Winter Solstice 2013

The northern hemisphere winter solstice occurs on 21 December 2013, at 1711 GMT. At this point the Earth’s north pole will be tipped away from the Sun. As seen from Earth, the Sun will stop its slow daily decent south in our sky – over the past six months the Sun’s mid-day height above the horizon has been decreasing steadily – and once again turn north, getting higher in the sky at noon each day, until it gets to its highest point in midsummer 2013.

The actual day of the winter solstice – in this case 21 December 2013 – is commonly known as midwinter, the shortest day, and is the day when the Sun spends least time above the horizon. The further north of the equator you are, the more profound the effect. Indeed if you live within the arctic circle the Sun won’t actually rise today.

Winter Solstice 2012

The northern hemisphere winter solstice occurs on 21 December 2012, at 1112 GMT. At this point the Earth’s north pole will be tipped away from the Sun. As seen from Earth, the Sun will stop its slow daily decent south in our sky – over the past six months the Sun’s mid-day height above the horizon has been decreasing steadily – and once again turn north, getting higher in the sky at noon each day, until it gets to its highest point in midsummer 2013.

The actual day of the winter solstice – in this case 21 December 2012 – is commonly known as midwinter, the shortest day, and is the day when the Sun spends least time above the horizon. The further north of the equator you are, the more profound the effect. Indeed if you live within the arctic circle the Sun won’t actually rise today.

Winter Solstice 2011

The northern hemisphere winter solstice occurs on 22 December 2011, at 0530 GMT At this point the Earth’s north pole will be tipped away from the Sun. As seen from Earth, the Sun will stop its slow daily decent south in our sky – over the past six months the Sun’s mid-day height above the horizon has been decreasing steadily – and once again turn north, getting higher in the sky at noon each day, until it gets to its highest point in midsummer 2012.

The actual day of the winter solstice – in this case 22 December 2011 – is commonly known as midwinter, the shortest day, and is the day when the Sun spends least time above the horizon. The further north of the equator you are, the more profound the effect. Indeed if you live within the arctic circle the Sun won’t actually rise today.

I’m not that far north, but by most standards I’m pretty far north, in Orkney delivering a midwinter astronomy festival. Orkney sits between 58°41′and 59°24′ North, and on midwinters day the Sun rises around 0905 and sets around 1515, and only spends 6h10m above the horizon. The winter nights in Orkney are long and dark.

But the morning after midwinter, the days will be lengthening. For many cultures then, midwinter symbolised the rebirth of the year, and ancient peoples often built monuments to celebrate the returning of the light.

And people in neolithic Orkney built some of the most incredible midwinter monuments that still exist. I’ll be spending this afternoon inside the 4700 year old chambered cairn at Maeshowe, built so that the passageway – which one has to crawl through to get into the inner chamber – points directly towards sunset on the shortest day.

Maes Howe sections

Given clear skies, the last rays of midwinter sunlight stream into the burial chamber for a few moments before the sun sets.

Maeshowe midwinter sun, Charles Tait

The Orkney poet George Mackay Brown said of midwinter at Maeshowe:

The most exciting thing in Orkney, perhaps in Scotland, is going to happen this afternoon at sunset, in few other places even in Orkney can you see the wide hemisphere of sky in all its plenitude.

The winter sun just hangs over the ridge of the Coolags. Its setting will seal the shortest day of the year, the winter solstice. At this season the sun is a pale wick between two gulfs of darkness. Surely there could be no darker place in the be-wintered world than the interior of Maeshowe.

One of the light rays is caught in this stone web of death. Through the long corridor it has found its way; it splashes the far wall of the chamber. The illumination lasts a few minutes, then is quenched

Winter after winter I never cease to wonder at the way primitive man arranged, in hewn stone, such powerful symbolism.

Winter Solstice

The northern hemisphere winter solstice occurs today, 21 December 2010 at 2338 GMT.

But surely the winter solstice is just the shortest day. How can it “occur” at a specific instant?

That’s because we astronomers define the solstice as the instant when the Sun gets to its furthest south below the celestial equator. Or to put it another way, the instant when the north pole of the Earth is tipped directly away from the Sun.

And this happens at exactly 2338 GMT on 21 December 2010.

It’s important to remember though that while we are in the midst of a deep, cold winter, the southern hemisphere are celebrating their summer solstice, and their longest day.

Total Lunar Eclipse on the Winter Solstice

This Tuesday 21 December 2010 is the Winter Solstice, and in addition there will be a total lunar eclipse, occurring at sunrise in the UK.

Total Lunar Eclipse, image by Nick James

Total Lunar Eclipses occur when the Moon passes into the shadow of the Earth. That this does not happen every 29 days (the time it takes for the Moon to orbit the Earth) is due to the fact that the Moon’s plane of orbit is not the same as the Earth’s orbital plane around the Sun, and so the Moon passes above or below the cone of the Earth’s shadow most of the time. Every so often, however, these two planes align to create the conditions for a Lunar Eclipse.

When this happens, the Moon will begin to darken in the sky, eventually turning a dark red colour. Unlike a Solar Eclipse, where the Sun’s light is totally blocked out by the Moon, in a Lunar Eclipse the Moon is still visible.

Tuesday’s Lunar Eclipse will begin at 0528 GMT when the Moon enters the Penumbra, the outer part of the Earth’s shadow. This will begin a slight darkening of the Moon, the darkness extending across the Moon’s surface slowly, taking around an hour. At 0632 GMT the Moon will enter the central, darkest part of the Earth’s shadow, form which point it will darken appreciably until, at 0740 it will be in total eclipse, with the full face of the Moon darkened red. This will last until 0854 GMT, at which point the Moon will slowly begin to darken again.

At this point, however, the Moon will have set for some UK observers, or be very low in the sky, on the western horizon, as it is about to set. The time at which it finally sets depends on where you are. In London it sets at 0812 GMT, while in Glasgow (my home town) it sets at 0857 GMT, just minutes after total eclipse ends.

This means that observers in Scotland will have the best view, and the further north you are the more you’ll see.

This lunar eclipse also has the rare distinction of being one where you can see the eclipsed Moon and the Sun in the sky at the same time, as Sun rises around 11 or 12 minutes before the Moon sets, wherever you are in the UK.