At 12:38 p.m. EDT on Sunday, June 21st, (which is also Fathers’ Day), the Sun will reach that point where it will appear to shine farthest to the north of the equator, over the Tropic of Cancer, thus marking the moment of the Summer Solstice. Since last December 21st, the altitude of the midday Sun has been getting progressively higher as its direct rays have been gradually migrating to the north.
The Sun’s altitude above the horizon at noontime is 47 degrees higher now, compared to six months ago. Your clenched fist held at arm’s length measures roughly 10-degrees, so the Sun at midday is now nearly “five fists” higher in the southern sky compared to Dec. 21st.
As “armistice” is defined as a staying of the action of arms, “solstice” is a staying of the Sun’s apparent motion over the latitudes of the Earth. At the summer solstice, the Sun stops its northward motion and begins heading south. At the winter solstice, it turns north. Technically, at one minute past the moment of the Summer Solstice, at 12:39 p.m. EDT, the Sun has already turned around and started its southward migration. It will cross the equator at the autumnal equinox, passing into the Southern Hemisphere on September 23rd, at 4:21 a.m. EDT.
From temperate latitudes, the Sun can never appear directly overhead. From our Almanac headquarters in Lewiston, Maine, for instance, on June 21st at 12:42 p.m. EDT, as the Sun is crossing the meridian, it will attain its highest point in the sky for this entire year, standing 70 degrees above the southern horizon. Since the Sun will appear to describe such a high arc across the sky, the duration of daylight is now at its most extreme, lasting 15 hours and 29 minutes for Lewiston. Daylight lasts longer are more northerly latitudes; less at more southerly latitudes. North of the Arctic Circle, for instance, the Sun now remains above the horizon 24/7 (providing the so-called “midnight Sun” effect). On the other hand, at the equator, days and nights are equal, lasting 12 hours (a circumstance there that lasts all year long).
However, contrary to popular belief, the earliest sunrise and latest sunset do not coincide with the Summer Solstice. In fact, at mid-northern latitudes, the earliest sunrise actually occurred back on June 14th, while the latest sunset is not due until June 27th.
During the year, varying amounts of sunlight strike different regions of the planet and as a consequence both the angle of the Sun’s path across the sky and the number of hours it is above the horizon change significantly.
If insolation alone – the total energy received from the Sun at a given moment – governed the temperature, we should now be experiencing the year’s hottest weather. But the atmosphere in temperate regions continues to receive more heat than it gives up to space, a situation that lasts several weeks or more. A reverse process occurs after the Winter Solstice in late December. Thus, there is a temperature lag of roughly about a month: thus our hottest weather usually comes in late July and our coldest in late January.
So enjoy your time with Dad for Father’s Day; after the 21st, the days will start getting shorter!