First look
The idea, in plain words
Everything on this site began with someone going outside and looking up. You can do the same tonight, and you need nothing but your eyes. The first thing to give them is time. Step out of a lit room and you see a handful of stars. Wait a quarter of an hour and there are many more. After about thirty minutes your eyes are as sharp as they will get. One glance at a phone screen undoes it. If you need a light, use a red one, which does far less harm.
The second thing is darkness. Street lamps and buildings throw light up into the air, and the glow drowns the fainter stars. This picture from space shows how much of it there is. From the middle of a big city only the Moon, the planets and the brightest stars get through. Even a short trip out of town helps, and so does a night with no Moon.
Under a properly dark sky you will see something most people in towns never do: a pale, ragged band of light from one horizon to the other. That is the Milky Way, our own galaxy seen from the inside. The photograph here shows the whole of it. By eye it has no colour, only a soft grey glow.
Start with the easy things. The Moon is best when it is not full, because the shadows along its edge of night pick out the craters. A bright light that does not twinkle is a planet: Venus, Jupiter, Mars and Saturn are all easy. From Britain the Plough is up on every clear night. The Pleiades are a tight little cluster in which most people can count six or seven stars. On a dark autumn night a faint smudge in Andromeda is another galaxy, two and a half million light years away.
When you want more, try binoculars before a telescope. They are easy to point, and they turn the Milky Way into clouds of separate stars. And before you go out, look at the sky map on this site. It shows what is over your own roof tonight.
Go deeper
That was the idea. The same subject is written again below for readers who want more, each on a page of its own.
Words used here
- Constellation
- One of the 88 named areas into which the whole sky is officially divided.
- Apparent magnitude
- How bright a star or planet looks from the Earth, on a scale where smaller numbers mean brighter.
- Milky Way
- The galaxy we live in. From inside it shows as a pale band of light across a dark sky.
- Star cluster
- A group of stars that formed from the same cloud and are held together by gravity.
- Planet
- A body that orbits the Sun, is massive enough to have pulled itself round, and has cleared other bodies from around its orbit.
- Meteor shower
- A night or more with many meteors, all seeming to come from one part of the sky, as the Earth passes through dust left along a comet's orbit.
Where this comes from
- NASA Night Sky Network, Stargazing for beginners
- Royal Museums Greenwich, Astronomy without a telescope
- Sky & Telescope, Why we can see in the dark
- ESO, The Milky Way panorama
The words are written for this site. The pictures are drawn by the page from the figures in the lesson, and each one says underneath what it is based on.