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Evening drizzle blocked the view for most Evanston stargazers hoping to see the Great Conjunction of the planets Saturn and Jupiter just after sunset on Dec. 21 in the southwestern sky. Anticipating that, many people on Dec. 20 took their masks and binoculars to parks, the lakefront and other places where visibility was strong.
Both planets were visible then; the conjunction that would make them appear as one bright star would occur about 24 hours later. The bright “star” is thought by some to be the Christmas star that, according to the Christian bible, led the magi to Bethlehem at the birth of Jesus.
The planets regularly appear to pass each other in the solar system, according to the NASA website, with the positions of Jupiter and Saturn being aligned in the sky about once every 20 years. However, it has been nearly 400 years since they have passed so closely and nearly 800 years since the alignment occurred at night. Such a rare occasion prompted today’s Google Doodle of Saturn and Jupiter in an “air high-five” and Saturn tipping its rings as a hat.
The NASA website said that Italian astronomer Galileo Galilei in 1610 “pointed his telescope to the night sky, discovering the four moons of Jupiter – Io, Europa, Ganymede, and Callisto. In that same year, Galileo also discovered a strange oval surrounding Saturn, which later observations determined to be its rings. These discoveries changed how people understood the far reaches of our solar system.
“Thirteen years later, in 1623, the solar system’s two giant planets, Jupiter and Saturn, traveled together across the sky. Jupiter caught up to and passed Saturn, in an astronomical event known as a ‘Great Conjunction.’”
From the Earth, the two planets appear to merge, but in space they are still hundreds of millions of miles apart.
The NASA website quoted Henry Throop, astronomer in the Planetary Science Division at NASA Headquarters in Washington: “Conjunctions like this could happen on any day of the year, depending on where the planets are in their orbits. The date of the conjunction is determined by the positions of Jupiter, Saturn, and the Earth in their paths around the Sun, while the date of the solstice is determined by the tilt of Earth’s axis. The solstice is the longest night of the year, so this rare coincidence will give people a great chance to go outside and see the solar system.”