Simple Stargazing. Anton Vamplew
Чтение книги онлайн.
Читать онлайн книгу Simple Stargazing - Anton Vamplew страница 7
Название: Simple Stargazing
Автор: Anton Vamplew
Издательство: HarperCollins
Жанр: Физика
isbn: 9780007441464
isbn:
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…
Depending on the hemisphere you are in, either the Plough or the Southern Cross is easy to spot if you know in which direction to look and how big they are. This idea of size is useful to understand, so I’m going to take a moment to show you how to measure things in the sky.
Let’s start with the Moon. Most people would say that it is a lot bigger than it really looks. You may be surprised when you realise that the end of your little finger held at arm’s length easily covers the Moon – with room to spare. Have a go next time the Moon is out.
The Plough appears only slightly longer than your outstretched hand – though it depends on how big your hands are, of course.
Of course, you can cover different amounts of the sky using more of your hand, arm or even your feet if you’re fit enough. For now it is useful to know that the Plough, as viewed from the Earth, is slightly longer than your outstretched hand held at arm’s length. However, there are loads of tiny things to see, so it is time to get a little more scientific.
You probably know that if we want to divide any circle into smaller units, we use degrees – or, more accurately, angular degrees – and that 360 of them make up a full circle. If you imagine the circle as a clock, the minute hand moves through 360 degrees when it goes all the way round, which takes one hour.
A single degree is a very small measurement, equal to the barely visible movement that the minute hand on a clock makes in 10 seconds. But in space many objects are extremely small, so we need incredibly small units to measure with. The space boffins have therefore divided the degree into 60 smaller segments, and each one of those into a further 60 even smaller segments.
Unfortunately the names of these smaller segments sometimes lead to confusion, because the 60 smaller segments of an angular degree are called angular minutes (or arc minutes) and the 60 smaller segments of the angular minute are angular seconds (or arc seconds).
These units are represented by the following symbols:
| ° degrees | ’ minutes | ” seconds |
You can avoid confusion simply by remembering that if you see the word angular or arc anywhere, the measurements are to do with angles, not time.
With all this information about measuring, let’s take a look at the sizes of some space things in degrees, arc minutes and arc seconds:
| Thing | Approximate angular size |
| Distance from the Pointers in the Plough to Polaris | 28° |
| Length of the Plough | 24° |
| Your outstretched hand at arm’s length (roughly) | 22° |