Polar bears finally see the light
Post categories: weather
| 15:35 UK time, Tuesday, 20 March 2012
Today is the spring equinox when the sun is directly overhead the equator. Day and night are almost the same length, twelve hours all over the world and some people take today as the "official" start of spring.
At the North Pole, the polar bears are celebrating the first appearance of the sun in six months but at the South Pole the penguins are preparing for six months of darkness.
Apparently today is the earliest start to spring since 1896 but if it wasn't a leap year, spring would start on 21 March.
The word "equinox" comes from the Latin words aequus (equal) and nox (night). It means equal day and night but in reality, the day is slightly longer than the night at an equinox.
Sunrise over Holywell by Dilwyn Lloyd.
In Wales, day and night were almost equal on 17 March before the spring equinox so why wasn't St. Patrick's Day the equinox? Well, it all depends on the precise moment when the centre of the sun crosses the equator.
Sunrise and sunset occur when the top of the sun, not the centre, is on the horizon. That's why there are a few extra minutes of daylight on the equinox.
The earth's atmosphere also refracts, or bends, light from the sun. So, the top of the sun appears to be above the horizon when it is actually below it.
The best of the sunshine today has been in parts of the north and east with temperatures in Flintshire rising as high as 15 Celsius.
Last month was drier than normal in Wales with only half the average rainfall, 57.8mm and we would normally expect 114 mm in February.
So far this month has been dry in Wales and up until the 14 March, only 20.8mm, (17% of the monthly average rainfall) has fallen.
Looking ahead, there may be some rain and showers later on Thursday, overnight into Friday but apart from that, the outlook for this week and next is dry with high pressure over us.
Cloud amounts and sunshine will vary from day to day as will temperatures - rising well above average during the day, but at night it will turn chilly with a risk of some ground frost, low cloud, plus a few mist and fog patches as well.
Derek
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