The Universe is made up of everything that exists be it gases, cosmic energy or particulate matter. It includes all the galaxies, asteroids, solar systems, meteors. All the existing matter and space as a whole is considered as universe. The universe is believed to be at least 10 billion light years in diameter and contains a vast number of galaxies each containing millions or billions of stars. Our native planet Earth and the solar system is also a part of one of such numerous galaxies i.e. Milky Way. The gaps around the stars and galaxies mostly contain scattered particles of dust or a few hydrogen atoms per cubic centimeter. Empty spaces are also filled with radiation (e.g. light and heat), magnetic fields and high energy particles such as cosmic rays.
It is ascertained that at the start, the whole Universe was concentrated in a single mass. It is believed that an explosion occurred in this concentrated mass and all the particles scattered forming the universe present today. This is known as the Big Bang Theory. It also states that the universe is still continuing to expand and the galaxies are moving apart every second leading to continuous expansion of the Universe.
Stars are celestial bodies consisting of a mass of gas held together by its own gravity which generate light and other radiant energy by thermonuclear fusion of hydrogen into helium in their core. The lifecycle of a star begins as a nebula which is a cluster of dust particles and gases giving it the fuel to shine for many years. However, as the fuel begins to deplete slowly over a period of time, the star shrinks in size and enters its next stage of lifecycle turning into a Red Giant. After the Red Giant stage, the next stage in a star’s life is determined by the mass of the star. A small star like sun turns into a White Dwarf star. However, a star with a massive weight will undergo an energetic and enormous explosion to turn into a Supernova which later on turns into a neutron star or a black hole.
Sun is the closest star to earth-our home planet and is situated exactly at the centre of our solar system. Sun is located at a distance of 149.6 million Km from earth with an average diameter of 696000 Kms. The main constituents of the Sun’s surface are Hydrogen and Helium and continuous fusion of hydrogen to form Helium molecules provides the energy emitted by the Sun.
The visible surface of the Sun is known as photosphere. During a total solar eclipse, when the disk of the Sun is covered by that of the Moon, the Sun's surrounding atmosphere can be seen. It is composed of three distinct parts: the chromosphere, the transition region, and the corona, that together form the heliosphere. The coolest layer of the Sun has a temperature of about 4100 K which exists at about 500 km above the photosphere. The Sun today is roughly halfway through the most stable part of its life. It has not changed dramatically for four billion years, and will remain fairly stable for four billion more. However, after hydrogen fusion in its core has stopped, the Sun will undergo severe changes, both internally and externally.
Asteroids are minor planets, primarily located in the inner Solar System. The larger asteroids are also known as planetoids. The large majority of known asteroids orbit in the asteroid belt between the orbits of Mars and Jupiter. Individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups: C-type, M-type, and S-type. Only one asteroid, 4 Vesta, which has a relatively reflective surface, is normally visible to the naked eye, and this only in very dark skies when it is favorably positioned. The largest of the asteroids, Ceres, was the first to be discovered. A second minor planet – Pallas – was found by Wilhelm Olbers in 1802. This was followed by Juno (1804) and Vesta (1807).
Meteors are also known as the shooting stars or falling stars and are visible in the sky as the streak of bright light when a meteoroid, when a comet or asteroid enters the Earth's atmosphere at a speed of around 20 km/s, due to friction in earth’s atmosphere produces a streak of light. Almost all meteoroids contain extraterrestrial nickel and irons. They have three main classifications: irons, stones and stony-irons. Some stone meteoroids contain grain-like inclusions known as chondrules and are called chondrites. Stoney meteoroids without these features are called "achondrites". The most famous “meteor storms” are linked with the Leonid shower, which takes place every year between 14 and 20 November. The shower has been so active in the past that it resembled falling snow!
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