Buying a first telescope is where many budding astronomers stall, because the market is full of impressive-sounding numbers and the most important one is rarely on the box in large print. That number is aperture, the diameter of the lens or mirror that gathers light, and it matters more than magnification, more than the number of eyepieces included, and more than any electronic gadget. A telescope is, above all, a light bucket, and a bigger bucket shows fainter, more detailed objects, provided you can carry it and set it up without dreading the effort.

Beginners are often sold on magnification claims of five hundred times or more, but such powers are mostly useless: the atmosphere blurs fine detail long before that, and a small telescope at extreme magnification shows a dim, shaky smudge. Useful magnification is roughly twice the aperture in millimetres under excellent conditions, and most enjoyable observing happens far below that, at low and medium powers that give bright, steady views. A modest telescope used at sensible powers will show the Moon's craters, Jupiter's cloud bands, Saturn's rings, and dozens of star clusters beautifully.

Aperture also determines what you can see beyond the planets. A small sixty-millimetre refractor shows the brightest clusters and nebulae as faint patches, while a one-hundred-and-fifty-millimetre reflector begins to resolve individual stars in clusters and reveal structure in brighter galaxies. The jump from one to the other is the difference between glimpsing and exploring, which is why experienced observers advise buying the largest aperture you will genuinely carry outside regularly, not the largest you can afford.

The mount matters as much as the optics, because a wobbly mount turns every observation into a struggle and a complicated mount discourages use altogether. For most beginners, a simple Dobsonian mount, a sturdy box that rocks up and down and swivels side to side, is the easiest path: it is stable, intuitive, and puts most of your money into the mirror rather than into gears. Equatorial mounts, which track the sky's rotation, are powerful for photography but fiddly to set up, and a beginner who spends the evening aligning a mount instead of observing will soon stop observing.

Go-to computerised mounts, which find objects automatically, sound tempting, but they need alignment, batteries, and patience, and they can leave a beginner unable to find anything when the electronics fail. Learn the sky first with binoculars and a star chart, then decide whether automation will help or hinder you. Whatever you choose, test the mount's stability if you can: tap the tube gently and count how long the image takes to settle, because a mount that vibrates for seconds after every touch will frustrate you on every target.

Set a budget that includes accessories, not just the telescope: at least one low-power eyepiece for wide views, one medium-power eyepiece, and a red torch, with a Moon filter as a useful extra. Avoid department-store telescopes with tiny apertures, shaky tripods, and absurd magnification claims; buy from an astronomy retailer, second-hand from a local club, or a reputable brand recommended by experienced observers. Check the telescope's weight and packed size against your storage and your car, and be honest about how far you will carry it in the dark.

Finally, join a local astronomy club or attend a public observing night before you buy, because looking through other people's telescopes for an evening teaches you more than weeks of catalogue reading. You will discover which views excite you, which mounts feel natural, and which size you are happy to lift. The best first telescope is not the most powerful one, it is the one that gets used on clear nights, month after month, until you know exactly what you want next.