# Space is big

Space, our universe, is big. Let’s think about how big space really is, starting with our planet Earth.

So how big is our planet? From one point to another going through the centre, it’s about 13’000 km (about 8’000 miles). Around the equator, it’s about 40’000 km (about 25’000 miles).

A car on a good road, or a train on a good track, will normally travel at about 100 km/h (60 mi/h). So if there were a good road around the equator (with some bridges for the oceans), driving non-stop it would take about 400 hours, which is almost 17 days, more than two weeks.

A modern passenger aeroplane, the Airbus A380, has a maximum speed of 1’000 km/h (about 600 mi/h), about ten times faster than our car. Non-stop it would take 40 hours to fly around the equator, but the Airbus would actually have to land after about 17 hours, when it runs out of fuel.

So our planet is quite big! What if our aeroplane could fly to the moon; how long would it take?

The distance to the moon is 385’000 km (240’000 miles), so it would take 385 hours, almost exactly 16 days, a bit more than two weeks.

The moon orbits the earth every 28 days, e.g. four weeks. It travels about 2.5 million km (1.5 million miles) during this time, so its speed is about 85’000 km per day (55’000 miles per day), or about 3’600 km/h (2’300 mi/h).

So in fact if our aeroplane got to the moon, it would be too slow to keep up with it.

It’s a long way to the moon, but compared to the size of our sun, it’s small! From our planet the sun looks like a disc (although it’s in fact a sphere), The distance across this ‘disc’ is about 1.4 million km (865’000 miles), which is about 3.5 times the distance from the earth  to the moon.

Looking from planet earth, the moon and the sun look the same size, although the sun is much, much bigger. In fact the moon’s diameter is only 3’500 km (2’200 miles); the sun’s diameter is 400 times bigger.

They look the same size because the sun is much further away. The distance from the earth to the sun is 150 million km (94 million miles), 390 times the distance to the moon.

That’s why during a solar eclipse the moon completely blocks the sun.

The earth moves around the sun with the other planets. This is called the solar system.

The solar system is part of the Milky Way galaxy. The word galaxy comes from the Greek word for milk.

There are lots of stars in our galaxy. There are lots of galaxy’s in our universe.

The universe is very big; so big we don’t even know how big it is. In fact, it might go on forever.

Also we don’t know how old the universe is. Maybe it has been there forever and maybe it will be there forever.

Space is so big it takes light a long time to travel from the stars to us, even though light travels really, really fast. Many scientists believe light is the fastest thing there is.