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I think we all know that how planets are moving around sun, how moons are moving around their planets, we also know that what are the time taken to complete one cycle of their orbit of different planets and moons. Now here in this blog there is some astronomical hypothesis and their observations. Let me Xplore -

We all know that every material object is attracted towards the earth. The examples are:

- Any Object thrown up attains maximum height and then falls down towards the earth.

- It is more tiring to go uphill than to go downhill. Etc.

**Galileo**recognized this fact and stated that all bodies, irrespective of their masses, are accelerated towards the earth with a constant acceleration, called the acceleration due to gravity.

### Models proposed by Ptolemy

Since early times, the motion of stars, sun, and planets has been the subject of interest. The earliest model of planetary motion was proposed by **Ptolemy **according to which all celestial objects; the stars and the sun revolve around the earth in circular paths. This model was called the** "geocentric model". **To explain the observed motion, Ptolemy put forward a complicated scheme of motion of planets.

### Models proposed by **Nicolas Copernicus**

He stated that the planets revolve in circles around the earth and the centers of these circles themselves moved in larger circles. Attempts were made to modify such a complicated model. In this attempt, a polish monk named **Nicolas Copernicus** proposed a new model according to which all planets revolve in circles around the sun. This model was named as** "heliocentric model".** In fact, this model was already mentioned by **Aryabhata.**

In the same time as **Galileo**, an astronomer **Tycho Brahe** recorded a number of observations of the planets. These observations were analyzed by **Johannes Kepler (1571 - 1640)** and were stated in three elegant laws now known as **Kepler's laws of planetary motion.**

### Kepler's Laws of Planetary Motion

Kepler's 3 laws describe however planetary bodies orbit the Sun. They describe however (1) planets move in elliptical orbits with the Sun as a spotlight, (2) a planet covers identical space of area within the same quantity of your time in spite of wherever it's in its orbit, and (3) a planet’s orbital amount is proportional to the dimensions of its orbit (its semi-major axis).

Kepler's first Law: every planet's orbit concerning the Sun is associate conic. The Sun's center is usually placed at one focus of the orbital conic. The Sun is at one focus. the earth follows the conic in its orbit, that means that the earth to Sun distance is continually ever-changing because the planet goes around its orbit.

Kepler's Second Law: the unreal line change of integrity a planet and therefore the Sun sweeps equal areas of area throughout equal time intervals because the planet orbits. *Basically, that planets don't move with constant speed on their orbits.* Rather, their speed varies so the road change of integrity the centers of the Sun and therefore the planet sweeps out equal components of a section in equal times. the purpose of nearest approach of the earth to the Sun is termed point of periapsis. the purpose of greatest separation is point of apoapsis, thus by Kepler's Second Law, a planet is moving quickest once it's at point of periapsis and slowest at point of apoapsis.

Kepler's Third Law: the squares of the orbital periods of the planets are directly proportional to the cubes of the semi-major axes of their orbits. *Kepler's Third Law implies that the amount for a planet to orbit the Sun will increase speedily with the radius of its orbit.* so we discover that Mercury, the innermost planet, takes solely eighty eight days to orbit the Sun. the planet takes twelve months, whereas Saturn needs ten,759 days to try and do identical. the stargazer hadn't renowned concerning gravitation once he came up together with his 3 laws, they were instrumental in physicist derivation his theory of universal gravitation, that explains the unknown force behind Kepler's Third Law.

stargazer and his theories were crucial within the higher understanding of our scheme dynamics and as a springboard to newer theories that additional accurately approximate our planetary orbits.

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