Glossary

Introduction

In the last lesson, we saw that the planets revolve around the Sun. We also learned that the inner planets are small and solid while the outer planets are large and gaseous or made up of ice. But how big are they as compared to the size of the Earth? Let us compare the sizes of the planets and their distances from the Sun.

Activity 1: Relative sizes of planets and distances in Solar System (Model)

Material: A measuring tape, a chalk and objects given in Table 1

Table 1: Objects showing relative sizes of planets and relative distances from the Sun

Procedure:

1. Mapping the sizes: Table 1 gives a list of objects showing relative sizes of planets. If the Earth is the size of a marble of diameter 1 cm then, the biggest planet, Jupiter would be the size of a coconut of diameter around 11 cm. Gather all this material and arrange it in correct order.

2. Mapping the distances: Did you put the above objects in line? Surely, they are not as close as you must have put on a large table. How spread out are they? Let us find out. Go on the school playground, a long corridor or on a quiet road. We need at least 120 metres of space in one direction.

3. If the Earth is imagined to be of diameter 1 cm, then the Sun would be of diameter 109 cm. Draw a circle of diameter 109 cm on the ground. Imagine that there is a sphere of this diameter here. This is your Sun. (It is difficult to get hold of such a large sphere, so we are drawing a circle and imagining a sphere.)

4. Now measure 453.9 cm from centre of the Sun. Place the small bead of diameter 0.4 cm here. In the shrunken Solar System, this is where the tiny (!) Mercury would be!

5. Now, measure another 40 metres (85 metres from the centre of the Sun). Place the marble of Venus there.

6. Measure 32 metres (117 metres from the centre of the Sun). Place the marble of the Earth there.

7. If you have not already run out of space, place Mars, that is the bead of 0.5 cm at 178 metres from the centre of the Sun (61 metres from the Earth).

8. The next planet, Jupiter, which is a coconut in our model, would be at 601 metres from the Sun, that is more than half a kilometer. You will need a good 10 minutes to walk this distance, So henceforth, only imagine where the rest of the planets are in the shrunken solar system.

9. Saturn, which is an orange in our model, is more than 1 km from the Earth and a 15-minute walk away.

10. Uranus, the table tennis ball, is two-and-a-quarter km, more than a 25-minute walk away. No wonder, it is hardly visible from the Earth.

11. Finally Neptune is at a good three and a half km distance from Earth (about 40 minutes walk)! Imagine how big its orbit would be. Now you know why Neptune takes almost 165 years to complete one revolution around the Sun!

Apart from the Sun and the planets, there are other smaller objects in our Solar System. Let us learn more about these objects.