Spacewarp: Colliding Comets and Other Cosmic Catastrophes

By Fred Watson

Age range 10+Why do stars twinkle? What's the best way to start spotting constellations and comets? Is there life beyond Earth? What's the chance of a catastrophic collision with a killer asteroid?He's covered the big space questions for adults, now Australia's very own Astronomer-at-Large, Fred Watson, embarks on a grand tour of the Universe especially for children. From stargazing to telescopes, space travel to black holes, killer comets to aliens, Fred covers every question kids might ask about space and then some.With incredible illustrations by Fred himself, and a mix of mind-boggling facts, Spacewarp is a fascinating book that kids will love and parents and friends will undoubtedly learn a thing or two as well!

• Language: English
• Publisher: NewSouth
• Release date: Dec 21, 2021
• ISBN: 9781742238296

Book preview

Chapter 1

STARGAZING

Stargazing is where astronomy starts for many people. It certainly did for me, even though the place where I grew up was often cold, wet and cloudy, and you sometimes had to wait for weeks to see the stars. But a clear starry night is worth waiting for. There is something beautiful and awe-inspiring about standing underneath a sky full of shimmering stars, even if you don’t really know what you’re looking at. But when you do, it gets even better.

It was the wish to know more that interested me in astronomy and space when I was still a youngster in Britain, and took me to my first job in an observatory. Over the years, I worked on asteroids, planets and stars, enthralled by their mysteries. I even made a few discoveries. The chance to work with some of the biggest telescopes in the world eventually brought me to Australia, where I helped to run the national observatory at Coonabarabran in north-western New South Wales.

It was a bit like being the manager of a lolly shop, and I got involved with lots of different projects, from counting shooting stars to mapping distant galaxies. My fascination with space has never gone away, and as Australia’s Astronomer-at-Large, I now get to talk about it to anyone who will listen. And the best part of that is being able to write about it for people like you!

Ancient sky-watchers

Our fascination with the stars goes back to the earliest times, particularly in Australia, where people have been watching the sky for tens of thousands of years. The stars have a special place in the knowledge and traditions of Aboriginal people, and their stories about them often include important information related to everyday life.

Certain star groups rising in the eastern sky might tell you it’s time to go looking for particular edible plants, for example. ‘There are Aboriginal stories explaining what to do, when to gather, when to hunt,’ says Darren Wighton, who is an elder of the Wiradjuri people of central and southern New South Wales and a keen sky-watcher. ‘Different animals and stories [to do with the stars] are reflected in the creatures of Australia in ways that help us learn. There are goannas, emus, eagles – all these different creatures we see every day – and they are used in a way to explain the constellations.’

Constellations are groups of stars in the sky, and the 500 or so different Aboriginal nations in Australia had their own constellations, many of which are still familiar today within their communities. But the constellations recognised all over the western world come from ancient Greek star patterns, which go back only 4000 years or so.

Astronomy and astrology were once the same thing.

The words themselves give a clue from their Greek roots – astronomy is ‘numbering the stars’ while astrology is ‘words about the stars’. They’re both very old words (‘astronomy’ is 12th century; ‘astrology’ is 14th century) and they meant the same thing for hundreds of years. Astronomers practised what we now call astrology right up until the 1600s, using the stars and planets to try and predict the future. Today, of course, astronomy means observing the sky in a knowledgeable way, while astrology means … well, trying to predict the future.

Joining the dots

Most of us are familiar with the constellations of the zodiac, the region of sky along which the Sun seems to travel as it makes its year-long journey around the heavens. We know those constellation names because the old custom of astrology gave everyone a ‘birth sign’, corresponding to the constellation the Sun was passing through when they were born. My birth sign is Sagittarius. Do you know what yours is? By the way, most people also know that astrology is just that – an old custom. There’s no point in trying to use it to predict the future. Science has proved that astrological predictions are no better than complete guesses. Oh well, it was a nice idea.

Apart from the constellations of the zodiac, there are many more star groupings over the whole sky, with names like Orion the Hunter, Aquila the Eagle, and Canis Major, the Great Dog. I have to admit that many of these star patterns don’t look anything like what they’re supposed to depict. The ancient people who invented them must have had good imaginations. There are exceptions, however. Scorpius, the Scorpion, is one, and I’ve always thought Leo, the Lion, is quite lifelike, although in our southern skies he’s upside-down.

Modern astronomers recognise 88 constellations altogether. Some of them can’t be seen from Australia because they’re always below our northern horizon. Ursa Minor, the Little Bear, for example, and the Ethiopian Queen, Cassiopeia – a favourite of mine because she looks like a big letter W for Watson in the sky. From northern Europe or North America you can see these constellations all year round. But those places never see some of our well-known southern constellations like Centaurus the Centaur, and Crux, the Southern Cross. By the way, Crux is the smallest of all the constellations, but it’s also one of the brightest.

This night sky picture shows real constellations and star clusters, but their names have been ‘improved’ with an Australian flavour. They haven’t changed all that much, and are all still connected in some way with the old ones. Can you work out what each improved constellation or cluster was originally called? And I wonder if you can work out in what direction those two young stargazers are looking? North, south, east or west? (Hint: check out your star wheel or night sky app.)

Answers on page 253.

Navigating the sky

How do you find the constellations? Today, there are apps that can help you with this, but let me start by telling you about one of my favourite methods of finding your way around. You need a little gadget called a planisphere, more commonly known as a ‘star wheel’, which you can buy in science stores or online. The name gives a good idea of how it works, and early versions of it were used by astronomers in the Middle East more than a thousand years ago. (They were called ‘astrolabes’, and can sometimes be seen in museums.) Today’s star wheels are usually made of card or plastic, and are simply two discs, one of which has a map of the sky printed on it and the other an oval window through which you can see the map. Pivoted at the centre, they let you dial up the date and time around the edge, and voilà! The window shows you what the night sky looks like at that time.

The nice thing about star wheels is that you can see the whole sky at a glance, making it easy if there’s a particular constellation you want to find. The other advantage is that they don’t need batteries or charging up. But you will need a flashlight to see what you’re doing on a dark night. Choose one that’s fairly dim so you don’t spoil your eyes’ sensitivity to starlight. And a flashlight with red cellophane over it is even better for preserving your night vision.

But what about the planets?

The one thing that star wheels don’t show is where the planets are. That’s because, like the Sun and Moon, the planets move against the background of stars. In fact, that’s where their name originates, since the word ‘planet’ comes from a Greek word meaning ‘wanderer’. The trouble with planets is that to your unaided eye, they look just like stars. There’s no sign saying ‘I’m Jupiter’, or ‘Yes, you’ve found Venus’. (Actually, those two planets are pretty easy to spot, since they’re brighter than the stars.) But it was by their wandering through the sky that ancient people realised planets were something different from stars.

They also noticed – as you might, too, once you start finding your way around the sky – that planets always stay close to an imaginary straight line. It’s called the ecliptic, and it’s actually the path that the Sun follows as it makes its yearly journey right around the sky. (In reality, of course, it’s the Earth revolving around the Sun that makes it appear to move against the background of stars.) If there are two or three planets visible – and perhaps the Moon, too – you can often trace out the line of the ecliptic among the stars with your finger.

Going digital

But the easiest way to see where the planets are when you’re stargazing is to go electronic, with a computer, tablet or smartphone. There are several packages available for computers and tablets, but one of my favourites is the free Heavens Above website (<heavens-above.com>). It has what they call an Interactive Sky Chart, which gives you a picture of the whole night sky rather like the star wheel – but including the Moon and planets.

Even when you’re standing still, you are racing eastwards at hundreds of kilometres per hour because of the Earth’s rotation.

It’s perfectly true, and you don’t feel a thing! That’s because everything else (including the air around you) is being carried along at the same speed. In fact, your exact speed depends on your latitude. In London or Berlin you are doing around 1000 kilometres per hour, in New York or Beijing almost 1300 kilometres per hour, while in Sydney or Cape Town you are cruising at about 1400 kilometres per hour. Your speed is greatest on the equator, at 1674 kilometres per hour. By the way, this is why space launch facilities are built near the equator. If satellites are launched towards the east, they get a free gift of 1600 or so kilometres per hour to help them reach their orbital speed.

The Sky Chart has another advantage over the star wheel, in that you can set it to show you the night sky anywhere in the world. Star wheels only work for particular latitudes. The one for Australia, for example, would work equally well in South America, but you’d need a different one for Europe and North America.

Another kind of app is great on a handheld device (such as your phone) that you can take outside with you. Once again, there are several apps available, most of which you have to pay for, although you can find free ones. These are generally called sky viewing apps, in which you simply point your device at the sky, and it shows you the details of what you’re looking at. It’s a wonderful use of modern technology, and a fantastic guide to the night sky, especially for beginners. Constellations, individual stars and planets all show up in the app – even when the real ones are hidden by cloud!

Moonstruck

Of course, one thing that’s hard to miss in the night sky is the Moon, but it’s not always there, and it’s not always the same shape. Because the Moon is like a ball lit by sunlight, only half of it is illuminated at any one time. And because the Moon goes around the Earth once a month (or ‘moonth’ – yes, that’s where the word comes from), our view of the illuminated half changes from night to night. We call its changing appearance the ‘phases’ of the Moon.

Early in the Moon’s monthly cycle, it’s a slender crescent setting in the western evening sky. It’s a crescent because most of the bright side is pointing away from us. It appears to grow night by night until we see a half Moon that sets at midnight. We call this phase ‘first quarter’ because the Moon is a quarter of the way around its orbit. A week later, at full Moon, the whole face of the Moon is brightly illuminated as it rises at sunset, and is visible throughout the whole night.

After that, the Moon steadily shrinks in the late evening and early morning sky, until two weeks after full Moon, it’s in the same direction as the Sun, and not visible. That’s the phase known as new Moon. Don’t forget to have a look at the Moon when you’re stargazing, and see if you can work out its phase.

This is what the Moon does every month as seen from our southerly latitudes. The ten little sketches show how the Moon slowly makes its eastward journey through the sky. Astronomers sometimes talk about the ‘age’ of the Moon – not in billions of years, but in days since new Moon, when it’s in approximately the same direction as the Sun and invisible against the glare of sunlight. The full cycle from one new Moon to the next takes 29½ days – which is a lunar month.

In the upper picture, you can see the phase (shape) of the Moon and its position in the sky as seen at sunset throughout the first half of the month. When the Moon is full, it rises as the Sun is setting, so it’s visible all night. The lower sketch is the same for the second half of the month, but as it would be seen in the morning at sunrise. Because the new Moon is invisible, I’ve coloured it in a darker shade.

Now you know all that, why don’t you keep a lookout for the Moon next time you’re out of doors? Depending on its phase, it’s often visible during daylight as well as at night. See if you can work out how ‘old’ it is. And while you’re watching, can you rearrange the letters of ‘astronomer’ to describe what you’re doing?

Answer on page 254.

Meteors and mission control

Something else to look for on clear nights is stuff that doesn’t stand still. A bright pinprick of light that flashes across the sky is a meteor, or shooting star, though it really has little to do with stars other than being in the sky at night. Meteors are actually particles of dust or small stones that enter Earth’s atmosphere from space at speeds of up to 70 kilometres per second. That would get you from Perth to Sydney in 47 seconds. Their speed through the thin air 90 or so kilometres high heats them quickly, and they flare into brilliance for half a second or so before disappearing.

Other things you might see moving through the sky are satellites, which are spacecraft that orbit around Earth. Properly, they are called artificial satellites to distinguish them from Earth’s natural satellite (the Moon), and you can read more about them in chapter 3. Satellites travel much more slowly among the stars than meteors, and sometimes seem to vanish unexpectedly. That’s because they are so high that they’re lit up by the Sun, even though it’s dark at ground level. They don’t shine by any light of their own, so if they enter Earth’s shadow, they disappear. Usually, it’s only within an hour or two of sunset (or an hour or two before sunrise) that satellites are visible.

The brightest of all satellites is the International Space Station, simply because it’s by far the biggest. It is quite unmistakable as it moves eastwards across the sky, its light completely steady, unlike the flashing beacons of aircraft. If you want to know when and where to see it, the Heavens Above website I mentioned earlier gives all the details. The space station usually has six astronauts on board – sometimes more – working to increase our understanding of how we can live and work in space. Not a bad job.

Shadows in the sky

If you look again at the night sky on your star wheel or app, you might see a smudgy-looking strip running across the sky window. That represents the Milky Way, a band of light that actually encircles the whole sky – including the part beneath your feet! It’s the light of millions of stars too faint to see individually without a telescope, combining to produce a haze of brightness. The Milky Way is our view through the thickness of a gigantic disc of stars and glowing gas that we call the Milky Way Galaxy. We’ll explore it later in this book.

You might also notice from the star wheel or app that the Milky Way is quite patchy, and when you view the real thing, you can see it has areas of darkness in it. These are clouds of dust particles far off in space, almost like smoke, but in such vast quantities that they block out the light of the stars behind them. One of these dust clouds is right next to the Southern Cross. Because of its intense blackness, it was called the ‘Coal Sack’ by European astronomers who visited the southern hemisphere 200 years ago.

But Australian Indigenous people have been watching these same dust clouds for