Proper motion facts for kids
Proper motion is how stars appear to slowly move across the sky. This movement is seen when we look at them from Earth. It's like watching a very slow-motion race in space!
All stars, including our own Sun, are always moving. They travel through space at super fast speeds. We are talking hundreds of kilometres every second! But stars are incredibly far away. Because of this, it takes a very long time to see them move. Even then, you usually need a strong telescope to notice the change. For a long time, people thought stars didn't move at all. Even the ancient Greeks, who knew a lot about stars, didn't discover proper motion.
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What is Proper Motion?
Proper motion describes the tiny shift in a star's position. This shift happens over many years. It's different from other star movements. For example, it's not about stars getting brighter or dimmer. It's about their actual change in location in the sky.
Why is it Hard to See?
Imagine a car driving very far away. It looks like it's barely moving, right? Stars are even farther! They are so far that their fast movement seems tiny to us. This is why it took so long for people to notice proper motion. It's a very slow dance across the sky.
Who Discovered This Movement?
Proper motion was first proven in 1718. An astronomer named Edmond Halley made the discovery. He compared old star maps with what he saw. The old maps were drawn by Hipparchus around 130 BC. Halley noticed that stars like Sirius, Arcturus, and Aldebaran had moved.
Even after more than 1,800 years, their positions had changed very little. They moved less than half a degree. That's a tiny amount! It shows how slow proper motion appears from Earth.
How Do Astronomers Use It?
Proper motion is very helpful for astronomers. It helps them figure out how far away a star is. Stars that are closer to Earth usually have a bigger proper motion. This means they seem to move faster across the sky. Stars that are farther away move slower.
For example, Barnard's star has the biggest proper motion of any star. It moves 10.3 arcseconds each year. To give you an idea, that's like moving half the size of the Moon in the sky in just 87 years! Barnard's star is also the second-closest star to Earth. It is only 5.98 light years away. Also, eight of the ten stars with the biggest proper motions are less than 15 light years away. This shows the link between proper motion and how close a star is.
Images for kids
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Proper motion of 61 Cygni in one year intervals.
See also
In Spanish: Movimiento propio para niños
