The Summer Solstice Is Here!
Today — June 20, 2024 — is the northern summer solstice. In the Northern Hemisphere, it marks the longest day of the year and the official start to summer.
Summer Starts in the Northern Hemisphere!
Today is the first day of summer in the Northern Hemisphere – the solstice! People located in the Northern Hemisphere will have the longest day of the year today, and people located in the Southern Hemisphere will have the shortest day of the year.
The angle between the Earth’s orbit and the axis of its rotation creates our seasons, tilting each hemisphere toward the Sun during summer in that half of the Earth. This is summer in the Northern Hemisphere, and winter in the Southern Hemisphere. The other half of the year, the Northern Hemisphere is tilted away from the Sun, creating winter in the north and summer in the south.
Solstices happen twice per year, at the points in Earth’s orbit where this tilt is most pronounced.
These days are the longest (in the summer hemisphere) and shortest (in the winter hemisphere) of the year, and mark the change of seasons to summer and winter, respectively.
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Special Celestial Events in June 2020
Earth and the Moon are in a constant dance as they orbit the Sun — and in June 2020, they’ll create two special celestial events.
June 20: Summer solstice in the Northern Hemisphere
Earth has a slight tilt as it orbits the Sun, and June is one of two times each year when that tilt is most prominent: a solstice. At the solstices, which happen each year in June and December, Earth’s tilt is at the greatest angle with respect to the plane of its orbit, meaning that one hemisphere is tilted towards the Sun, and the other hemisphere is tilted away.
In the Northern Hemisphere, June 20 is the summer solstice — the Northern Hemisphere is tilted towards the Sun, so the June solstice is the day on which the Northern Hemisphere receives the longest stretch of daylight for the year.
In both hemispheres, the Sun will rise and set at its northernmost point on the horizon. After June 20, the Sun will appear to travel south.
This view from our Earth Polychromatic Imaging Camera on the National Oceanic and Atmospheric Administration's DSCOVR satellite shows the change in Earth’s tilt between the June and December solstices.
During the June solstice, the Southern Hemisphere is tilted away from the Sun, meaning the June solstice marks its shortest stretch of daylight for the year. June is the Southern Hemisphere’s winter solstice.
June 21: Annular solar eclipse in Africa and Asia
The day after the solstice will see another special celestial event: an annular eclipse. Eclipses happen when the Moon lines up just right between the Sun and Earth, allowing it to block out part or all of the Sun’s bright face and cast a shadow on Earth. Though the Moon orbits Earth about once a month, its orbit is tilted by five degrees, so the perfect alignment that creates an eclipse is relatively rare. Often the Moon is too high or low in our sky to block out the Sun.
The June 21, 2020, eclipse is an annular eclipse visible primarily in Africa and Asia. During an annular eclipse, the Moon is too far from Earth and its apparent size is too small to entirely block out the face of the Sun, leaving a sliver of the Sun visible around the Moon’s edge during the eclipse and creating a “ring of fire” effect.
Outside the path of annularity, people in other parts of Africa, Asia and even some of Europe and the Pacific have a chance to see a partial solar eclipse, weather permitting. The degree of the partial eclipse depends on how close you are to the path of annularity. Locations far from the path of annularity will see only a small part of the Sun covered by the Moon, while places close to the path will see almost all of the Sun obscured.
No matter where you are, you must take safety precautions to watch the eclipse safely. There is no part of an annular eclipse during which it is safe to look directly at the Sun. You must use a proper solar filter or an indirect viewing method during all phases of the eclipse — even if only a tiny sliver of the Sun is visible around the Moon’s edge, that’s still enough to cause damage to your eyes.
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The Summer Solstice Has Arrived!
This year’s summer solstice for the northern hemisphere arrives at 11:54 a.m. EDT, meaning today is the longest day of the year! The number of daylight hours varies by latitude, so our headquarters in Washington, D.C. will see 14 hours, 53 minutes, and 51 seconds of daylight. A lot can happen in that time! Let’s find out more.
If you’re spending the day outside, you might be in the path of our Earth Science Satellite Fleet (ESSF)! The fleet, made up of over a dozen Earth observation satellites, will pass over the continental United States about 37 times during today’s daylight hours.
These missions collect data on atmospheric chemistry and composition, cloud cover, ocean levels, climate, ecosystem dynamics, precipitation, and glacial movement, among other things. They aim to do everything from predicting extreme weather to helping informing the public and decision makers with the environment through GPS and imaging. Today, their sensors will send back over 200 gigabytes (GB) of data back to the ground by sunset.
As the sun sets today, the International Space Station (ISS) will be completing its 10th orbit since sunrise. In that time, a little more than 1 terabyte-worth of data will be downlinked to Earth.
That number encompasses data from ground communications, payloads, experiments, and control and navigation signals for the station. Approximately 330 GB of that TB is video, including live broadcasts and downlinks with news outlets. But as recently-returned astronaut Serena Auñón-Chancellor likes to point out, there’s still room for fun. The astronauts aboard the ISS can request YouTube videos or movies for what she likes to call “family movie night.”
Astronauts aboard the station also send back images—LOTS of them. Last year, astronauts sent back an average of 66,912 images per month! During today’s long hours of daylight, we expect the crew to send back about 656 images. But with Expedition 59 astronauts David Saint-Jacques (CSA), Anne McClain (NASA), and Oleg Kononenko (RKA) hard at work preparing to return to Earth on Monday, that number might be a little less.
Say you’re feeling left out after seeing the family dinners and want to join the crew. Would you have enough daylight to travel to the ISS and back on the longest day of the year? Yes, but only if you’re speedy enough, and plan your launch just right. With the current fastest launch-to-docking time of about six hours, you could complete two-and-a-half flights to the ISS today between sunrise and sunset.
When returning from orbit, it’s a longer ordeal. After the Expedition 59 trio arrives on Earth Monday night, they’ll have to travel from Kazakhstan to Houston to begin their post-flight activities. Their journey should take about 18 hours and 30 minutes, just a few hours longer than the hours of daylight we’ll see today.
Happy solstice! Make sure to tune in with us on Monday night for live coverage of the return of Expedition 59. Until then, enjoy the longest day of the year!
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