The 2024 summer solstice will occur on June 20 at 4:51 p.m. Eastern Time, according to the U.S. Naval Observatory. A day later, on June 21, the full moon will rise at 9:08 p.m. Eastern Time. The “strawberry moon” is the lowest full moon of the year, remaining near the horizon as the sun rises toward its highest point in the sky.
What exactly happens at the solstice?
Most years, the summer solstice occurs on June 21. This is when Earth’s North Pole reaches its maximum tilt toward the sun, and the sun appears at its northernmost point, directly above the Tropic of Cancer, 23.5 degrees north from the earth’s equator. In the Northern Hemisphere, the sun takes its longest and highest path in the sky, which is why we experience our longest daylight hours and shortest nights of the year.
Daylight hours on the summer solstice depend on latitude: the closer you get to the North Pole, the more time the sun spends above the horizon. The sun has been rising since 4 p.m. in Seattle, but only 13 hours and 45 minutes in Miami.
Washington, D.C., experiences about 14 hours 54 minutes of daylight on the summer solstice, with sunrise at 5:42 a.m. and sunset at 8:36 p.m., according to timeanddate.com.
There are two ways to directly observe the solstice: observing your shadow and the location of sunrise and sunset. The sun’s high arc means you will cast your shortest midday shadow of the year at the summer solstice. You’ll also see the sun rise and set at its northernmost points along the horizon.
Why is the solstice early this year?
The main reason for the early solstice is that human calendars are not perfect. While a normal year (or non-leap year) has 365 days, Earth’s orbit around the sun each year is not exactly that long. On average, it takes about 365 days, 5 hours and 49 minutes, or 365.24219 days, according to timeanddate.com. To account for this extra quarter of a day, the Gregorian calendar that we adopted at the end of the 16th century adds an extra day (February 29) to the calendar every four years. This is why we have leap years which last 366 days.
During leap years like 2024, the solstices and equinoxes occur approximately 18 hours and 11 minutes apart. earlier than the previous year. Then, in successive non-leap years, the seasons begin at 0.24219 days. later than the previous year (approximately 5 hours and 49 minutes).
Over time, this means that the solstices and equinoxes move forward by about 45 minutes every four years, or about three-quarters of a day per century. By 2096, the solstice will occur at the earliest of this century.
To correct this discrepancy, the Gregorian calendar introduced a special rule: any year divisible by four is a leap year, with the exception of century years, which can only be leap years if they are divisible by 400. Thus, 1600 and 2000 were leap years, while 1700, 1800, 1900 and 2100 are not.
Skipping three leap years every 400 years means that the average length of the Gregorian calendar we use is 365.2425 days instead of 365.25 days. These extra decimal places may seem small, but they keep our calendar in sync with the actual time it takes for Earth to orbit the sun (365.24219 days).
Without this calibration, the solstices would advance indefinitely earlier. Instead, the solstices (and equinoxes) will arrive earlier every leap year until the end of the 21st century. However, the cycle will eventually reset. Because 2100 is not a leap year, the solstice time will start to drift again later.
The reason for the seasons
Seasons on Earth occur because the planet is tilted on its axis about 23.5 degrees, causing each hemisphere to receive different amounts of sunlight throughout the year.
In June, the northern hemisphere tilts toward the sun, bringing us more direct sunlight and warmer weather. In the Southern Hemisphere, the June solstice is the first day of winter and the shortest day of the year. Halfway between the winter and summer solstices are the equinoxes, when the length of day and night are almost equal everywhere on Earth.
While the summer solstice marks the first day of astronomical summer, meteorologists define summer as the three hottest calendar months of the year, spanning June, July, and August. In most of North America, the three warmest months of the year correspond more to meteorological summer (June 1 to August 31) than to astronomical summer. according to climatologist Brian Brettschneider.
The warmest time of the year usually doesn’t arrive until the second half of July for much of the United States, according to the National Oceanic and Atmospheric Administration. This seasonal shift occurs because the amount of solar energy arriving at the ground is greater than the amount leaving the Earth for several weeks after the solstice. This is largely due to oceans, which take longer than land to warm and cool, and which release heat slowly over time.
Yet even as the summer heat begins to intensify, we will slowly begin to lose daylight after Thursday’s solstice.
