Components of the Solar System, Planets and Their Major Moons

[UPSC Prelims 2001] Who amongst the following was the first to state that the earth was spherical?

1. Aristotle
2. Copernicus
3. Ptolemy
4. Strabo

Explanation:

• The idea of a spherical Earth was floated by Pythagoras around 500 BC & later validated by Aristotle in 340 BC.
• Ptolemy placed the Earth at the centre of his geocentric model of the solar system. Nicolaus Copernicus refuted the geocentric model with his heliocentric model.
• Strabo is best known for his work Geographica (“Geography”), which presented a descriptive history of people and places from different regions of the world know during his lifetime.

Kepler’s Laws of Planetary Motion

1. The orbit of a planet is an ellipse with the Sun at one of the two foci.
2. A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.
3. The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.

Planet

Surface Temp in ֯C

Period of Rotation

Period of Revolution

Distance in AU

Diameter (km)

Size

Rank

Moons

Density (gm/cm³)

Specific gravity (m/s²)

58 days

87 days

0.4

4,878

0.38

8

+480

243 days

224 days

0.7

12,104

0.95

23:56 hrs

365 days

1

12,756

1.00

1

5.5

9.8

1.025 days

687 days

1.5

6,787

0.53

9.9 hrs

11.9 years

5.2

1,40,000

11.19

1

24.9

2.53

10.7 hrs

29 years

9.6

1,16,000

9.46

82

0.7

17 hrs

84 years

19.2

51,000

4.11

16 hrs

164 years

30.0

48,000

3.88

Pluto (dwarf)

6.39 days

248 years

39.5

2,377

0.18

Some of the values given in the table are rounded off.