How Do We Measure the Distance to Stars?

The closest stars to our solar system are
about 4.3 light years away from Earth. But how do we know that distance? It seems like measuring a star’s distance
should be impossible. It’s not like we can stretch out a cosmic
tape from here to Aldebaran, a giant red star that’s over 400 trillion miles away. Fortunately, we have triangles. Try this. Shift to the left. Then to the right. Everything in front of you appears to move
back and forth. But objects that are farther away move less
than stuff that’s nearby. This effect is called parallax, and we can
use it to measure large distances. As our planet goes around the sun, the stars
appear to shift back and forth relative to more distant stars. The farther away a star is, the less it moves. This shifting is incredibly tiny. The closest star to our sun moves no more
than the width of a soccer ball seen from 40 miles away. By looking at a star in January and then again
in July, we can draw a triangle. The base is the diameter of earth’s orbit. The opposite angle is how far the star appears
to shift. Dig up some high school trigonometry, and
you can calculate the triangle’s height, which in this case is the distance to the
star. Knowing these distances lets us measure other
things, like the brightness of stars or the size of galaxies. It’s so essential that in 2013, the European
Space Agency launched a telescope called Gaia to measure parallax with more precision than
we’ve ever seen. Above the turbulence of Earth’s atmosphere,
Gaia has been plotting the distances to over a billion stars, creating a map of the Milky
Way and some of its galactic neighbors. All that from the lowly triangle. For Scientific American, I’m Deboki Chakravarti.