Lesson 21 — Activity 1: Orbits
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Lesson 21 — Activity 1: Orbits
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In our solar system, the moon orbits around Earth. Earth — and the other planets — orbit around the sun. The stars also orbit around the sun. Have you ever wondered why the Earth, the other planets, the moon, and the stars just don’t go flying off
on their own into space? What keeps them on their track? In this activity, you will learn about orbits and how beliefs in orbits have changed over time.
At the simplest level, an orbit is how something goes around an object in space. It is a regular, repeating path that one object in space takes around another object. Orbits are the result of a perfect balance between the forward motion of
a body in space, such as a planet or moon, and the pull of
gravity on it from another body in space, such as a large planet or star.
At the simplest level, an orbit is how something goes around an object in space. It is a regular, repeating path that one object in space takes around another object. Orbits are the result of a perfect balance between the forward motion of a body in space, such as a planet or moon, and the pull of gravity on it from another body in space, such as a large planet or star.
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The reason why these objects stay on their tracks and don't go flying off into space is because of gravitational forces. The sun (as well as the planets) has a magnetic field that attracts smaller objects and holds them in place.
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The reason why these objects stay on their tracks and don't go flying off into space is because of gravitational forces. The sun (as well as the planets) has a magnetic field that attracts smaller objects and holds them in place.
But, you ask, why don’t the planets fall into the sun? When you point a magnet at a paper clip, the paper clip becomes attached to the magnet. Why don’t the planets do the same thing? The planets and stars travel on an elliptical path around the sun, which keeps them from falling into the sun.
Say
Superman threw a ball across the sky. The ball would go a long way, but
eventually it would begin to fall. Because Superman threw it with such
force, the ball would go all the way to the horizon, or the rounded edge
of the Earth. Because the Earth is turning, the ball falls, but it
never actually drops to the ground. It simply travels around the Earth.
This is how orbit works. The moon orbits around the Earth, while the
Earth orbits around the sun.
Say
Superman threw a ball across the sky. The ball would go a long way, but
eventually it would begin to fall. Because Superman threw it with such
force, the ball would go all the way to the horizon, or the rounded edge
of the Earth. Because the Earth is turning, the ball falls, but it
never actually drops to the ground. It simply travels around the Earth.
This is how orbit works. The moon orbits around the Earth, while the
Earth orbits around the sun.
We now know that the Earth orbits the sun and that the sun orbits the centre of the galaxy. But it wasn't always this way.
Roughly 2,000 years ago, a Greek philosopher named Aristotle came up with a model to explain planetary motion. It was a geocentric model, or Earth-centred model. Instead of the sun being at the centre of the solar system, the Earth was the centre of the universe. The sun, moon, and the five known planets at the time all orbited around the Earth. To explain why the stars didn't move, he hypothesized that they were attached to the outer orbit and stayed in place as if they were "glued to a ceiling."
In 1530, a Polish astronomer called Nicholas Copernicus came up with a different model. It was called the heliocentric model. This model puts the sun at the centre of the universe, with everything orbiting around it. It was considered quite revolutionary at the time.
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Heliocentric Model
Take a look at the images below that shows the Geocentric Model of the planets.
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The heliocentric model was closer to what we know today, but it still didn't explain everything. Scientists were having problems explaining why the planets sometimes seemed to change their "movement across the sky." It wasn't until German mathematician
Johannes Kepler worked out that the orbits of the planets were ellipses (like an oval shape), and not circles, that the motion of the planets could be properly explained.
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The heliocentric model was closer to what we know today, but it still didn't explain everything. Scientists were having problems explaining why the planets sometimes seemed to change their "movement across the sky." It wasn't until German mathematician Johannes Kepler worked out that the orbits of the planets were ellipses (like an oval shape), and not circles, that the motion of the planets could be properly explained.
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