Page 251 - Big Ideas Year 9 sciPAD 2025

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SCIPAD - BIG IDEAS - BOOK 1
SPACE SYSTEMS
Measuring Distances in Space
When stating distances between cities in New Zealand we use kilometres, as it gives us easy
numbers to work with. For example, the distance between Tauranga and Auckland is about 200 km.
When we start looking at distances in space, such as the distance between the Sun and Earth,
using kilometres becomes unhelpful because they are very large numbers. Instead, astronomers
use another unit to measure these vast distances, called ‘Astronomical Units’ (A.U.). An A.U. is the
average distance between the Earth and the Sun.
1. Convert the following space distances from kilometres (km) to astronomical units (A.U.) by
dividing the distance in kilometres by the number of kilometres in an astronomical unit.
Average Distance Distance in million km Distance in Astronomical Units (A.U.)
Sun to Venus 104
Earth to Jupiter 588
Saturn to Pluto 4 470
Light Years
Light travels at approximately 300 000 kilometres per second. This speed is almost unimaginable
to most people. To give you an idea of how fast this is, if you were travelling at the speed of light
it would take 0.0067 seconds to get from Cape Reinga (the top of the North Island) to Bluff (the
bottom of the South Island). Or to put it more simply, you could drive the length of New Zealand
and back approximately 75 times in one second!
2. Use the formula given below to calculate how long it would take to travel between the
two objects if you were travelling at the speed of light.
Distance
Speed of Light
Time =
Formula:
Sun to Earth
Distance = 150 000 000 km
Working =
Time = 
Earth to Neptune
Distance = 4 350 000 000 km
Working =
Time = 
The speed of light is useful for measuring astronomical distances - simply because the distances
between objects in space is so large. A ‘light year’ is the distance that light can travel in one year.
3. Use the speed of light to calculate how far light could travel in:
(a) one minute (b) one hour
(c) one day (d) one year
4. The closest star to Earth (apart from our own Sun) is called ‘Proxima Centuri’. It is 43 trillion
(43 000 000 000 000) kilometres away from Earth. If we could build a spaceship capable of
travelling at the speed of light, calculate how many years it would take to get there.


150 000 000 km = 1 Astronomical Unit (A.U.)
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