A Beginner's Guide to Astronomy E-Book

David Geddes

• Herausgeber: G2 Rights Ltd
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Veröffentlichungsjahr: 2016

Beschreibung

This little guide will encourage more people to take a greater interest in the sky above them. Even in these light polluted days, much can be seen with the naked eye and a simple telescope is not an expensive item. It is really thrilling to observe the surface of the moon in detail or, using your telescope, study the rings of Saturn, the phases of Venus or discover Andromeda, which is a galaxy as immense as our own. Astronomy is not a cold science. The sky and the stars have always captivated man and influenced his emotions as well as his mind.

Leseprobe

A BEGINNER’S GUIDE TO

ASTRONOMY

A BEGINNER’S GUIDE TO

ASTRONOMY

First published in the UK in 2014

© G2 Rights Ltd

www.demand-media.co.uk

All rights reserved. No part of this work may be reproduced or utilised in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without prior written permission of the publisher.

Printed and bound in Europe

eISBN 978-1-782813-53-8

The views in this book are those of the author but they are general views only and readers are urged to consult the relevant and qualified specialist for individual advice in particular situations. Demand Media Limited hereby exclude all liability to the extent permitted by law of any errors or omissions in this book and for any loss, damage or expense (whether direct or indirect) suffered by a third party relying on any information contained in this book.

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Contents

Introduction

The Beginnings of Astronomy

The New Era

The Telescope

The Solar System

The Sun

The Moon

The Space Age

The Inner Planets

The Outer Planets

Solar System Debris

To The Stars

Anatomy Of The Stars

Special Stars And Groupings

Galaxies And Deep Space

The Heavens Viewer’s Guide

The Continuing Quest

Glossary

Introduction

Astronomy is one of the oldest sciences and one which has intrigued and fascinated mankind since the beginning of time. It is often confused with astrology, much to the chagrin of astronomers and amateurs deeply interested in the subject. One of the most popular astronomers in the country has said that astrology, which suggests that human character and destiny are influenced by the stars, is totally without foundation, and the best that can be said for it is that it is fairly harmless so long as it is confined to seaside piers, circus tents and the columns of tabloid newspapers. Now you know!

At 10.56 p.m. Washington time on 20 July 1969. 3.56 a.m. on 21 July in London, a huge, incredulous, worldwide audience first listened and then watched as the first man stepped onto the moon. On the radio we were able to follow every manoeuvre of the lunar module Eagle as it neared the surface of the moon and we listened with bated breath to the conversations between the astronauts and Mission Control at Houston in Texas. At last the transmission came from Mission Control, ‘We copy you down, Eagle.’ and Neil Armstrong’s reply,

‘Houston, Tranquillity Base here, the Eagle has landed.’

Mission Control confirmed, ‘Roger, Tranquillity, we copy you on the ground. You’ve got a bunch of guys about to turn blue. We’re breathing again. Thanks a lot.’

This writer followed every word and then went out to the garden to gaze in wonder at the moon, which was now inhabited by two men from earth. After a few hours, we were then able to watch as Neil Armstrong descended from the lunar module, placed his left foot on the moon and uttered his famous statement, ‘That’s one small step for man, one giant leap for mankind’.

The landing on the moon must have signalled the high tide in world interest in astronomy and space travel, but in a year or two that interest had waned and a flight to the moon seemed to become commonplace, although it had been the dream of man for thousands of years. The world’s attention span is not very long! The only other period of high interest came when tragedy almost struck Apollo 13. Since these days there has been an increased awareness of astronomy, however, and television programmes by experts such as the late Patrick Moore have appealed to a large audience. The great attraction of astronomy is that amateurs can not only enjoy an absorbing pastime and hobby but also, through their observations, make contributions to the advancement of knowledge. This is one science where the professionals really do appreciate the help of amateurs, who, over the years, have made many important discoveries including comets, minor planets and supernovae.

It is hoped that this little guide will encourage more people to take a greater interest in the sky above them. Even in these light polluted days, much can be seen with the naked eye and a simple telescope is not an expensive item. It is really thrilling to observe the surface of the moon in detail or, using your telescope, study the rings of Saturn, the phases of Venus or discover Andromeda, which is a galaxy as immense as our own. This is not a cold science. The sky and the stars have always captivated man and influenced his emotions as well as his mind. R.L. Stevenson in Travels With a Donkey said ‘No one knows the stars who has not slept, as the French happily put it, a la belle etoile. He may know all their names and distances and magnitudes, and yet be ignorant of what alone concerns mankind, - their serene and gladsome influence on the mind. The greater part of poetry is about the stars; and very justly, for they are themselves the most classical of poets. These same far-away worlds, sprinkled like tapers or shaken together like a diamond dust upon the sky.......’.

The Beginnings of Astronomy

China

To trace the beginnings of astronomy we go back to the very start of recorded history. It is difficult to get a really cohesive picture of the development of this very ancient science as we are dealing with an immense span of time, during which observations, investigations and the formulation of theories were being carried out in widely disparate parts of the world. Although astronomers are adamant that their discipline should not be confused with astrology, it is impossible to know which science came first. In the beginning most astronomers were also astrologers and the real division between the two did not come until the seventh century ad. The ancient peoples studied the skies with a view to divining what lay in the future and this portent astrology required detailed and regular observation of the skies. It was important that the results of these observations were carefully documented and this is, perhaps, the biggest contribution made by the Chinese to early astronomy and to its future development.

The Chinese believed that their country was the centre of the world and, indeed, in Chinese the name of the country is ‘Middle Kingdom’. Their belief was that the stars and planets came under the authority of the emperor. Over very many years Chinese astronomers observed and noted solar eclipses until they were able to establish a cycle in which the sun, moon and earth were aligned in the same way every 18 years or so. They, therefore, became quite accurate in their prediction of eclipses. During eclipses the Chinese reckoned that the sun was being attacked by a dragon, which seemed to take bites out of it and the way to combat this was to gather as many people as possible to make as much noise as possible, with a view to frightening off the dragon. This, of course, always worked and so the emperor’s sun would be saved once again!

Hipparchus

Chinese astronomers made very great contributions to the study of the science. Although coming from the unique Chinese position of the belief in the total involvement of the people with the emperor and with natural events, they produced calendars which worked, charts of the stars, sophisticated astronomical instruments and the development of clocks to control the instruments. The Chinese also contributed theories to cosmology, the science or study of the universe. They proposed three main possibilities. The first was the theory of the sky as a gently curved roof above and parallel to the earth. They estimated that the distance between the earth and the sky was 46,000 km. The second theory was developed about 100 years BC and is referred to as the ‘celestial sphere’ or ‘enveloping sky’ theory. It described the heavens as being like a hen’s egg with the earth lying in the centre, like the yolk of the egg. The third Chinese cosmological theory was that the sun, moon, planets and stars all float freely in infinite space. This theory emerged in the second and third centuries AD, although it is said to reflect much earlier thinking. This ‘infinite empty space’ theory ran into trouble with later Chinese astronomers, but it is interesting to note that, in addition to the great contributions already mentioned, the Chinese were the first to propose the possibility of an infinite universe.

Egypt

The basis of what could be called astronomy in Egypt goes back into the mists of time before 3000 BC. It was from these times that the early study of the skies formulated into myths which eventually became the core of Egyptian religion. It was also at this stage of the development of Egypt that the observation of the movements of the sun and the moon resulted in the creation of a time unit of 365 days and a fairly sophisticated lunar calendar. These were created for purely religious reasons, in order to set the timings for offerings and feast days, but gradually a simplified version of the calendar was introduced to enable the people to carry out business dealings and structure their normal lives.

In these earliest times, the sun god Ra emerged as the most important god and the annual movement of the sun was noted and its turning points in the north and south were called the solstices. The ancient Egyptians came to see the Milky Way as depicting the female god Nut, who conceived and gave birth to Ra at times which were recognised by observing the sky. The belief that Ra recreated himself though Nut established the matrilineal inheritance of the royal line in Egypt. The worship of Ra also explains the siting and the shape of many of the temples and especially the pyramids. The famous pyramids at Giza are thought to reflect the way in which clouds and blowing dust in the sunlight seemed to portray stairways leading to heaven. The pyramids, therefore, were built as stone stairways to the heavens, by which the soul of the dead pharaoh could reach the northern stars, which were known as ‘the immortal ones’.

The Egyptians were well aware of the movements in the skies and these movements governed their religious life and also their secular calendar. The experts of today, however, consider that the only really significant scientific advances which they left to us are the civil calendar of 365 days and the division of day and night into 12 hours each.

Greece

The Egyptians had a remarkable grasp of mathematics, witness the fact that they had measured the fall of the Nile over a distance of some 700 miles with an error of only a few inches. They had also discovered, and had used in practice, the fact that the square on the hypotenuse of a right- angled triangle is equal to the sum of the squares on the other two sides. The ancient Greeks did not think that way. Their thought had dealt with moral, religious and social problems and most speculation on the physical universe had pondered on how it had come into existence rather than how it worked. The first Greek to express his ideas on astronomy in logical instead of mythological terms was Thales of Miletus. He was a merchant who had travelled to Egypt and had learned something of mathematics in that country and also Chaldean astronomy. He knew enough to be able to predict that there would be a total eclipse of the sun during the year 585 BC, which did indeed take place.

Long before the time of Thales, the Greeks regulated their agricultural activity by observing the rising and setting of major stars or groups of stars, such as Sirius, Arcturus or Orion, the Pleiades and the Hyades. From these early beginnings came almanacs and calendars. As early as around 350 BC, the great philosopher and scientist Aristotle made a very significant advance. The assumption from the beginning of time was that the earth was flat, but Aristotle was not convinced. He realised from the curved shadow of the earth on the moon during an eclipse that it must be a sphere, not flat. He then went further to prove his theory by observing the southern star Canopus. He pointed out that the star was visible from Alexandria in Egypt but not further north in Athens. This would not be the case if the earth was flat. This theory had been proposed by Pythagoras some 200 years earlier but the proof provided by Aristotle, and the respect in which he was held, convinced the Greeks of the day.

Another important figure in Greek astronomy was Hipparchus, who lived around 150 BC. He was born in Asia Minor, although he carried out most of his work in Rhodes. He was conversant with the great volume of knowledge on astronomy which was held at Babylon, although it is not clear how he had gained access to this. It is known that astronomers in Mesopotamia had amassed observational records going back as far as the eighth century BC and, in particular, they had perfected accurate ways of calculating and predicting events affecting the moon and the planets. Hipparchus was undoubtedly a genius and he made great contributions in the areas of mathematical geography and the design of instruments. His major achievement, however, was to understand the vast amount of information which he obtained from Babylon, adapt it to a calendar recognised in Greece, and so spark off a revolution in Greek astronomy.

One of the most important characters in Greek astronomy, and perhaps the one most remembered today, was Claudius Ptolemaeus, better known as Ptolemy. Working in Alexandria between 140 and 180 ad, he improved and added to the work done by Hipparchus and produced a great volume, known as the Almagest. This book has come down to us from the Arab translation and is a synthesis of all the accumulated Greek astronomical knowledge from the earliest times. Ptolemy produced the first map of the world based upon astronomical observation and he developed a model of the solar system with the earth at the centre. This geocentric model had long been accepted in Greece and was generally approved until the heliocentric theory of Copernicus appeared in 1543. Ptolemy brought together the various strands of Greek astronomy and it has been said that true astronomy began with the Greeks.

Mesopotamia and India

We have seen how the wealth of astronomical knowledge in Mesopotamia was taken by Hipparchus and incorporated into the body of Greek learning on the subject. What is clear is that astronomy and astrology were inextricably linked in this area and it would appear that regular observation of the moon and the planets began in Babylon. Babylonia and Assyria were the main components of Mesopotamia. All forms of divination were practiced, the study of the skies being an important part of this fascination with possible future events. If, for instance, it had been noted in the past that an eclipse of the moon had taken place at a certain date of a certain month and soon thereafter a great king had died, then it would be assumed that there was a risk of a similar death when the next such eclipse occurred. The king and his court were the centre of all this activity and regular messages reached the king from astronomer- astrologers, who were constantly monitoring the movements of the sun, moon and planets in various parts of the country.

A calendar was in use from the third millennium BC and this was luni-solar, the month beginning on the evening when the lunar crescent was first visible. The months seem to have been of 30 days. In the old texts, reference is made to a water-clock, which may have been used initially to mark the three watches of the night. The clock would have been filled at the beginning of the watch, which would end when the water-clock was empty. These primitive clocks became more and more sophisticated until they would be able to be used for quite complicated astronomical calculations. Mesopotamian cosmology was limited and the study of the planets and stars was completely bound with religion and the place of the gods in the scheme of things. One of the main features of the astronomy carried out in Mesopotamia was the meticulous listing and detailing of information and observations. This is what was incorporated into Ptolemy’s Almagest and had such a significant influence on Greek astrology.

Tycho Brahe wearing Order of the Elephant

The knowledge of astronomy arrived in India from Mesopotamia and in India also it was very closely tied to religious rituals. The early texts appeared probably just after 1000 BC and they gave information and advice on the carrying out of the great rituals, which had to be performed at set times within the solar year. Between the second and fourth centuries ad, revised information on the planets began to appear in Sanskrit texts. These texts were translations from Greek treatises which had been based on theories formulated in Babylonia as far back as the third century BC. The texts contained new information on astronomy and also on astrology, which was then adapted to conform to the Indian culture. There were various schools of thought throughout India and some of the calculations made were amazingly accurate, which suggests that the Indian astronomers were in contact with international developments and were also capable of very accurate time measurements. The Indian astronomers seemed to take theories and observations from other cultures, check them thoroughly, and then adapt them for their major requirements, which were the computations of calendars, the prediction of solar and lunar eclipses, time-keeping and the casting of horoscopes. Observation of the skies was not a major feature of astronomy in India, but rather the use of mathematics. Many of these mathematical advances were not recognised outside of India but some did travel and influenced astronomy in the Islamic world and Western Europe.

In a relatively short time after the death of the Prophet Muhammad in 632 AD, the Arabs had established an area of Muslim influence which ranged from Spain to Central Asia and India. The new Islamic culture brought together the old knowledge of the heavens from Arabia and the Middle East and merged this with the mathematical traditions of the Indians, Persians and Greeks to establish its own individual style of astronomy. What could be called Islamic astronomy was in place by the tenth century AD. The Koran states that man should use the celestial bodies to guide him and the sun, moon and stars are mentioned in the holy book. Accurate star catalogues were drawn up, the movements of the sun, moon and planets were measured more precisely than before and the Arabs made a real contribution to the sum to the knowledge available on astronomy. Advances were made in the area of astronomical instruments and observatories were set up, including an elaborate one in Samarkand in the 15th century: From about this time, however, astronomy in the Islamic world declined and less and less innovative work was done.

Europe

During much of the period between the death of Ptolemy and the fall of Constantinople to the Turks in 1453, astronomy in Greece and Europe generally seemed to stagnate. It was still a well-respected science which received a great deal of study, but very few new avenues were opened or new thinking put forward. Ptolemy’s belief that the earth was positioned at the centre of the universe was studied and discussed, but no new radical thinker came forward to question it.

This period coincided with the rise of Christianity and much of the learning took place in the new monastic schools, which concentrated on the understanding of the bible and gave scant attention to research and observation in relation to astronomy. One very important advance did, however, take place around 570 AD. The Christian belief in one god was gradually taking over from the many spirits and gods who had been thought to govern all things in nature and at this time Bishop Isidore of Seville drew a distinction between astronomy and astrology for the first time. In his Twenty Books of Etymologies he showed that everything concerned with nature and man could be considered and discussed without referring to mythology. This persuaded people that there was a real difference between astronomy and astrology and that the former was a serious science, whereas the latter was merely a superstition which depended on some connection between the twelve signs of the zodiac and the organs of the body. The Christian calendar required astronomical help to fix the times for movable feasts such as Easter and Lent and these were covered extensively in the major work written in 725 by the Venerable Bede of Jarrow - On the Theory of Time-reckoning. This was an impressive example of monastic science, and it is interesting to note that in another of his volumes Bede, for the first time, numbered the years from the birth of Christ.