The
Vernal Equinox - Spring has sprung
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hope that a mild spring will bring a hot summer! |
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At
1916 GMT on Wednesday 20th, the Vernal Equinox will officially mark
the beginning of spring.
It is the time at which the sun crosses the celestial equator. |
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Wednesday
20th marks a significant date in the astronomical calendar.
At 1916 GMT the Vernal Equinox will officially mark the beginning
of spring. March is a month which always seems to cause some confusion
amongst weather watchers.
The Met Office, along with many other organisations, is categorical
that 1st March marks the beginning of spring.
But this is always a case for dispute until the equinox arrives on,
or around, the 20th. (The equinox can occur as early as the 19th and
as late as the 22nd.)
The significance of the Vernal Equinox is that it is the point at
which the sun crosses the celestial equator.
On that day the sun will rise directly in the east and set directly
in the west. Everywhere on the Earth will experience 12 hours of daylight
and 12 hours of darkness.
For the first time in six months, the sun will rise at the North Pole.
The occurrence of the Vernal Equinox and its counterpoint the Spring
Equinox (which occurs around March 21st) is a consequence of the Earth’s
movement around the sun.
The axis of the Earth’s orbit around the sun is inclined at an angle
of about 23.5. So at the Winter Solstice the sun is 23.5 degrees south
over the Tropic of Capricorn.
The Vernal Equinox sees the sun crossing the celestial equator, bringing
daylight to the North Pole and six months of darkness to the South
Pole.
The Summer Solstice marks the sun’s northernmost foray - the Tropic
of Cancer. As the sun then heads back south towards the equator the
days begin to shorten, until the Autumnal Equinox marks an evening
out around the globe of daylight and darkness.
It is sometime claimed that this event has an effect on our weather.
Mariners often talk of ‘equinoctial gales’. But the evidence for this
is debatable at best.
This year it looks as though the lengthening days will coincide with
a spell of milder weather. So for once, meteorologists, horticulturalists
and astronomers can all agree that spring is here to stay.
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