Discover: The Night Sky

Because the Sun shines much brighter than the other objects in space during the day, darkness allows a better view of the moon, the planets, and other stars. Much of what we know about how objects move in space has been learned by watching and recording the locations of the objects in night sky as they change over time.

Because we are standing on Earth and do not feel ourselves moving, we can understand how people might think that everything else is moving around us.

Ptolemy, an Egyptian astronomer, mathematician, and geographer believed that the Earth stood still and the Sun, Moon, and the stars all moved around the Earth. This “Earth-centred” theory looks something like this:

However, observations made by Copernicus, Galileo and other astronomers suggested that this theory was incorrect. Now, we know that the Earth is moving in at least two ways: Earth orbits the Sun and Earth rotates about its own axis. 

If you were to stand outside and stare at the stars in the night sky for a few hours, some of the stars would seem to move. The apparent daily motion of the stars in relation to the Earth is the result of the rotation of the Earth.

You can imagine that, as the Earth rotates, our view of the stars changes. The stars appear to be moving across the sky when, in fact, the Earth is moving.

Watch this video that demonstrates this.

Polaris, the North Star, remains in a constant place in the night sky. Other constellations appear to move across the night sky. Watch this video to see this movement. Be sure that you watch from 0:55 to 2:30.

Some constellations are visible to us only at certain times of the year. Other constellations such as the Big Dipper and the Little Dipper move through the sky each night, but they are always visible in the sky no matter the time of the year.

Check the Synaptic Sky website to see what the Big Dipper and Little Dipper look like during each of the four seasons. (Read up to “Using constellations as pointers”.)

You will be making your own observations of the night sky and recording them in a viewing log.

You can use your star wheel to help you locate constellations you might see. The idea is to watch the same spot in the sky for several hours to see if you notice how it changes over time.

Think about Galileo making these same observations during his time. Would you have made the same conclusions that he did?