Solar System and Sun: Geography UPSC

Universe and Solar system Planets information

Solar System: The Solar System is the gravitationally bound system of the Sun and the objects that orbit it, either directly or indirectly.


  • Cosmic energy engines which produce heat, light, ultraviolet rays, x-rays, and other forms of radiation.
  • Composed largely of gas and plasma, a superheated state of matter composed of subatomic particles
  • Luminosity: Brightness-a factor of how much energy they put out
  • The primary building block of stars: Hydrogen


  • The Earth’s only natural satellite
  • 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 rise and fall of the tides on Earth are caused by the Moon: There are two bulges in the Earth due to the gravitational pull that the Moon exerts; one on the side facing the Moon, and the other on the opposite side that faces away from the Moon, The bulges move around the oceans as the Earth rotates, causing high and low tides around the globe.
  • A person would weigh much less on the Moon: The Moon has much weaker gravity than Earth, due to its smaller mass, so you would weigh about one-sixth of your weight on Earth.
  • The Moon has quakes: These are caused by the gravitational pull of the Earth. Lunar astronauts used
    seismographs on their visits to the Moon and found that small moonquakes occurred several kilometers beneath the surface, causing ruptures and cracks. Scientists think the Moon has a molten core, just like Earth.


  • A group of stars forming a recognizable pattern that is traditionally named after its apparent form or identified with a mythological figure
  • Pole Star/North Star: Indicates the north direction (Locate the position of the Pole Star with the help of the Saptarishi)


Planets do not have their own heat and light and are lit by the light of the stars. A planet is a celestial body that:

  • is in orbit around the Sun
  • has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and has cleared the neighborhood around its orbit.

Planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

  • 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.
  • 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
  • Outer planets: Jupiter, Saturn, Uranus and Neptune
  • Planet Orbit: An orbit is a path an object takes in space as it revolves around another object. While a planet travels in one direction, it is also affected by the Sun’s gravity causing it to take a curved route that eventually brings it back to its starting point. This complete revolution equates to a single orbit.

Milky Way Galaxy

  • Our solar system is a part of this galaxy
  • Ancient India: Was imagined to be a river of light flowing in the sky and thus, named Akash Ganga.


  • The center of the solar system and is made up of extremely hot gases; is the ultimate source of heat and light for the solar system
  • Provides the pulling force that binds the solar system
  • Contains more than 99.8% of the total mass of the Solar System (Jupiter contains most of the rest)
  • The Sun is, at present, about 70% hydrogen and 28% helium by mass everything else (“metals”) amounts to
    less than 2%. This changes slowly over time as the Sun converts hydrogen to helium in its core.
  • Light travels at the speed of about 300,000 km per second—the light of the sun takes about eight minutes to reach the earth.


  • The third nearest planet to the Sun
  • Fifth largest planet
  • Geoid shaped: It is slightly flattened at the poles and that is why its shape is described as a Geoid (an earth-like shape)
  • Blue Planet: its two-thirds surface is covered by water.


  • Natural Satellite: A celestial body that moves around the planets in the same way as the planets move around the sun.
  • Human-made Satellite: An artificial body designed by scientists to gather information about the universe or for communication. It is carried by rocket and placed in the orbit around the earth.


  • Numerous tiny bodies moving around the sun
  • Found between the orbits of Mars and Jupiter
  • Largest asteroid: Ceres


  • Small pieces of rocks moving around the sun
  • Some meteors while entering the Earth’s surface with a flash of light signifying the air getting heated up due to friction
  • Sometimes these meteors without being completely burnt to fall on the earth and creates a hollow.


Sunspots (some as large as 50,000 km in diameter) are areas that appear dark on the surface of the Sun (photosphere). They appear dark because they are cooler than other parts of the Sun’s surface.

  • However, the temperature of a sunspot is still very hot —around 6,500 degrees Fahrenheit.
  • Photosphere is a visible surface of the Sun, from which is emitted most of the Sun’s light that reaches Earth directly.

They are relatively cool because they form at areas where magnetic fields are particularly strong. These magnetic fields are so strong that they keep some of the heat within the Sun from reaching the surface.

  • Magnetic field in such areas is about 2,500 times stronger than Earth’s.

They typically consist of a dark region called the ‘umbra’, which is surrounded by a lighter region called the ‘penumbra’.


In every solar cycle, the number of Sunspots increases and decreases. The current solar cycle, which began in 2008, is in its ‘solar minimum’ phase, when the number of Sunspots and solar flares is at a routine low.


Solar Flares

  • The magnetic field lines near sunspots often tangle, cross, and reorganize. This can cause a sudden explosion of energy called a solar flare.
  • Solar flares release a lot of radiation into space. Solar flares, when powerful enough, can disrupt satellite and radio transmission on the Earth, and more severe ones can cause ‘geomagnetic storms’ that can damage transformers in power grids.
    • A geomagnetic storm is a major disturbance of Earth’s magnetosphere that occurs when there is a very efficient exchange of energy from the solar wind into the space surrounding Earth.
      • The magnetosphere is a region around the Earth dominated by the Earth’s magnetic field.
      • It protects the Earth from solar and cosmic radiation as well as erosion of the atmosphere by the solar wind – the constant flow of charged particles streaming off the Sun.
  • Solar flares are sometimes accompanied by a Coronal Mass Ejection (CME).
    • CMEs are huge bubbles of radiation and particles from the Sun’s Corona (outermost region of the Sun’s atmosphere). They explode into space at very high speed when the Sun’s magnetic field lines suddenly reorganize.
    • They can trigger intense light in the sky on Earth, called auroras.
      • Some of the energy and small particles travel down the magnetic field lines at the north and south poles into Earth’s atmosphere.
      • There, the particles interact with gases in the atmosphere resulting in beautiful displays of light in the sky. Oxygen gives off the green and red light. Nitrogen glows blue and purple.
      • The aurora in Earth’s northern atmosphere is called an aurora borealis or northern lights. Its southern counterpart is called an aurora australis or the southern lights.
solar flares

Solar Cycle

  • The Sun is a huge ball of electrically-charged hot gas. This charged gas moves, generating a powerful magnetic field. The Sun’s magnetic field goes through a cycle, called the solar cycle.
  • Every 11 years or so, the Sun’s magnetic field completely flips. This means that the Sun’s north and south poles switch places. Then it takes about another 11 years for the Sun’s north and south poles to flip back again.
  • The solar cycle affects activity on the surface of the Sun, such as sunspots which are caused by the Sun’s magnetic fields. As the magnetic fields change, so does the amount of activity on the Sun’s surface.
  • One way to track the solar cycle is by counting the number of sunspots. The beginning of a solar cycle is a solar minimum, or when the Sun has the least sunspots. Over time, solar activity—and the number of sunspots—increases.
  • The middle of the solar cycle is the solar maximum, or when the Sun has the most sunspots. As the cycle ends, it fades back to the solar minimum and then a new cycle begins.

Get detailed Article on Solar System planets information: Click Here

References: NCERT Geography, Certificate Physical And Human Geography: G C Leong

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