Why Do We See Different Stars in Different Seasons? Teach the Night Sky with a Paper Sun

Step outside on a clear winter evening in the Northern Hemisphere and Orion, with its three-star belt, is easy to spot. Come back in July and it’s gone. Where did the stars go? The answer comes from Earth’s orbit, and a classroom walk makes it clear.

First: where do the stars go in the daytime?

Stars don’t leave. They’re still there, but we can’t see them. The Sun is a star too, and it’s so much closer that its light floods the sky and outshines everything else. The next nearest star, Proxima Centauri, is about 4.2 light-years away and too faint to see with the naked eye anyway.

You can show how brightness depends on distance. Sort ten real star cards by their distance and then by how bright they look. Closer doesn’t always mean brighter-looking, because stars differ in real brightness too, but the Sun wins the sky because it’s by far the closest.

The year-long walk

You need: a paper Sun on the floor of the room, labels for the four seasons around it, and a star-pattern chart pinned to each wall, which will be the “background stars.”

A student stands at the “winter” position, facing away from the Sun. That’s the night side of Earth. What stars are in front of you?
The student walks a quarter of the way round to “spring” and faces away from the Sun again. Which stars are in front now?
Continue through summer and autumn.

Students quickly find that at each season, the night side of Earth faces a different part of space. Orion is behind the Sun, in the daytime sky, during Northern Hemisphere summer. That’s why you can’t see it then.

The big idea

Earth orbits the Sun once a year. As it moves, the direction we face at night changes gradually, so different constellations are visible in different seasons. Over a night, the stars seem to move across the sky because Earth rotates. Over a year, the stars shift slowly because Earth orbits.

Hemispheres

People south of the equator see different stars, such as the Southern Cross, and some constellations appear upside down compared with the Northern Hemisphere view. Orion is visible from both hemispheres, but in the Southern Hemisphere it appears inverted and the best viewing season is reversed.

Try it at home

Pick a bright pattern and note where it is at 8 p.m. Check again a month later, at the same time. Is it in the same place? It will have shifted by about 30°, one twelfth of a full circle each month, a nice real-world test of the model.

Light pollution

City lights hide faint stars. A simple star count in one small patch of sky can measure how bright your sky is. Compare counts in your backyard with those from a darker place.

The activities above are Why do stars come out at night? and Why do we see different stars in different seasons? from Stars and the Night Sky, which also includes Why do the stars seem to move across the sky? Sign up for three lessons free.