Distances between objects in space are huge. So huge, in fact that miles or kilometers are difficult to use
Consequently, astronomers usually measure space distances in light years.
One light year is the distance light travels in one year.
Light travels pretty fast – 186,000 miles per second (and according to the theory of relativity, nothing, but nothing, can travel any faster).
A light year therefore works out to be 6 million million miles.
So let us take an imaginary journey from the Sun, riding on a beam of light that has just been created from the nuclear reactions of the Sun
Our light-beam transporter leaves the Sun and heads out into the Solar System.
Let look at how it takes us to get to objects, even when travelling a the speed of light. This may give us some sense of some of the vastness of Space.
We set off from the Sun (and let us assume that all the planets are in a line)… NOW!
After 3 minutes we pass Mercury and after another 3 minutes, we speed past Venus.
It takes 9 minutes in total to reach the Earth, even at the speed of light (so we actually “see” the Sun as it was 9 minutes ago)
Just 1 second later, we pass the Moon.
Then we are heading towards Mars, and reach it 4 minutes later. We have now travelled a total of 142 million miles since we set-off from the Sun.
At 45 minutes into our journey, we reach Jupiter. Gosh! Isn’t it big and red?
Saturn is nearly twice as far from the Sun as Jupiter. On our light beam takes 80 minutes in total to reach it. We fly past Saturn and it also looks big, although not quite as big as Jupiter was.
We continue, on out into the far reaches of our Solar System.
Uranus goes past at 3 hours of travel.
Followed by Neptune at over 4 hours
We might catch a glimpse of Pluto (now no longer thought of as a planet) at around 6 hours, although Pluto has an eccentric orbit and is sometimes inside Neptune’s orbit.
That is the end of our Solar System. We are now heading out into deep space on our light beam.
It is would be sensible to get some sleep now. It is going to take over four YEARS to reach the nearest star!
The nearest star is the alpha Centauri binary star plus its companion, at around 4.3 light years, in the constellation of Centaur.
The brightest star we see from Earth is Sirius in the constellation of Canis Major. It would take us nearly nine years to reach Sirius, even travelling at the speed of light.
So when we look at Sirius from Earth, we see it not as it is now, but as it was, nearly 9 years ago.
Other bright stars we see from Earth are further away. Vega in the constellation of Lyra is 26 light years away, whereas Rigel in Orion is 800 light years distant.
Even at the great distance of Rigel, we are still with in our own galaxy, the Milky Way.
We believe that our galaxy the Milky Way, has a diameter of 100,000 light years.
The nearest galaxy outside our own, is the Andromeda nebula. This can be seen from Earth with the unaided eye, as a fuzzy blob in the constellation of Andromeda. It is the most distant object with can see without a telescope and it is 2.5 million light years away.
So even at the speed of light, it would take us 2.5 million years to reach the nearest galaxy. From Earth, we see the Andromeda galaxy as it was 2.5 million years ago, not as it is now.
It could actually have disappeared for all we know!
Yet to us on Earth, it would look as though it was still there, for the next 2.5 million years.
Other galaxies (and there are countless) are much further for the Earth and could take hundreds or thousands of million years to reach.
Space is big!
