Among the many things we seek to understand about the Earth is how it moves. This is important since it orbit and rotation affect many important aspects of life on planet Earth. Earth’s solar orbit determines the length of our year and the rotation of the earth gives us the day and night that helps to regulate the climate of our planet. One important question is what direction does the Earth rotate.
To simply answer the question the Earth rotates to the east. This has some interesting side effects on how we observe celestial bodies. Deepening on where you are on the Earth this rotation direction causes some interesting things for amateur astronomers to observe. The most common is the way sun rises in the east and sets in the west. This optical illusion led ancient astronomers to believe that the sun revolved around the Earth.
First we need to understand what is involved with the rotation of the Earth. We already know that the Earth has something called a sidereal day. This is the exact time that it takes for the earth to rotate once. For the Earth, the sidereal day is just over24 hours. The Earth’s rotation is not completely independent. Changes in the tilt of the axis and its orbit change the sidereal period of rotation by a slight margin making for the longer and shorter days during the year.
Another interesting fact about the Earth’s rotation is that it was actually determined long before it the Earth or the sun for that matter, were even formed. According to astronomers the rotation and orbits of the planets and stars are largely determined by conservation of angular momentum. Essentially as the nebulas that form star systems are always spinning. As the nebula collapses on itself it loses a lot of momentum, but not all of it is lost. The remainder of it goes into the new star and its planets as the form causing them to have their present rotations. The direction of the rotation largely relies on gravity and other conditions in play as each celestial body is formed and enters its orbit.
As you can see knowing more about the rotation of the Earth can tell us a lot about our planet, from how it was formed. We can know what type of nebula it was formed from and the types of stars that it forms. This can be of great help to astronomers looking to find out if there are other nebulas that are candidates for creating planet bearing stars.
We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.