Lesson 3: Spaceship Earth
In this lesson, we will be looking at the Earth"s movement through space as
well as the characteristics of its orbit around the Sun. We will also talk
about the movement of stars within our Milky Way galaxy, and the movement of
galaxies through 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.