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1. Isaac Newton first proposed the law of Universal Gravitation.
2. Nicolaus Copernicus single-handedly laid the foundation of modern astronomy. His
famous book on astronomy is “On the Revolutions of the Heavenly Spheres”. It was
published in 1543, when he was on his death bed.
3. By definition, epicycle is some small circle, whose center moves along the circumference
of a larger circle. It can be understood by below diagram:
Here, green circle is an epicycle, whose center moves around the circumference of red
To explain the motion of heavenly bodies, Copernicus assumed Sun (yellow body at the
center is the Sun) to be at the center of red circle. Blue body is some planet, which is
revolving in green epicycle, which itself is moving on the circumference of red
circle(deferent) around Sun.
Galileo invented telescope. He was the first person to use telescope to study heavenly
bodies. With his telescope, he saw four moons orbiting Jupiter. This observation was
contrary to Ptolemaic model that all heavenly bodies orbit around Earth, but this
observation can be explained by Copernicus’ idea that Sun is the center of solar system
and all planets are orbiting around Sun. In his idea, as Earth’s moon is orbiting around
Earth, other planets’ moons are orbiting around them, which explains Galileo’s
Kepler's first law tells that planets don't orbit in an exactly circular orbit around Sun.
They orbit in an elliptical orbit with sun at one of the foci of ellipse, so their distance
from sun is not constant, it keeps on varying.
Kepler's second law tells that speed of a planet is not same all the time, while orbiting
around Sun. When planet is close to Sun, it moves faster.
Kepler's third law compares the time taken by different planets in orbiting around Sun. It
tells that time taken by a planet in orbiting around Sun depends on size of its orbit. The
bigger the orbit, the more will be the time taken in competing one cycle.
According to Newton's law of gr...