You are here

Night Watch

StarDate: 
April 3, 2016

When you take a picture of your friends or family, it’s a moment frozen in time — you see everyone and everything in the picture as they appeared at the same instant. A shot of the night sky, on the other hand, is like hundreds or thousands of individual snapshots all pasted together. That’s because you’re seeing every star as it appeared at some point in the past — anywhere from a few years to thousands of years ago.

The light from each star races through space at 670 million miles per hour — faster than anything else in the universe. Yet the gulf between stars is vast — trillions of miles to even the closest of them. So even light takes a long time to travel from one star to another.

As night falls this evening, for example, look in the southwest for Sirius, the brightest star in the night sky. The light you see from the star tonight actually began its journey 8.6 years ago. That means the star is 8.6 light-years away.

Orion is off to its right, marked by the hunter’s three-star belt. The constellation’s brightest stars bracket the belt — Betelgeuse above, and Rigel below. Each of these stars is hundreds of light-years away, so we see them as they looked hundreds of years in the past.

Betelgeuse and Rigel are both expected to end their lives with titanic explosions. In fact, it’s possible that one of the stars could have exploded already, and the light from the blast is racing toward us — the light for a future snapshot of the night sky.

 

Script by Damond Benningfield

Get Premium Audio

Listen to today's episode of StarDate on the web the same day it airs in high-quality streaming audio without any extra ads or announcements. Choose a $8 one-month pass, or listen every day for a year for just $30.