SOURCES: BBC Science Focus Magazine & Space.com
For our friends, family and neighbours in the Northern Hemisphere, Summer officially began today, Tuesday 21 June 2022 at 5:14 am EDT (0914 GMT), marking the longest day of the year.
According to Space.com, during the June solstice (or summer solstice), the sun reaches its highest and northernmost points in the sky—specifically, the sun reached a point directly overhead of the Tropic of Cancer (at latitude 23.5 degrees north of the Equator). It is expected to remain at almost the same declination for roughly two weeks.
Chris Vaughan, an amateur astronomer with SkySafari Software who oversees Space.com's Night Sky calendar, notes that today’s solstice will deliver the maximum daylight hours of the year for the Northern Hemisphere and minimum daylight hours of the year in the Southern Hemisphere.
BBC Science Focus Magazine points out that there are two solstices every year, one in June and one in December. That is, the solstices (and the equinoxes) are the result of Earth’s tilt and its orbit around the Sun.
“The Earth’s axis of rotation is tilted by around 23.4 degrees relative to its orbit around the Sun. This means that during the summer Solstice, the northern hemisphere is at its maximum tilt towards the Sun, resulting in the longer daylight hours. Similarly, during the winter solstice, the northern hemisphere is tilted furthest away from the Sun,” explains BBC Science Focus Magazine.
Position of Earth in relation to the Sun during the June solstice. (Image © timeanddate.com)
“To put it simply, when one of the poles is tilted more towards the Sun, that hemisphere receives more sunlight than the other hemisphere, giving us summer. If the Earth were not tilted, the Sun would remain directly above the Earth’s equator for the entire year. This means we wouldn’t have seasons as we know them, although we may have ‘climate zones’,” the BBC article points out.
While today is the longest day for the Northern Hemisphere countries, it is by no means the hottest, which typically occurs during July or August, and is yet to be recorded for 2022. This is because of what is called a ‘seasonal temperature lag’.
“It takes a while for the maximum heating effect on air temperatures to occur,” BBC Science Focus Magazine observes. “As the oceans and land masses release the heat absorbed from the longer days back into the atmosphere, this will typically lead to an increase in temperatures later in July and August.”
The word ‘solstice’ itself is derived from two Latin words—‘sol’, meaning ‘sun’; and ‘sistere’, meaning ‘to stand still’. The Sun reverses its apparent annual north-south motion at both at the June solstice (longest day) and the December solstice (shortest day).
The dates of the summer solstice tend to hover around either the 20th or 21st or 22nd of the month of June, because it depends on when the Sun reaches its most northerly point from the celestial equator.
“This is because the Earth takes a little more than 365 days to complete a single orbit around the Sun,” BBC Science Focus Magazine notes. “Specifically, it takes 365.25 days for us to orbit around our star (this is also known as one ‘tropical year’). In the Gregorian calendar, they accounted for this by adding one extra day every four years, and this is why we have leap years.”
And with regard to a mystical connection between the solstices and the famous Stonehenge on Salisbury Plain in Wiltshire, England?
Sunset at Stonehenge. Image by Howard Walsh from Pixabay.
There may be a reason why people continue to celebrate the solstice there, annually. The stones themselves have been the centre of ritual celebration for millennia but there is debate as to whether they originally were built for a specific solstice or both.
BBC Science Focus Magazine notes that the standing stones are oriented to mark the position of the rising Sun at the solstices, and thousands of people flock to the Neolithic monument in honour of the occasion.
The most famous stone is the Heel Stone, which might have a direct connection to the summer solstice observance.
“The different stones at Stonehenge have been designated different names, and beyond the main circle is a stone called the Heel Stone. It lies a little over 78m (256 feet) to the north-east of the main circle and marks the point of the rising Sun on the summer solstice, as seen from the centre of the circle. It’s likely that it once had a partner, and together they would have framed the sunrise, however, that stone has been lost to history,” BBC Science Focus Magazine reports.
Incidentally, our home world Earth is not the only planet that experiences solstices. While every planet in the Solar System has seasons, they are not the same as those experienced here on Earth, but the principle remains that the summer solstice occurs when the planet’s north pole tilts towards the Sun, and the winter solstice happens when the south pole tilts towards the Sun.
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Article content adapted from “Summer solstice 2022: Everything you need to know”, by Holly Spanner, Staff Writer, BBC Science Focus; and “Summer solstice 2022 marks the longest day in the Northern Hemisphere”, by Daisy Dobrijevic, Reference Writer, Space.com.
