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GUIDE TO CHOOSING A TELESCOPE
BBC Stargazing LIVE 2012� Guide to choosing a telescope�|�01
NAKED EYEBefore you part with any cash to buy equipment, why not take a look at the sky with just your eyes? It’s amazing what you can see when you simply look up! Take your Stargazing LIVE Star and Moon Guide or Audio Guide out on a clear night and get started.
TRY OUT BINOCULARSBefore�thinking�about�buying�a�telescope,�consider�getting�a�good�pair�of�binoculars�first.�They�are�very�useful�for�viewing�the�Moon,�stars�and�other�bright�objects�and�a�reasonable�pair�will�cost�from�£50.
Many�people�new�to�astronomy�are�keen�on�acquiring�a�telescope�but�are�not�aware�that�a�good�pair�of�binoculars�can�outperform�many�entry-level�telescopes�more�cost�effectively.
Binoculars�are�simple�and�there�are�only�a�few�points�you�need�to�consider�when�buying�them�or�using�them�for�astronomy:
● For�stargazing,�a�decent�sized�pair�of�binoculars�to�start�with�will�be�anything�from��7�x�50�up�to�15�x�70�as�they�will�collect�plenty��of�light�and�won’t�be�too�heavy�to�hold.�
● Starting�out,�avoid�binoculars�with�high�magnifications�(that’s�the�first�number�before�the�‘x’)�as�these�will�be�tricky�to�hold�still�without�a�tripod.�Up�to�15�x�should�be�fine.
● Similarly,�avoid�binoculars�which�are�too�small�(the�number�after�the�‘x’�is�the�diameter�in�mm).�A�pair�with�50mm�optics�(e.g.�7�x�50)�is�a��good�minimum.
● Every�pair�of�binoculars�is�defined�by�two�numbers�separated�by�an�‘x’,�e.g.�10�x�50.��The�first�number�represents�magnification,��the�second�the�diameter�of�each�front�lens��in�millimetres.�Dividing�the�diameter�by�the�magnification�defines�a�value�known�as�the��exit�pupil,�the�diameter�of�the�light�beam�that�leaves�the�eyepiece.�An�exit�pupil�of�5mm�or�larger�is�preferable�for�stargazing�and�should�help�make�the�view�more�comfortable.�
Choosing�the�right�pair�of�binoculars�can�make��a�big�difference�to�a�beginner’s�stargazing�experience�so�it’s�worth�investigating�the�best�magnification�and�aperture�for�you.
TELESCOPESThere�are�so�many�different�types�of�telescope�available�for�the�beginner�that�selecting�one�can�be�a�bewildering�experience.�Before�buying�a�telescope�it�is�important�to�ask�yourself�what�objects�you�want�to�see�through�it�and�how�much�you�can�afford�to�pay.
Not�all�telescopes�are�the�same,�nor�do�they��give�the�same�results,�but�many�offer�a�good�compromise�and�many�different�types�of�astronomical�object�should�be�visible��through�them.�
Once�you�have�decided�on�what�you�want�to��see�through�your�new�telescope,�choosing�one��is�much�easier.�With�the�exception�of�the�Moon,�planets�and�bright�stars,�night�sky�objects�are�faint;�in�fact�most�will�appear�just�as�points�of�light�or�fuzzy�grey�blobs.�
TELESCOPE TYPES AND SIZESTo�observe�the�Moon,�planets�and�brighter�objects�in�the�night�sky,�a�small�telescope�or�binoculars�will�suffice.
To�see�more�detail�and�fainter�objects�such�as�galaxies�and�nebulae,�you�will�need�a�larger�telescope�with�more�light-gathering�ability.
Main types of telescope: ● Refractor telescopes�use�lenses�to�produce�
magnified,�high�contrast�views�of�the�night�sky.�Cheaper�ones�can�suffer�from�colour�fringing�around�the�edge�of�bright�objects,�so�if�possible�always�try�them�out�before�buying.�Anything�with�a�diameter�of�75mm�(3�inches)��or�larger�is�ideal�and�should�give�great�views��of�the�Moon,�brighter�planets�and�deep�sky�objects.�Refractors�are�also�commonly�used��for�astrophotography.
Light from celestial body
Objective lens Eyepiece
REFRACTOR TELESCOPE
● Reflector telescopes�use�mirrors�rather�than�lenses.�They�are�a�popular�choice�for�astronomical�use�because�mirrors�cost�a�lot�less�to�manufacture�than�lenses�of�equivalent�size.�The�most�common�type�of�reflector�is��that�designed�by�Sir�Isaac�Newton,�known�as��a�Newtonian.�A�150mm�(6�inch)�or�larger�Newtonian�is�ideal�for�viewing�deep�sky�objects�such�as�galaxies�and�nebulae,�as�well�as�detail�on�brighter�targets�like�the�Moon�and�planets.�
Light from celestial body
Eyepiece
Primary (objective) mirror
Secondary mirror
REFLECTOR TELESCOPE
BBC Stargazing LIVE 2012� Guide to choosing a telescope�|�02
● Dobsonian telescopes�are�one�of�the�best�choices�for�a�general�telescope�and�have�many�advantages�including�simplicity,�economy�and�large�light-gathering�ability.�Dobsonians�are�actually�large�Newtonian�telescopes�on�a�simple�manual�Alt/Az�(up,�down,�side�to�side)�mount.�Due�to�the�mount�and�optical�tube�assembly�being�so�simple,�Dobsonian�telescopes�are�the�most�economical�on�a�cost�per�inch�basis.�More�detail�can�be�seen�on�bright�objects�such�as�the�Moon�and�planets�and�a�lot�of�fainter�objects�are�within�the�grasp�of�the�amateur.�These�telescopes�are�usually�well�within�budget,�with�mirror�diameters�from�150mm�to�400mm�(6�to�16�inches)�or�larger.
DOBSONIAN TELESCOPE
Side bearings
Tube
Side board
Bottom board
Front board
RockerCradle board
Tube box
Stiffening ring
Ground board
On�all�telescopes,�magnification�is�governed�by�dividing�the�focal�length�of�the�telescope�by�the�focal�length�of�the�eyepiece�being�used.�You�can�use�different�eyepieces�with�the�same�telescope,�giving�you�access�to�a�whole�range�of�different�magnifications�to�study�what�you’re�viewing.
You�should�expect�to�pay�in�the�region�of�£150�upwards�if�you�want�to�purchase�a�usable�telescope.�If�you’re�looking�to�spend�a�larger�sum�and�make�a�greater�investment,�you’ll�get�more�for�your�money�with�a�Dobsonian.
Hybrid telescopes – Schmidt Cassegrain, Maksutovs and othersSome�modern�telescope�designs�use�both�lenses�and�mirrors�to�produce�their�images�and�because�of�this�are�known�as�hybrid�telescopes.�Typically,�these�designs�fold�their�optical�paths�to�produce�a�telescope�tube�which�is�much�shorter�than�the�actual�focal�length�of�the�telescope.�This�makes�them�easier�to�handle.�Many�hybrids�come�on�computerised�mounts�which�can�help�you�find�your�way�around�the�night�sky�via�a�control�handset.�
They�are�more�the�domain�of�the�intermediate�or�advanced�amateur�and�many�are�quite�expensive.�They�are�fantastic�telescopes,�but�it�is�much�wiser�to�start�off�with�a�refractor�or�reflecting�telescope.
AccessoriesIf�you�are�purchasing�a�tripod�you�will�need��to�consider�how�stable�and�rigid�it�is�with�your�telescope�fitted.�A�good�telescope�can�be��made�almost�useless�by�having�an�unstable�mount!�You�might�also�like�to�discuss�which�types�of�attachment�could�be�useful�to�you�with��a�reputable�telescope�supplier�or�seasoned�astronomer.
Making a decisionWatch�our�How�To�Video�at�bbc.co.uk/stargazing and�let�Mark�Thompson�talk�you�through�the�various�options�open�to�you.
Consider�how�you�want�to�use�your�telescope�and�what�your�budget�is.�Avoid�buying�low�end,�cheap,�budget�telescopes�to�avoid�disappointment.�Save�up�a�little�longer�and�get�a�good�telescope�from�a�reputable�telescope�supplier.�
Visit�your�local�astronomy�store�or�telescope�distributor�and,�before�you�buy,�ask�an�astronomer�or�go�to�a�Stargazing�LIVE�event�and�meet�your�local�astronomical�society.�They�will�be�glad�to�help�and�you�will�get�the�chance�to�sample�the�equipment�on�offer�before�parting�with�your�cash.
BBC Stargazing LIVE 2012� Guide to choosing a telescope�|�03
BBC Stargazing LIVE 2012� Guide to choosing a telescope�|�04
WHAT YOU CAN SEEBinoculars: ● The�Disc�of�the�Moon
● Lunar�seas�(Maria),�large�features�such�as�the�Bay�of�Rainbows�and�some�of�the�large�mountain�chains
● The�planets�Mercury,�Venus,�Mars,�Jupiter,�Saturn,�Uranus�and�Neptune�(just!)
● Star�fields�in�the�Milky�Way
● Some�brighter�galaxies�and�open�star�clusters
● Bright�comets
Small telescope:● Lunar�seas�(Maria),�craters�such�as�Copernicus�
and�Tycho,�mountains�and�valleys
● The�planets�including�several�of�the�brighter�moons�around�Jupiter�and�Saturn
● Double�stars,�star�clusters,�brighter�galaxies
● Comets�and�brighter�asteroids
Large telescope:● Details�within�craters�on�the�Moon
● Cracks�in�the�Moon’s�surface;�mountains,�valleys,�volcanic�domes
● Cloud�belts�and�the�Great�Red�Spot�on�Jupiter,�detail�in�Saturn’s�rings
● Faint�galaxies,�star�clusters�and�nebulae
Before�getting�started,�why�not�assemble�your�telescope�indoors�or�in�the�daylight�as�it�can�be�difficult�when�you’re�in�the�dark!
OBSERVING THE MOONThrough�binoculars�or�a�telescope,�the�best�views�are�to�be�had�close�to�the�terminator�–�the�line�that�divides�the�bright�portion�of�the�Moon’s�surface�from�the�dark�part.�This�is�because�features�such�as�craters,�mountains�and�valleys�cast�impressive�shadows,�making�them�much�easier�to�see.
A�large�telescope�may�need�filtering�as�the�Moon�is�bright!
For�a�closer�look�at�the�features�of�the�Moon�and�an�atlas,�showing�where�they�can�be�found,�see�our�Stargazing�LIVE�Star�and�Moon�Guide.�
OBSERVING OTHER OBJECTS IN THE NIGHT SKYFor�tips�on�getting�started�and�setting�up�to�enjoy�a�night�of�stargazing�with�your�binoculars�or�telescope,�see�the�Star�Guide�advice�on�‘Getting�Started’.�Use�the�star�maps�to�make�the�most�of�the�night�sky.�Many�objects�are�very�faint�and�difficult�to�identify,�but�can�be�seen�with�practice.
A�good�planisphere�or�star�atlas�can�also�help�you�identify�and�find�many�objects�as�well�as�the�variety�of�star�apps�available�for�smartphones�and�tablet�computers.�See�our�guide,�Stargazing�on�your�mobile,�for�an�introduction.
BAY OF RAINBOWS, SEA OF COLD – ADRIAN JANNETTA VIA BBC SKY AT NIGHT AND STARGAZING LIVE FLICKR GROUP