By Stacy Palen

Gaia’s latest data haul, from December 2020, includes the proper motions of more than 1 billion stars. So the Gaia astronomers did the fun thing and mapped their future positions as they move against the background of the Milky Way.

Below are some questions to ask your students based on this article.

1). There are two motions that are discussed in this article. One of them, “proper motion,” is the “nearly imperceptible motions across the Galaxy year after year.” The other is parallax. How could astronomers tell these two motions apart?

Answer: Parallax is a back-and-forth motion. The star returns to its starting point after a year. The proper motion adds every year, with the star moving farther and farther from its starting point.

2). Why is it important to know the distance to stars?

Answer: Because the distance measurement is connected to the luminosity measurement, and the luminosity is necessary to find out about stars' size, age, structure, and evolution.

3). Study the image in the article that shows the star trails. Are there any trends in the motions of the stars shown here?

Answer: Yes. As you look toward the galactic center, they seem more random, whereas the farther out, toward the corners of the image, the trails are more parallel to one another.

4). How many years will it take each of these stars to travel along one of those trails?

Answer: 400,000 years.

5). Do you expect that you will see any of these stars move a significant distance in your lifetime?

Answer: Absolutely not.

6). Working backwards from the trails that you see here, have the visible constellations changed significantly since the pyramids were built…a bit more than 4,000 years ago?

Answer: No. The stars will have moved about 1/100th of the way along a track in that time, which is not very far.