Solar System

Solar System

The Solar System is located at a radius of about 27,000 light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust. Astronomers have agreed that the Milky Way probably has two major spiral arms – Perseus arm and the Scutum-Centaurus arm – with several smaller arms and spurs. The Solar System is located in a region in between the two arms called the Orion-Cygnus arm. This arm measures 3,500 light-years across and is 10,000 light-years in length, where it breaks off from the Sagittarius Arm. Sun is a star with a diameter of 109 times of earth and a mass of 3.30 lakh times of Earth, roughly accounting for 99.9% of the total mass of the Solar system. Sun is mostly made of Hydrogen (71%) and Helium (26%) and is the main sequence, yellow dwarf. It was formed some 4.6 billion years ago.
Our solar system consists of an average star we call the Sun, the planets – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
The planets of the inner circle (as they lie between the sun and the belt of asteroids) or the inner planets or the ‘terrestrial planets’ (meaning earth-like as they are made up of rock and metals, and have relatively high densities) and the planets of the outer circle or outer planets or the ‘gas giant planets or the Jovian planets.


  1. Mercury is the closest planet to Sun. Due to this proximity, mercury’s orbit is very much stretched into a long elliptical shape. Other important facts about mercury are as follows:
  2. Mercury takes 88 Earth days to complete one revolution around the sun, however, it takes 59 Earth days to complete one rotation.
  3. Its’s surface is covered with deep craters, separated by plains and huge banks of cliffs.
  4. Mercury’s very thin atmosphere is made primarily of sodium, potassium, helium, and hydrogen.
  5. No moons present in mercury planet.
  6. Images obtained by MESSENGER spacecraft in 2004 have revealed evidence for pyroclastic flows (vulcanicity) and water ice at Mercury’s poles.


  1. It is similar to Earth in many ways and is closer in distance to Earth than any other planet, and it has a similar size and composition.
  2. a day on Venus is longer than a year because an year is equal to 225 days while a day is equal to 243 days.
  3. It rotates on its polar axis backward compared to Earth, so the sunrise occurs in the west and sunset in the east.
  4. It is blanketed by a thick atmosphere nearly 100 times denser than Earth; it is made mostly of carbon dioxide, along with some nitrogen and trace amounts of water vapor, acids, and heavy metals.
  5. No terrestrial life is possible on It.
  6. It is visible in the sky either just after dark or just before sunrise, depending on the season, so it is called Morning or Evening Star.
  7. No moons present in Venus’s planet
  8. Indian Space Research Organization (ISRO) has announced that it is expecting to launch the Venus mission by December 2024. The aim of the mission is to study Venus’ atmosphere


  1. Earth is the third planet from Sun and Fifth Largest Planet in the solar system.
  2. It was formed 4.54 billion years ago.
  3. Earth is the largest of the terrestrial planets in the Solar System in terms of diameter, mass and density.
  4. Moon is the natural satellite of the earth.
  1. Rotation: Earth’s Period of rotation on the Polar Axis is 23 hrs. 56 minutes 4.09 seconds. It is also called a Solar Day. The direction of Rotation is from West to East.  The rotational velocity at the equator is 1667 km per hour which decreases while progressing towards the Poles and becomes zero at the poles.
  2. Revolution: Earth’s sidereal period or the time taken in completing one orbit around Sun is 365.25636 days. Its orbital speed is 29.8 km/s per second. The one circuit which is about 365 days, 48 minutes, and 45.68 seconds is called a tropical year. For convenience in calendars, every fourth year is made a ‘leap year’ with 366 days.
    1. The maximum distance of the earth from the Sun is 152.10 million Kms at Aphelion, which is in the first week of July (July 2-5)
    2. The minimum Distance of earth from the Sun is 147.10 km at Perihelion (January 2-5)
    3. Earth’s escape velocity is 11.2 km per second.

Impacts of Rotation and Revolution:

The spinning of the Earth causes the day to turn night, while the full rotation/the revolution of the Earth causes summer to become winter. Combined, the spinning and the revolution of the Earth causes our daily weather and global climate by affecting wind direction, temperature, ocean currents, and precipitation.


  1. Mars is known as the red planet because it looks red from Earth. The reddish color comes from the high concentration of iron oxide compounds—that is, rust—in the rocks of the Martian surface.
  2. Martian year is of 687 days and Martian day is 24h 37m.
  3. The atmosphere is mostly carbon dioxide, with tiny fractions of oxygen, nitrogen, and other gases.
  4. At the equator, during the warmest times of the Martian summer, the temperature can reach nearly –18°C at the poles, during the coldest times of the Martian winter, temperatures drop to -85°C and beyond.
  5. Mars has two small satellites, Phobos and Deimos (fear and terror), which were discovered by the American astronomer Asaph Hall in 1877.
  6. Mangalyaan, India’s Mars Orbiter Mission spacecraft has completed seven earth years in its orbit in 2021. According to ISRO officials, the spacecraft has successfully covered three Martian years.
  7. It was originally made to last just six months but has enough punch left for more than a decade in the Martian orbit

Do You Know This?

Light year
 Light travels at a speed of 300,000 km/second. Considering this, the distances the light will travel in one year is taken to be one light year.