Since December the Sun has been moving northwards and the days have been getting longer. Tomorrow morning (Friday 21st June) at 06:04am, UK Time (05:04 GMT), the Sun reaches its furthest point North. As seen from space, the Earth’s North Pole will be tilted at its maximum towards the Sun (23 and a half degrees). The Arctic regions will be bathed in perpetual sunlight (while the Antarctic and its Emperor penguins experience perpetual night). This marks the Summer Solstice, the longest day of the year (in the Northern Hemisphere). On this day the sun rises at its furthest north, reaches its highest altitude at noon (just after 13:00 as we put the clocks forward in March), and sets at its furthest north. The longest day will be 16 hours 38 minutes 20 seconds (in London) as compared to 7 hours 49 minutes in late December, more than twice as long. At Noon tomorrow (and today, let’s face it), the Sun will stand over 61 degrees above the horizon. That’s two thirds of the way up from the horizon to the zenith (“zenith” means the overhead point and is, incidentally, an Arabic word). The Sun’s high altitude plus the long days means that the Northern Hemisphere should be experiencing warm conditions. In late December the Sun’s midday altitude is only about 15 degrees, just a sixth of the way up and barely high enough to get above the trees. This low altitude combined with December’s short days give us the frigid conditions at that time of year. Let’s hope someone has informed the weather that it is almost Summer. At the beginning of June, local noon occurred at 12:58 but this has been moving forward throughout the month and June will end with midday occurring at 13:04. Remember the clocks went forward last March so midday is around 13:00. Midday was at exactly 13:00 for a few days around the 10th and this matchup of clock and sun only happens four times a year. When it happens, sundial time is identical to clock time. The moving forward of the time of midday has had the effect of shunting the daylight from the morning into the afternoon by a small amount. An interesting effect results from this movement. In June 2013 the longest day is on 21st (tomorrow). However the earliest sunrise (04:43) occurred a week or so earlier. Conversely, the latest sunset (21:22) occurs next week, a few days after the longest day. All that remains is for me to wish you all a HAPPY SOLSTICE.
Posted on: Thu, 20 Jun 2013 08:02:52 +0000
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