Simple Stargazing
Simple Stargazing
Anton Vamplew
A first-time skywatcher’s guide from bright new talent, BBC Blue Peter astronomer, Anton VamplewMost books on stargazing claim to be for beginners, but by page 12 are talking about celestial equators and sidereal months. No wonder so many people have planispheres but no idea how to use them.Working at the planetarium in Greenwich, Anton has met hundreds of enthusiastic but utterly bemused beginners of all ages, and has made sense of the night sky for them. In this book he introduces the night sky just as if he were by your side, pointing everything out. And contrary to popular belief, you don't need any expensive equipment to start skygazing. Anton takes you through all the things you can discover with just the naked eye.The book is suitable for use in the northern and southern hemispheres – two sections give equal coverage to where to start and what you can see wherever you are in the world, whenever.
Contents
Cover (#u482212ec-ec41-5ae0-a904-9455fc77d3e7)
Title Page (#uab5dae45-de05-5c82-96a2-689a4abe0abc)
Dedication (#ubd2a4ae5-eb11-5e23-8409-6141f48e90d7)
Introduction (#u435ce41b-3da3-5d6c-b745-23b483dd51b5)
PART 1 (#u427618c6-38d8-5013-a005-a689d4966e36)GETTING STARTED (#u427618c6-38d8-5013-a005-a689d4966e36)
A Brief History (#ulink_25e6e215-33db-5e22-92c3-c05ae37a18e7)
Constellations (#ulink_0551d24f-c08f-56a2-954a-1ebd9687e1e3)
Adventures in Darkness (#ulink_35d059f2-e602-51dd-a18f-e996889efa2d)
Travels into the Darkness (#ulink_60a77276-487f-5ad8-a17c-169ec72c57e0)
How Big is the Darkness (#ulink_13a352bf-3910-5678-9872-befb32d548d1)
How to Use the Star Charts (#ulink_aed780f4-69dc-514e-b9dd-92849385e89b)
Bright or Dim? (#ulink_93980ded-d567-5ad5-ab63-1681f071a233)
Stars (#litres_trial_promo)
Starry Objects (#litres_trial_promo)
PART 2 (#litres_trial_promo)THE NORTHERN CHARTS (#litres_trial_promo)
January to March Skies (#litres_trial_promo)
April to June Skies (#litres_trial_promo)
July to September Skies (#litres_trial_promo)
October to December Skies (#litres_trial_promo)
PART 3 (#litres_trial_promo)THE SOUTHERN CHARTS (#litres_trial_promo)
January to March Skies (#litres_trial_promo)
April to June Skies (#litres_trial_promo)
July to September Skies (#litres_trial_promo)
October to December Skies (#litres_trial_promo)
PART 4 (#litres_trial_promo)SUN, MOON AND PLANETS (#litres_trial_promo)
The Moon (#litres_trial_promo)
Eclipses (#litres_trial_promo)
The Planets (#litres_trial_promo)
Planets and Days (#litres_trial_promo)
The Milky Way (#litres_trial_promo)
Watching Satellites and the ISS (#litres_trial_promo)
Comets (#litres_trial_promo)
Shooting Stars (#litres_trial_promo)
A Final View of Everything (#litres_trial_promo)
Astro Glossary (#litres_trial_promo)
Going Further (#litres_trial_promo)
Index (#litres_trial_promo)
Acknowledgements (#litres_trial_promo)
Copyright (#litres_trial_promo)
About the Publisher (#litres_trial_promo)
Dedication (#ulink_fbf99d6a-29b7-5998-9baa-36e0dd713129)
For Morten, Etienne and Dad
Introduction (#ulink_c4ba8962-1ae8-5b07-ab89-df2964a38d0c)
Prepare yourself for an adventure… that will take you deep into space and far back in time. This great journey begins the moment you cast your eyes up into the night sky. After a while you’ll be looking beyond the stars, wondering about distant life or maybe thinking just how fantastically big this whole Universe thing is.
I vividly remember when I was six, gazing out of my bedroom window with a desire to learn the names of the bright stars and the patterns I knew existed in the form of constellations. Little did I know what I had started – a lifelong trip which never ceases to amaze me. We are now in the age of Hubble, Cassini, Galileo, Hipparchos and Messenger (etc., etc.) – spacecraft that open up the vistas of the Universe to realms that excite while causing us to constantly rearrange our jigsaw of… well, everything. And this is not going to slow down. Look out for specially trained astronauts on the Moon and Mars, and ‘ordinary’ astronauts (that’s you and me) taking short trips into space.
Hopefully I can share some of my wonderment through these pages. None of this is rocket science (apart from the rocket science stuff). The name of the stargazing game is easy, short observing whenever you have a few spare moments while the stars are twinkling overhead.
‘Oh, but I can’t see the stars from where I live,’ is always a good one. Read carefully, as this will be written only once: living in a town, city or anywhere with light-polluted skies need not deter anyone from stargazing. Although the sky glow washes out the fainter stars, the major constellations will still be visible. So you won’t be hindered from learning the main star patterns. No excuse there, then!
Don’t underestimate the power of ‘doing’ something. Simply by taking a few minutes each day over the course of a year you’ll soon be amazing your friends as you point out Leo and say, ‘Of course, Regulus is a B7-type star about 85 light-years away.’ Or you might glance at the Square of Pegasus, remarking casually, ‘Messier 15 over there was discovered by the wonderful Italian, Maraldi.’ Or even dreamily waft your hand in the direction of Orion, and with a certain authority launch into, ‘The dimensions of M42 are 66 by 60 arc minutes.’ It won’t take long to learn the night sky, and I hope this book will inspire you to make a start.
The night sky is out there. As this old map shows, it’s all prepared and ready for you to explore.
Part 1 Getting Started (#ulink_cae2898c-0950-5dd8-8248-b3d983a75b9a)
A fine sunset is worth a picture itself as well as the hint that it’s going to be a fine, clear, starry-skied evening. Just the prompt you need to get you into the stargazing frame of mind.
A Brief History (#ulink_5ee85514-7a20-5924-8900-008e1fcc9f72)
In the distant past, astronomy and astrology were as one. Ancient rulers needed to know their fortune and, as the sky was where their gods lived, it was also where their destiny lay. Along with all the ‘fixed’ stars of the constellations were seven things that moved: the Sun, Moon and five planets – Mercury, Venus, Mars, Jupiter and Saturn (this was, of course, in the days when everyone believed that the Earth was the centre of the Universe and other sky objects moved round it).
It was an absolute belief that leaders who could understand how these objects moved could stay in control and defeat their enemies. One thing was clear: to these ancient watchers of the skies these seven objects followed a ‘path’ around the heavens – just like a car on a race track that takes the same route round again and again. It was the constellations situated along this ‘path’ that became our 12 famous signs of the zodiac.
Of course, in order to know where any object would be in the zodiac at any given time, a certain amount of calculation was required. This is when the science of astronomy was born. So, strangely, the necessity for fortune-telling encouraged the formation of science. By the way, zodiac means ‘line of animals’ (11 of the original 12 constellations are still animals) and is also linked to the word zoo.
So, why do the planets, Sun and Moon appear to move through the skies? Well, they each appear to move for different reasons. Of course the main movement you see is due to the Earth spinning – this gives us things like sunset, the Full Moon rising over frosty trees, time for your cornflakes for breakfast as the Sun rises, etc. The Moon, if it is up, additionally appears to move extremely slowly hour by hour in front of the stars because it is orbiting the Earth. The Sun changes its position against the stars day by day due to the fact that we are orbiting it. The planets move because they too are orbiting the Sun – plus each planet is moving at a different speed. No wonder it was all difficult to calculate, and indeed it’s hardly surprising that some early astronomers ended up having their heads chopped off, when their erroneous adding up was followed by a total overreaction from their bad-tempered rulers.
Constellations (#ulink_2a882bd8-6e65-53e9-8b2b-8cc4822cdb25)
A word worth defining before we launch ourselves into space is constellation. It’s based on a word from Latin meaning ‘group of stars’. In total you’ll find 88 of them filling the entire sky, but thankfully you don’t need to know them all to enjoy the hours of darkness. Other starry terms that crop up throughout the book are written in bold and explained in the AstroGlossary in here (#litres_trial_promo).
The story of organising things up there in the darkness of the night began thousands of years ago with civilisations such as the Sumerians, Babylonians, Egyptians, Greeks and Romans (as well as many other cultures from around the world). They decided the starry skies could do with a bit of order and a tidy up. So they joined up many of the stars, just like a dot-to-dot picture, putting their myths and legends into the sky as they did so.
Don’t think that there was any rhyme or reason for making a particular pattern. For example, Cepheus, King of Ethiopia, and his wife, Queen Cassiopeia, both have constellations named after them, and yet these look like a house and a set of stairs respectively. Imagination is the key here, I feel. As far as these early civilisations were concerned, the gods and goddesses needed a place to reside in the starry vault, so it was probably a case of first come, first served, and pot luck as to which stars were assigned to which group.
We get our earliest knowledge of the constellations from Aratos, the first Greek astronomical poet, in his work Phaenomena (which was probably based on an earlier ‘lost’ work by another Greek, Eudoxus). Then in AD 150 Ptolemy, a Greek working at the great library of Alexandria in Egypt, recorded them in a book known by its Arabic name, Almagest, which means ‘the greatest’. Hundreds of years ago, other astronomers who wanted to be famous added extra groups (some more successfully than others) to give us our present fixed total of 88 constellations.
Constellation names are traditionally written in Latin. This is because Ptolemy’s book was brought from the Middle East to Italy, where it was translated – and Latin, for centuries, was the language of scholars. So, for example, we know the Great Bear as Ursa Major.
Here are all the 88 constellations of the starry skies. Details of those with interesting things to see are given in Parts 2 and 3.
Adventures in Darkness (#ulink_10a1ed62-fe45-5c37-8cc8-96a20e51f7df)
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 (#u29e4b815-b4cb-4f5f-9cbc-e34285901d93)) … while southerly humans go here (Southerly humans read this (#ud0565a60-25cc-4f24-9ad3-c023dce2ca46))…
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 (#ulink_2de26d00-0639-515e-9145-bc8a4467f4fc)
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? (#ulink_8beba1a5-7035-58a4-9c15-9eb48f3cefe8)
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 (#ulink_754efff4-eacd-5a59-b345-cc0b36199717)
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.
As we’ve seen with the Plough and Crux, several distinctively shaped and therefore easily recognisable constellations – or parts or combinations of constellations – make useful ‘signposts’ around the night sky. These can be used to find all manner of starry splendours, so I will point them out as we go.
Here’s a rough map of the planet that I knocked together using a plastic washing-up-liquid bottle, some sticky-backed plastic and an old coathanger. The equator divides the world into a northern and a southern hemisphere, which is your cue to choosing which of the seasonal charts to look at. The nearer to the equator you travel, the more of the opposite hemisphere’s chart you can use. For example, if you live somewhere in Norway, you’ll be using just the northern chart. If one summer you decide to go on holiday to Italy, you can use half of the southern chart with all its fascinating new starry sights.
The sections have also been divided into those for northerly people and those for southerly, because exactly what you’ll see depends on whereabouts on our planet you live. If you’re well into the northern hemisphere (the bit above the equator on the map) then go for the northern charts, while if you’re in the southern… well, you get the idea. As most of the land – and the majority of the world’s population – is in the northern hemisphere, the charts appear as if you are looking south. The closer to the equator you are in the northern hemisphere, the more of the southern chart you can use. For those lucky souls who live on the equator, the whole sky is visible and you can use both charts at once.
Each constellation of interest is introduced with the following useful information:
LATIN NAME
Ursa Major
ENGLISH NAME
The Great Bear
ABBREVIATION
UMa
LATIN POSSESSIVE
Ursae Majoris
α STAR
Dubhe
MAGNITUDE
1.79
STAR COLOUR
Orange
First, you’ll find the constellation names in the original Latin, and then the English equivalent. The following three-lettered abbreviation is an internationally recognised way of identifying a constellation without having to use its full name.
The Latin possessive means ‘of the constellation’ or ‘belonging to’. This is used for sounding important and as if you know what you’re talking about – something like: ‘Oh, Castor. Of course you mean alpha Geminorum.’
The alpha (a) star is the main star of the named constellation, though it is not always the brightest and not all constellations have alpha stars with names (or even alpha stars at all). In 1603 the German astronomer Johann Bayer worked through each constellation, usually assigning alpha (a) to the brightest star, beta (β) to the next brightest, then gamma (γ), delta (δ) and so on. As a result, stars are often labelled on charts with a letter of the Greek alphabet, known as the Bayer Letter. The full Greek alphabet is given on the right.
Proper names, such as Dubhe, are only generally given to the brighter stars. Many of the names are Arabic, but there are splatterings of Greek and Roman ones too. Check out the constellation Libra (see Libra (#litres_trial_promo)) for the best star names in the Universe.
Star magnitude (mag.), or ‘visual magnitude’, lets you know how bright a star appears in the sky. The Greek astronomer Hipparchus, who lived around the mid-second century BC, introduced the system of classifying starry magnitudes that you can see with your eye from 1, the brightest, down to 6, the faintest. We’ll be talking more about magnitude in just a moment or two, and as you will see, it’s now a little more complicated.
As well as the colour of a star indicating the obvious, it can also tell you how hot its surface is. You may be surprised to learn that the coolest stars are red, their surfaces being about 3,000°C. Warmer stars are yellow, the hotter ones white and the hottest are blue, with temperatures up to 40,000°C. Not only that, but they can change colour! This most notably happens when stars have used up all their fuel and internal forces take over, causing all manner of starry events (like red giants, supernovae and black holes, for example).
Greek alphabet
Bright or Dim? (#ulink_be355185-7a76-5883-a39a-f550e7ce3ae8)
Конец ознакомительного фрагмента.
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Anton Vamplew
A first-time skywatcher’s guide from bright new talent, BBC Blue Peter astronomer, Anton VamplewMost books on stargazing claim to be for beginners, but by page 12 are talking about celestial equators and sidereal months. No wonder so many people have planispheres but no idea how to use them.Working at the planetarium in Greenwich, Anton has met hundreds of enthusiastic but utterly bemused beginners of all ages, and has made sense of the night sky for them. In this book he introduces the night sky just as if he were by your side, pointing everything out. And contrary to popular belief, you don't need any expensive equipment to start skygazing. Anton takes you through all the things you can discover with just the naked eye.The book is suitable for use in the northern and southern hemispheres – two sections give equal coverage to where to start and what you can see wherever you are in the world, whenever.
Contents
Cover (#u482212ec-ec41-5ae0-a904-9455fc77d3e7)
Title Page (#uab5dae45-de05-5c82-96a2-689a4abe0abc)
Dedication (#ubd2a4ae5-eb11-5e23-8409-6141f48e90d7)
Introduction (#u435ce41b-3da3-5d6c-b745-23b483dd51b5)
PART 1 (#u427618c6-38d8-5013-a005-a689d4966e36)GETTING STARTED (#u427618c6-38d8-5013-a005-a689d4966e36)
A Brief History (#ulink_25e6e215-33db-5e22-92c3-c05ae37a18e7)
Constellations (#ulink_0551d24f-c08f-56a2-954a-1ebd9687e1e3)
Adventures in Darkness (#ulink_35d059f2-e602-51dd-a18f-e996889efa2d)
Travels into the Darkness (#ulink_60a77276-487f-5ad8-a17c-169ec72c57e0)
How Big is the Darkness (#ulink_13a352bf-3910-5678-9872-befb32d548d1)
How to Use the Star Charts (#ulink_aed780f4-69dc-514e-b9dd-92849385e89b)
Bright or Dim? (#ulink_93980ded-d567-5ad5-ab63-1681f071a233)
Stars (#litres_trial_promo)
Starry Objects (#litres_trial_promo)
PART 2 (#litres_trial_promo)THE NORTHERN CHARTS (#litres_trial_promo)
January to March Skies (#litres_trial_promo)
April to June Skies (#litres_trial_promo)
July to September Skies (#litres_trial_promo)
October to December Skies (#litres_trial_promo)
PART 3 (#litres_trial_promo)THE SOUTHERN CHARTS (#litres_trial_promo)
January to March Skies (#litres_trial_promo)
April to June Skies (#litres_trial_promo)
July to September Skies (#litres_trial_promo)
October to December Skies (#litres_trial_promo)
PART 4 (#litres_trial_promo)SUN, MOON AND PLANETS (#litres_trial_promo)
The Moon (#litres_trial_promo)
Eclipses (#litres_trial_promo)
The Planets (#litres_trial_promo)
Planets and Days (#litres_trial_promo)
The Milky Way (#litres_trial_promo)
Watching Satellites and the ISS (#litres_trial_promo)
Comets (#litres_trial_promo)
Shooting Stars (#litres_trial_promo)
A Final View of Everything (#litres_trial_promo)
Astro Glossary (#litres_trial_promo)
Going Further (#litres_trial_promo)
Index (#litres_trial_promo)
Acknowledgements (#litres_trial_promo)
Copyright (#litres_trial_promo)
About the Publisher (#litres_trial_promo)
Dedication (#ulink_fbf99d6a-29b7-5998-9baa-36e0dd713129)
For Morten, Etienne and Dad
Introduction (#ulink_c4ba8962-1ae8-5b07-ab89-df2964a38d0c)
Prepare yourself for an adventure… that will take you deep into space and far back in time. This great journey begins the moment you cast your eyes up into the night sky. After a while you’ll be looking beyond the stars, wondering about distant life or maybe thinking just how fantastically big this whole Universe thing is.
I vividly remember when I was six, gazing out of my bedroom window with a desire to learn the names of the bright stars and the patterns I knew existed in the form of constellations. Little did I know what I had started – a lifelong trip which never ceases to amaze me. We are now in the age of Hubble, Cassini, Galileo, Hipparchos and Messenger (etc., etc.) – spacecraft that open up the vistas of the Universe to realms that excite while causing us to constantly rearrange our jigsaw of… well, everything. And this is not going to slow down. Look out for specially trained astronauts on the Moon and Mars, and ‘ordinary’ astronauts (that’s you and me) taking short trips into space.
Hopefully I can share some of my wonderment through these pages. None of this is rocket science (apart from the rocket science stuff). The name of the stargazing game is easy, short observing whenever you have a few spare moments while the stars are twinkling overhead.
‘Oh, but I can’t see the stars from where I live,’ is always a good one. Read carefully, as this will be written only once: living in a town, city or anywhere with light-polluted skies need not deter anyone from stargazing. Although the sky glow washes out the fainter stars, the major constellations will still be visible. So you won’t be hindered from learning the main star patterns. No excuse there, then!
Don’t underestimate the power of ‘doing’ something. Simply by taking a few minutes each day over the course of a year you’ll soon be amazing your friends as you point out Leo and say, ‘Of course, Regulus is a B7-type star about 85 light-years away.’ Or you might glance at the Square of Pegasus, remarking casually, ‘Messier 15 over there was discovered by the wonderful Italian, Maraldi.’ Or even dreamily waft your hand in the direction of Orion, and with a certain authority launch into, ‘The dimensions of M42 are 66 by 60 arc minutes.’ It won’t take long to learn the night sky, and I hope this book will inspire you to make a start.
The night sky is out there. As this old map shows, it’s all prepared and ready for you to explore.
Part 1 Getting Started (#ulink_cae2898c-0950-5dd8-8248-b3d983a75b9a)
A fine sunset is worth a picture itself as well as the hint that it’s going to be a fine, clear, starry-skied evening. Just the prompt you need to get you into the stargazing frame of mind.
A Brief History (#ulink_5ee85514-7a20-5924-8900-008e1fcc9f72)
In the distant past, astronomy and astrology were as one. Ancient rulers needed to know their fortune and, as the sky was where their gods lived, it was also where their destiny lay. Along with all the ‘fixed’ stars of the constellations were seven things that moved: the Sun, Moon and five planets – Mercury, Venus, Mars, Jupiter and Saturn (this was, of course, in the days when everyone believed that the Earth was the centre of the Universe and other sky objects moved round it).
It was an absolute belief that leaders who could understand how these objects moved could stay in control and defeat their enemies. One thing was clear: to these ancient watchers of the skies these seven objects followed a ‘path’ around the heavens – just like a car on a race track that takes the same route round again and again. It was the constellations situated along this ‘path’ that became our 12 famous signs of the zodiac.
Of course, in order to know where any object would be in the zodiac at any given time, a certain amount of calculation was required. This is when the science of astronomy was born. So, strangely, the necessity for fortune-telling encouraged the formation of science. By the way, zodiac means ‘line of animals’ (11 of the original 12 constellations are still animals) and is also linked to the word zoo.
So, why do the planets, Sun and Moon appear to move through the skies? Well, they each appear to move for different reasons. Of course the main movement you see is due to the Earth spinning – this gives us things like sunset, the Full Moon rising over frosty trees, time for your cornflakes for breakfast as the Sun rises, etc. The Moon, if it is up, additionally appears to move extremely slowly hour by hour in front of the stars because it is orbiting the Earth. The Sun changes its position against the stars day by day due to the fact that we are orbiting it. The planets move because they too are orbiting the Sun – plus each planet is moving at a different speed. No wonder it was all difficult to calculate, and indeed it’s hardly surprising that some early astronomers ended up having their heads chopped off, when their erroneous adding up was followed by a total overreaction from their bad-tempered rulers.
Constellations (#ulink_2a882bd8-6e65-53e9-8b2b-8cc4822cdb25)
A word worth defining before we launch ourselves into space is constellation. It’s based on a word from Latin meaning ‘group of stars’. In total you’ll find 88 of them filling the entire sky, but thankfully you don’t need to know them all to enjoy the hours of darkness. Other starry terms that crop up throughout the book are written in bold and explained in the AstroGlossary in here (#litres_trial_promo).
The story of organising things up there in the darkness of the night began thousands of years ago with civilisations such as the Sumerians, Babylonians, Egyptians, Greeks and Romans (as well as many other cultures from around the world). They decided the starry skies could do with a bit of order and a tidy up. So they joined up many of the stars, just like a dot-to-dot picture, putting their myths and legends into the sky as they did so.
Don’t think that there was any rhyme or reason for making a particular pattern. For example, Cepheus, King of Ethiopia, and his wife, Queen Cassiopeia, both have constellations named after them, and yet these look like a house and a set of stairs respectively. Imagination is the key here, I feel. As far as these early civilisations were concerned, the gods and goddesses needed a place to reside in the starry vault, so it was probably a case of first come, first served, and pot luck as to which stars were assigned to which group.
We get our earliest knowledge of the constellations from Aratos, the first Greek astronomical poet, in his work Phaenomena (which was probably based on an earlier ‘lost’ work by another Greek, Eudoxus). Then in AD 150 Ptolemy, a Greek working at the great library of Alexandria in Egypt, recorded them in a book known by its Arabic name, Almagest, which means ‘the greatest’. Hundreds of years ago, other astronomers who wanted to be famous added extra groups (some more successfully than others) to give us our present fixed total of 88 constellations.
Constellation names are traditionally written in Latin. This is because Ptolemy’s book was brought from the Middle East to Italy, where it was translated – and Latin, for centuries, was the language of scholars. So, for example, we know the Great Bear as Ursa Major.
Here are all the 88 constellations of the starry skies. Details of those with interesting things to see are given in Parts 2 and 3.
Adventures in Darkness (#ulink_10a1ed62-fe45-5c37-8cc8-96a20e51f7df)
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 (#u29e4b815-b4cb-4f5f-9cbc-e34285901d93)) … while southerly humans go here (Southerly humans read this (#ud0565a60-25cc-4f24-9ad3-c023dce2ca46))…
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 (#ulink_2de26d00-0639-515e-9145-bc8a4467f4fc)
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? (#ulink_8beba1a5-7035-58a4-9c15-9eb48f3cefe8)
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 (#ulink_754efff4-eacd-5a59-b345-cc0b36199717)
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.
As we’ve seen with the Plough and Crux, several distinctively shaped and therefore easily recognisable constellations – or parts or combinations of constellations – make useful ‘signposts’ around the night sky. These can be used to find all manner of starry splendours, so I will point them out as we go.
Here’s a rough map of the planet that I knocked together using a plastic washing-up-liquid bottle, some sticky-backed plastic and an old coathanger. The equator divides the world into a northern and a southern hemisphere, which is your cue to choosing which of the seasonal charts to look at. The nearer to the equator you travel, the more of the opposite hemisphere’s chart you can use. For example, if you live somewhere in Norway, you’ll be using just the northern chart. If one summer you decide to go on holiday to Italy, you can use half of the southern chart with all its fascinating new starry sights.
The sections have also been divided into those for northerly people and those for southerly, because exactly what you’ll see depends on whereabouts on our planet you live. If you’re well into the northern hemisphere (the bit above the equator on the map) then go for the northern charts, while if you’re in the southern… well, you get the idea. As most of the land – and the majority of the world’s population – is in the northern hemisphere, the charts appear as if you are looking south. The closer to the equator you are in the northern hemisphere, the more of the southern chart you can use. For those lucky souls who live on the equator, the whole sky is visible and you can use both charts at once.
Each constellation of interest is introduced with the following useful information:
LATIN NAME
Ursa Major
ENGLISH NAME
The Great Bear
ABBREVIATION
UMa
LATIN POSSESSIVE
Ursae Majoris
α STAR
Dubhe
MAGNITUDE
1.79
STAR COLOUR
Orange
First, you’ll find the constellation names in the original Latin, and then the English equivalent. The following three-lettered abbreviation is an internationally recognised way of identifying a constellation without having to use its full name.
The Latin possessive means ‘of the constellation’ or ‘belonging to’. This is used for sounding important and as if you know what you’re talking about – something like: ‘Oh, Castor. Of course you mean alpha Geminorum.’
The alpha (a) star is the main star of the named constellation, though it is not always the brightest and not all constellations have alpha stars with names (or even alpha stars at all). In 1603 the German astronomer Johann Bayer worked through each constellation, usually assigning alpha (a) to the brightest star, beta (β) to the next brightest, then gamma (γ), delta (δ) and so on. As a result, stars are often labelled on charts with a letter of the Greek alphabet, known as the Bayer Letter. The full Greek alphabet is given on the right.
Proper names, such as Dubhe, are only generally given to the brighter stars. Many of the names are Arabic, but there are splatterings of Greek and Roman ones too. Check out the constellation Libra (see Libra (#litres_trial_promo)) for the best star names in the Universe.
Star magnitude (mag.), or ‘visual magnitude’, lets you know how bright a star appears in the sky. The Greek astronomer Hipparchus, who lived around the mid-second century BC, introduced the system of classifying starry magnitudes that you can see with your eye from 1, the brightest, down to 6, the faintest. We’ll be talking more about magnitude in just a moment or two, and as you will see, it’s now a little more complicated.
As well as the colour of a star indicating the obvious, it can also tell you how hot its surface is. You may be surprised to learn that the coolest stars are red, their surfaces being about 3,000°C. Warmer stars are yellow, the hotter ones white and the hottest are blue, with temperatures up to 40,000°C. Not only that, but they can change colour! This most notably happens when stars have used up all their fuel and internal forces take over, causing all manner of starry events (like red giants, supernovae and black holes, for example).
Greek alphabet
Bright or Dim? (#ulink_be355185-7a76-5883-a39a-f550e7ce3ae8)
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Anton Vamplew
Тип: электронная книга
Жанр: Астрономия
Язык: на английском языке
Издательство: HarperCollins
Дата публикации: 28.04.2024
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О книге: A first-time skywatcher’s guide from bright new talent, BBC Blue Peter astronomer, Anton VamplewMost books on stargazing claim to be for beginners, but by page 12 are talking about celestial equators and sidereal months. No wonder so many people have planispheres but no idea how to use them.Working at the planetarium in Greenwich, Anton has met hundreds of enthusiastic but utterly bemused beginners of all ages, and has made sense of the night sky for them. In this book he introduces the night sky just as if he were by your side, pointing everything out. And contrary to popular belief, you don′t need any expensive equipment to start skygazing. Anton takes you through all the things you can discover with just the naked eye.The book is suitable for use in the northern and southern hemispheres – two sections give equal coverage to where to start and what you can see wherever you are in the world, whenever.