Eyepieces: Most of the smaller telescopes come with a couple of eyepieces. These will typically be a low power 25 (or 26)mm and higher powered 10 (or 9)mm. When beginning a session it is normal to use the 25mm to start with then, if the viewing conditions are good you switch to the higher magnification 10mm. You may also get 2x Barlow lens which you can insert in front of the eyepiece. This doubles the magnification of that eyepiece - and halves the field of view making objects more difficult to find. Used with the 25mm these will give you the equivalent of a 12.5mm eyepiece and a high magnification 5mm with the 10mm. Unfortunately the Barlows with cheaper scopes are often not that good.
Although you can get away with just these two eyepieces, it can be rather frustrating to find that the 25mm gives you too low a magnification whilst the 10mm is too high and merely makes everything fuzzy. A zoom eyepiece such as the Skywatcher 7 - 21mm at around £40 is a relatively cheap solution to this. This eyepiece has steps of 21, 15, 11, 9 and 7 and by simply turning the knob and a little refocussing and recentering you can find out the best power for the current conditions. The 8 - 24mm zoom, which costs a little more is reckoned to be much better because it has wider fields of view.
If you then become really hooked on astronomy you can then go out and buy more expensive, better quality single eyepieces. A good place to look for detailed advice and information on eyepieces is the Televue web site. However, it is important to remember that viewing conditions in the UK and indeed much of Europe will seldom be good enough to use high powered eyepieces. Far better to spend your money on good quality medium powered ones.
Red light Torch: Our eyes take time to adapt to the dark - the longer the better - and any bright light will destroy that adaptation. Red light has the least effect on that adaptation, so a red light torch is an important tool to enable you to see what you are doing. Sometimes you will get this as a freebie with your scope, but an ordinary torch covered with red cellophane will also work well. This Celestron red light torch costs around £11. They use 9v batteries like those from Varta which I have found to be better than Duracell.
Sky Guides: There are many books which will enable you to find your way round the sky. Patrick Moore's Guide to Stars and Planets is a good general purpose book, but another much praised book is 'Turn Left at Orion'. This is said to be very useful (or off-putting if you expect colour!) in that it also gives you an idea as to what you can actually expect to see through your scope, though I never found it particularly helpful.
Much better to use your computer with the free Stellarium program. Simply enter your latitude, longitude, time and date and see exactly what is visible in the sky from your back garden, even adjusting the view for light pollution. And there are many apps for your mobile phone like Sky Safari from as little as $3 - there are other free ones which you can use.
With Stellarium you can also enter your telescope details and 'view' an object using different eyepieces. However this takes no account of light pollution and isn't all that accurate when it comes to double stars as it scales these rather than leaving them as points of light. The other point to remember concerns the limiting magnitude of your scope. This is theoretical and in 'normal' light polluted skies the actual limit will probably be a couple of magnitudes lower - say 11 rather than 13 - so you won't see nearly as many stars as is shown in this and other programs.
Power Pack - for a GOTO scope: Batteries don't last long so the only sensible option is a portable rechargeable power pack - First Light Optics suggest using the Maplin 97W DC Fixed Voltage Bench Power Supply which costs about £45. A charge will normally last more than long enough for most viewing sessions, but if you are brave and stay up all night(!) and it is cold the charge may not last. And if you have a Catadioptric or a Refractor you will certainly need a
Dew Shield: Catadioptric telescopes - Schmidt-Cassegrain and Matsukov-Cassegrain, etc - are dew magnets and as the temperature drops so dew forms on the collector plates. Reflectors are usually ok, but dew will also form on any lens such as the finderscope and eyepieces. Dew shields can be bought for the catadioptrics, or you can make your own by buying black felt foam sheets and creating tunnels to place over the front of the telescope and finderscope. The dew shield should usually project at least twice the aperture beyond the end of the scope. Alternatively you can buy an electronic dew shield which wraps around the end of the scope and warms it sufficiently to keep the dew at bay.
Dew Shields can also be useful for refractors - if they don't already have one
and can be used with reflectors to keep out stray light.
Please note that all prices quoted are approximate, subject to change
and for guidance only
Skywatcher 7 - 21mm
Red Light Torch
Rechargeable Power Pack for GOTO Telescopes
Orion electronic dew zapper attached via velcro to a