Its all about Physics.

  Galaxy : Introduction: A galaxy is a collection of stars, stellar remnants, interstellar gas, dust, and dark matter that is gravitationally bound. The name comes from the Greek word galaxias, which means "milky" and refers to the Milky Way galaxy, which houses the Solar System. Galaxies range in size from dwarfs with fewer than one hundred million (108) stars to the largest galaxies known as supergiants with one hundred trillion (1014) stars, each orbiting its galaxy's centre of mass. Galaxies are thought to contain an average of 100 million stars.   Galaxy According on their optical shape, galaxies are classified as elliptical,[5] spiral, or irregular. It's believed that the centres of several of them contain supermassive black holes. Sagittarius A*, the name of the Milky Way's primary black hole, is four million times more massive than the Sun. GN-z11 is the oldest and furthest away galaxy as of March 2016. It can be seen as having existed only 400 million yea...

  Solar System : Introduction: The gravitationally bound system comprising the Sun and the asteroids that orbit it is known as the Solar System. A massive interstellar molecular cloud gravitationally collapsed to make it 4.6 billion years ago. The Sun contains 99.86% of the system's mass, with Jupiter holding the majority of the remaining mass. Mercury, Venus, Earth, and Mars are the four terrestrial planets in the inner solar system, and they are made mostly of rock and metal.The four enormous planets in the outer solar system dwarf the terrestrial planets in both size and mass. The next two, Uranus and Neptune, are ice giants, being primarily composed of volatile substances with relatively high melting points compared to hydrogen and helium, such as water, ammonia, and methane. Jupiter and Saturn, the two largest, are gas giants, being primarily composed of hydrogen and helium. All eight planets have approximately circular orbits that are located close to the ecliptic, the plane ...

  Pluto: Introduction: Pluto is a dwarf planet in the Kuiper belt, a ring of planets beyond Neptune's orbit. Its minor-planet name is 134340 Pluto. It directly orbits the Sun and is the ninth-largest and tenth-most massive object known to exist. It is marginally bigger than Eris in terms of mass, but it is the largest trans-Neptunian object by volume. Pluto is significantly smaller than the inner planets and is mostly formed of ice and rock, like other Kuiper belt objects. Pluto has only one-sixth the mass and one-third the volume of the moon of Earth.   Pluto Pluto's orbit, which ranges from 30 to 49 astronomical units (4.5 to 7.3 billion kilometers; 2.8 to 4.6 billion miles) from the Sun, is fairly eccentric and inclined. At its typical distance, light from the Sun takes 5.5 hours to reach Pluto (39.5 AU [5.91 billion km; 3.67 billion mi]). Although Pluto's eccentric orbit occasionally gets it closer to the Sun than Neptune, their paths are kept apart by a steady orbital ...