Test: Introduction To Earth & Universe (Easy Level)

 Our solar system having a disc-like shape includes everything that is gravitationally drawn into the sun's orbit and consists of 8 planets (e.g. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune) and one star (the Sun).

Planets are non-luminous bodies whereas stars are luminous bodies of the universe.

A nebula is an interstellar cloud of dust, hydrogen, helium, and other gases. Nebulae are often star-forming regions, where gas, dust 'clump' together to form larger masses, which eventually become massive enough to form stars.

Our solar system is a small part of the system of stars collectively known as the spiral nebula or the galaxy, the Milky Way. The diameter of our galaxy or the Milky Way is about 10⁵ light years. 

  The Gaseous Hypothesis was proposed by Immanuel kant. According to him, the hard particles were supernaturally formed and then collided with one another. 

  According to the Tidal Hypothesis, there was a great impact of the tidal force of the intruding star on the surface of the primitive sun. When the ‘intruding star’ came nearest to the ‘primitive sun’ its gravitational force became maximum, resulting in a giant cigar-shaped mass called a filament- thick in the centre and thin and sharp at the ends.

In 1838, Sir George Darwin suggested that initially, the earth and the moon formed a single rapidly rotating body.

According to the Collision Hypothesis proposed by Harold Jeffreys, there were three stars in the Universe before the origin of the solar system. primitive sun, the ‘companion star’ and the ‘intruding star’ which was moving towards ‘companion star’. 

According to the Big Bang theory, everything in the universe developed from a point known as singularity, 15 billion years ago at an affixed moment in time. “As the universe expanded for 15 billion years, the hot radiation in the original fireball also expanded with it, and cooled as a result.”

Out of the eight planets, Mercury, Venus, Earth and Mars are called “the inner planets” as they lie between the Sun and the belt of asteroids.

  The rotatory motion of the planets (expect Venus and Uranus) is in the same direction as their revolution around the sun. 

It was suggested that the material forming the moon was separated from what we have at present the depression occupied by the Pacific Ocean.

Halley's Comet is the most famous comet. It is a "periodic" comet and returns to Earth's vicinity about every 75 years, making it possible for a human to see it twice in his or her lifetime. The last time it was here was in 1986, and it is projected to return in 2061.

Some meteoroids endure passage through the atmosphere of Earth & hit the ground. These are known as meteorites.

Before and after the quarter-moon phases are the gibbous and crescent phases. During the gibbous moon phase, the moon is more than half lit but not full.  During the crescent moon phase, the moon is less than half lit and is seen as only a sliver or crescent shape.