Phases of the Moon

The Moon never changes shape and it never goes dark. Half of it is lit by the Sun at every single moment of every single day. What actually changes is how much of that lit half happens to be turned towards you.

New Moon 🌑

At new moon the Moon sits roughly between us and the Sun, so its lit face points away and the side we see is in shadow. It also rises and sets with the Sun, so a new moon is in the sky all day and completely lost in the glare.

Solar eclipse

Two or three times a year the line up is exact and the Moon's shadow actually touches Earth. By an astonishing coincidence the Sun is about four hundred times wider than the Moon and about four hundred times further away, so the two look the same size in our sky.

Waxing Crescent 🌒

A thin lit sliver appears low in the west just after sunset and grows a little more each evening. Waxing simply means growing. The bright bulge of the crescent always faces the Sun, so it points straight down at the spot where the Sun has just set.

First Quarter 🌓

One week in you see exactly half a disc. It is called first quarter not because a quarter is lit but because the Moon has finished one quarter of its journey around us. This is the best night for a telescope, because long shadows along the middle line make every crater stand out.

Waxing Gibbous 🌔

Gibbous means humped. More than half is lit now and the Moon rises in the middle of the afternoon, which makes it easy to spot in a bright blue sky. Most people simply never think to look up before dark.

Full Moon 🌕

Now Earth lies between the Sun and the Moon and the whole lit face is turned our way. A full moon rises exactly as the Sun sets and sets as the Sun rises. It is roughly ten times brighter than a half moon, not twice, because a half moon is full of shadows.

Lunar eclipse

When the alignment is exact, Earth's shadow falls across the Moon. It does not vanish, it turns a deep rusty red, because the only sunlight still reaching it has been bent through our atmosphere. You are watching every sunrise and sunset on Earth projected at once.

Supermoon

The Moon's orbit is an oval, so its distance from us swings by more than forty thousand kilometres over a month. A full moon at the near point looks about a seventh wider and roughly a third brighter than one at the far point, though almost nobody can tell by eye without a photograph to compare.

Waning Gibbous 🌖

Waning means shrinking, and now the lit part retreats from the opposite edge. Every day the Moon slides about thirteen degrees eastward against the background stars, so Earth has to turn that little bit further to bring it back into view. That is why moonrise falls about fifty minutes later each night.

Last Quarter 🌗

Half lit once more, but the other half this time, with three quarters of the orbit behind it. A last quarter moon climbs into the sky around midnight and is still hanging up there while you eat breakfast, pale against the morning blue.

Waning Crescent 🌘

A shrinking sliver in the east before dawn. The Moon actually completes one orbit in twenty seven and a third days, but Earth has travelled along its own orbit meanwhile, so the Moon needs two extra days to catch the Sun up again.

Earthshine

Look closely at a thin crescent and the dark part glows faintly. That is sunlight bounced off Earth's clouds and oceans onto the Moon, and astronomers call it the old moon in the new moon's arms. The whole loop takes twenty nine and a half days, which is where our word month comes from.