How to Oberve the Sun Safely 2nd by Macdonald

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Patrick Moore’s Practical Astronomy Series

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How to Observe
the Sun Safely

Second Edition
Lee Macdonald


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Lee Macdonald
Cambridge,UK

ISSN 1431-9756
ISBN 978-1-4614-3824-3

ISBN 978-1-4614-3825-0 (eBook)
DOI 10.1007/978-1-4614-3825-0
Springer New York Heidelberg Dordrecht London
Library of Congress Control Number: 2012937044
© Springer Science+Business Media New York 2012
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Preface

There is now more interest in observing the Sun than ever before among amateur
astronomers. Go to any major astronomical meeting or convention and you will see
at least one solar telescope in action, and it is sure to draw a crowd. The Sun indeed
has much to offer the amateur astronomer with modest equipment. On most days,
it shows sunspots and other features that display a 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 an ordinary 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 well 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 Chap. 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.
However, provided you use the correct techniques, such as projecting the solar
image onto a screen or using a specially designed high-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 telescopes – 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 can 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 a busy town just as successfully as from the remote countryside.

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vi

Preface

Our nearest star is studied intensively by professional astronomers and is monitored around the clock, using space-based observatories as well as telescopes 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 making major scientific contributions, like some other
branches of amateur astronomy, such as supernova hunting or variable star observing. But monitoring solar features and keeping careful records of them is still
important. Throughout the world, many amateur astronomers systematically monitor the Sun and send their observations to solar observing organizations for analysis. Monitoring levels of sunspot activity is particularly useful, as it continues a
long series of observations made with small telescopes since the nineteenth century,
which provide by far the best long-term record of solar activity that we have and is
vital to our understanding of the Sun’s behavior and any effects it might have on
Earth’s climate. More observers are always welcome in these sunspot counting
programs. 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. Indeed, as well as
amateur astronomers, this book is also intended for those bringing astronomy to a
wider audience, such as professional scientists engaged in public outreach activities, which are increasingly important in the present age of budget cutbacks, when
scientists are under increasing pressure to bring their subject to the public and justify its value to the taxpayer.
The first edition of How to Observe the Sun Safely (Springer, 2003), was mostly
written during 2001. But since that time, solar observing – and amateur astronomy
as a whole – has undergone radical changes. The most fundamental of these has
been the digital revolution and the almost complete substitution of digital imaging
for film photography. The first edition had a chapter on digital photography, but the
book’s main emphasis was on 35-mm work. Digital cameras were still in their
infancy: their resolution and exposure capabilities were modest, and they were
difficult to use with telescopes.
Digital SLRs did exist, but they cost over $2,000, putting them out of the reach
of most amateurs. And no one had thought of using a webcam, costing (and weighing) less than an eyepiece to take high-resolution images. All this has now changed.

Digital SLRs now start at under $500 and take better images than their 35-mm
predecessors, with all the benefits of digital imaging − the ability to see and evaluate your results on the spot, and no more waiting to finish a roll of film and have it
developed.
At the same time, amateurs are routinely using webcams to take images of sunspots and H-alpha solar features with a resolution once reserved for professional
observatories. Another revolution has taken place in the affordability, and availability, of telescopes and filters for observing the Sun in H-alpha. In 2001, the revolution was beginning, with the appearance of the Coronado SolarMax 40, the first
“sub-angstrom” H-alpha filter to be available for under $1,000. And, since then, the

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Preface

vii

revolution has continued. Now, some solar telescopes costing as little as $500 can
show spectacular solar features that before 2001 would have required instruments
costing five to ten times as much. Two other companies – Lunt and Solarscope –
have appeared and are producing high-quality H-alpha filters and telescopes, as has
a revived DayStar (long the only source of sub-angstrom H-alpha filters for amateurs), with the result that the amateur now has a vast and potentially confusing
array of equipment to choose from.
Therefore, there is all the more need for an up-to-date guide to show the amateur
what to look for on the Sun, how to record observations, and what equipment to use.
This second edition is aimed at the amateur who knows the basics of astronomy and
wants to know how to go about observing the Sun. What is emphasized is what is
possible using commercially available equipment that is easy to get hold of in most
parts of the world. For this reason, I have deliberately eschewed some specialized
topics, such as observing the Sun’s radio emissions, which requires homemade
equipment and a fair amount of technical know-how. Neither do I discuss 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, the emphasis is 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 hope that he or she will explore further.


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Acknowledgments

I would like to thank Dave Tyler for permission to use his exceptionally detailed
images – surely among the best solar images ever taken by an amateur astronomer
– and Derek Hatch for his fine solar eclipse pictures. Thanks are also due to Richard
Bailey (Solar Section Director of the Society for Popular Astronomy) for supplying
photographs of his H-alpha filter.
I owe a particular debt of gratitude to Dr. Dominic Ford of the Cavendish
Laboratory, Cambridge University, UK for his time in preparing the exquisite line
diagrams from my freehand sketches, using the PyXPlot software that he wrote
himself.
Another Cambridge colleague, Mark Hurn, kindly provided access to library
facilities and enabled me to photograph some equipment at the Institute of

Astronomy at Cambridge. Peter Meadows generously gave me permission to reproduce one of his Stonyhurst solar disks, and Lyn Smith, Solar Section Director of the
British Astronomical Association, allowed me to use BAA Solar Section data to
plot a graph of solar activity from 2001 to 2010.
I am grateful to David Hathaway (NASA Marshall Space Flight Center) for
permission to use the diagram in Fig. 4.8. Last, but by no means least, I must thank
John Watson, my editor at Springer for the first edition of How to Observe the Sun
Safely, for starting off the process that has led to this new edition and Maury
Solomon, Springer’s current Editor for Astronomy and Physics, for seeing this new
book through the press.
Cambridge, UK
June 2012

Lee Macdonald

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Contents

1

Our Sun ......................................................................................................
The Sun’s Place in the Universe .................................................................

How the Sun Shines ....................................................................................
The Sun’s Atmosphere ................................................................................
Solar Activity ..............................................................................................
The Sun’s Influence on Earth ......................................................................

1
2
3
4
6
12

2

Equipment for Observing the Sun ...........................................................
The Sun’s Radiation ....................................................................................
Telescopes for Solar Observing ..................................................................
The Refractor ..........................................................................................
The Reflector ..........................................................................................
Catadioptric Telescopes ..........................................................................
Telescope Mountings ..................................................................................
Viewing the Sun’s Image ............................................................................
Solar Projection ......................................................................................
Solar Filters ............................................................................................
Other Observing Methods ......................................................................
Observing the Sun with the Naked Eye and Binoculars.........................

17
17
19

19
23
24
25
27
27
31
36
37

3

What Can We See on the Sun? ................................................................
When to Observe the Sun ...........................................................................
Where to Observe the Sun ..........................................................................
Aiming the Telescope .................................................................................
Viewing the Sun’s Surface ..........................................................................
Granulation .............................................................................................

41
41
43
45
47
47

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Contents

Limb Darkening .....................................................................................
Sunspots..................................................................................................
Flares ......................................................................................................

48
49
61

4

Solar Position Measurements ...................................................................
Drawing Using the Projection Method .......................................................
Making a Projection Grid .......................................................................
Orienting the Image ................................................................................
Making the Drawing ...............................................................................
Deriving Sunspot Positions ....................................................................
Example ..................................................................................................
What We Can Learn from Drawings ......................................................
Detailed Drawings ..................................................................................
Cooperation with Other Observers .............................................................

63
64
64
67
68

71
74
78
80
81

5

Measuring Solar Activity .........................................................................
The Mean Daily Frequency.........................................................................
The Relative Sunspot Number ....................................................................
Observing Faculae and White-Light Flares ................................................
Observing Naked-Eye Sunspots .................................................................

83
84
86
97
98

6

Observing the Chromosphere ..................................................................
Equipment for Observing the Chromosphere .............................................
H-Alpha Telescopes................................................................................
H-Alpha Filters .......................................................................................
Choosing an H-Alpha System ................................................................
Calcium-K and Other Systems ...............................................................
Prominences and Filaments ........................................................................
Counting Prominences ...........................................................................

Prominence Position Measurements ......................................................
Flares ...........................................................................................................

101
106
110
114
121
124
125
128
128
131

7

Imaging the Sun with a Digital Camera .................................................
Choosing a Digital Camera .........................................................................
“Compact” Cameras ...............................................................................
Digital SLRs ...........................................................................................
Telescopes and Mounts ...............................................................................
Filters ..........................................................................................................
Mounting the Camera .................................................................................
Photographic Techniques ............................................................................
Shooting the Projected Image.................................................................
The Afocal Method ................................................................................
Prime Focus Photography.......................................................................
Using a Teleconverter .............................................................................
Eyepiece Projection ................................................................................

135
137
137
142
144
146
148
150
150
151
151
154
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Contents

8

xiii

Taking Pictures............................................................................................
Taking Pictures with a Compact Digital Camera ...................................
Taking Pictures with a DSLR .................................................................
Photographing the Chromosphere...............................................................

159

162
164
168

Webcam Imaging and Image Processing ...............................................
Webcams and Accessories ..........................................................................
Do You Need a Webcam? .......................................................................
Advantages of Webcams ........................................................................
Choosing a Webcam for Solar Imaging..................................................
Computers and Accessories....................................................................
Taking Webcam Images ..............................................................................
Processing Webcam Images ........................................................................
Enhancing Digital Images ...........................................................................
File Formats ............................................................................................
Cropping and Trimming .........................................................................
Image Orientation ...................................................................................
Changing the Brightness and Contrast ...................................................
Removing Dust and Scratches ................................................................
Sharpening the Image .............................................................................
Changing the Color ................................................................................
Making Composite Images .....................................................................

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174
174
174
176
178
179
182

186
188
190
190
191
192
192
193
195

Appendix A

................................................................................................. 197

Appendix B

................................................................................................. 203

Appendix C

................................................................................................. 205

Appendix D

................................................................................................. 207

Index ................................................................................................................. 211


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List of Figures

Fig. 1.1
Fig. 1.2

Fig. 1.3

Fig. 1.4

Fig. 1.5

Fig. 1.6

Cutaway diagram showing the structure of the Sun .......................
Total solar eclipse, photographed by Derek Hatch
on August 1, 2008, showing the extensive white
corona around the black silhouette of the Moon ............................
The Sun’s photosphere (“surface”), showing a very
large sunspot group and several smaller groups,
photographed by the author in August 2002 ..................................
The planet Mercury in transit across the Sun,
photographed by the author on May 7, 2003, with an 80 mm
refractor and full-aperture solar filter. Note how the silhouette
of Mercury, visible near the bottom of the picture, appears jet

black, while the small sunspot near the top has a brownish tint,
because sunspots appear dark only by contrast ..............................
Total solar eclipse, August 1, 2008, showing prominences
around the silhouette of the Moon. This is a short exposure
of the same eclipse as in Fig. 1.2; it allows the prominences
to show up without being drowned out by the bright inner
corona (Photograph by Derek Hatch) .............................................
The Sun’s corona, imaged in the extreme ultraviolet by the
SOHO satellite in September 1997, showing bright active
regions and dark coronal holes. The active regions broadly
correspond to sunspot groups in visible light. The photosphere
appears dark because it is too cool to emit at this wavelength
(Image courtesy of NASA) .............................................................

4

5

7

8

10

11

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Fig. 1.7

Fig. 1.8

Fig. 2.1
Fig. 2.2

Fig. 2.3

Fig. 2.4

Fig. 2.5

Fig. 2.6

Fig. 2.7
Fig. 2.8
Fig. 2.9
Fig. 2.10
Fig. 2.11
Fig. 3.1

List of Figures

A coronal mass ejection (CME) imaged in visible light by the
SOHO satellite in November 1997. The Sun’s brilliant disc
has been artificially hidden by an occulting disc inside
the telescope (Image courtesy of NASA) .......................................

A major display of the aurora borealis, photographed
from southern England by the author on April 6, 2000.
The display was triggered by a major geomagnetic storm .............

12

14

The electromagnetic spectrum........................................................
The author’s 80 mm (3.1 in.) refracting telescope on a German
equatorial mount with electronic slow motion controls.
A home-made balsa wood projection box is attached
to the eyepiece end of the telescope for safe viewing
of the Sun’s image ..........................................................................
The author’s 60 mm (2.4 in.) f/5.9 Takahashi apochromatic
refractor. Its short tube makes it extremely compact
and portable ....................................................................................
A Meade ETX 90 mm (3.5 in.) Maksutov telescope equipped
with a glass aperture filter. Note that the finderscope has been
removed. This is an important safety precaution, because the
Sun is just as dangerous to look at through the finderscope
as at the main telescope, and careless people, particularly
children, could look through it by accident ....................................
Projecting the Sun’s image onto paper for safe solar viewing.
A card has been fitted over the eyepiece end of the telescope
to shade the image from direct sunlight .........................................
A solar projection screen, designed by Roderick Willstrop of
Cambridge University, attached to the 200 mm (8-in.)
Thorrowgood refractor at the Institute of Astronomy
in Cambridge, England. Here the screen is made from a light

framework of plywood – heavier than balsa wood – attached
to a large and heavy telescope ........................................................
A balsa wood projection box made by the author and attached
to an 80 mm (3.1-in.) refractor .......................................................
Aperture filter made from Baader AstroSolar Safety Film
in a home-made mount, fitted to an 80 mm refractor .....................
A glass aperture filter mounted to fit the Meade ETX 90 mm
(3.5 in.) Maksutov telescope pictured in Fig. 2.4 ...........................
A Herschel wedge or Sun diagonal made by Lunt
Solar Systems .................................................................................
A naked-eye solar viewer made from black polymer (left)
and a pair of Mylar eclipse glasses (right) .....................................

38

Diagram showing the principle of a solar finderscope
(Courtesy of Dominic Ford) ...........................................................

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List of Figures

Solar finderscope on the author’s 80 mm refractor.
This replaces the “normal” finderscope, which has been
removed as a safety precaution.......................................................
Fig. 3.3 Whole-disc photograph of the Sun, showing sunspots
and limb darkening. The latter has been exaggerated
by the high contrast of the image (Photograph by the author) .......
Fig. 3.4 A small, simple sunspot, showing the dark central umbra
and lighter surrounding penumbra (Image by Dave Tyler) ............
Fig. 3.5 In this remarkably high-resolution image by Dave Tyler
of a bipolar sunspot group, taken on April 23, 2011, the
penumbral filaments are clearly visible in two of the group’s
spots, especially the large spot on the right. The granulation
of the surrounding photosphere also shows up strikingly ..............
Fig. 3.6 A small, symmetrical sunspot showing the Wilson Effect:
the penumbra on the side of the spot nearest the center
of the disc is narrower than that on the side nearest the limb,
making the spot look like a depression on the Sun’s surface
(Image by Dave Tyler) ................................................................

Fig. 3.7 A large sunspot group, photographed by the author
in July 2004, showing multiple light bridges in the umbra
of its leader spot .............................................................................
Fig. 3.8 Some examples of sunspot group types, ranging from
simple to complex, showing their McIntosh classifications.
All images by Dave Tyler. (a) Very small group
of class Axx, (b) Small bipolar group, class Bro,
(c) Spot group of class Dao, (d) Spot group of class Ekc,
(e) Symmetrical spot, class Hhx .....................................................
Fig. 3.9 The giant sunspot group of March 2001, McIntosh
classification Fkc. This was one of the largest sunspot
groups ever recorded and was associated with widespread
auroral displays (Photograph by the author) ..................................
Fig. 3.10 Another of the giant sunspot groups of Solar Cycle 23,
this time the largest of the groups of October 2003,
McIntosh classification Fkc (Photograph by the author) ................
Fig. 3.11 A sunspot group near the limb, showing extensive faculae,
imaged by Dave Tyler on March 7, 2011. An image of the
same group in H-alpha light, shown for comparison,
appears at top ..................................................................................

xvii

Fig. 3.2

Fig. 4.1

A solar drawing grid, consisting of a 152 mm (6 in.) circle
divided into ½ in. squares, as used in the projection box
and underneath the drawing. The 5° intervals marked out

around the circumference are for determining the Sun’s
true orientation for sunspot counting purposes (see Chap. 5)
(Courtesy of Dominic Ford) ...........................................................

46

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51

51

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xviii

List of Figures

Fig. 4.2

Close-up of the author’s solar projection box, showing
the rotatable projection grid .............................................................
Fig. 4.3 Orientation of the Sun’s image at midday as seen in various
telescope arrangements. (a) Straight projection through a refractor
or Newtonian (northern hemisphere). (b) Projection using a star
diagonal (northern hemisphere). (c) Filtered solar image as seen
directly in a refractor, Schmidt-Cassegrain or Maksutov telescope,
using a star diagonal or 90° mirror (northern hemisphere).
(d) Straight projection through a refractor or Newtonian
(southern hemisphere). (e) Projection using a star diagonal
(southern hemisphere). (f) Filtered solar image as seen directly in a
refractor, Schmidt-Cassegrain or Maksutov telescope, using a star
diagonal. In all arrangements with a star diagonal, these diagrams
assume that the observer is standing or sitting directly behind the
eyepiece and facing the front of the telescope tube (Courtesy of
Dominic Ford) ................................................................................
Fig. 4.4 An example of a Stonyhurst disc, for a solar tilt (B0) of 6°
(Courtesy of Peter Meadows) ..............................................................
Fig. 4.5 Illustrating the Sun’s changing position angle (P) and “nodding”
towards and away from us (B0) during the course of the year
(Courtesy of Dominic Ford) ...........................................................
Fig. 4.6 Whole-disc drawing, made by the author on October 12, 2008,
showing a small bipolar sunspot group. The position angle
P is marked .....................................................................................
Fig. 4.7 The author’s drawing of October 12, 2008, shown laid over a
Stonyhurst disc representing B0 = 6.0° (Stonyhurst disc courtesy
of Peter Meadows) ..........................................................................

Fig. 4.8 The “Butterfly Diagram,” plotted from the 1880s up to 2011
(top), matched up with the graph of sunspot numbers for the
same time period (below). The migration of sunspots from
high to low latitudes in each cycle is clearly seen
(Courtesy of NASA/David Hathaway) ...........................................
Fig. 5.1

Fig. 5.2

Fig. 5.3

Whole-disc image of the Sun, showing three sunspot groups.
The active area count for that day should therefore be recorded
as 3 (Photograph by the author) .....................................................
This image of a sunspot group gives a good demonstration
of which internal spots should and should not be counted as spots
for the purpose of determining the Relative Sunspot Number,
R. All the dark umbrae towards the left and right ends of the
group should be counted, but the pores and gray penumbral
material at the center should not (Image by Dave Tyler) ...............
Diagram showing how to determine the Sun’s true orientation
by eye. Note also that the Sun’s true equator is usually curved
northwards or southwards, and this needs to be taken into

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List of Figures

Fig. 5.4
Fig. 5.5
Fig. 5.6

Fig. 5.7

Fig. 6.1

Fig. 6.2

Fig. 6.3

Fig. 6.4

Fig. 6.5

Fig. 6.6

Fig. 6.7

xix

account when determining which hemisphere
a spot is in (Drawing by Dominic Ford) .........................................
Sample page from the author’s solar notebook, showing
sunspot counts recorded in tabular form ........................................
Graph plotted from the author’s sunspot counts, showing
the variation in the MDF between 2001 and 2010 .........................
Graph plotted from the author’s sunspot counts, showing
the variation in the Relative Sunspot Number R between
2001 and 2010 ................................................................................
Graph showing the variation in the Relative Sunspot Number R
between 2001 and 2010, based on British Astronomical Association
collective sunspot data (Permission to use BAA data kindly
supplied by Lyn Smith, BAA Solar Section Director) ...................
Diagram of the visible light spectrum, showing the wavelengths
of some major chromospheric emission lines (Diagram by
Dominic Ford) ................................................................................
Example of how the level of white-light sunspot activity is
no accurate guide to what might be visible in H-alpha.
This giant solar prominence was photographed by the author
on April 4, 2004, when sunspot activity was very moderate
(see text). Picture taken using a Canon EOS 300D digital SLR

camera attached to an 80 mm refractor with Baader “H-alpha
coronagraph” prominence viewer. Exposure 1/250 s with the
camera set to ISO 400 ....................................................................
The Sun’s disc in hydrogen-alpha. The dark linear features are
filaments (i.e., prominences seen in absorption against the disc),
and the bright regions are plages. Whole-disc mosaic image
by Dave Tyler .................................................................................
An example of a “filaprom” – a filament seen in absorption
against the solar disc extending beyond the Sun’s limb and
becoming a prominence seen in emission against the apparent
blackness of space (In reality, it is seen against the corona, but the
latter is much too faint to be seen in an H-alpha filter.)
(Image taken by Dave Tyler on November 20, 2009) ....................
The Coronado Personal Solar Telescope (PST) – the 40 mm
dedicated H-alpha telescope that made sub-angstrom H-alpha
views of the Sun available for under $500. The large dark sheet
is a Sun shade to shield the observer from direct sunlight
(Photograph by the author) ................................................................
The Lunt Solar Systems 152 mm (6 in.) dedicated H-alpha solar
telescope. In the background are Lunt’s 50 and 100 mm models
(Photograph by the author) .............................................................
The Solarview 50 H-alpha telescope made by Solarscope Ltd.
(Photograph by the author) ......................................................................

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xx

Fig. 6.8

Fig. 6.9

Fig. 6.10

Fig. 6.11
Fig. 6.12
Fig. 6.13

Fig. 6.14

Fig. 6.15
Fig. 7.1

Fig. 7.2

Fig. 7.3

Fig. 7.4

List of Figures

A 40 mm Coronado SolarMax filter fitted to the author’s
Takahashi FS-60C 60 mm apochromatic refractor.
(Photograph by the author) .............................................................
A DayStar T-Scanner sub-angstrom H-alpha filter, a popular
model with amateur astronomers for many years and still used by
many solar observers. (a) The filter unit housing the etalon.
(b) The filter unit mounted on a Meade SCT (Photographs
by Richard Bailey)..........................................................................
Attaching a Moon filter in front of the eyepiece will increase the
contrast of disc features in an H-alpha image – though it does not
narrow the passband and the prominences will be fainter
(Photograph by the author) .............................................................
A Baader H-alpha coronagraph on an 80 mm (3.1 in.) refractor
(Photograph by the author) .............................................................
A typical hedgerow prominence (Image by Dave Tyler) ...............
H-alpha image of a sunspot group, showing an active region
filament. Note that this type of filament is smaller and darker
than typical quiescent filaments (Image by Dave Tyler) ................

H-alpha image of a flare in the large sunspot group AR11158,
taken by Dave Tyler on February 17, 2011. The flare is the
intensely bright region near the center of the group .......................
A spectacular limb flare (Imaged by Dave Tyler
on March 8, 2011) ..........................................................................

114

118

119
120
126

127

132
132

A typical compact digital camera: a 10-megapixel Canon
PowerShot A640. This camera’s LCD viewfinder screen unfolds
from the main body of the camera and can be adjusted to a great
variety of angles – a handy feature when the camera is mounted
on a telescope and the screen is at an awkward angle if left in its
conventional position ...................................................................... 138
A heavily compressed JPEG image, occupying only about
100 KB on the computer’s hard drive but rendered almost
useless by the variation in tone caused by the limb darkening
being reduced to a series of layers. The original image was taken
on a 6.3-megapixel DSLR, demonstrating that the degree of image

compression is more important than the size of the image in
megapixels ...................................................................................... 140
The author’s 6.3-megapixel Canon EOS 300D digital single lens
reflex (DSLR) camera, shown with 18–55 mm zoom lens
separated from the camera body. With the lens removed, cameras
of this type can be securely clamped to the telescope with suitable
adapters to take high-quality images of the Sun (and other
astronomical objects) ...................................................................... 143
A filter made from Baader AstroSolar Photo Film, in a
home-made mount and fitted to the author’s 80 mm refractor.

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List of Figures

Fig. 7.5

Fig. 7.6
Fig. 7.7

Fig. 7.8

Fig. 7.9

Fig. 7.10

Fig. 7.11

Fig. 7.12

xxi

This type of filter transmits a brighter image than visual filters
and so allows very short exposures to be used with DSLR
cameras. All photographic filters should carry a warning label
like this one, indicating that they are not safe for visual use .......... 147
Three methods of using a compact digital camera at the telescope
eyepiece to image the Sun. (a) A Canon PowerShot A640 camera
held up to the eyepiece by hand. (b) The PowerShot A640
mounted on a tripod and pointed into the eyepiece. (c) A Nikon
Coolpix 900 camera clamped to the eyepiece using a
commercial digital camera adapter................................................. 148
Prime focus photography with a DSLR: the camera body
is attached directly to the telescope drawtube with an adapter ...... 152
Prime focus photography can be a good method for imaging
a partial solar eclipse. This image of the partial eclipse seen
just after sunrise from the UK on January 4, 2011, was taken
by the author using a Canon 300D at the prime focus of a Vixen
80 mm refractor (focal length 910 mm), with a Baader AstroSolar
Photo Film (ND3.8) filter. Exposure 1/125 s at ISO 400 ............... 153
A small telescope of short focal length gives only a very small
solar image when the camera is used at the prime focus. Image
taken by the author on March 14, 2010, using a Canon 300D
DSLR at the prime focus of a Takahashi FS-60C 60 mm refractor,
focal length 355 mm, equipped with a full-aperture Baader
AstroSolar (ND5) filter. Exposure 1/2,000 s .................................. 155
Whole-disc solar image, showing a large sunspot group.
Image taken by the author on September 13, 2005, using a Canon

300D DSLR on an 80 mm f/11.4 refractor with a 1.4× teleconverter,
giving an effective focal length of 1,274 mm. The Sun’s disc nicely
fills the frame in many DSLRs using this sort of focal length. Filters
used were Baader full-aperture AstroSolar Photo Film (ND3.8)
and No. 8 (light yellow) secondary filter. Exposure was 1/3,200
of a second at ISO 100 .................................................................... 156
Diagram showing the principle of eyepiece projection using a
refractor or Newtonian telescope, using a camera adapter
and T-ring ....................................................................................... 157
Eyepiece projection arrangement on the author’s 80 mm refractor,
showing Canon EOS 300D DSLR (with cable release), T-ring and
camera adapter ................................................................................ 157
Close-up of two sunspot groups, an enlargement of an image
photographed by the author on December 4, 2005, using an 80 mm
refractor and eyepiece projection with a 15 mm eyepiece to give
an effective focal length of 5,763 mm at f/72. Filters used were
Baader full-aperture AstroSolar Photo Film (ND3.8) and No. 8
(light yellow) secondary filter. Exposure was 1/1,250 s at ISO 400
on a Canon 300D DSLR ................................................................. 159


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xxii

Fig. 7.13

Fig. 7.14

Fig. 7.15

Fig. 7.16

List of Figures

The Canon “Angle Finder C” focusing magnifier fitted to
a Canon 300D camera mounted on the author’s 80 mm
refractor ..........................................................................................
Partial solar eclipse, March 29, 2006, focused using the method
for focusing a DSLR described in the text. Image taken with
Canon 300D on 80 mm refractor with full-aperture Baader
AstroSolar Photo Film (ND3.8) filter and 1.4× teleconverter.
Exposure 1/3,200 of a second at ISO 100 ......................................
The Sun in H-alpha, taken by the author with a Canon PowerShot
A640 hand-held to a 25 mm eyepiece on an 80 mm refractor
equipped with a Coronado SolarMax 40 filter. This image
demonstrates the difficulty in obtaining good H-alpha images
with color cameras. Two filaments, some plage detail and a
sunspot are faintly visible ...............................................................
Prominences photographed through a coronagraph attached
to an 80 mm refractor. A finely detailed prominence is visible
to the upper right of this image originally shot on 35 mm film......

Fig. 8.1

166

167

170

171

The author’s 80 mm refractor with webcam connected to
laptop computer .............................................................................. 175
Fig. 8.2 Celestron NexImage astronomical webcam attached
to the author’s 80 mm refractor ...................................................... 176
Fig. 8.3 The tiny Flea3 webcam-type CCD camera on Dave Tyler’s
130 mm Astro Physics refractor mounted “piggyback” on his
14-in. Celestron SCT. The Flea3 is smaller than the Barlow
lens it is attached to! ....................................................................... 178
Fig. 8.4 A single frame from a webcam movie has a grainy appearance
and low resolution. This image of a group of prominences
was taken by the author on February 11, 2008. It is one frame
from a 900-frame movie taken with a Celestron NexImage
webcam attached to a 60 mm refractor with a Coronado
SolarMax 40 H-alpha filter ............................................................. 183
Fig. 8.5 The same prominences as in Fig. 8.4, after the webcam movie
has been through the stacking and aligning process....................... 185
Fig. 8.6 The final image of the prominences, after wavelet processing....... 186
Fig. 8.7 Steps in enhancing a digital image of the Sun using Adobe
Photoshop Elements. (a) Original image, taken by the author on
March 8, 2011, with a Canon 300D on an 80 mm refractor with a
1.4× teleconverter and a Baader AstroSolar Photo Film filter,
(b) The image cropped to center the Sun’s image and exclude
some of the black background, (c) The image flipped to show east to
the right, (d) The brightness decreased by 20 points and contrast
increased by 40 points, (e) Image after applying “Sharpen” twice and
then with contrast and sharpness enhanced further using
“Unsharp Mask,” (f) Image with red and green channels
adjusted to give a distinct yellow color........................................... 189

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List of Figures

Fig. 8.8

Fig. 8.9

xxiii

Whole-disc solar image, originally taken by the author
on June 19, 2001, on Kodak Technical Pan 2415 black-and-white
film, then more recently scanned and tinted yellow using
Adobe Photoshop Elements............................................................ 195
The webcam image of the Sun shown in Fig. 8.6, with the
overexposed solar disc blacked out using Adobe Photoshop
Elements, mimicking the effect of a coronagraph or a total solar
eclipse ............................................................................................. 196

Fig. A.1 Diagram showing the construction of the author’s projection box.
The projection distance d determines the diameter of the
projected solar image...................................................................... 199
Fig. A.2 The author’s projection box, attached to an 80 mm (3.1 in.)
refractor with a pipe bracket ........................................................... 201


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