Chapter 7, Problem 100A

To determine

The history of how the distance between the Sun and the Earth is determined.

Explanation of Solution

Introduction:

The distance from Earth to Sun is called an astronomical unit (AU), which is further used to measure the various distances in the solar system.

1 AU = 1.49597870 $\times {10}^{11}\text{m}$

• Historically, the Greek astronomer, Aristarchus was the first man to measure the distance to the Sun around the year 250 B.C. He used the different phases of the moon by taking into account the angles formed by the three celestial bodies. But it was hard to locate and find the exact positions of sun and the moon.Before Copernicus proposed his solar system, model named heliocentric model, Aristarchus concluded that earth goes around the sun.
• In 1653 astronomer Christian Huygens evaluated the distance between earth and sun by using phases of Venus, to calculate the angles in Venus-Earth-Sun triangle. During the appearance of Venus as half illuminated by Sun, theses three form right triangle. He then guessed the size of Venus andwas able to find distance from Venus to Earth.
• In 1672, Giovanni Cassini used an angular distance method to calculate the distance to mars as well as distance to the sun at the same time.
• Today we use the astronomical unit for the measurement of distance using the speed of light.