What is the spring equinox?

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  • Diagram to show positioning of the earth during the equinoxes and solstices (TimeandDate.com, 2015)

    Stonehenge lit up at night in November 2014 (Photo: Andrew Matthews, PA Wire).

    People gathering at Stonehenge to celebrate the Winter solstice in December 2014 (Photo: Ben Birchall, PA Wire).

    Pyramid of the Sun in Teotihuacan (Garyline 2015)

  • What is the spring equinox?
    21.03.2015 12:42

     

    For meteorologists, the start of spring is the 1st March, as mentioned in our previous weather story; First signs of spring. However, last night was the start of the astronomical spring! 

    Last night, at 2245 (GMT) on Friday 20th March 2015, the spring equinox occurred which marks the start of the astronomical spring. The equinox occurs when the day and night are nearly exactly the same length, ~12 hours, around the world and it occurs twice a year, once in March and once in September. The reason the day and night are equal lengths is because it marks the moment the Sun crosses the celestial equator; the imaginary line above the Earth’s equator that reaches into the sky. The Sun crosses the celestial equator at this time because for that brief moment the Earth’s axis is perpendicular to the Sun’s rays and the Earth’s axis is neither tilted in the direction of or away from the Sun. In the southern hemisphere, last night marked the autumnal equinox with them entering autumn. 

    In addition to the equinox we also have solstices, which occur in June and December and these mark the longest/shortest day of the year as well as the mid-point of summer and winter. In the northern hemisphere, the June solstice marks the longest day of the year and the December solstice, the shortest day of the year. The solstices also mark when the Arctic Circle and Antarctic Circle have daylight for over 24 hours or darkness for over 24 hours.

    For those that follow the astronomical calendar or Mayan calendar, there are often celebrations when the equinoxes and solstices occur. In the UK these celebrations are often held at Stonehenge as shown in the photos, where people dance and party. However, in the past there have been far more unusual celebrations, such as in Chichen Itza, Mexico where the Mayan’s used to perform a sacrificial ritual to mark the equinoxes at the “The snake of sunlight” pyramid. Today, many people visit the “Pyramid of the Sun” in Teotihuacán instead to celebrate the equinox, but instead of a sacrificial ritual, children dressed as animals and flowers walk down the stairs.

    The next equinox will be at 0820 (GMT) on Wednesday 23rd September 2015, and the next solstice will be at 1638 on Sunday 21st June 2015 (Time and Date, 2015).

    By: Sally Webb