Want to stay on top of all the space news? Follow @universetoday on TwitterI’d hate to have to tell my nine year-old this, but the Earth revolves around the Sun, not her. That is a concept that is understood and known to be true. This is called the heliocentric view of the solar system. It hasn’t always been the truth accepted by most people. Until the 16th and 17th centuries most people, scientists included, believed that the solar system revolved around the Earth. That was the geocentric belief. Let’s talk about some facts about the Earth’s orbit and some of the basics of the heliocentric view of the universe.
The Earth sits about 150 million kilometers from the Sun and completes an orbit every 365.242199 mean solar days. The extra time in each orbit causes the need for a ”leap year”. This Earths orbital motion causes the Sun to appear to move 1° across the sky each day. The Earth orbits the Sun at a speed of 108,000 km/h. The Earth is never the exact same distance from the Sun day to day. It moves closer(called perihelion when it is closest) and further(aphelion at its furthest) away from Sol as it makes its orbit. Earth is at perihelion(147,098,074 km) around January 3, and at aphelion(152,097,701 km) around July 4th of each year. Because of many different forces in the solar system, perihelion and aphelion for Earth have changed over the course of time and will continue to change until the end of time.
Broadly, heliocentrism is the theory that the Earth and planets revolve around the Sun and that the Sun is stationary and at the center of the universe. It seems somewhat common sense today, because that is the only view we have ever been taught. The heliocentric view had been proposed on and off since the 3rd century B.C. Most of the early proponents were ridiculed, others were actually burned as witches and heretics. It wasn’t until the 16th century that a fully predictive mathematical model of a heliocentric system was presented by Nicolaus Copernicus. Galileo Galilei made many of the early supportive observations with the first telescopes. We also have learned that the Sun is not actually at rest in space. Like everything is the known Universe, it is in constant motion.
Try this link for more information about heliocentrism. Here on Universe Today we have a great article about how the Earth’s orbit affects the seasons. Astronomy Cast offers a good episode about solar system positions.