As the planet Mercury aligns with the sun and the Earth today, UA community members can go to Flandrau Science Center to observe the surface of Mercury – a phenomenon that occurs about once a decade.

Usually, Mercury passes above or below the line of the Earth and the sun, but today it will pass directly in alignment with Earth, allowing people to observe the size of the planet relative to the sun, said Mike Terenzoni, planetarium coordinator for Flandrau Science Center and Planetarium.

Flandrau will be setting up telescopes with special filters on its lawn from noon to 5 p.m. so that the public can view the transit of Mercury for free, said Robert Vugteveen, director of marketing and outreach for Flandrau.

“”We have a special hydrogen alpha filter which knocks out most of the light coming from the sun,”” Vugteveen said. “”It allows us to see a great deal of detail in the sun, including sun spots and sun flares.””

The telescopes on the lawn will have light solar filters on the front of the lenses that block out 99.99 percent of the sun’s light to prevent accidental blindness, Terenzoni said.

“”Mercury is so small it would be very difficult to see it with the naked eye,”” Terenzoni said. “”I wouldn’t recommend using filters at home unless you’re an expert.””

There will also be a camera set up on the main observatory telescope that will be used to project an image on a big screen in the exhibit hall, Vugteveen said.

This rare event is open to everybody, said Ann Sprague, a senior research associate at the Lunar and Planetary Laboratory.

“”You don’t need to be taking any science courses to appreciate watching Mercury pass in front of the sun,”” Sprague said. “”It would be a very nice opportunity for any student to go look.””

The transits of Mercury as seen from the earth occur about 13 times per century and only in May or November, Terenzoni said.

“”It gives us perspective about the universe and our place in it,”” Terenzoni said.

At 1 p.m., Sprague will host a free lecture titled “”Mercury: Planet Closest to the Sun.””

Sprague works with the Messenger spacecraft, which is now en route to Mercury and will fly past the planet in January 2008, Terenzoni said.

“”We only know what about 45 percent of Mercury looks like because we haven’t sent a spacecraft there in so long,”” Terenzoni said. “”Mercury’s slow rotation leaves most of its surface in the dark.””

Today’s transit will end when the sun drops below the horizon of buildings around 5 p.m., Terenzoni said.

Limited free parking is available from 7 a.m. to 5 p.m. at the Flandrau Science Center, and some campus garages are open to the public for a fee. Side-street and meter parking are also available in the area.

Nov. 11, 2019, will be Mercury’s next long transit across the sun’s disk, according to the Flandrau Web site.