Measuring the Distance to Stars

Measuring the Distance to Stars

Measuring the distance to stars is not as hard as you might think. As an earth science teacher at Riley High School in South Bend, Indiana, I enjoyed seeing a student’s eyes light up when they came to understand some scientific fact. They had thought it was beyond them, and suddenly it made sense. Knowing the distance to a star was always one of those facts. Let me show you how easy it is:

Look at a picture on the other side of the room. Hold your finger in front of your face and close one eye. Line up your finger and the object on the wall. Now close that eye and open the other eye, Does your finger appear to jump? If you drew a line between your eyes and extended a line from each eye to the picture, you would have a triangle. The apex angle at the picture is controlled by how far away it is from you. If you do the same experiment with an object that is closer, there will be a different angle.

The illustration on the right shows the Earth making its yearly orbit around the Sun. A line from the Earth to the Sun will establish a triangle. In six months, it will look like objects at the apex angle have moved. How much they will have moved depends on how far away they are. My classes do simulations of these measurements on the football field, and it becomes apparent how easy measuring the distance to stars can be.

The measurement unit astronomers use is based on how far away a star must be for the angle at the apex to be one arcsecond. We call that distance one parsec, and it is 3.26 light-years. If the parallax angle is .5 seconds of arc, the star must be 6.52 light-years away. The smaller the angle, the farther away the object is. The European Space Agency’s Gaia mission, which has been underway since 2013, can measure the parallax angle to a millionth of a second of arc. Objects that move such a small amount are tens of thousands of light-years away.

The cosmos is much larger than most of us can imagine. The light we see from some of those stars left the stars hundreds of thousands of years ago. Measuring the distance to stars gives new meaning to passages like Isaiah 40:22: “He stretched out the heavens as a curtain and spread them out as a tent to dwell in.”

If it has taken the light from the stars God created many tens of thousands of years to get here, it is evident that the creation didn’t happen a few thousand years ago. Verses describing the process of creation are untimed and undated. Let us not allow human traditions to challenge the integrity of the Bible. God created time, and He certainly is not limited by anything He created.

— John N. Clayton © 2020