Summer Solstice?

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  • Gathering at Stonehenge to celebrate the Summer Solstice. Photo: Lewis Whyld (PA Wire)

    Diagram to show why noctilucent clouds are best seen at twilight. Photo: NASA, 2013

    Noctilucent clouds in Billund, Denmark. Photo: NASA, 2011

    Aurora from ISS orbit. Photo: NASA, 2011

  • Summer Solstice?
    21.06.2013 15:11

     

    Whilst the clouds are keen to hide it from us, today is in fact the summer solstice. In the northern hemisphere, today is the day where our planet is most inclined toward the sun, meaning it is at maximum elevation overhead, giving us the greatest possible intensity and length of sunshine. 

    An estimated 21,000 people including Pagans and Druids gathered around Stonehenge last night and this morning to watch the sun rise over our wonder of the world. Unfortunately, Wiltshire was covered by mist and low lying cloud this morning, meaning not a single soul of those gathered managed to visually document this annual celestial event.

    Here in the UK, we will receive 16 hours, 38minutes and 30 seconds of daylight today, which sounds a lot but every location north of the Arctic Circle will receive 24 hours of sunlight today, creating a day without a night.

    Noctilucent clouds are the highest clouds found in Earth’s atmosphere. These mesospheric clouds (clouds which reside in the mesosphere, 85km above Earth’s surface) are composed of tiny crystals of ice which form around a nucleus of dust. The source of this dust is debated and it is likely to be from space shuttles, volcanoes and some recent research suggests dust may also come from meteorites.  Noctilucent clouds are most likely to be spotted between 50-70° latitude in the summer. As the mesospheric atmosphere is so thin, there is a very limited amount of moisture meaning this ice can only form in temperatures of -120°C! As the mesosphere is the coldest in the summer (counter intuitively!) and we’re now in our British summer season, we should start to get sightings of these nocturnal shining clouds.

    Our previous solstice, the winter solstice, fell on the 21st December 2012, which was the shortest day of the year. So it follows that our length of daylight has increased since then and, after today, will begin to decrease again. 

    The solstices and equinoxes tend to be surrounded with folklore and rituals. The summer solstice is often celebrated by Pagans to mark the beginning of the summer season. The winter solstice 2012 marked the end of the 13th Baktun for the Mayan population (i.e the beginning of the next Mayan calendrical cycle), which may appear strange, but the Mayan Civilisation lived in central and South America; therefore, our winter solstice is their summer solstice.

    Because of our 23.4° tilt, when one hemisphere enjoys a summer season the other experiences a winter season. In the same effect, one hemispheres summer solstice is the other’s winter solstice, meaning today is the darkest day of the year for the southern hemisphere.

    It’s not all doom and gloom during the winter solstice. Darkness is fundamental to be able to see the beautiful optical phenomenon of the Aurora, meaning that today is the day that the Aurora Australis is visible for longest in the southern hemisphere.

    So has our summer solstice been worth celebrating? Whilst it’s been a warm, dry day for most, convective clouds have littered the sky producing the odd scattered shower over the UK. We have not enjoyed the most meteorologically pleasant day of the year and the bad news is that it certainly isn’t on its way this weekend either. Better luck next summer solstice!

    By: Rosie Jones