Motion of the Earth

The motion of the Earth is of two kinds – one is called rotation, which is the spinning of the Earth on its axis, and the motion of the Earth around the sun is called revolution. They both follow different rules and succumb to the rules of gravity. It is the gravitational pull that affects and defines the motion of the Earth as well as all other celestial bodies. We will try to understand a little bit more about the Earth, how it moves, and how these movements affect everything else around it as well as on it, including the changing of seasons and temperatures across the world as the result of the motion of Earth.

What is the Rotation of Earth?

Imagine a ball, and imagine that you have poked it with a stick directly through its center. If you spin this stick, the ball will spin too, but only in the way that you are making the stick move. Rotation refers to this exact motion of Earth, but on a much larger scale than a ball. In the case of the Earth, which is a sphere-like ball, there is an imaginary line like the stick running through it which we call the axis of the Earth, where one spin of the Earth takes exactly 24 hours to complete.

The Earth spins on its axis to create a rotational movement. It is because of this movement that we have days and nights alternating every 12 hours. This axis, though, is not a straight line – it is, in fact, slanted, so it is not an even distribution of left and right. You must know that some places on earth are affected by the motion of Earth such that they don’t see the sun for days, such as Alaska, because of the angle at which the Earth’s axis is placed.

What is the Axis?

The axis is an imaginary line running from the North Pole to the South Pole. It lies at an angle of 23.5° and is, thus, slightly slanted. The axis is what causes the motion of the Earth called rotation, and it does so at this angle of 23.5°.

What is the Revolution of the Earth?

The motion of the Earth around the sun is called the revolution of the Earth. It is the movement of our planet in an orbit around the sun. Because of the angles of the motion of the Earth, while revolving, it causes changing of seasons. One revolution or round around the sun by the Earth takes exactly 365.25 days. In these many days, the Earth sees the five seasons – winter, spring, summer, autumn, and in some places, monsoons.

The Northern hemisphere of the Earth sees opposite temperatures and climates like the Southern hemisphere. For example, when it is a sunny summer in the United States, Australia would be deep into winter, and vice versa. People in the Northern Hemisphere are all used to celebrating Christmas in sweaters and cold weather, but Australia celebrates Christmas in the summer. This is the result of the revolutionary movement of the Earth. It is because the axis of the Earth is at an angle, and while revolving, the Earth also rotates. Thus, depending on which angle the Earth would be at, at which point in the revolution, and simultaneous rotation, would determine not only whether it would be day or night in one place on Earth, but also its temperature.

What is an Orbit?

An orbit is an imaginary path that celestial bodies follow while they move. These paths are created by the gravitational pulls of celestial bodies. The motion of the Earth while revolving around the sun is an oval path. All planets in the solar system have orbits around the sun in all different sizes. It takes these planets their own time to revolve around the sun. For example, it takes Jupiter nearly 12 Earth years to make a full revolution around the sun, whereas it takes Venus about 243 Earth days to do the same in its orbit.

What is a Leap Year?

There are 365.25 days in one year. However, if we continue to ignore the quarter of a day forever, there will be a massive imbalance in time. Thus comes the concept of a leap year, which is facilitated by the motion of earth causing 0.25 of a day extra.

• Every year, we count only 365 days
• At the end of four years, there should be 1 extra day as 0.25 days over four years will become one full day
• This extra day is added to the shortest month of February to make it 29 days
• This is done every four years
• Every fourth year is called a ‘leap year’ and all leap years have the 29th of February

How are the Seasons Affected by the Motion of Earth?

As we know, the Earth is constantly rotating while revolving. While going around the sun, the distance between the Earth and Sun keeps alternating (because of the oval shape of the orbit), days and nights keep shifting, etc. and in the process, we get different seasons.

The different parts of the Earth get the Sun at different points in time. The places and angles which don’t get the Sun as much over a few months, have Winter season. The part that gets the Sun for a long time at a specific time has the Summer season.

You would notice that the higher North or lower South you go from the equator, the colder it gets. That’s why the North and South poles are always full of snow, because of the collective motion of the earth of revolution as well as rotation.