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Scientific American Instant Egghead
That star is 25 light years away.
That one's 400.
But how do we know that?
It seems like measuring distances to stars should be impossible.
It's not like we can stretch out a cosmic tape measure from here to Aldebaran,
a giant red star that's over 400 trillion miles away.
Fortunately, we've got 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 wobbles 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.
In fact, measuring parallax lets us map out the entire universe.
It's so essential that the European Space Agency has developed a telescope called Gaia.
Its mission is to measure parallax with more precision than we've ever seen.
Above the turbulence of Earth's atmosphere, Gaia will make a three-dimensional map of over a billion stars
all the way to the core of our galaxy...roughly 30,000 light-years away.
All that, from the lowly triangle.
For Scientific American's Instant Egghead, I'm Christopher Crockett.