Starting Astronomy FAQ

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Hello,

This page answers some commonly asked questions. To help support this page, you can direct a question to the main contact on the Home page.

Q How do I best use my first telescope?
Q What is an eyepiece?
Q What is a Barlow lens?
Q What is a finder?
Q What is an equatorial or Alt-Az mounting?
Q What is Universal Time?
Q What is "collimation" ?
Q Who can advise me?
Q What equipment do I need to start astronomy?
Q What telescope should I buy ?
Q Can I photograph the stars?

How do I best use my first telescope?
The instructions that come with a telescope are often not as clear as one might hope! Half an hour with someone who knows the "routine" will probably save you hours/days of frustration. So dont worry - it will all work out in the end. Then you will be able to follow the Moon, locate Saturn or find some of the wonderful clusters of stars in the night sky.

Advice: Pay attention to alligning the finder (if nessesary) and get the telescope ballanced. Practice setting it up in daylight before using it at night. Use the low magnification eyepiece and wait for a clear sky. The Moon is the best place to start observing.

What is an eyepiece?
An eyepiece is used to magnify the image formed by the telescope's lens or mirror. A telescope needs two optical parts: 1) A glass lens, or a mirror (or both) and 2) an eyepiece. Telescopes are often supplied with two eyepieces, one for low magnification the other for high. Sometimes a 2x Barlow is also part of the kit. Typical eyepieces supplied are a 25mm and 10mm focal lengths.

Advice: keep the optical parts covered when not in use. Dust will spoil your equipment.

What is a Barlow lens?
A Barlow is an extra lens which doubles the focal length of the telescope, and therefore doubles the magnification with that eyepiece. Named after Peter Barlow an engineer.

Advice: Using a Barlow with a 10mm eyepiece might give too high a magnification. Make sure you can find and track the object before using a high magnification (e.g. x 100 and above).

What is a finder?
A finder is a small telescope or other device which is used like a sight on a gun. Looking through the finder tells you where the telescope is pointing. The better the finder, the easier it is to find things in the main telescope. The finder and telescope must be aligned with each other for proper use ( a simple operation).

Advice: The quality of the finder is important. A finder with 30mm lens is a minimum requirement. Some telescopes are sold with very small finders. Ask If you can upgrade the finder before you buy.

What is an equatorial or Alt-Az mounting?
A mounting has two axis of movement to locate and follow the object as the Earth rotates. If one of the axis point towards the Pole Star then the mount is equatorial. If one axis point to the zenith then the mounting is an Alt-Az.

Advice: Invest in a good solid mounting if you have a choice.

What is Universal Time (UT)?
UT is equivalent to Greenwich Mean Time (GMT). GMT is based on the Earth's rate of rotation, but UT is based on an atomic clock. The Earth's rotation is not constant and is slowing down due to tidal forces with the Moon, so the Earth rotation is not a particularly accurate clock (by today's standards). The speaking clock pips are UT because they are controlled by an atomic standard.

GMT and UT are in step with each other, but can differ by up to 1 second during a year.

Advice: Some telescopes use GPS in there set-up. An accuracy of 1 min or better is desirable for computer driven telescopes.

What is "collimation"?
The optical components of a reflecting telescope (Mirror / flat / eyepiece) can become misaligned during transportation. A small misalignment might not be noticeable. Incorrect adjustment of collimation screws can make things worse very quickly. So be careful !

Advice: Not advisable for a beginner unless you have previous experience of collimation. Either take the instrument back to the supplier for checking, or approach your local Astronomical Society for help.

Who can advise me on astronomy?
We suggest you visit your local astronomy group or society, or contact the Society of Popular Astronomy (SPA). Your nearest society may be Maidenhead AS. There are lots of groups in Southern England, and the SPA has a useful forum for beginners. Your local society is an excellent starting point.

What equipment do I need to start astronomy?
Optics: A pair of binoculars is an important accessory, and 8x40, 7x50 or 10x50 are typical. You don't need a telescope to start astronomy, but most people buy one to look at detail on the Moon, cloud belts and moons of Jupiter, the rings of Saturn or the phases of Venus.

Finding aids: A planisphere is highly recommended. There are home-made ones on the internet, but in the UK you can purchase the Philip's Planisphere and Guides in any good high street book shop.

Camera: If you have a camera which will expose for 10 seconds or more on a tripod, you can photograph the stars, aurora or the International Space Station. The Moon and planets (out to Saturn) can be recorded easily, and can make a nice panorama with foreground objects.

The Moon is bright enough to photograph through a telescope. To photograph planets and deep sky objects, a motor driven equatorial mount is needed. Its a good idea to read up on the subject (internet).

Computer: There are some excellent free or shareware planetarium programs that will show you many astronomical objects and the positions of the Moon and Planets. Stellarium is a good one to start with. There are many others available.

What telescope should I buy ?
First consider if you want a portable telescope to take on holiday like a wild-life spotting 'scope with a zoom eyepiece, or a telescope that gives a magnification of up to about 100 for looking at detail on Moon and planets. Maybe you are confident to buy a larger semi-portable instrument. Whatever your choice may be, you should attempt to use an astronomical instrument before you buy your first one.

Try before you buy
Astronomical societies often have a telescope for use by members. Its 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. If you can get to an astro-camp (there are several well known ones) 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 at Kensington Town Hall in February (London) is a good exhibition of UK and EU equipment manufactures.

Criteria for a telescope
The purpose of a telescope is to: 1) magnify the Moon and planets to see detail and, 2) to collect 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.

Dobsonian
A Dobsonian telescope fits these criteria well. "Dobos" come in all sizes from 6" aperture upwards. Sky Watcher, Orion Optics and Telescope House can supply Dobsonians in the UK. There are more equipment suppliers on our Links page. A Dobsonian is a reflecting telescope (using mirrors) on an alt-az mounting. They have many advantages for the amateur astronomer over a traditional refractor. When browsing the internet you will also find 60 and 80mm ED refractors which although they have less light grasp than a reflector, will be more portable and also highly suited to astro-photography if a motor driven equatorial mount is bought later as an up-grade.

Other telescope types
The Telescope House web site conveniently describes most of the common types available and some of the other factors effecting performance.

Can I photograph the stars?
Yes. A camera on a tripod, with a maximum exposure time of 10 seconds (or more) and an ISO setting of 400 or greater can record the brighter stars including planets, Iridium flares, ISS transits, and Aurora. Long exposure and high ISO settings are found in manual (M) mode of most digital cameras.

Advice: Use a cable (Bulb) release with the lens at maximum aperture (eg F2.8). Digital or film can be used, and with very wide angle lenses, exposures between 30s and 1 min on a tripod can be used in dark sky areas. Here are two examples [ Moon ] [ Leo ].

 

More specific help and links can be found on the beginners page.

 

Updated: 07 June 2009