Solar System
- The Solar System is the gravitationally bound system of the Sun and the objects that orbit it, either directly or indirectly.
- Our solar system consists of our star, the Sun, and everything bound to it by gravity – the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune; dwarf planets such as Pluto; dozens of moons; and millions of asteroids, comets, and meteoroids.
- The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud.
Stars
- A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity.
- Stars are cosmic energy engines that produce heat, light, ultraviolet rays, x-rays, and other forms of radiation.
- Stars were formed when the galaxies were formed during the Big Bang.
- They are composed largely of gas and plasma, a superheated state of matter composed of subatomic particles.
- Stars are the fundamental building blocks of galaxies.
Moon
- The Moon is Earth’s only natural satellite.
- At about one-quarter the diameter of Earth, it is the fifth largest satellite in the Solar System, the largest satellite in the Solar System relative to its major planet, and larger than any known dwarf planet.
- Moon was formed 4.6 billion years ago around some 30–50 million years after the formation of the solar system
- It is in synchronous rotation with Earth meaning the same side is always facing the Earth.
- The Moon revolves around the Earth in 27 days 7 hours 43 minutes and 11.47 seconds and rotates on its own axis exactly the same time. That is why only one face of the Moon is seen from Earth.
- The total forces of the Moon and the Sun are in the ratio of 9: 4.
- Study of the Moon is known as Selenology.
Constellation
- Thousands of stars appear in the sky during the night. Some of these stars form a pattern in a group, which have recognizable shape. This group of stars is called constellation. At present there are about 88 constellations. Each constellation has been given a name according to its shape. Some of the important constellations are Ursa Major, Ursa Minor, Orion, Leo Major and Cassiopeia.
- Ursa Major: It is also known as Great Bear or Saptarishi. It consists of seven bright stars, which appear in the shape of a bear. It is visible during the summer season in the early part of the night and can be seen clearly during the month of April in the northern part of the sky. It also helps us to locate the position of the pole star in the sky. At night it appears to move from east to west as the pole star remains fixed in its position.
- Orion: This constellation is also known as hunter. The Indian name is Mriga. It consists of seven or eight bright stars. The orientation of stars in Orion is similar to the figure of hunter. This constellation is visible in the sky during the winter season in the late evening. One of the brightest stars in the sky at night is the Sinus, which is very close to the Orion constellation.
- Leo Major: This constellation mainly consists of 9 or 10 stars. Its orientation is similar to that of lion, hence its name is Leo. It is visible during the summer in the early part of night.
- Cassiopeia: It mainly consists of five stars, which are arranged in the form of letter W or M depending on its position in the sky. It is supposed to represent an ancient queen named Cassiopeia. It is visible during the winter in the early part of the night.
Planets
Outer planets: Jupiter, Saturn, Uranus and Neptune
A planet is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
(c) has cleared the neighbourhood around its orbit.
Planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
A “dwarf planet” is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,
(c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
Pluto now falls into the dwarf planet category on account of its size and the fact that it resides within a zone of other similarly sized objects known as the transneptunian region.
All other objects, except satellites, orbiting the Sun shall be referred to collectively as “Small Solar System Bodies”.
Planets with rings: Jupiter, Saturn, and Uranus have rings around them – belts of small debris
Smallest planet: Mercury
Largest planet: Jupiter
Inner planets: Mercury, Venus, Earth, and Mars