Placing the Pleiades
HOW FAR AWAY ARE THE STARS? You might think that astronomers should know, but distances to the stars are something very difficult to figure out. In daily life, we estimate nearby distances using a trigonometric trick built into our bodies: Our eyes see the world from two slightly different perspectives, and our brain processes this difference to build a three-dimensional image of our environment. This shift in an object’s apparent position, called parallax, enables us to complete a myriad of tasks, from threading a needle to catching a ball in mid-air.
Since classical antiquity astronomers have laboured to use the same method on the stars, by observing the apparent shift of the position of a star while the Earth moves along its orbit. But the stars are so far away that it was only in the 19th century that astronomers finally succeeded in measuring a handful of stellar parallaxes. Measurements on a grand scale had to wait for modern technology.
