Unit 1: The Earth in the Universe                                            1   2   3   4

1.3. Sizes and distances in the Universe

Distances in the Universe are so large that astronomers have to use special units to measure them.

Usually they use one of these units:

• Astronomical unit (AU)

            This is the distance from the Earth to the Sun.

            It is approximately 150 million kilometers.

            It is used to measure distances within the Solar System.

• Light-year 

            This is the distance light travels in one year.

            Speed of light is 300,000 km/s.

            It is used to measure distances between stars or galaxies.

1.9.  Calculate how many kilometers is one light-year. 

1.10. Alpha-centauri is the closest star to the Sun. It is 4.2 light-years

        from it. Express this distance in kilometers.

1.11. Mercury is 0'39 AU from the Sun.

          How many kilometers is this distance?