The universe

The Universe is defined as the totality of existence, including planets, stars, galaxies, the contents of intergalactic space, the smallest subatomic particles, and all matter and energy.

It embeds in itself many solar systems like ours and is known to be constantly destroying a little and creating again itself. The stars we see in the sky are basically like the Sun present in our solar system.

The universe, commonly stated as Space, is known to have formed due to a Big Bang. The Big Bang theory is the prevailing cosmological model for the early development of the universe. The key idea is that the universe is expanding. Consequently, the universe was denser and hotter in the past. It is said that when universe was formed, it was just 5% of what it is today.

Milky Way

The galaxy we live in was named Milky Way for its appearance and Akash Ganga by Indians for its size. Its name “milky” is derived from its appearance as a dim glowing band arching across the night sky in which the naked eye cannot distinguish individual stars.

Milky Way is considered to be 13.2 billion years old and is comprising 300 billion stars like Sun which may mean 300 billion solar systems. Until the 1920s, it was fiercely debated whether the Milky Way was the entire Universe, or whether the "spiral nebulae" such as the Great Nebula in Andromeda were galaxies in their own right external to our own. This debate was finally resolved when Cepheid variables were used to measure distances to the globular clusters surrounding our own galaxy and to galaxies like Andromeda (M31). These measurements showed that Andromeda was much further away than the globular clusters, indicating that it was a separate galaxy.

The Milky Way; it is composed primarily of stars that are too faint to be resolved so that we see their combined light as a faint glow. The Milky Way is an example of a gigantic collection of stars, gas, and dust that we call a galaxy.

Solar System

The solar system consists of the Sun; the eight official planets, at least three "dwarf planets", more than 130 satellites of the planets, a large number of small bodies (the comets and asteroids), and the interplanetary medium. (There are probably also many more planetary satellites that have not yet been discovered.) The inner solar system contains the Sun, Mercury, Venus, Earth and Mars. The main asteroid belt lies between the orbits of Mars and Jupiter. The planets of the outer solar system are Jupiter, Saturn, Uranus, and Neptune (Pluto is now classified as a dwarf planet).  The first thing to notice is that the solar system is mostly empty space. The planets are very small compared to the space between them. The orbits of the planets are ellipses with the Sun at one focus, though all except Mercury are very nearly circular. The orbits of the planets are all more or less in the same plane (called the ecliptic and defined by the plane of the Earth's orbit). The ecliptic is inclined only 7 degrees from the plane of the Sun's equator. The above diagrams show the relative sizes of the orbits of the eight planets (plus Pluto) from a perspective somewhat above the ecliptic (hence their non-circular appearance). They all orbit in the same direction (counter-clockwise looking down from above the Sun's North Pole); all but Venus, Uranus and Pluto also rotate in that same sense.

The classification of these objects is a matter of minor controversy. Traditionally, the solar system has been divided into planets (the big bodies orbiting the Sun), their satellites (a.k.a. moons, variously sized objects orbiting the planets), asteroids (small dense objects orbiting the Sun) and comets (small icy objects with highly eccentric orbits).