Lesson Objectives:- The Earth's movement through space
- The Earth's orbit
- Movement in the Milky Way and in the universe
How is the Earth moving through space? This is a common question and important to understand. The Earth rotates or spins on its own axis daily west to east, which is why it appears that the Sun and stars rise in the east and set in the west every day.
The Earth orbits or revolves around the Sun once a year. 1 astronomical unit (AU) is the average orbital distance of the Earth from the Sun.
The Earth does both at the same time - it is rotating on its own axis and revolving around the Sun. These movements are fast - the Earth's rotation is roughly 600 miles per hour (1000 kilometers per hour). The Earth revolves around the Sun at an even more impressive speed of 60,000 miles per hour - faster than any spacecraft that has ever been launched.
The Ecliptic plane is the flat plane from which the Earth's axis is tilted 23 1/2 degrees in a perpendicular direction. This axis tilt makes the Earth's axis point or tilt towards a star called the North Star or Polaris.
Up or down has no relevance in terms of tilt. Instead, away or towards the center of the Earth makes more sense in terms of describing positions. The Earth orbits the Sun in the same counter-clockwise direction that it rotates on its axis.
The Sun and other stars and planets are all moving in the Milky Way. The Sun is moving at a speed of 40,000 miles per hour. This is roughly 3 times the speed of the International Space Station. Stars all move at different speeds.
Stars are also constantly moving in the Milky Way but we are unable to discern this movement because of the vast distances between stars and our planet. That is why constellation patterns appear fixed. However, over a long span of time, say 10,000 years, constellations will be noticeably different.
Galactic rotation carries us around the center of the galaxy once every 230 million years.
How do galaxies move in the Universe? Each part of a galaxy (star systems, stars, planets and other celestial objects) is moving. Billions of galaxies are constantly moving in the Universe. Some move towards each other, some move away.
The Milky Way galaxy that contains our Sun, Earth and the solar system rotates at a speed of 800,000 km/hour and rotates once every 230 million years. The Milky Way and Andromeda galaxies, both in the Local Group of galaxies, move towards each other at 180,000 miles per hour. It will be billions of years before they come into close proximity.
Almost every other galaxy is moving away from us. The more distant the galaxy, the faster it appears to be racing away. This happens because the universe is expanding.
While we cannot feel the motion of Earth, the associated speeds are very high. Our Earth is constantly moving through the solar system around the Sun, which in turn is rotating and moving. All these planets and stars in turn are moving through the galaxy, which in turn, is rotating and moving through the universe. The universe is in a constant state of motion and expansion.