It happens Tuesday. It won’t happen again for more than a hundred years.
The transit of Venus across the face of the sun takes place Tuesday afternoon, as the planet Venus will move between the Earth and the sun.
The St. George Observatory in Schriever is hosting a viewing of the rare event.
“It’s a historical event,” Ken Stage, curator of the St. George Observatory, said.
Venus makes one orbit around the sun in about 224.7 Earth days, about two-thirds of the time it takes for the Earth to do the same. Because there is a slight difference — about 3.4 degrees — between the Earth’s orbit and that of Venus, the inner planet only passes between the Earth and the sun four times in a 243-year period.
The next chance to view a transit of Venus will be in December 2117. If the orbits of the Earth and Venus were coplanar, a transit of Venus would be viewable about every 1½ years.
Stage said that visitors will be able to view more than just the transit of Venus at the observatory.
“We’re going to have a photo spread, a collage of pictures that Magellan (the NASA satellite) took of Venus,” he said.
A full transit of Venus normally takes about six hours, though the sun will set in the local area Tuesday before the transit is complete.
Stage described the 1768-1769 voyage led by Capt. James Cook with astronomer Charles Green to the island of Tahiti to observe the 1769 transit of Venus, an event that helped to determine the distance between the sun and the Earth as nearly 94 million miles.
“They recorded that the fuzziness of Venus while gliding across the disc of the Sun revealed that the planet had a very intense atmosphere, which was later proven true,” Stage said. “I take my hat off and stand in awe to James Cook and Charles Green.”
The 1768-1769 expedition used special telescopes supplied by King George III of England, Stage said.
“Any kid today can get online and buy something far superior to what they were working with,” he said.
The Transit of Venus next week will come 1½ days after another completely unrelated but similar cosmic event; at 5:30 a.m. this morning in the western sky, the Moon was partially covered by Earth’s shadow in a partial lunar eclipse, though the event will be hard for most people to view from ground level, as it will only be a few degrees above the horizon and may therefore be obstructed by trees.
More information about both the observatory and the viewing event can be obtained by visiting the observatory’s website, www.stgeorgeobservatory.com.