It’s a long way from Earth to the center of the galaxy. But the exact distance is uncertain — measurements vary by several thousand light-years. The most accurate method of measuring astronomical distances is called parallax. To understand how it works, hold out a finger and look at it with first one eye, then the other. The finger appears to shift against the background. The angle of the shift reveals how far the finger is from your eyes. Astronomers determine parallax by looking at an object when Earth is on opposite sides of the Sun. The change in position causes a target to shift a tiny bit compared to the background of more-distant objects. As the distance increases, though, the angle gets smaller. Eventually, it gets so small that it’s almost impossible to measure. That’s especially true when you’re looking through Earth’s atmosphere, which blurs the view. New technology has sharpened the view, but there’s still a lot of wiggle room in the measurements. Another technique looks at
