How to Observe the Sun Safely

188 Pages·2003·5.463 MB·English

by  Lee Macdonald (auth.)

Patrick Moore' s
Practical Astronomy Series
Springer-Verlag London Ud.
Other titles in this series
Telescopes and Techniques
Chris Kitchin
The Art and Science of CCD Astronomy
David Ratledge (Ed.)
The Observer's Year
Pa trick Moore
Seeing Stars
Chris Kitchin and Robert W. Forrest
Photo-guide to the Constellations
Chris Kitchin
The Sun in Eclipse
Michael Maunder and Pa trick Moore
Software and Data for Practical Astronomers
David Ratledge
Amateur Telescope Making
Stephen F. Tonkin
Observing Meteors, Comets, Supernovae
and other Transient Phenomena
Neil Bone
Astronomical Equipment for Amateurs
Martin Mobberley
Transit: When Planets Cross the Sun
Michael Maunder and Pa trick Moore
Practical Astrophotography
Jeffrey R. Charles
Observing the Moon
Peter T. Wlasuk
Deep-Sky Observing
Steven R. Coe
AstroFAQs
Stephen F. Tonkin
The Deep-Sky Observer's Year
Grant Privett and Paul Parsons
Field Guide to the Deep Sky Objects
Mike lnglis
Choosing and Using a Schmidt-Cassegrain Telescope
Rod Mollise
Astronomy with Small Telescopes
Stephen F. Tonkin (Ed.)
Solar Observing Techniques
Chris Kitchin
Observing the Planets
Peter T. Wlasuk
Light Pollution
Bob Mizon
Using the Meade ETX
Mike Weasner
Practical Amateur Spectroscopy
Stephen F. Tonkin (Ed.)
More Small Astronomical Observatories
Pa trick Moore (Ed.)
Observer's Guide to Stellar Evolution
Mike lnglis
Lee Macdonald
With 46 Figures
, Springer
British Library Cataloguing in Publication Data
Macdonald, Lee
How to observe the sun safely. - (Patrick Moore's practical
astronomy series)
1. Sun - Observers' manuals
I. Title
523.7
ISBN 978-1-85233-527-4 ISBN 978-1-4471-0053-9 (eBook)
DOI 10.1007/978-1-4471-0053-9
Library of Congress Cataloging-in-Publication Data
Macdonald, Lee, 1973-
How to observe the sun safely / Lee Macdonald.
p. cm. - (Patrick Moore's practical astronomy series,
ISSN 1617-7185)
Inc1udes index.
1. Sun-Observers' manuals. 2. Sun. I. Title. 11. Series.
QB521 .M23 2002
523.7-dc21 2002070456
Apart from any fair dealing for the purposes of research or private
study, or criticism or review, as permitted under the Copyright,
Designs and Patents Act 1988, this publication may only be
reproduced, stored or transmitted, in any form or by any means,
with the prior permission in writing of the publishers, or in the case of
reprographie reproduction in accordance with the terms of licences
issued by the Copyright Licensing Agency. Enquiries concerning
reproduction outside those terms should be sent to the publishers.
Patrick Moore's Practical Astronomy Series ISSN 1617-7185
ISBN 978-1-85233-527-4
© Springer-Verlag London 2003
Originally published by Springer-Verlag London Berlin Heidelberg in 2003
The use of registered names, trademarks, etc. in this publication does
not imply, even in the absence of a specific statement, that such names
are exempt from the relevant laws and regulations and therefore free
for general use.
The publisher makes no representation, express or implied, with
regard to the accuracy of the information contained in this book and
cannot accept any legal responsibiIity or liabiIity for any errors or
omissions that may be made. Observing the Sun, along with a few
other aspects of astronomy, can be dangerous. Neither the publisher
nor the authors accept any legal responsibility or liability for personal
loss or injury caused, or alleged to have been caused, by any
information or recommendation contained in this book.
Typeset by EXPO Holdings, Malaysia
58/3830-543210 Printed on acid-free paper SPIN 10842242
Contents
Introduction ................................ vii
Acknowledgements ........................... ix
Introducing the Sun . . . . . . . . . . . . . . . . . . . . . .. 1
The Sun's Place in Space .................... 2
How the Sun W orks . . . . . . . . . . . . . . . . . . . . . .. 3
Solar Activity ............................ , 5
The Sun's Influence on the Earth. . . . . . . . . . .. 10
2 Equipment for Observing the Sun ........... 15
Telescopes for Solar Observing .............. 16
Mounts ................................. 22
Observing the Sun by Projection ............ 23
Solar Filters .............................. 30
Other Observing Methods .................. 34
Observing the Sun with the Naked Eye
and Binoculars ......................... 35
3 What We Can See on the Sun .............. 37
Setting up for Solar Observing .............. 37
The Sun's Surface ......................... 44
Faculae ................................. 54
Flares ................................... 55
4 Solar Drawings and Position Measurements .. 57
Drawing Using the Projection Method ........ 58
Deriving Sunspot Positions ................. 65
What We Can Learn from Drawings ......... 71
Detailed Drawings ........................ 72
Co-operation with Other Observers .......... 74
5 Measuring Solar Activity ................... 77
The Mean Daily Frequency ................. 78
The Relative Sunspot Number .............. 80
Recording and Reporting of Results .......... 84
Observing Faculae and White-Light Flares .... 90
Observing Naked-Eye Sunspots ............. 93
vi How to Observe the Sun Safely
6 Observing the Sun in Hydrogen-Alpha ........ 95
Equipment for H-Alpha Observing ........... 99
Prominences and Filaments. . . . . . . . . . . . . . . . 108
Flares .................................. 116
7 Solar Photography - Part 1: Photography
with Film ............................. 119
Equipment .............................. 121
Photographic Techniques .................. 131
Taking Pictures .......................... 137
Photography in Hydrogen-Alpha ............ 140
8 Solar Photography - Part 2: Digital
Techniques ............................ 145
Equipment for Digital Photography. ......... 148
Taking Digital Images ..................... 152
Handling and Processing Digital Images ...... 155
Appendix A Equiprnent Suppliers ............ 167
Appendix B Solar Observing Organisations .... 169
Appendix C Further Reading ................ 171
Index ..................................... 175
Introduction
The Sun is the brightest and most accessible object in
the sky, and it has much to offer the amateur
astronom er with modest equipment. On most days it
shows sunspots and other features that displaya wealth
of fine detail and change their appearance strikingly
from day to day. But observing the Sun can be
dangerous. NEVER look at the Sun through a telescope
or other optical aid, even for a brief instant. The Sun's
intense radiation, amplified and focused by a telescope,
will almost certainly cause eye injury and could weIl
lead to complete blindness. Do not attempt any solar
observing until you have read and understood the
safety precautions and observing advice set out in
Chapter 2 of this book - even if you think you have the
correct equipment. Be especially wary about using
filters to observe the Sun. If you have a filter that makes
the Sun look dark, it is not necessarily safe, as it is
largely the Sun's invisible radiation that is harmful to
the eye.
But provided you use the correct techniques, such as
projecting the solar image onto a screen or using a
specially designed, quality solar filter that fits over the
telescope aperture, it is quite easy to observe the Sun
safely. One of the joys of solar observing is that useful
observations are possible even with very small tele
scopes - such as the small refractors, Schmidt
Cassegrains and Maksutov telescopes that are readily
available off the shelf. In fact, due in part to the fact that
the Sun has more than enough light, a small telescope
will actually give better results than a large one!
Observing the Sun is also not affected by light pollution
- a major advantage for the many amateur astronomers
whose view of the night sky is obscured by the glow of
streetlights and security lighting. The Sun can be
observed from the town just as successfully as from
the country.
As I shall explain in Chapter 1, solar activity affects
the Earth in a number of important ways. For this
viii How to Observe the Sun Safely
reason, our nearest star is studied intensively by
professional astronomers and is being monitored
round the dock. The Sun is observed using space
based observatories as well as from the ground, and
both the level of research and the equipment required
to carry it out are far beyond the amateur's means.
Therefore solar observing does not offer the potential
for discoveries or major scientific contributions like
some other branches of amateur astronomy, such as
variable star observing or supernova hunting. But
monitoring solar features and keeping careful records
of them is still a useful contribution. Throughout the
world many amateur astronomers systematically moni
tor the Sun and send their observations to solar
observing organisations for analysis. Monitoring levels
of sunspot activity is particularly useful, as it continues
a long series of observations made with small telescopes
over many years, and more observers are always
welcome. In my view, solar photography is also useful,
as it has considerable educational value. Professional
solar images tend only to show small parts of the Sun or
show our nearest star at invisible wavelengths, where its
appearance is radically different from that in visible
light. Amateur images, on the other hand, portray the
Sun more realistically and so are more meaningful to
the wider public.
Recent years have seen some major advances in
equipment for the solar observer. Filters for white-light
observing have improved, allowing better photography
and visual observing. Hydrogen-alpha filters for viewing
the chromosphere and prominences are now more
affordable than ever, allowing amateurs with modest
budgets to have views - and take photographs - once
reserved for well-off individuals or professionals. Im
provements to photographic films have made it easier to
take good solar photographs. In the last few years, the
rise of digital imaging has opened up yet more horizons.
Digital cameras of the type obtainable from a camera
store, intended for everyday photography, can be used to
take excellent solar photographs, and the images can be
processed and enhanced using ordinary image proces
sing software on a horne computer.
For all that, not much has been written about
amateur solar observing in recent years. Books on
general astronomy and even those specifically about the
Sun te nd to relegate practical solar observing to a single
chapter, and so the techniques involved are not
Introduction ix
described in enough detail. The few books on the
subject that have appeared have generally been either
too technical or too specialised for the beginn er. This
book attempts to fill the current gap in the literat ure. I
have written it primarily for the amateur who knows
the basics of astronomy and wants to know how to go
about observing the Sun. All the time I have
emphasised what is possible using commercially avail
able equipment that is easy to get hold of in most parts
of the world. For this reason, I have deliberately
eschewed so me specialised topics, such as observing the
Sun's radio emissions, which requires horne-made
equipment and a fair amount of technical know-how.
Neither have I discussed in much detail the Sun-related
topics of eclipses and the aurora. Both are major fields
in astronomy by themselves and some good books on
them have already been published.
Throughout the book my emphasis has been on
practical solar observing - what you can do with
ordinary equipment, provided you take the proper
safety precautions. I have tried to avoid unnecessary
theory and have not attempted detailed scientific
explanations, as these are available elsewhere. Rather,
this book is intended as a basic guide to give the
amateur a taste for observing our ever-changing nearest
star, in the ho pe that he or she will explore further.
Acknowledgements
I would like to thank Derek Hatch and Eric Strach for
allowing me to use some of their fine solar images in
the text, and Harold Hill for his masterly drawings of
solar prominences. Thanks are also due to David Boyd
for supplying photographs of his solar observing
equipment and to Geoff Elston, Director of the Solar
Section of the British Astronomical Association, for
putting me in touch with some of the contributors. Last,
but by no means least, I am grateful to John Watson,
Astronomy Editor at Springer-Verlag, for giving me the
opportunity to write about observing the Sun and for
all his help in seeing the work through the press.
Lee T. Macdonald
Newbury, Berkshire
June 2002
The Sun is important to astronomers for two reasons.
The first is that it is Earth's only natural "power station",
producing the light and heat essential to life on our
planet. Without the Sun, the Earth would be more or less
a frozen ball of rock, with no atmosphere, no weather, no
life and no people. The Sun can also be harmful to us,
because it emits huge quantities of radiation that would
be fatal to humans and allliving matter, were our planet
not protected from it by a thick atmosphere and
powerful magnetic field. But intense bursts of solar
activity can still harm communications and electrical
power systems, so we need to keep a constant watch on
the Sun so that we are forewarned of its next powerful
outburst. We also need to understand it so that we can
predict future activity and its likely consequences.
The second reason for studying the Sun is that the
Sun is astar, much like the three thousand or so other
stars that we can see in the night sky. All the stars in the
night sky, however, are exceedingly remote from uso
Even the dosest known star, Proxima in the southern
constellation of Centaurus, is some 60 million million
kilometres (40 million million miles) from Earth - so
far away that its light takes over four years to reach uso
Most stars - even the majority of those visible to the
naked eye - are much further away still. Even the
world's most powerful telescopes show the stars as
mere points of light and give us just basic information
as to what they are and how they work. But at only
150 million kilometres (93 million miles) from Earth,
the Sun is easily dose enough for us to have a detailed
view and learn much about it. Armed with a detailed