Humanities › Geography What is Revolution in Astronomy? How Does the Sun Affect Our Orbit? Share Flipboard Email Print CLAUS LUNAU/Getty Images Geography Basics Physical Geography Political Geography Population Country Information Key Figures & Milestones Maps Urban Geography By Matt Rosenberg Geography Expert M.A., Geography, California State University - Northridge B.A., Geography, University of California - Davis Matt Rosenberg is an award-winning geographer and the author of "The Handy Geography Answer Book" and "The Geography Bee Complete Preparation Handbook." our editorial process Matt Rosenberg Updated September 11, 2018 Revolution is an important concept to understand when you're studying the stars. It refers to the movement of a planet around the Sun. All of the planets in our solar system revolve around the sun. The path of the earth around the sun which is one complete cycle of an orbit is approximately 365.2425 days in length. Planetary revolution can sometimes be confused with planetary rotation but they are two separate things. Difference Between Revolution and Rotation While revolution and rotation are similar concepts each is used to describe two different things. Planets, like Earth, revolve or travel around the sun. But the Earth is also spinning on what is called an axis, this rotation is what gives us our night and day cycle. If the Earth didn't spin then only one side of it would face the sun during its revolution. This would make the other side of the Earth very cold as we need the sun for light and heat. This ability to spin on an axis is called rotation. What Is a Terrestrial Year? A full revolution of the Earth around the Sun is known as a terrestrial, or earth year. It takes roughly 365 days for the Earth to complete this revolution. This is what our calendar year is based on. The Gregorian Calendar is based on the revolution of the earth around the sun to be 365.2425 days in length. The inclusion of a "leap year", one where we have an extra day happens every four years to account for the .2425. As Earth's orbit changes the length of our years' changes as well. These types of changes usually happen over millions of years. Does the Moon Revolve Around Earth? The moon orbits, or revolves, around the Earth. Each planet affects the other one. The moon has some interesting effects on the Earth. Its gravitational pull is responsible for the rise and fall of the tides. Some people believe that the full moon, a stage in the moon's revolution, causes humans to act strangely. However, there is no scientific proof to back up the claim that strange things happen during the full moon. Does the Moon Rotate? The moon does not rotate because it is gravitationally locked with the Earth. The moon has synched up with the Earth in such a way that the same side of the moon is always facing the earth. This is why the Moon always looks the same. It's known that at one point the moon did rotate on its own axis. As our gravitational pull on the moon got stronger the moon stopped rotating. What Is a Galactic Year? The time it takes for the solar system to orbit the center of the Milky Way Galaxy is referred to as a galactic year. It's also known as a cosmic year. There are 225 to 250 Million terrestrial (earth) years in one galactic year. That's a long trip!