Читать книгу Simple Stargazing - Anton Vamplew - Страница 16

How big is space itself? The large distances on Earth still amaze me, let alone trying to imagine the great gaps between the planets. It’s worth just a thought or two – see how much distance you can imagine. Take my house, for example: I have to walk about 1 km to get from there to the cake shop. That’s a nice, easy stroll that takes me 10 minutes; I can picture that. Now the Moon, our nearest neighbour in space, is 384,000 times further than the cake shop. That is, of course, 384,000 km. Walking there would take me nearly nine years – and yet the Moon is only next door as far as space is concerned.

Your imagination can take you anywhere on the space super-highway. Then again, maybe this will become reality.

I’m already having a slight problem trying to imagine this relatively tiny Earth-to-Moon distance, so what chance do I have with larger gaps? For example, the distance from my house to the Sun is a massive 150 million km – that’s already getting pretty big and we haven’t left our solar system. The nearest star after the Sun, called Proxima Centauri, is about 40 trillion km from my front door and, by moving deeper into space, we can find the Andromeda galaxy, a close star system that is 26 quintillion km away!

And still these biggish numbers are just peanuts compared to the size of distances in the Universe – there really is a lot of space out there.

What does a quintillion mean to you? I have to say it doesn’t mean much to me. So, if I’m having trouble with the distance to the Moon, what hope do I have with 26 of these quintillion thingies?

Help is at hand, though, as astronomers have a different way of measuring very large distances in space, and it’s called the light-year. A light-year is simply the distance that light, zipping along at nearly 300,000 km per second, travels in one year. Now, instead of our nearest star being 40 trillion km away, it becomes a more manageable 4.27 light-years.

16 April 2002 at 20.55. The Moon and Saturn at the top, with the bright star Aldebaran at the bottom. All these objects look as if they’re the same distance away from us, but Saturn is really 3792 times further away than the Moon, while Aldebaran is 911.5 million times more distant.

Even so, the Universe as a whole space-time thingamajig is still a whopping 13.7 billion light-years across – something you should only try to convert into kilometres if you’ve got a very big piece of paper.

This is as far as we can go (at the moment!).

We can use the speed of light to measure times other than a year. Here’s a table full of bits and bobs to give you some idea of the vastness of space:

Thing (planet times given are when they are at their closest to Earth)	One-way Light-travel time from or to Earth
Moon	1.25 seconds
Venus	2.3 minutes
Mars	4.35 minutes
Sun	8.3 minutes
Pluto	5.3 hours
Voyager II (furthest spacecraft as of 2004)	1 day
Proxima Centauri (our nearest star after the Sun)	4.27 years
Deneb (main star of Cygnus, the Swan)	~2,100 years*

* ‘~’ means approximately, and is also used in the constellation of Cygnus.

Anyway, let’s now amaze ourselves with just how big the ‘space’ you can see up there is…