Summer will officially arrive in the Northern Hemisphere on Thursday (June 20) at 4:51 PM EDT (2051 GMT) – the June solstice.
At that moment, the sun will reach the point where it is farthest north of the celestial equator. To be more precise, when the solstice occurs, the sun will appear to be shining directly overhead, at a point on the Tropic of Cancer (23.5 degrees north latitude) in the eastern Pacific Ocean, about 1,100 miles southwest of Los Angeles. Angeles.
From mid-northern latitudes we can never see the sun directly overhead, but (as an example) as seen from Boston at 12:46 a.m. EDT on the day of the solstice, the sun will be its highest point in the sky this entire year reaches. standing 71 degrees above the southern horizon. To measure how high that is, your clenched fist at arm’s length measures about 10 degrees, so from the city known locally as ‘The Hub’ it looks like the sun is climbing more than seven fists above the southern horizon. And because the sun will describe such a high arc the skythe duration of daylight will be the most extreme, namely 15 hours and 17 minutes.
Twilight zones
But this doesn’t mean we can spend the nearly nine hours left on the solstice day looking at the stars, because we also have to take twilight into account. Around the June solstice, at 40 degrees north latitude, morning and evening twilight lasts two hours each, leaving the sky completely dark for only five hours.
Further north, twilight lasts even longer. At 45 degrees it lingers for 2.5 hours, and at 50 degrees the twilight lasts all night; the sky never becomes completely dark. In contrast, twilight is shorter in a southerly direction. At latitude 30 degrees it takes 96 minutes, while at the latitude of San Juan, Puerto Rico it takes only 80 minutes. That’s why northern US travelers visiting the Caribbean this time of year are so surprised at how quickly it gets dark after sunset, compared to back home.
By the way, the earliest sunrise and the latest sunset do not coincide with the summer solstice. The first took place on June 14, the second only on June 27.
Related: The Brightest Planets in June’s Night Sky: How to See Them (and When)
So far, so good
Most people probably have the impression that Soil is closest to the sun in its orbit at this time of year, but it’s actually quite the opposite. In fact, on July 5 at 1:06 a.m. EDT (0506 GMT), we will be at the point in our orbit farthest from the Sun (called aphelion), a distance of 94,510,539 miles (152,099,969 km) . Conversely, on January 2, Earth was at perihelion, the point closest to the Sun. The difference in distance between these two extremes is 3,106,444 miles (4,999,337 km), or 3.3%, which means a difference in radiant heat received by the Earth of almost 7%. So for the Northern Hemisphere the difference should warm our winters and cool our summers.
In reality, however, the predominance of large landmasses in the Northern Hemisphere works the other way, making our winters generally colder and our summers hotter than those in the Southern Hemisphere.
Interestingly enough, it would be a very different story if we continued Mars. Compared to our nearly circular orbit, the Red Planet’s orbit is noticeably more eccentric (elliptical). When Mars reaches aphelion, it receives only 69% as much sunlight as it did at perihelion. This situation creates a seasonal asymmetry; The southern hemisphere of Mars always experiences greater extremes between summer and winter than the northern hemisphere.
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After August 6, it gets ‘early late’
After the sun reaches the solstice point, it will begin to migrate back south, and the amount of daylight in the Northern Hemisphere will begin to decrease. Think about this: after June 20, day length won’t increase again until three days before Christmas. But actually, if you think about it, the sun is making a high arc across the sky, and the length of daylight has been quite long since about mid-May. And the lowering of the sun’s path in the sky and the decrease in daylight hours in the coming days and weeks will be quite subtle, at least initially.
August 1 is marked on some Christian calendars as Lammas Day, the name of which is derived from the Old English “bread mass,” because it was once celebrated as a harvest festival and traditionally considered the middle of the summer season. In reality, however, the midpoint of summer – that moment that falls exactly between the summer solstice and the autumnal equinox in 2024 – won’t occur until August 6 at 12:47 a.m. EDT (1647 GMT). On that day, as seen from Boston, the sun sets again at 7:56 PM, with the loss of daylight since June 21 being only 63 minutes.
But it is in the second half of summer that the effects of the southward shift of the sun’s direct rays begin to become much more apparent. When fall officially arrives on September 22, the sun will set well before 7 p.m. (6:41 p.m.) for Bostonians, while the length of daylight will have been shortened by more than two hours (two hours and 6 minutes, exactly). to be) since August 6.
Baseball Hall of Famer Yogi Berra primarily played catcher for the Yankees. However, he played left field occasionally and said he didn’t mind the outfield except in August and September. During that time of year, the shadows across the ball field grew longer and longer in the afternoon, making it increasingly difficult for him to see a baseball hit in his direction. Yogi may not have been able to explain the science of why the sun’s altitude dropped so noticeably during the second half of summer, but – as only Yogi could do – he could sum it all up in a simple yogism: ‘It becomes there early late.”
Joe Rao is an instructor and guest lecturer in New York Hayden Planetarium. He prescribes on astronomy Natural history magazinethe Farmer’s almanac and other publications.