What happens on the solstice?
Humans throughout history have celebrated the summer solstice with rituals such as bonfires and ceremonial dances to mark the passage of the seasons.
On the June solstice, the sun’s vertical rays strike the Tropic of Cancer, a line of latitude 23.5 degrees north of the equator. Geographically speaking, it’s the northernmost point where the sun appears straight overhead (90 degrees above the horizon) all year. In the Northern Hemisphere, daylight reaches its annual peak, and the sun takes its longest and highest path through the sky.
The reason we have solstices, and seasons, is because Earth doesn’t orbit the sun completely upright. Instead, our planet is tilted on its axis by about 23.5 degrees, which means one hemisphere receives more of the sun’s light and energy at different times of year.
On the June solstice, the Northern Hemisphere leans most toward the sun, giving us longer days and more intense sunlight. It’s the opposite in the Southern Hemisphere, where June 21 marks the start of winter and the shortest day of the year.
Daylight hours on the solstice
In the Northern Hemisphere, the length of day depends on how far you live from the equator. In Washington, the sun is up for 14 hours and 54 minutes on June 20, rising at 5:42 a.m. and setting at 8:36 p.m.
Locations to our north see even more daylight. New York, Boston and Chicago all see over 15 hours of daylight on the solstice, while in Seattle, the sun is up just shy of 16 hours.
The map above, created by climatologist Brian Brettschneider, illustrates how much daylight varies across the Northern Hemisphere. Each red circle is a distinct line of latitude and represents a 30-minute increase or decrease in daylight. Cities connected by the same line have the same number of daylight hours. For example, London and Paris both see more than 16 hours of daylight on June 21 — more than most of the contiguous United States.
Northernmost sunrise and sunset
The word “solstice” comes from the Latin word solstitium, which means “sun standing still.” On the June solstice, the sun’s daily northward movement in the sky appears to pause, and we see the sun rise and set at its northernmost points on the horizon. After the solstice, the position of sunrise and sunset slowly begin to shift southward again.
Our northern-oriented sunrises and sunsets mean the sun takes a steep climb through the sky. In Washington, the sun climbs 74.5 degrees above the horizon at solar noon (1:09 p.m.) on the solstice, the highest it gets all year.
You’ll see evidence of the sun’s intensity just by looking at your shadow. As the sun appears nearly overhead, your midday shadow on the summer solstice will be the shortest of the year.
Earliest sunrise and latest sunset not on the solstice
While the summer solstice has the longest day length, it’s not when we see our earliest sunrise or latest sunset. In Washington, the earliest sunrise (5:42 a.m., calculated precisely to the second) occurred June 14, according to timeanddate.com. Meanwhile, our latest sunset (8:37 p.m.) is not until June 27. We can thank Earth’s tilt and our elliptical orbit around the sun for this astronomical misalignment.
The maps below show the local time and date of the earliest sunrise and latest sunset in North America. Red lines indicate the date of the earliest sunrise or latest sunset, while the shaded colors correspond to sunrise and sunset times. Notice how the dates of the earliest sunrise and latest sunset almost coincide with the solstice near the Arctic Circle, while in lower latitudes (Florida and Texas, for example) the earliest sunrise and latest sunset happen more than two weeks apart.
The patchwork of colors illustrates how both time zones and latitude affect local sunrise and sunset times. In Maine, the earliest sunrise occurs before 5 a.m., while in southwestern Texas, the sun doesn’t rise until after 6:30 a.m.
Many parts of the country see their latest sunset after 8:30 p.m. just after the solstice, and in some areas — including the northern tier and the western regions of each time zone — the sun sets after 9 p.m.
Most of Alaska sees its latest sunset around midnight, that is, if the sun even sets at all. In areas along and north of the Arctic Circle, the sun continuously circles through the sky all day, and it never gets dark.
Long-lasting twilight
While most of us live in the mid-latitudes, where we still experience several hours of nighttime, the summer solstice is unique for its extended morning and evening twilight. On the summer solstice, dawn and dusk last slightly longer compared with the spring and fall equinoxes, because the sun crosses the horizon at a shallower angle and takes longer to rise and set.
The difference is most noticeable at higher latitudes, but even in Washington, civil twilight (which occurs when the sun is 6 degrees or less below the horizon) lasts five minutes longer in mid-June than it does on the equinoxes.
At sunset, the sun’s lingering light in the northwestern sky can be a great time for photography. And if you’re lucky enough to live between 45 and 60 degrees latitude, where the sun doesn’t dip far below the horizon, you may even spot shimmering blue noctilucent clouds at night.
Hottest days usually after the solstice
After the solstice, we slowly start to lose daylight. Washington will lose a few seconds each day over the coming week. Starting July 10, we will shave off a full minute of daylight with each passing day.
Though daylight peaks on the solstice, our hottest summer days, on average, don’t arrive until mid-July. This delay, or seasonal lag, happens because the amount of solar energy arriving at the ground continues to outpace the amount leaving the Northern Hemisphere for several weeks after the solstice. It’s largely driven by the oceans, which take much longer than land to warm up and cool down, and release heat slowly over time.
While much of the western United States is experiencing an exceptional heat wave and severe drought, summer in the eastern half of the country has so far been relatively tame. Whatever the rest of summer brings, one thing is certain: These long, bright days will eventually recede as we turn the corner toward fall.
"all day" - Google News
June 20, 2021 at 08:13PM
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Summer solstice arrives Sunday night, marking year’s longest day - The Washington Post
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