MAS Frequently Asked Questions
Frequently Asked Questions about astronomy (see also MAS Beginners page)
This page answers many commonly asked questions about astronomy. If you have a question on a subject any not covered here, please help support this page by using our on-line enquiry form (requires Java Script to be enabled).
Much of the material here has been taken from topics presented at out monthly meetings. If any member has subject they would like to present for 15-20 miniutes as a 'second half' topic, please contact the Meetings Secretary (to contribute directly to this page, please contact the Webmaster
(+) 0001 How do I find a local Astronomical Society ?
(+) 0002 How is Star brightness measured ?
(+) 0003 What are the Constellations ?
(+) 0004 What is the shape of the Earth ?
(+) 0005 What equipment do I need to start astronomy ?
(-) 0007 What telescope should I buy ?
PLEASE don't be 'tempted' by the cheap toys offered by chain stores and supermarkets, which are often 'advertised' with unobtainable 'magnifications' of '250x' or '300x' etc. (this, by the way, is how to spot the 'toys' .. real telescopes come with a mirror (or lens) size and focal length specification, not with irrelevant 'magnifications').
Such instruments are only really useful for teaching your kids the basics of telescope use and should never be expected to deliver decent stable images for serious observing. However, if, for some reason, you inherit or are given one of these toys, don't throw the 'tube' away - they often come with quite acceptable mirrors of 3" or more and are capable of delivering an acceptable image when used with a decent eyepiece (on the other hand, the 'H' or 'A' type eyepieces sold with the tube are indeed best dropped into the nearest garbage bin)
So having got that out of the way, what you need to look for is an instrument that's suitable for your intended use (and fits your budget, of course) :-)
What do you want to use it for ?
1) Do you want a portable telescope to take on holiday ? If so, binoculars or a wild-life "spotting 'scope" (with a zoom eyepiece) might best fit the bill.
2) Will you want to observe and photograph Galaxies, Nebula and star 'groups' (such as the Pleiades (M45) star cluster) ? If so, a 'fast' (short focal length) refractor (glass lens) telescope of 3" or above will be just fine and you will likely spend more on the 'GoTo' mount than on the 'OTA' (Optical Tube Assembly) !
3) Do you want a telescope that gives high magnifications for looking at (and photographing) surface detail on Mars, Jupiter and Saturn ? If so, you will be looking for one with at least an 8" mirror (or 6" lens) along with a good tracking mount, and these are typically expensive (as well as being large and heavy, so only 'semi-portable').
4) Is actual observation and speed of set up more important than taking photo's ? If so, a Dobsonian is the ideal choice, although (if you can afford one) modern mounts with GPS are almost as fast to set up.
However, for most people, your budget is likely to be the main constraint (the cost of a 'high-end' mount, telescope, eyepieces and accessories can be truly 'astronomical' !)
Advise: Whatever your plans may be, you should make an effort to 'try out' as many telescope 'types' as possible before you buy your first one, especially if you are thinking of buying at 'full price' (i.e. from a specialist dealer). Join a Society and see what the other members use. You don't need a telescope to be a member of MAS or any other Society. MAS typically holds at least one meeting a year at which some members bring along their telescopes and talk about the advantages (and disadvantages) to anyone who is interested. You can also attend our members Observing sessions and look through other members telescopes to get a 'feel' for what might suit you best
Try before you buy :
Many Astronomical societies (including MAS) will have one or more telescopes available for use by members. It's really only after using a telescope that you begin to appreciate what they can or can't do. Group observing or public viewing evenings are good hands-on venues = so if you can get to an 'astro-camp' or 'star party' (there are several very well known ones = see the list on the MAS Links page) then this would be the ideal occasion to "try-before-you-buy". If you are browsing for ideas and advice from experts, then the annual 'Astrofest' held in Kensington Town hall (London), usually in February, is a good exhibition of UK and EU equipment manufactures (in 2014 Tickets for 'exhibition only' entry were £8 and available from the ticket desk on the day - the February issue of Astronomy Now contained a coupon for £2 off the price of exhibition entry).
Criteria for a telescope :
The purpose of a telescope is to:
1) magnify the Moon and planets to see detail and,
2) to collect sufficient light to make faint objects brighter, so that you can see: comets, star cluster, nebulae and galaxies.
At the same time the telescope should be easy to set up and point at the object, and it should have a good finder attached.
Refractor : A traditional glass lens 'tube' type telescope best for general observing. Look out for the highly portable 'short tube' 60 - 80mm ED refractors which, although they have less light grasp than a reflector, will be easier to setup and use (and can even be used with a (robust) camera tripod). They are also highly suited to astro-photography (a motor driven equatorial mount can be bought later as an up-grade). Larger aperture refractors (5" - 6") have very long tubes, and whilst really good results can be achieved, they are really only 'semi-portable'.
Dobsonian : A Dobsonian is a reflecting telescope (using mirrors) on a simple alt-az mounting (so not suitable for astro-photography). They have many advantages for the amateur astronomer over a traditional glass lens refractor HOWEVER almost all 'Dobs' are manually guided and thus totally unsuitable for astro-photography (except, perhaps, of the Moon). 'Dobs' come in all sizes from 6" aperture upward. Sky Watcher, Orion Optics and Telescope House can supply Dobsonians in the UK. There are more equipment suppliers on our Links page.
Other telescope types: The Telescope House web site conveniently describes most of the common types available and some of the other factors effecting performance.
If you already have a telescope, MAS holds at least one 'Telescope Workshop' each year which is open to the public and is specifically aimed at those who need assistance in setting up and using their telescope.
This note last modified: 11th Jun 2019 10:58.
(+) 0008 How much Magnification can I get ?
(+) 0013 What are Equatorial and Alt Az mounts ?
(+) 0100 How do I use my first telescope ?
(+) 0109 What is a finder ?
(+) 0110 What is an eyepiece ?
(+) 0111 What is a Barlow ?
(+) 0112 What is a focal reducer ?
(+) 0114 What are Nebular filters ?
(+) 0116 How do I use Setting Circles ?
(+) 0120 What is collimation ?
(+) 0125 How can I safely observe the Sun ?
(+) 1030 How can I take photos of the stars ?
(+) 1033 How to take photos of the Aurora ? - (Northern Lights)
(+) 1035 How to calculate FOV for prime focus ?
(+) 1036 How do I calculate FOV for Eyepiece projection ?
(+) 1037 How do I use a Raspberry Pi camera for astrophotography ?
(+) 1038 What is Star trailing ?
(+) 1039 How can I take photos of Meteors ?
(+) 2100 What is Universal Time (UTC) ?
(+) 2114 What are AUs Parsecs and Light Years ?
(+) 2115 What is Bodes Law ?
(+) 3010 When was Neptune discovered ?
(+) 4000 How do I update Stellarium with new Comet data ?
(+) 5000 How To build the MAS (Raspberry Pi) photoframe ?