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Motion of Celestial Bodies in Space

The celestial bodies in space, like the planets and satellites, move in paths that obey the laws of motion. In this article, let’s study the motion of the Celestial Bodies and the law which governed them.

Celestial Body

Celestial bodies or heavenly bodies are objects in space such as the sun, moon, planets, and stars. They form a part of the vast universe we live in and are usually very far from us. The glorious night sky is dotted with such objects, and when we observe them using a telescope, they reveal fascinating worlds of their own.

Motion of the Celestial Body

Paths of the celestial bodies are usually elliptical or parabolic. The planets move in elliptical orbits around the sun, whereas satellites move in elliptical orbits around the planets. The sun and the solar system itself move in an elliptical orbit around the centre of our galaxy – The Milky Way!. 

Celestial Mechanics

The branch of astronomy that deals with the study of the motion of objects in space are known as celestial mechanics. These heavenly bodies move in such a way due to the attractive force of gravity. The elliptical orbit is kind of an elongated circle. Instead of having a single centre like a circle, ellipses have two centres called foci (singular=focus).

Elliptical Orbit

For planets in space, the centre of the sun is always at one of the focus as shown in the figure above. The larger the distance between the two foci, the more elongated the ellipse is.  The amount of the elongation of the orbit is given by the eccentricity of the orbit. Most planets have a very small eccentricity. The Earth’s orbit has such a low eccentricity that both the foci lie within the sun itself! So you can say that the earth’s orbit is almost circular.

Kepler’s Laws of “Planetary Motion” in Space

Motion in elliptical orbits is governed by three laws known as Kepler’s Laws of planetary motion. These laws tell us how fast a planet goes at any point in the orbit and the time a planet takes to orbit the sun. The moon also follows an elliptical orbit around the earth following Kepler’s Laws.

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Frequently Asked Questions – FAQs

State Kepler’s first law of planetary motion.

According to Kepler’s first law,” All the planets revolve around the sun in elliptical orbits having the sun at one of the foci”. The point at which the planet is close to the sun is known as perihelion, and the point at which the planet is farther from the sun is known as aphelion.

State Kepler’s second law of planetary motion.

Kepler’s second law states, “The radius vector drawn from the sun to the planet sweeps out equal areas in equal intervals of time”

What is Kepler’s law of periods?

According to Kepler’s law of periods,” The square of the time period of revolution of a planet around the sun in an elliptical orbit is directly proportional to the cube of its semi-major axis”.

What are the seven celestial bodies?

The seven celestial bodies: Sun, Moon, Venus, Jupiter, Mars, Mercury, and Saturn.

How do celestial bodies move in space?

All the heavenly bodies like planets and satellites move in an elliptical orbit due to the attractive force of gravity. Their centrifugal motion is balanced by gravitational attraction.
Test your Knowledge on Motion Of Celestial Objects In Space

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