After our long stay-at-home spring, it's time to welcome summer. Saturday is the summer solstice, our longest day the year and the first day of astronomical summer in the Northern Hemisphere.
Thanks to 2020 being a leap year, this year's solstice arrives June 20 at 5:43 p.m. eastern time, about a day earlier than usual.
It also happens to coincide with another rare celestial event: an annular "ring of fire" solar eclipse will darken the sun on the first day of summer across parts of Africa and Asia. While the eclipse won't be visible in North America, a few sites will be streaming it live.
Similar to the eclipse, Saturday's solstice is a fleeting astronomical event. Technically, the solstice isn't a full calendar day. It's actually a precise moment when the sun appears directly over the Tropic of Cancer, a circle of latitude 23.5 degrees north of Earth's equator. It's as far north as the sun ever gets before starting its six-month journey southward again. Here in the Northern Hemisphere, we see our greatest amount of daylight as the sun takes its longest and highest path through the sky.
The reason we have solstices, and seasons, is because the Earth doesn't orbit the sun completely upright. Instead, our planet is tilted on its axis about 23.5 degrees, which means one hemisphere receives more direct sunlight than the other at different times of year.
On the June solstice, the Northern Hemisphere leans most toward the sun, giving us the most intense sunlight and longest days of the year. It's the opposite down under, where places in the Southern Hemisphere are kicking off winter and their shortest day of the year.
The number of daylight hours you'll see today depends on how far you live from the equator. The farther north you are, the longer the sun is up. The map below, created by climatologist Brian Brettschneider, shows daylight on the summer solstice ranges from less than 14 hours in parts of Florida and southern Texas to more than 16 hours in northern Montana, North Dakota and Minnesota.
Washington, D.C., enjoys 14 hours and 54 minutes of daylight Saturday, with sunrise at 5:42 a.m. and sunset at 8:36 p.m., according to timeanddate.com. Our latest sunset of the year — at 8:37 p.m. — comes June 27.
Places farther north will see the sun up longer. New York, Boston and Chicago all see more than 15 hours of daylight Saturday, while in Seattle the sun is up just under 16 hours.
But if you're looking for round-the-clock daylight, you'd have to head toward the Arctic Circle, where the sun continuously circles through the sky all day (though from a low angle, which is why places like Alaska and northern Canada aren't what most of us would consider warm and summery, despite all the sunlight they get during this time of year).
If you're trying to watch the sunrise or sunset on our longest day of the year, you'll want to look toward the northeast and northwest. No matter where you are, the June solstice brings us our northernmost sunrise and sunset of the year.
Our northern-oriented sunrises and sunsets mean the sun takes a steep climb through the sky. In Washington, the sun reaches an impressive 74.5-degree angle above the horizon at solar noon (1:09 p.m.) on the solstice, the highest its gets all year. The high sun angle means the sun's ultraviolet rays are especially strong, so keep the sunscreen handy, even on cloudy days.
If you've ever noticed how dawn and dusk last a bit longer this time of year, it's not your imagination. On the solstice, we see not only our longest daylight, but also our our longest morning and evening twilight periods. In other words, even after the sun sets, its light doesn't fade from the sky as quickly.
This happens because the sun crosses the horizon at a shallower angle and takes a bit longer to rise and set than it does around the spring and fall equinoxes. Twilight lasts longest around the summer solstice because the sun's disc lingers just below the horizon instead of dropping quickly. This keeps the sky illuminated a bit longer than usual.
In northern latitudes, the sun hardly dips below the horizon and twilight lasts all night long. That's why even in places south of the Arctic Circle where the sun technically sets (think Fairbanks, Alaska), it never gets fully dark for several weeks around the solstice. These conditions are ideal for sighting noctilucent clouds, shimmering blue clouds composed of ice crystals that form in the mesosphere some 50 miles above Earth. They're most commonly seen between 45 and 60 degrees latitude, according to EarthSky.
After the summer solstice, we start losing daylight. D.C. will lose a scant few seconds each day over the coming week. But starting July 9, we'll shave off a minute of daylight with each passing day.
But even as the days slowly get shorter, it's safe to assume that summer's hottest days still lie ahead. Though we experience the greatest solar heating around the solstice, thanks to a phenomenon called "seasonal lag", most parts of the Northern Hemisphere — including the U.S. — don't see their hottest days until July or even August.
That's good news if you like summer, which happens to be our longest astronomical season. Clocking in at 93 days, summer in the Northern Hemisphere is about four days longer than winter. You can thank the fact that the Earth doesn't orbit the sun in a perfect circle. Every year, we're about three million miles farther from the sun in July than we are in January.