bbc stargazing live 2012 guide to buying a telescope

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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

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