John Griffiths Astro Pages

GCSE Astronomy — Facts you have to know

 

GCSE Astronomy >  [Lesson Summary Sheets]  >  Facts you have to know  >  [Buying telescopes ]

Image: Hubble Ultra Deep Field —

Hubble STScI / NASA

· Any relevant formulae you need to use will be given in the question. However you will need to know and use the relationship

 

Speed  = Distance/Time

 

(You will not be required to use the difference between speed and velocity  but for information velocity is speed in a specific direction. For those who are interested speed is a scalar quantity, velocity is a vector (vector indicating a specified direction))

 

· You will need to REMEMBER these numbers (they are used in the course and in the examination, but do not forget they are rounded figures – you will see slightly different figures quoted in books and web sites)

 

All measurements in kilometres (km)

 

Earth diameter                                13,000

Moon diameter                                3500

Sun diameter                                  1.4 million

Earth - Moon distance                    380,000

Earth - Sun distance                      150 million

 

· Useful astronomical relationships

 

Earth diameter is about 4 times the Moon OR Moon diameter is ¼ that of the Earth.

 

Sun diameter is around 100 times the Earth. Hence volume of Sun is 1,000,000 (100 cubed) that of the Earth OR you could fit over 1,000,000 Earth's inside the Sun.

 

The Sun is about 400 times further away than the Moon and the Moon is about 400 times smaller (in diameter) than the Sun which means that in the sky they appear about the same apparent size. Hence when there is an eclipse of the Sun, the Moon blocks out the Sun completely – what a wonderful coincidence.! As far as  I am aware this is unique to the Solar System.

Last updated Oct 6, 2006

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