Mercury will move across sun Monday morning

Mercury will move between Earth and the sun Monday morning, giving viewers with proper eye protection the opportunity to see the dark disk of Mercury crossing the face of the sun.

Astronomers describe the passage of a planet across the sun’s disk as a transit.

South Sound astronomers will have to be patient because this particular transit will begin about 4:10 a.m., before the sun rises.

The planet will reach the center of the sun at 7:57 a.m. and the transit will end about 11:40 a.m.

“Mercury will appear as a small black dot against the face of the sun when viewed through appropriate filters,” said Dana Rush, who is in charge of the observatory at Pacific Lutheran University.

Rush said he plans to have the observatory open from 8-10 a.m. for anyone interested in seeing the event, weather permitting.

Monday’s forecast calls for mostly cloudy skies in the morning.

What makes the transition a rare event is a slight tilt to Mercury’s orbit.

“Because Mercury has an orbit that is inclined about 7 degrees from Earth’s orbit around the sun, it usually is above or below our direct line of sight to the sun when it is on the same side of the sun as Earth,” Rush said.

Since Mercury orbits the sun every 88 days, Earth-based observers usually don’t see it lining up with the sun.

The last alignment occurred in 2006. The next transits won’t be until 2019, and then not until 2032.

Rush stressed the importance of not viewing the transit without proper eye protection.

One way to view it on your own is by using a pair of eclipse glasses that have several layers of metal-coated mylar plastic in their frames, he said. Those layers reflect most of the sun’s intensity and only let a small amount of light filter through.

Another way would be to view the sun through a piece of No. 14 welders glass.

Or you can project an image of the sun through a pair of binoculars onto a viewing screen such as a white piece of paper or a white sheet. Using a small mirror to reflect an image onto a white surface might work as well, Rush said.

This story was originally published May 6, 2016 at 4:05 AM with the headline "Mercury will move across sun Monday morning."