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Summary

Geography Class 06

## Last class revision(5.15 PM).

## Solar system(5.23 PM):

- ***Sun:***
- It is a dwarf star.
- The age of the sun is 4.8 billion years.
- Layers of the Sun:
- ***Core:***
- The innermost layer of the Sun's interior where nuclear fusion reaction happens.
- It has the highest temperature which is 15 million degrees C.
- ***Radiative Zone:***
- The energy from the Core is transferred outward by radiation through this zone.
- ***Convective Zone:***
- The energy is transferred through Convection currents to the surface.
- ***Photosphere:***
- It is the 1st layer of the Sun's atmosphere.
- Visible light originates from this zone.
- It is the brightest layer of the Sun.
- Its temperature is 5500 degrees C.
- ***Chromosphere:***
- It is the intermediate zone of the sun's atmosphere and emits colorful light.
- ***Corona:***
- It is the uppermost layer and is visible only during a total solar eclipse.
- It is hotter than the photosphere with a temperature of 2 million degrees Celsius.
- ***Solar Flare:***
- It is the sudden burst of energy with a storm of hot atoms released into space.
- ***Sunspots:***
- These are the dark spots in the Photosphere.
- They experience reduced temperature but strong magnetic activity.
- The Number of sunspots increases or decreases over some time.
- Solar maxima are when the sunspots are highest and solar minima are when they are lowest.
- The period between solar maxima or minima is 1 sunspot cycle(11 years).

## Planets of our solar system(6.06 PM):

- They are of two types, Terrestrial planets (Earth-like) and Jovian Planets (Jupiter-like).
- ***Differences between the Terrestrial and Jovian Planets:***
- |  |  |
  | --- | --- |
  | **Terrestrial Planets** | **Jovian Planets** |
  | Earth-like | Jupiter-like |
  | High density | Low density |
  | Rocky | Gaseous |
  | Smaller in size | Large in size |
  | High solar winds | Lower solar winds |
  | High temperature | Low temperature |
  | Thin/no atmosphere | Thick atmosphere |
  | Less no. of satellites | Large no. of satellites |
  | No rings | Rings |
  | Speed of rotation lower | Very high speed of rotation |
- ***Mercury:***
- It is the smallest planet.
- It is nearest to the sun.
- It has no atmosphere.
- ***Venus:***
- It is called Earth's twin.
- It is the hottest planet (very high greenhouse effect due to the presence of Co2)
- ***Earth:***
- It is called a Blue planet.
- It is the densest planet of all.
- ***Mars:***
- It is called a Red planet.
- the possibility of life due to its presence in Goldilocks Zones**(**habitable regions in the universe).
- ***Jupiter:***
- The largest planet in the solar system (11 times bigger than the earth).
- The giant red spot (a spinning cyclonic storm that appeared on Jupiter 400 years ago) is the most characteristic thing about Jupiter.
- ***Saturn:***
- It has the most prominent and spectacular ring system.
- It is the lightest planet in the solar system.
- ***Uranus:***
- Its axis of inclination is tilted by 98 degrees.
- It rotates from East to West(Retrograde rotation).
- ***Neptune:***
- It is the farthest planet.
- It cannot be seen with the naked eye.

## Satellites(7.06 PM):

- It is a body that revolves or orbits around another planet (and not around the sun).
- Mercury and Venus have no satellites.
- Earth has one satellite - Moon.
- Mars has two satellites-  Phobos and Deimos.
- Jupiter has 79 satellites, four of which are important (discovered by Galileo/ Galilean satellites) Io, Europa, Ganymede(the largest satellite), and Callisto.
- Saturn has the maximum number of satellites i.e. 82.
- One of the important satellites is Titan, which is the second-largest satellite in the solar system.
- Titan is one of the most probable regions in the solar system where there is the possibility of life's existence.
- Satellites of the Uranus are named after the characters of the play written by Shakespeare, for example, Miranda, and Oberon.
- Triton, a satellite of Neptune, rotates in the opposite direction of Neptune.
- ***Moon:***
- The period of rotation of the moon is equal to the period of revolution of the moon around the earth, which is equal to 27.3 days.
- Therefore the other half of the moon is not visible from the earth.

## Dwarf planet(7.36 PM):

- In 2006, the International Astronomical Union set the conditions for a body to be declared a Planet:
- It should have an independent orbit around the Sun.
- It should have enough mass to achieve hydrostatic equilibrium i.e. spherical shape.
- It should have a cleared neighborhood.
- Officially there are 5 dwarf planets, there are the bodies that fulfill 1st 2 conditions but not the 3rd one, for example, Pluto, Eris, Ceres, Haumea, and Makemake.

## Other important bodies in solar system(7.51 PM):

- ***Asteroid belt:***
- It is a belt of Asteroids which are small rocky and metallic bodies with cores made up of Iron and Nickel.
- They are orbiting around the Sun in a belt between Mars and Jupiter.
- ***Kuiper Belt:***
- This is a belt of remnants of planets with frozen gases, rocks, and debris materials.
- ***Oort cloud:***
- It is a layer of Ice pieces of space debris surrounding the entire solar system.
- ***Meteoroids:***
- When an asteroid comes out of its orbit and moves toward the earth.
- ***Meteor:***
- It is a flash of light due to the burning of meteoroids in the earth's atmosphere.
- It is also called a Shooting star.
- ***Meteorite:***
- It is the remnant of a meteoroid that has survived its passage through the earth's atmosphere.

## The topic for the next class: Comet, Solar, and Lunar eclipses.