Astronomers use the speed of light as a cosmic measuring stick to find distances in space through a method called “light travel time.” Here’s how it works:
- Light travels at a constant speed (about 299,792 kilometers per second in a vacuum). When astronomers observe light from distant objects like stars or galaxies, that light has taken time to reach Earth.
- By measuring how long the light has been traveling, they can calculate how far away the object is. For example, if light from a star takes 10 years to reach us, the star is said to be 10 light-years away.
- For relatively close objects like the Moon or planets, astronomers can send signals (like radar waves) and measure the time it takes for the signal to bounce back. Multiplying the travel time by the speed of light gives the distance.
- For very distant galaxies, astronomers combine light travel time with other methods (like redshift, which measures how much the light’s wavelength has stretched due to the universe’s expansion) to estimate enormous cosmic distances.
Using the speed of light as a constant, astronomers turn the universe’s vastness into measurable distances, helping us understand the size and structure of the cosmos.