Astrometry facts for kids
Astrometry is a branch of astronomy. It's all about carefully measuring where objects in space are. It also tracks how these objects move. Think of it like mapping the universe! Scientists use astrometry to study stars, planets, and even galaxies. Two important ways to measure these objects are called proper motion and parallax.
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What is Proper Motion?
Proper motion describes how a star or other space object changes its position over time. This is how it looks to us when we observe it from Earth. Imagine watching a car drive by. You see its position change. Stars do the same, but much, much slower!
To measure a star's proper motion, astronomers look at the same part of the sky at different times. Then they see how far the star has shifted. Because stars seem to move so slowly from Earth, we measure their movement in tiny units. These units are called arcseconds per year. One arcsecond is a very small angle, like dividing a circle into 360 degrees, and then dividing each degree into 3,600 arcseconds!
If a star has a large proper motion, it usually means it's quite close to us. For example, Barnard's Star has the largest known proper motion. Yet, it still takes about 348 years for it to move just one degree across the sky. That's 3,600 arcseconds!
Understanding Parallax
Parallax is when an object seems to shift its position when you look at it from two different places. You can try this yourself! Hold your finger out in front of your face. Now, close one eye, then open it and close the other. Your finger seems to jump against the background, right? That's parallax!
In astronomy, parallax is measured using the angle between two lines of sight. Imagine looking at a star from one side of Earth's orbit around the Sun. Then, six months later, you look at the same star from the other side of Earth's orbit. The star will appear to have moved slightly against the distant background stars.
Measuring Distances with Parallax
Astronomers use parallax to figure out how far away the nearest few thousand stars are. The bigger the apparent shift of the star, the closer it is.
These distances are often measured in units called parsecs. One parsec is equal to about 3.26 light years. A light year is the distance light travels in one year. Since light travels incredibly fast, a light year is a huge distance!
Images for kids
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Illustration of how interferometry helps measure star positions very precisely.
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Concept art for the TAU spacecraft. This 1980s idea would have used a probe to help calculate stellar parallax from a much greater distance.
See also
In Spanish: Astrometría para niños
