That is why we start with your eyes. Knowing where things are is the part no telescope can give you.
1 · Your own eyes cost you nothing
With no equipment at all you can find:
the Moon, and the dark patches on it that people call seas;
the four bright planets —
Venus, Jupiter,
Mars and Saturn
— which do not twinkle the way stars do;
a meteor shower, on the right night;
and from a really dark garden, the Milky Way — our own
galaxy, seen from inside it.
Go outside at the same time three evenings running and watch the Moon move along
against the stars.
2 · Binoculars the cheapest real step
The next step is probably in a drawer in your house already. Any ordinary pair
works.
Jupiter’s moons. Four little points of light in a line
beside the planet. Look again the next night and they have moved. This is the
observation that changed everybody’s mind about where we live, and you can
repeat it from your own doorstep in a week.
The Andromeda Galaxy. A faint smudge, and it stays a
faint smudge. From a dark place your eyes alone can just find it, and then it is
about the furthest thing a human eye can reach: that light set
off before there were any people like us to see it.
For the grown-up doing the buying. If you are choosing a pair,
10×50 (ten times magnification, lenses 50 mm across) is the classic size and 8×42 is
lighter and easier for small hands to hold still. No tripod is needed — but
leaning on a fence, or lying on a blanket, lets a child see noticeably more,
because the wobble is what hides the faint things.
3 · One telescope, if it sticks
If the binoculars keep coming out of the drawer, then it is worth buying a
telescope. One. And we would pick the same one nearly every time: a
150 mm Dobsonian.
A Dobsonian is a mirror in a tube — the 150 mm is how wide the mirror is — sitting in a box that turns. You push the tube
where you want it and it stays there.
Why that one, and not the kind on three legs
The other kind sits high up on a tripod with the tube out to one side and a heavy
weight on the other end, to balance it. That kind can do something clever: line one
of its turning parts up with the Earth’s own spin, and a small motor on it
will then follow a star across the sky on its own. For long photographs of faint things it is
the usual way.
But for a child standing in the cold it has one problem that does not go away.
It wobbles. Touch the focuser (the knob that makes the view sharp) and the whole thing rings like a
bell.
The telescope magnifies a hundred times — so it magnifies the wobble a
hundred times too. A tap that moves the tube half a millimetre sets the planet
jumping across the view.
It settles down after a few seconds. A few seconds after every single
touch is what makes somebody give up and go indoors.
A Dobsonian does not fix that problem. It never has it. The tube
sits low, balanced on its own middle, in a box on the ground. Nothing rings and
nothing swings. Nudge it, and it stops when you stop.
And you can actually use it yourself
It points the way a person points. Push it up and it looks higher; push it left and it looks further left.
The other kind turns on two tilted circles that do not match the sky you are
looking at, so “a bit higher, please” means working out which knob does
that.
It does not fall over. A wide box on the ground is hard to
knock down, and it is low — so if the worst happens it is a fright rather
than a broken telescope.
It is ready in a minute. Carry it out, put it down, look. No
setting up in the dark while everybody gets colder.
At 150 mm it shows Saturn’s rings as rings, the stripes on Jupiter,
craters standing up in hard shadow, and the brightest nebulae as real things rather
than rumours. It is the smallest telescope that stops being a toy, and still small
enough to take outside on a whim.
Later, and not on the same day
None of these are needed to start, and none should be bought with the telescope.
Roughly in the order they earn their keep:
A filter for the Sun
A proper one fits over the front of the telescope and turns it into a Sun
instrument: sunspots, and the whole disc slowly turning from one week to the next.
Never with unprotected eyes
Only through a filter made for looking at the Sun. Check it for damage every single time. Safer still, and no filter needed: make a small hole in a piece of card, hold it up in the sunlight, and look at the bright little disc it throws onto a second card. That disc is the Sun. Look at the card, never at the sky.
The full rules
The Sun can burn the back of your eye for good. It does not hurt while it happens, so there is no warning to react to. If a child is looking, a grown-up must be in charge of this.
Only ever use a filter made for looking at the Sun. Eclipse glasses marked ISO 12312-2, or a proper solar filter that fits over the front of a telescope or binoculars.
Eclipse glasses are for your bare eyes only. Never look through binoculars or a telescope while wearing them. The gathered light burns straight through.
Check the filter every single time before you use it. Hold it up to a bright lamp and look closely at the filter itself. If you can see any scratch, pinhole, crease, bubble or peeling edge, or if the lamp looks clear and bright through it, throw it away. A damaged filter is worse than no filter at all. It feels comfortable while it lets the harmful light through.
Never use sunglasses, smoked glass, exposed camera film, a CD, or several pairs of sunglasses stacked up. All of them let through far too much of the Sun’s light, and some of it is light you cannot see.
Never put a filter on the eyepiece end of a telescope, the end you look into. The telescope focuses the Sun’s heat straight onto it. It can crack with no warning, while your eye is already there.
The little finder scope on the side needs capping too. It is a burning glass pointed at the same Sun.
Safest of all, and rather good fun: do not look at the Sun at all. Poke a small hole in a piece of card. Hold it up in the sunshine. It throws a little image of the Sun onto a second card in the shade. The gaps between leaves on a tree do the same thing. During an eclipse the ground under a tree is covered in dozens of tiny crescents.
A Barlow lens
One small piece of glass that doubles the magnification of every eyepiece you
already own (the eyepiece is the small lens you look into). It is the cheapest useful upgrade there is. Good on the Moon and the
planets; less good on faint things, which want light rather than size.
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