ALTThe 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.
ALTALTSummer 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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Celestial Mechanics Around the Solar System During December 2019
The dance of planets, moons and spacecraft around the solar system creates a host of rare alignments in late December 2019. Here’s what’s coming up.
Dec. 21: Winter solstice in the Northern Hemisphere
Dec. 21 is the 2019 winter solstice for the Northern Hemisphere. A solstice marks the point at which Earth’s tilt is at the greatest angle to the plane of its orbit, also the point where half of the planet is receiving the longest stretch of daylight and the other the least. There are two solstices a year, in June and December: the summer and winter solstices, respectively, in the Northern Hemisphere.
The winter solstice is the longest night of the year, when that hemisphere of Earth is tilted farthest from the Sun and receives the fewest hours of sunlight in a given year. Starting Dec. 21, the days will get progressively longer until the June solstice for those in the Northern Hemisphere, and vice versa for the Southern Hemisphere.
Dec. 26: Annular solar eclipse visible in Asia
On Dec. 26, an annular solar eclipse will be visible in parts of Asia. During an annular eclipse, the Moon’s apparent size is too small to completely cover the face of the Sun, creating a “ring of fire” around the Moon’s edge during the eclipse.
Solar eclipses happen when the Moon lines up just right with the Sun and Earth. Though the Moon orbits Earth about once a month, the tilt in its orbit means that it’s relatively rare for the Moon to pass right in line between the Sun and Earth — and those are the conditions that create an eclipse. Depending on the alignment, the Moon can create a partial, total or annular solar eclipse.
On Dec. 26, the Moon will be near perigee, the point in its orbit when it’s farthest from Earth. That means its apparent size from Earth is just a bit smaller — and that difference means that it won’t completely cover the Sun during the Dec. 26 eclipse. Instead, a ring of the bright solar surface will be visible around the Moon during the point of greatest eclipse. This is called an annular eclipse.
It is never safe to look directly at an annular solar eclipse, because part of the Sun is always visible. If you’re in the path of the annular eclipse, be sure to use solar viewing glasses (not sunglasses) or another safe viewing method to watch the eclipse.
Dec. 26: Parker Solar Probe flies by Venus
After the eclipse, more than 100 million miles away from Earth, Parker Solar Probe will pull off a celestial maneuver of its own. On Dec. 26, the spacecraft will perform the second Venus gravity assist of the mission to tighten its orbit around the Sun.
During the seven gravity assists throughout the mission, Parker Solar Probe takes advantage of Venus’s gravity to slow down just the right amount at just the right time. Losing some of its energy allows the spacecraft to be drawn closer by the Sun’s gravity: It will fly by the Sun’s surface at just 11.6 million miles during its next solar flyby on Jan. 29, 2020. During this flyby, Parker Solar Probe will break its own record for closest-ever spacecraft to the Sun and will gather new data to build on the science already being shared from the mission.
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