It will be no ordinary sight Monday when Mercury crosses in front of the sun, though looking into the sun is generally frowned upon.
Luckily, Joliet Junior College is hosting a viewing event for spectators who are interested in taking in this phenomenon.
“What’s happening is that Mercury will be going in between the Earth and the sun such that it will show up as a small black disk against the sun,” said Dr. Noella Dcruz, an astronomy professor for the college. “When you have a solar eclipse, you have the moon going between the Earth and sun. The moon is so much closer to us, so it can completely dark out the sun. … Mercury, being so much further away from us, it shows up as a small black disc.”
Dcruz said it’s not an everyday occurrence.
“You have about 13 or 14 of these transits of Mercury in one century,” she said.
The act of Mercury passing the sun will have already started Monday, Nov. 11 by sunrise in Joliet, but it is expected to continue until shortly after 12 p.m.
Dcruz said people will be able to witness most of the phenomenon through a telescope because “ it can be really hard to see Mercury.” The college intends to equip the telescopes with solar filters to promote safe viewing.
“Mercury is very small compared to the sun,” she said.
The Earth, the sun and the moon are expected to line up making it possible for spectators to see Mercury passing the sun.
Dcruz said there are 7 degrees between Mercury’s orbit and Earth’s orbital plane, and there are 5 degrees between the moon and Earth’s orbital plane.
When the three objects are not positioned in the Earth’s orbital plane to a degree, they do not line up to allow the phenomenon to be viewable.
“When the moon is between the sun and the Earth, it might not be in Earth’s orbital plane, so then you cannot have a solar eclipse at all,” she said. “If the moon is not in the orbital plane of the Earth when the Earth is between the sun and the planet, then there will not be a lunar eclipse. And Mercury is not in Earth’s orbital plane when it is between the sun and the Earth, then a transit of Mercury is not possible.”
The event begins at 10:30 a.m. on the east lawn outside the Event Center at the college’s Main Campus.