HOW FAR ARE STARS?

FOR YOUR NOTEBOOK:

Astronomers learned to measure distance in space by:

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1. Ancient Greeks were able to figure out the size of the Earth through a series of experiments.  Credit goes to Eratosthenes.

   1. First they figured out through observations of the moon and the horizon, that the Earth is spherical.

   2. In Greece, the distance from Syene to Alexandria​ is 830 km.  Both cities have a deep well in close proximity to the city.

   3. At the zenith (when the sun is directly over you) in Alexandria, the sun's light hit the bottom of Alexandria's well.  In Syene he saw a 7 degree difference in the shadow of the Syene well.  About 1/50 of a 360 Degree sphere.

   4. 830km x 50 = 42000 km.  The accepted value is now 40074 km.

2. Humans used lunar eclipses (Earth's shadow on the moon) and the Earth's diameter to calculate the distance to the moon with geometry.

3. We used trigonometry with the moon's distance and revolution to find the distance to the sun.  This was called using Parallax.

4. Using the Earth's distance to the Sun, we were able to do Trigonometry to calculate star distances in a method called Stellar Parallax.

5. Then we linked brightness to distance.​  The further the star, the dimmer the light.