Newgrange and the winter solstice

Newgrange and the Winter Solstice These are the darkest days. The midday sun is at its lowest position in the sky and the nights are at their longest, while the hours of daylight are at a minimum. To the people who lived in the Boyne valley five millennia ago, it was the end of their year. But they built a most remarkable structure to mark to beginning of each New Year; the national monument at Newgrange, classified as a UNESCO heritage site.

This year (2016), the December solstice falls on December 21st. Here in the northern hemisphere, we have the winter solstice, but of course it is the summer solstice in the southern hemisphere. The word ‘solstice’ means ‘sun stands still’ because, on this date, the sun appears to literally stop in its tracks. It appears to be at its most southerly position relative to us, and it seems to pause, before beginning its journey back north again. In reality, of course the sun does not actually move towards the south during our winter; it is the tilt of the earth’s axis that creates this illusion. The axis, around which our planet rotates, is tilted at an angle of 23.5 degrees to the vertical. As a result, during the earth’s annual orbit, the sun’s rays reach us at different angles, giving rise to the four seasons.

At the December solstice, the sun is directly over the Tropic of Capricorn and all places within the Antarctic Circle have 24 hours of daylight. At the same time, in our northern latitudes, since the sun is at its lowest in the sky, we have the shortest day of the year and the sun does not rise at all within the Arctic Circle for 24 hours. The night of December 21st to 22nd is the longest night of the year and after that date, the nights will become shorter and the days will become longer, thought we will not really notice the stretch in the evenings until about the beginning of February.

The National monument at Newgrange is an amazing feat of science and engineering, dating from prehistoric time, during the new stone (Neolithic) age.

The people who built it had an expert knowledge of Astronomy and were also capable of carrying out very precise measurement. Archaeologists estimate it to have been built sometime around 3,000 B.C., making it 500 years older than the great pyramid at Giza in Egypt and 1,000 years older than Stonehenge. Experts differ as to the exact purpose of the construction at Newgrange. It is classified as a passage tomb, but it is no ordinary burial place. Like other passage tombs, it consists of a narrow passage, leading to a wide inner chamber, where the remains of the dead were laid. What is so very special about Newgrange, is what happens every year at the winter solstice. The passage is oriented towards the south-east and above the entrance there is an opening, known as a ‘roof box’. As the sun rises above the eastern horizon at the winter solstice, its rays enter the orifice and a narrow beam of light illuminates the passage, eventually reaching the rear of the chamber, so that the whole interior is filled with light. It is a dramatic spectacle for those fortunate enough to witness it. The event lasts for about 17 minutes, beginning at about nine o’clock in the morning and it can be observed (weather conditions permitting) not only on the day of the solstice itself, but for a few days on either side of it, from December 19th to 23rd.

The actual date of the solstice varies from year to year, but it usually falls on December 21st or 22nd. It was on the 22nd last year (2015). The December solstice also fell on December 22nd in 2011 and it will do so again in 2019 . It can be as

late as December 23rd, but this is very rare. It happened in 1903 and will not occur again until 2303. The solstice can be as early as December 20 th, but this is also very rare; the next one is not due until 2080. The reason for the variation in the dates is mainly due to the Gregorian calendar system, which is in use in most countries in the western world. As we know, this is based on a year of 365 days, with a leap year every four years. However, it takes the earth 365.24 days to return to the same point in its orbit around the sun, each year. (It doesn’t take an extra day to make the journey in leap year!) So this is the principal reason for the variation in the dates of the solstices and equinoxes. There is also a slight precession, or ‘wobble’ in the earth’s axis, which affects the dates to a lesser extent. Apart from this, the earth’s orbital speed is not uniform, because its path is not a perfect circle, but is somewhat elliptical. The earth is actually slightly closer to the sun during our winter (but remember it is summer at the same time down south) so it travels slightly faster than it does when it is farther away from the sun. It may be of some comfort to know that we have slightly shorter winters in the northern hemisphere because of this!

Nowadays, the first light of dawn enters the Newgrange passage about four minutes after sunrise. However, astronomers have worked out that when the monument was built, about 5,000 years ago, the light would have entered exactly at sunrise. The difference is due to the precession of the earth’s axis. It is a testament to the scientific knowledge and engineering skills of our ancestors of long ago that this amazing sight can still be observed today. Newgrange is part of our archaeological and cultural heritage; it is also part of our scientific heritage and one of which we can be proud.