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Moons of our Solar System
Moons of our Solar System

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1.7 Sizing moons

This is an image of the Moon and Tethys, shown to correct relative scale.
Figure 12 The Moon and Tethys, shown to correct relative scale

To give you a feel for the sizes of some moons, have a go at Activity 2 below. There you will see we have provided images of eight moons, but not shown them to scale. All you have to do is guess the correct diameter for each moon (for markedly non-spherical moons we require the length of their long axis). If you get stuck, try consulting the moons data table from Week 1.

These are the moons we have chosen.

  • Enceladus: the sixth-largest moon of Saturn and named after a mythological giant of ancient Greece.
  • Deimos: the outer moon of Mars and named for the Greek personification of terror.
  • Phoebe: thought to have been captured by Saturn’s gravity. It is named after a Titan of Greek mythology who was grandmother to Apollo.
  • Iapetus: the third-largest satellite of Saturn, named after the Titan who fathered Atlas and Prometheus.
  • Tethys: a medium-sized satellite of Saturn, named after a Titan and aquatic sea goddess.
  • Pandora: a satellite of Saturn named after the Greek mythological figure who inadvertently unleashed all the evils of humanity from a jar.
  • Prometheus: a moon of Saturn, named after the Titan who stole fire from the gods. Zeus then condemned him to have his liver eaten daily by an eagle for all time.
  • The Moon: which goes by many names in different cultures; our own name derives from a Proto-Germanic word, mǣnōn.

Activity 2 Sizing moons – what do you know?

Timing: Allow approximately 20 minutes.
Enceladus
Figure 13 Enceladus

What is the diameter of this moon?

a. 

504 km


b. 

1062 km


c. 

1470 km


d. 

12.4 km


The correct answer is a.

a. 

Well done.


Deimos
Figure 14 Deimos

What is the diameter of this moon?

a. 

3474 km


b. 

104 km


c. 

12.4 km


d. 

213 km


The correct answer is c.

c. 

Well done.


Phoebe
Figure 15 Phoebe

What is the diameter of this moon?

a. 

213 km


b. 

1470 km


c. 

271 km


d. 

208 km


The correct answer is a.

a. 

Well done.


Iapetus
Figure 16 Iapetus

What is the diameter of this moon?

a. 

1062 km


b. 

3474 km


c. 

104 km


d. 

1470 km


The correct answer is d.

d. 

Well done.


Tethys
Figure 17 Tethys

What is the diameter of this moon?

a. 

136 km


b. 

3474 km


c. 

1062 km


d. 

504 km


The correct answer is c.

c. 

Well done.


Pandora
Figure 18 Pandora

What is the diameter of this moon?

a. 

12.4 km


b. 

104 km


c. 

271 km


d. 

3474 km


The correct answer is b.

b. 

Well done.


Prometheus
Figure 19 Prometheus

What is the diameter of this moon?

a. 

136 km


b. 

1062 km


c. 

3474 km


d. 

213 km


The correct answer is a.

a. 

Well done.


The Moon
Figure 20 The Moon

What is the diameter of the Moon?

a. 

1470 km


b. 

1062 km


c. 

3474 km


d. 

504 km


The correct answer is c.

c. 

Well done.