Universe Part 1 - (UPSC & TNPSC Important Notes)

UNIVERSE - PART 1 (UPSC & TNPSC Important Notes)

•    The word universe derives from the Old French word univers, which in turn derives from the Latin word universum.
•    The Latin word was used by Cicero and later Latin authors in many of the same senses as the modern English word is used.
•    The Universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy.
•    While the spatial size of the entire Universe is still unknown, it is possible to measure the observable universe.
•    Further observational improvements led to the realization that our Sun is one of hundreds of billions of stars in a galaxy we call the Milky Way, which is one of hundreds of billions (perhaps trillions) of galaxies in the Universe.
•    Many of these stars have planets.
•    At the largest scale galaxies are distributed uniformly and the same in all directions, meaning that the Universe has neither an edge nor a center.
•    From studying the movement of galaxies, we know that the universe contain much more matter than we can detect in usual ways.
•    This unseen matter is known as dark matter (dark means that there is a wide range of strong indirect evidence that it exists, but we have not yet detected it directly.

MILKY WAY GALAXY
•    The Milky Way is the galaxy that contains our Solar System.
•    The descriptive “milky” is derived from the appearance from Earth of the galaxy – a band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye.
•    Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610.
•    Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe.
•    The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Supercluster, which is itself a component of the Laniakea Supercluster.
•    The constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much of the mass of the Milky Way does not emit or absorb electromagnetic radiation.
•    This mass has been termed “dark matter”.

THE SOLAR SYSTEM :   
•    The Solar System is the gravitationally bound planetary system of the Sun and the objects that orbit it, either directly or indirectly.
•    Of the objects that orbit the Sun directly, the largest are the eight planets, with the remainder being smaller objects, such as the five dwarf planets and small Solar System bodies.
•    Of the objects that orbit the Sun indirectly—the moons—two are larger than the smallest planet, Mercury.
•    The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud.
•    We can see the Sun, Moon, and the five planets mentioned before with Naked Eyes.
•    The Sun has Eight Planets, All Planets revolves around the sun.

•    The eight planets have been classified into Solid Planet and Gaseous Planets. Mercury, Venue, Earth and Mars are called as Solid Planets. While Jupiter, Saturn Uranus and Neptune are gaseous Planets.
•    The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly of the objects that orbit the Sun directly, the largest eight are the planets, with the remainder being smaller objects, such as dwarf planets and small Solar System bodies of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury.

Distances and scales
•    The distance from Earth to the Sun is 1 astronomical unit [AU] (150,000,000 km; 93,000,000 mi).
•    For comparison, the radius of the Sun is 0.0047 AU (700,000 km).
•    Thus, the Sun occupies 0.00001% (10−5 %) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly one millionth (10−6) that of the Sun.
•    Jupiter, the largest planet, is 5.2 astronomical units (780,000,000 km) from the Sun and has a radius of 71,000 km (0.00047 AU), whereas the most distant planet, Neptune, is 30 AU (4.5×109 km) from the Sun.

The four Smaller Inner Planets are,
1.    Mercury
2.    Venus
3.    Earth
4.    Mars
The Four Outer Or Giant Planets are,
1.    Jupiter
2.    Saturn
3.    Uranus
4.    Neptune