Simple Stargazing

Adventures in Darkness

Right, you’ve opened the door and are standing in the garden/yard/field/outback/ savanna/rocky landscape/swamp, etc. gazing up at the night sky searching for something wonderful to appear. How many stars can you see on a clear night? Millions? Squillions? Zillions? In fact, away from light pollution, with a good low horizon, the maximum number of stars you can see at any one time is 4,500(ish). Count them if you don’t believe me. Of course, if you live in a major city, then bright orange skies can easily reduce this number to less than 200, so the darker your location the better.

A few things to start with…

Step-by-step guide to stargazing

1

Before you go out, check where the Sun rises and sets from where you live. This will give you some idea of where to look when trying to find something in the night sky. Usefully, around 21 March and 23 September, the Sun rises exactly east and sets exactly west. However, in the northern hemisphere during the summer months the Sun appears (roughly and depending on the precise date) somewhere from the northeast and sets somewhere northwest, while in the winter it’s a southeast rise and a sort-of southwest set. In the southern hemisphere, the summer Sun rises somewhere in the southeast and sets somewhere southwest, while winter sees a northeast rise and a northwest set.

2

In order to see the most stars you need to let your eyes become accustomed to the dark. This is called dark adaptation. Ten minutes is a good time to sit in the dark without the lights on. Ponder, cogitate and muse over the wondrous spectacle that you are about to marvel at. How many constellations will you find? This process of dark adaptation not only widens your pupils to let in more light, but also allows various chemical reactions to take place in your eyes and activate your light-recepting rod cells. Now you will be able to see all those faint stars.

Help your dark-adapted eyes by making sure any torch is covered in red plastic.

3

Whilst outside in the dark the only way to see where you’re going, or to look at the great star charts in this book, is with a torch. However many you decide you need, each should be covered in red plastic or something similar. The resulting red light, you see, hardly affects your now dark-adapted eyes.

4

Grasp this book firmly and, if you are not one yourself, find a responsible adult and venture outside. Adults are very useful indeed for chatting to and for having someone who will marvel at your initial determination.

Where exactly to begin up there depends on where you live down here. For those in northerly climes, you need to go here (Northerly humans start here) … while southerly humans go here (Southerly humans read this)…

Empty space – or is it?

Northerly humans start here

Just look at the page opposite: it’s covered in what looks like a chaotic pattern of differently sized dots. Nothing could be further from the truth. Each dot is actually a star we can see in the night sky and, just like many things that look like chaos to start with, there’s order within this mess.

Lurking within these dots you will find a very useful pattern that is probably the best place to start your stargazing quest in the northern hemisphere. This group is known affectionately as the Plough – well, it is in Britain. Moving around our planet, we find that the Plough is called Karlsvogna (Carl’s Wagon) in Norway, the Big Dipper in the USA and the Saucepan in parts of France. This is definitely a good name for the shape, as you can see – a pan with a handle stretching out to the left. Anyone for space beans?

Now, the Plough is not actually a constellation itself, but part of a much larger group called Ursa Major, the Great Bear – we shall meet it very shortly.

The Plough is always visible from mid-northern latitudes if the skies are dark and the weather crisp and even. Also, all of its seven stars are quite bright, making it an easy group to find. In order to know which direction to look to find The Plough, you need to have some idea of north, south, east and west. As I said a moment ago, the Sun sets in the west(ish), so look to the right of that and up a bit (that’s a technical term) and there’s the Plough in the north(ish). Easy.

It’s not long before patterns begin to emerge from the ether. Ether is an old term for the stuff that scientists used to believe filled space – it doesn’t exist, but the idea’s nice.

Round and round the Plough goes. If you are far enough into the northern hemisphere, this is where you’ll find it at 8 p.m.(ish) at certain times through the year. The left of the diagram is the direction of northwest, whilst the right is northeast.

Because the Earth is constantly turning, don’t expect the Plough to stay in the same place for long. There’s also our movement around the Sun to consider, which means that each night at the same time the Plough will be in a slightly different position. How exciting is that!? Generally you’ll find the Plough higher in the sky during spring and summer evenings, and nearer the horizon in autumn and winter evenings.

As you may have noticed, there is a well-known star ‘locked’ in the centre of the image that the Plough rotates around. This is Polaris, also known as the North Star, or indeed the Pole Star. This last name means that it is the closest star to the North (Celestial) Pole, but because of the way the Earth spins on its axis, this is a temporary title and has been held over millennia by a number of the stars featured in this book.

You can always find Polaris by using the two right-hand stars of the Plough, which are called the Pointers. No need for Sherlock Holmes here – these two stars, Dubhe and Merak, simply ‘point’ up out of the ‘saucepan’ to Polaris. Elementary. And this is just one reason why the Plough is so useful. Through this book you’ll find plenty of ways that it can be used as a ‘signpost’ to many other stars and constellations.

The Pointers of The Plough doing their ‘pointing’ thing.

Polaris is the leading (main) star of Ursa Minor, the Little Bear.

Now, to break a myth: the North Star is not the brightest star in the night sky. It seems that for some unknown reason someone, somewhere, sometime told us that not only was it the brightest but it was also the first star you could see when it got dark. This is not true: Polaris happens to be only the 50th brightest star in our skies. Its fame is due to its position: almost directly above the North Pole. As the Earth spins we see the effect as the sky spinning, and in the northern hemisphere it’s Polaris that everything goes around. Being almost stationary in the sky means that if you’re looking at it you are looking north. And if you know where north is, you also know where east, south and west are. This is why Polaris was great in the olden days when mariners would ‘sail by the stars’.

There’s another group that can be found with supernoval ease by carrying on the line from the Pointers through Polaris to a ‘W’ shape that is Cassiopeia, the Queen. If your house/flat/hut/cave/tent/treehouse, etc. is in a position where the Plough never sets, then neither does Cassiopeia – they’ll both be up, somewhere. Because they are on opposite sides of Polaris, when the Plough is high, Cassiopeia is low and vice versa.

Following imaginary lines made by stars can lead you anywhere in the Universe.

Cassiopeia, the Queen, sits and ponders: ‘Hmmm, I know I’ve forgotten something?’

Southerly humans read this

Travelling to the southern part of the world, where the Plough may only be visible for half an hour in mid-April, or indeed may have totally vanished below the horizon, we need something else that can help us on our stargazing travels. Indeed, as for seeing the Plough (even for the briefest of periods), places near 23°S, like Alice Springs, Australia, São Paolo, Brazil, or Gaborone, Botswana, are really your most southerly locations.

A comparison in size between the Plough, a part of Ursa Major, and Crux, the Southern Cross.

What we’re looking for in the southern skies is a small constellation, the smallest in fact, known as Crux, the Southern Cross.

Of course, as with everything else, the years have performed transformations and rearrangements of the part of the sky where the Cross that we know today appears. For example, in Ptolemy’s day – the second century AD – the stars of Crux were part of the next-door constellation Centaurus, the Centaur. It was only in the late 16th century that the Cross began to take on its own personality as modern astronomers placed it in their star atlases.

Another change of names involves something you can see – or not see! – within the borders of Crux: a cloud of blackening dust and gas which obscures the Milky Way stars behind (we’ll be hearing a lot more about the Milky Way later in the book). Known today as the Coal Sack, in history this cloud has also been the Soot Bag and the Black Magellanic Cloud – which is a mysterious name I really like. It was once darkly described as ‘the inky spot – an opening into the awful solitude of unoccupied space’.

Crux, and some friends that we shall meet very shortly, are the southern equivalent of the Plough and Pole Star combined, because they too can be used to find your way about in the dark. By following various imaginary lines you can fairly easily discover the South Pole of the sky – the point about which the stars seem to revolve.

Unfortunately when you get to this point, darkness prevails, for there is no star equivalent of Polaris awaiting your arrival – there is no South Star, or Polaris Australis, as you could have called it. Astronomers with big telescopes who do not wash much will harp on about the star σ Octantis, which almost marks the southernmost point. However, it is extremely faint, difficult to find and therefore almost useless. So the Southern Cross and a couple of dazzlers next door do the admirable job of locating this starry (or celestial) pole of the south.

As the Earth spins and travels around the Sun, you’ll find Crux in different parts of the sky depending on the time and date. Its highest appearances occur during the autumn and winter evenings; in spring and summer evenings it’s nearer the horizon.

Round and round the Southern Cross goes. Using the Crux ‘Pointers’ and some useful jiggery-pokery with Rigel Kentaurus and Hadar, you easily can find the South Pole of the sky!

You can just glimpse a few stars of Crux from the Canary Islands off the north coast of Africa, but you’ll need to go below about 23°N – to Aswan, Egypt, Hong Kong or Dacca, Bangladesh, for example – to see it in all its glory. If your latitude is further south than about 34°S, like Sydney, Australia, Montevideo, Uruguay, or Cape Town, South Africa, then technically the Southern Cross never sets – although it still just skims the horizon until you go even further south, which you’ll have to do by boat as you run out of land!

Anyway, that’s the ‘where’ bit. Next, what about how big things are?

The appearance of the Plough we know and love really depends on where we live. In the northern hemisphere it may be visible whenever it’s dark. However, the further south you go, the less you see of it. Around 23°S it appears low over the northern horizon only during evenings in April – and even then it’s upside down!

Travels into the Darkness

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:

* ‘~’ 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…

How Big is the Darkness?

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:

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:

What’s interesting from this table is that technically we can see at least one of the moons of Jupiter as well as the crescent-shape phase of Venus simply by gazing skyward with our unaided eyes (the 20–20 variety is required). However, in practice the usually super-brightness of Jupiter drowns out the fainter light from its moons, while the dazzling appearance of Venus does the same for its crescent.

Look! You can use many bits of your hand to measure different sizes in the sky.

How to Use the Star Charts

What you can see depends on the time of year – the stars change from season to season due to our motion around the Sun. Therefore the constellations that we’ll be discussing a bit later on have been divided into the skies of spring, summer, autumn and winter. Some constellations are visible all year, but they are best viewed at certain times of the year.