Universe And Solar System (Part – 2)

When we talk about the distances to the stars, we no longer use the AU, or Astronomical Unit, commonly, the light year is used.

A light year is a unit of distance, not time. It represents the distance that light travels in one year in a vacuum.

Key Facts about a Light Year:

• Speed of light = approximately 299,792 kilometers per second (or about 186,000 miles per second).

• In one year, light travels about:

  • 9.46 trillion kilometers

  • or 5.88 trillion miles

• The nearest star to Earth (after the Sun) is Proxima Centauri, which is about 4.24 light years away.

When we talk about the distances to the stars, we no longer use the AU, or Astronomical Unit, commonly, the light year is used.

A light year is a unit of distance, not time. It represents the distance that light travels in one year in a vacuum.

Key Facts about a Light Year:

• Speed of light = approximately 299,792 kilometers per second (or about 186,000 miles per second).

• In one year, light travels about:

  • 9.46 trillion kilometers

  • or 5.88 trillion miles

• The nearest star to Earth (after the Sun) is Proxima Centauri, which is about 4.24 light years away.

While Mercury, Venus, Earth and Mars are the inner planets.

The main asteroid belt is located in the orbits of Jupiter and Mars.

8 Planets in Order:

1. Mercury – Smallest, closest to the Sun.

2. Venus – Hottest planet, thick atmosphere.

3. Earth – Our home, supports life.

4. Mars – The Red Planet.

5. Jupiter – Largest planet, gas giant.

6. Saturn – Known for its beautiful rings.

7. Uranus – Rotates on its side, icy giant.

8. Neptune – Farthest, cold and windy.

The average distance between the Earth and the Sun is about 140 million, 96 lakh km.

Explanation:

• Distance from Sun to Earth = about 149.6 million kilometers

• Speed of light = 299,792 kilometers per second

• Time = Distance ÷ Speed = 149.6 million km ÷ 299,792 km/s ≈ 500 seconds

• 500 seconds = 8 minutes and 20 seconds

Aphelion and Perihelion –

These terms describe the Earth’s varying distance from the Sun during its elliptical orbit.

Key Points:

• This is called counterclockwise rotation when viewed from above the North Pole.

• Because of this:

  • The Sun rises in the east and sets in the west.

  • All planets in the Solar System (except Venus and Uranus) also rotate in this direction.

But in the 26th General Assembly meeting of the "International Astronomical Union' held in Prague (Czech Republic) between 14-25 August 2006,

Pluto was removed from the category of planets and put in the category of the dwarf planet (Dwarf). So at present, the number of planets is 8.

Dwarf Planets –

A dwarf planet is a type of celestial body in space that shares some features with regular planets but does not meet all the criteria to be called a full planet.

Definition (as per IAU – International Astronomical Union):

A dwarf planet:

1. Orbits the Sun

2. Has enough mass to be almost round in shape

3. Has not cleared its orbit of other debris

4. Is not a moon of another planet