Jupiter and Saturn will have their big conjunction in 2020 today, which also happens to be the day of the December solstice. These two worlds will be visible in our sky closer than they have been since 1226. Jupiter and Saturn will be barely 0.1 degree apart at their closest. More Jupiter-Saturn images may be seen here.
Jupiter is currently shining very brightly from Earth due to an atmospheric phenomenon known as a "green flash". The color comes from the concentration of oxygen molecules along with methane near its cloud tops. The photo was taken on April 16, 2016 by NASA's Cassini spacecraft from a distance of approximately 1 million miles (1.5 million kilometers).
Cassini has been studying Jupiter for 13 years, during which time it has made numerous discoveries about this giant planet. For example, scientists have found that there are more hydrogen atoms than planets in orbit around Jupiter. This means that some other type of particle is carrying away the energy that should come from gravitational binding with hydrogen atoms.
Another discovery made by Cassini is that Jupiter has magnetic fields that are much stronger than expected from its size. It has been estimated that his magnetic field extends out to 15,000 miles (24,000 km) into space. This makes it significantly stronger than Earth's own magnetic field, which only reaches out to about 10,000 miles (16,000 km).
One way to put it is that it is the point at which two objects are closest to one other as seen from Earth. According to this definition, the 2020 grand conjunction of Jupiter and Saturn happened on December 21, 2020, about 18:20 UTC. Scroll down to watch a live webcast of the 2020 Great Conjunction!
The second way to put it is that it is when Jupiter and Saturn align in the night sky with their rings facing outward.
Jupiter and Saturn will be close together in the evening twilight tonight, but on Saturday they'll be separated by about half a degree (or 15 minutes of arc). On Sunday they'll be separated by about a degree (or 30 minutes of arc). The next great conjunction won't happen for another eight years when Jupiter and Saturn meet again in 2020/2021.
The 2020 great conjunction was visible throughout most of North America, where it was night during some part of the day on December 21st. It was also visible in Europe and parts of Asia including India and Australia. In fact, people across the world were able to see something special happening in the night sky.
Saturn and Jupiter have always been important planets for understanding astronomy because of how they affect each other visually. This conjunction is especially interesting because it coincides with an equinox so the Sun is rising due east and setting due west. This means that wherever you are located on the planet, daytime is lasting for a full 24 hours.
Jupiter and Saturn last had a close encounter in May 2000. Following this December 21, 2020 conjunction, the two planets appear to exchange places, with Jupiter overtaking Saturn. Throughout the decade of the 20s, Jupiter will move to the east, drawing farther and further away from Saturn. When Jupiter is finally removed from between Saturn and the Sun, the moment of maximum western elongation for Saturn will have occurred.
During the years leading up to the conjunction, people across the world will be able to see Jupiter and its four largest moons (Amalthea, Ganymede, Io, and Metis) joined together like a string of pearls on the horizon. The next time these objects will come into view together on the sky's surface will be in 2165. After that, they will never again be seen in the same part of the sky.
The evening of December 24, 2020, will see Jupiter reach its highest point in the night sky. It will be visible all night long, as it crosses the face of the moon. The next time this will happen is on April 4, 2033. By then, Jupiter will have moved far enough west for its next lunar standstill to occur.
The moon will pass between Earth and the Sun at the center of our galaxy on March 2, 2023. No significant activity is expected on our planet during this transit.
Our solar system's two largest planets, Jupiter and Saturn, will appear in the sky next to each other for the first time since 1623, and the closest observable from Earth since the Middle Ages in 1226. This will occur on December 21, 2020, during an occurrence known as a "great conjunction."
The night of December 21, 2020, will be full moon and there will be a great conjunction of the Moon and Jupiter. The Moon is not visible at its full extent but it is estimated that Jupiter is going to be about half-lit up by the Sun in the west-southwest corner of the sky around midnight your time.
Jupiter is the king of planets and its appearance should not be underestimated. It is a good idea to get someone to take a picture of the sky when it is dark so you can compare future appearances of Jupiter with this historic event.
Great conjunctions occur about every three years and eight months. The last one was in September 2017. After this year's conjunction, Jupiter will again retreat from the sun until 2034 when another great conjunction will take place.
These are special times when our planet is closely aligned with other planets in the Solar System. Because of this, astronomers often use observations of these planetary alignments to make precise measurements of time that could not be done otherwise.