every 24 hours. The movement we therefore observe is not their movement, but our own as we go zipping along on the surface of the Earth towards the East, and these celestial objects pass us overhead.
The North Star (Polaris) in Ursa Minor is useful for illustrating this point, as it is a pivot around which the entire northern sky revolves. If you stand facing North, your right hand-side will point due East, and your left hand-side due West, with the ground beneath you and everything on it is moving from your left to right. Therefore, if you look up at Polaris you will see the stars rotating in the opposite direction from right to left (counter-clockwise) once every 24 hours. In the same way, if you were to face due South the stars would naturally appear to rotate from left to right in a clockwise direction.
In other words, while the Sun, Moon and stars travel from East to West the direction we see them moving depends entirely on which direction we are facing at the time:
Facing North: Stars rotate counter-clockwise (right to left)
Facing South: Stars rotate clockwise (left to right)
Facing East: Stars rise in front, and set behind
Facing West: Stars rise behind, and set in front
In this video you can see how to locate Polaris (The North Star), and then see a time-lapse movie of the sky’s rotation. The Big Dipper makes a complete circle every year as do other circumpolar constellations. Some constellations disappear below the horizon for part of the year because the bulk of the Earth gets in the way. All constellations are circumpolar (how could they not be?) but the ones we refer to that way in the Northern Hemisphere are the ones we can see all year long, such as the Little Dipper, Big Dipper, Draco, Cepheus, Cassiopeia and some other less famous ones.
Seeing Is Believing
Most of us don’t spend enough time looking at the stars to be aware of what is going on. Unlike the ancients we have MP3 players, innumerable social activities, cars, and bright lights. There are so many things happening at eye-level that we have few impulses to ever look upwards, and if we do, it is very briefly. However, now that we know in which direction the star constellations are moving it doesn’t mean that we truly comprehend it. If you want to fully understand something, sometimes you have to get your hands dirty and get right in there and study it. So on the next clear night step outside and take a good look at the rotation of the stars and constellations in the celestial heavens. Therein lies the Proof.