Real Astronomy with Small Telescopes. Step-by-Step Activities for Discovery

155 Pages·2006·5.334 MB·English

by  Michael Gainer

Patrick Moore’s Practical Astronomy Series
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(continuedafterindex)
Real
Astronomy
with Small
Telescopes
Step-by-Step Activities
for Discovery
Michael K. Gainer
With 90 Figures
MichaelK.Gainer
P.O.Box244
NewDerry,PA15671
USA
[email protected]
BritishLibraryCataloguinginPublicationData
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LibraryofCongressControlNumber:2006927794
PatrickMoore’sPracticalAstronomySeriesISSN1617-7185
ISBN-10:1-84628-478-3
ISBN-13:978-1-84628-478-6
e-ISBN-10:1-84628-508-9
e-ISBN-13:978-1-84628-508-0
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To my son Michael with love and gratitude
No unregarded star
Contracts its light
Into so small a character,
Removed far from humane sight,
But if we steadfast looke
We shall discerne
In it, as in some holy booke
How man may heavenly knowledge learne.
William Habington, 1634
Preface
Thesmallrefractingtelescopewithitssimpledirectdesignandconstructionand
permanently aligned optics is the time tested standard for personal use. Easily
portable, it can be taken out of the house and set up at a moment’s notice. Or,
it can be packed conveniently into a small car for traveling to a dark observing
site. With moderate care and minimal maintenance, the telescope and mount
can last for generations.
These instruments provide sharp, crisp high-contrast images of the Moon
and planets. They are less susceptible to the effects of unstable air than larger
ones, and because of their low maintenance and durability they are ideal for
the parent educator or lifelong learner. Until recently, however, the high cost
of small telescopes of sufficient quality for serious astronomical use has limited
their accessibility.
During the past decade, innovations in optical design and manufacture have
loweredcostandimprovedquality.Currentdevelopmentsinlensdesignmakeit
possibletoproduceaffordablerefractingtelescopeswithshortertubelengthsand
greater versatility. The once very costly 90-mm Maksutov–Cassegrain, with its
optimum combination of effective optics and portability, now sells for a modest
price.
I have often seen small instruments referred to as “grab and go” or “quick
look,”notworthyofconsiderationforseriousobserving.Imaintaintheycanbe
much more. Despite their limits in types of observation, 80-mm refractors and
90-mm Maksutovs have sufficient aperture and magnifying power to provide a
lifetimeofobservingpleasure.Theyareidealforlunaroccultationmeasurements,
tracking the solar activity cycle, observing variable stars and measuring binary
ix
x Preface
stars. Although all the activities described here are equally applicable to larger
instruments, none of them require an aperture larger than 80mm.
Through the use of common digital cameras, the limiting stellar magnitude
andimagescaleofsmalltelescopescanbeincreaseddramatically,thusproviding
resultsonenormallyexpectsfromlargerinstruments.Muchofthisbookapplies
thatprincipletomakinginterestingandusefulastronomicalobservations.Ihave
takennovelapproachestoextendingtheuseofsmallinstrumentsforquantitative
observations by applying unique methods for the analysis of digital camera
photographs.
My intent is to demonstrate that useful and significant observations can be
madewithmodest,relativelylowcostequipment.Someoftheactivitiesdescribed
provide the necessary tools for making valuable contributions to various inter-
national astronomical data files. Others are of primarily educational value for
eithertheself-learnerorthescienceeducator.Thismaterialshouldbeofinterest
to both the beginning and the experienced observer. The emphasis is on what
you can do with a small telescope rather than only on what you can see.
Acknowledgement
I am deeply indebted to Madalon Amenta for her time and skill in editing the
manuscript.
Michael K. Gainer
June 2006
Contents
Preface................................................................. ix
Computer Hardware and Software........................................xv
ChapterOne The Celestial Sphere ..................................... 1
ChapterTwo The Measurement of Time................................ 5
Solar Time.............................................. 5
Sidereal Time........................................... 7
Dating Observations..................................... 8
ChapterThree The Equatorial Telescope Mount.......................... 9
Mount Stability.......................................... 9
The Polar Axis Drive.....................................13
Setting Circles...........................................13
Aligning an Equatorial Mount............................15
Using Setting Circles.....................................17
A Tabletop GEM ........................................19
Go-to Mounts...........................................20
ChapterFour Telescope Considerations.................................21
Limitations Imposed by Aperture.........................21
Limitations Imposed by the Environment..................23
xi
xii Contents
Limitations Unique to Refractors .........................23
Short Focus Achromatic Refractors .......................24
Limitations Unique to Maksutov Telescopes...............25
Newtonian Reflectors....................................25
Eyepieces...............................................26
Focusing................................................26
The Finder..............................................27
Recommended Accessories...............................27
Which Small Telescope Should You Buy?..................27
ChapterFive Astronomical Photography...............................29
Digital Photography .....................................29
Choice of Camera .......................................31
Mounting the Camera....................................31
The Afocal Field of View.................................31
Telephoto Conversion Lenses.............................32
Processing the Print .....................................33
Film Photography.......................................34
Printing the Image.......................................35
ChapterSix The Sun.................................................37
Visual Observations of the Sun...........................39
Classification of Sunspots................................39
Sunspot Number........................................40
Visual Observations......................................41
Digital Photography of the Sun...........................42
Processing the Photographs ..............................42
The Stonyhurst Disk.....................................43
Measuring the Sun’s Rotation.............................48
Film Photography of the Sun.............................49
ChapterSeven The Moon...............................................51
Visual Observations......................................51
Digital Camera Photographs of the Moon..................52
Analyzing the Photographs...............................52
Selenography............................................53
Measurements on the Computer Monitor..................56
Measuring Lunar Libration...............................57
Film Photography of the Moon...........................59
Lunar Occultations......................................59
ChapterEight The Planets..............................................61
Sketching the Planets....................................61
Filters..................................................62
Digital Photography of the Planets........................62
Plotting the Orbital Position of a Planet...................64
Ecliptic Coordinates.....................................64
The Phases of Venus.....................................71