The Autumn Equinox

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  • The sign of things to come - the last Autumn leaves cling to some trees, as seen in York last November. Credit: John Giles/PA.

    A depiction of how the Earth moves around the Sun, creating our seasons. Credit: NOAA.

    A watery sunrise over Stonehenge, where some will be gathering to celebrate the Autumn Equinox this year. Credit: Chris Young/PA.

  • The Autumn Equinox
    21.09.2013 14:24

     

    Although the start of this month heralded the beginning of autumn in a meteorological sense, many people traditionally await the Autumn Equinox to acknowledge the final sweeping away of summer. This year the Equinox falls on Sunday 22nd September (at 21.44 BST in fact), marking the point where day and night are around equal in length.

    So what exactly is an Equinox?

    Earth does not sit fully upright as it orbits the sun, but is instead tilted on its axis (by 23.5 degrees to be precise). On its annual march around the sun, the Earth’s tilt means the Northern Hemisphere is inclined toward the sun for half of the year, and away for the other half. During the months in which the Northern Hemisphere tilts sunwards it receives more solar light and heat than its southern counterpart. Summer Solstice marks the height of this period and we experience our longest day, whilst the winter Solstice gives us our longest night. The halfway point between the two is therefore known as the Equinox, which is derived from the Latin words aequus (equal) and nox (night). The North Pole represents the point in our hemisphere of maximum inclination (and declination) to the sun, resulting in the sun failing to struggle above the horizon for almost six months of the year. Luckily for us in the UK, we do not experience such a severe contrast as we track through the seasons, although many of us do bemoan the implication of the September Equinox ushering in the colder, darker nights.

    What does the Equinox mean to us?

    It would be hard to miss the increasingly tardy rise of the sun each morning, and the disappointing shift of sunset ever earlier in the day. Perhaps less noticeable is the ever more shallow arc of the sun across the sky, meaning its rays carry less solar and heat energy compared to summer. Whilst many birds head south for warmer climes, most of us must stay put in anticipation of what weakened sunlight and longer nights will bring from here on in. Although many of us (including a few in the MeteoGroup UK office) are not too keen on what the Equinox means in terms of impending winter weather, others find it a cause for celebration. Wicca and Paganism believe the Autumn Equinox (or Mabon) is a time for giving thanks; others still see it as a poetic and romantic time of changing colours of leaves, misty mornings and crisp nights; or more practically as a time of harvest.

    This weekend…

    So will the weather dish up some of the autumnal weather we might expect with the arrival of the Equinox this weekend? Well, much of the UK will wake up to rather misty and foggy conditions on Sunday morning, although without the nip in the air that might be expected. Mist, fog and low cloud will retreat to western hills and coasts, allowing for some rather warm sunny spells to develop elsewhere. Unfortunately, north-west Scotland will miss out on these improving prospects – expect cloudy, breezy and damp conditions here for much of the day.

    …and further ahead?

    Largely dry conditions, above average temperatures and foggy mornings are set to last for the next few days, although more unsettled weather may well arrive later in the week. In other words, broadly the uncertain, changeable conditions well within our expectations for the astronomical start of autumn.

    By: Laura Caldwell