The size of the Moon and Sun


The Sun, Earth and Moon
The Sun and the Moon seem to be the same size in the sky but the Sun is over four million times larger than the Moon. They look similar in size because the Sun is a long way from the Earth and the Moon is quite close. The Sun is 149,600,000 kilometres away and the Moon is only 380,000 kilometres away.


How long does sunlight take to reach Pluto?
It takes about five hours to reach Pluto. It then takes another half hour to pass through all the remaining bits of rock and ice at the edge of the Solar System.

How long does sunlight take to reach the next star?
It takes about four years three months to reach the nearest star. The star is called Proxima Centauri. If you wanted to make a model of the Sun and Proxima Centauri in space you would have to put them 985 kilometres apart. Look on a map and find a place that is about 985 kilometres from your school. You may have to look in another country!

How long does sunlight take to reach the furthest star?
Stars have been discovered so far away that it will take sunlight 13 billion years to reach them. There may be stars that are even further away.


Why are most objects in the sky just spots of light?
Most objects in the sky are a long way away and so they all seem very small. Two objects are large and seem to be the same size. These objects are the Sun and the Moon, but they only appear to be the same size because of an optical illusion. The Moon, which is much smaller than the Sun, is much nearer to the Earth than the Sun and so looks the same size as the Sun.

How do the planets look in the night sky?
Planets look like steady beams of light. They do not twinkle like stars. The reason for this difference is because the planets are much closer to us than the stars. Starlight has to travel such huge distances that it is very weak when it arrives here and the movement of air in the atmosphere makes it appear to wobble in its path. This is why stars twinkle. The light from the planet is reflected from the Sun, which is much nearer. This light is stronger than other starlight and does not appear to wobble in its path as it enters the atmosphere.

Why don't the planets look large in the sky?
They look like spots of light because they are so far away from us. Jupiter is over forty times as wide as the Moon, but only appears as a speck of light because the nearest it comes to Earth is 588 million kilometres.

Which planets can you see in the sky with the naked eye?
Mercury can sometimes be seen just before sunrise and just after sunset. Venus shines the brightest because it is the nearest, Mars shines with a reddish light, Jupiter shines brightly and Saturn shines more dimly. You need to look in the 'Sky at Night' section of a newspaper to find out which planets can be seen in the sky and where to see them. This section is found near the 'Weather' section in some newspapers.

If you were on another planet would the Sun look as large?
No. If you were on Mercury, the Sun would look nearly three times larger. If you were on Jupiter, it would be five times smaller, and on Pluto it would appear as just a very bright star.