Probably once in your lifetime: Venus transits across the sun Tuesday

Sunday, June 3, 2012 | 6:00 a.m. CDT; updated 5:57 p.m. CDT, Monday, June 4, 2012

COLUMBIA — You'll never see this again.

This spring’s series of celestial events wraps up Tuesday with a transit of Venus across the sun that will not occur again until the year 2117.

If you go...

Where: Laws Observatory, fifth floor of the MU Physics Building

Off College Avenue, north of Rollins Street (click for map)

When: 5 p.m. to sunset Tuesday

Who: Free and open to the public

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MU astronomers and the Central Missouri Astronomical Association are hosting a viewing event starting just before 5 p.m. and lasting until sunset Tuesday at Laws Observatory on the fifth floor of the MU Physics Building. They will have telescopes equipped with filters and solar glasses available to view Venus as it passes between the Earth and the sun.

Just like last month’s partial solar eclipse, eye protection is necessary to safely view the transit. Welder’s glasses equipped with a number 14 or darker hood or specially made solar glasses, which will be available at the observatory for free, are necessary for naked eye viewing. Projection methods can also be used to view the transit. 

Pinhole projections are made by poking a hole in a stiff piece of paper or cardboard using a pin. With your back to the sun, hold the piece of cardboard so the sunlight shines through the hole. This creates a projection which can be seen on another piece of paper held below the hole.

Unlike that blowout furniture sale advertised every month or that skydiving trip your friends want you to take, the transit of Venus truly only occurs once or twice in a lifetime, only two times in a century.

Because of Venus’s tilted orbit, it does not pass directly between earth and the sun with each orbit. Transits that are visible from earth occur in 8-year pairs. Each pair is separated by more than 100 years, according to NASA.

Angela Speck, professor and director of MU’s astronomy program, will host a talk following the transit explaining why a transit isn't visible every time Earth orbits the sun. She will also explain how astronomers used the transit to measure the size of the solar system for the first time.

“The transit is a way in which we can actually measure distances to planets and distances to everything else. It’s really important, especially historically,” Speck said. 

Speck’s talk will be held in room 114 of the Physics Building after sunset.

Tuesday’s transit is the second half of this century’s pair. The first transit of the pair occurred in June 2004. If you missed the 2004 transit, Tuesday will be the last chance to see the event for another 105.5 years. The next transit will not occur until Dec. 11, 2117.

The total path of Venus across the sun will take almost seven hours, according to NASA. However, only the first half will be visible in the U.S., because the sun sets before the transit ends.

Unlike last month’s partial solar eclipse, which obscured almost half the sun in Columbia, Venus’s silhouette will only appear as a tiny black dot creeping across the upper right corner of the sun, according to Speck's description. Then it will disappear into space again.

“While this isn’t exactly a visually stunning event like a total solar eclipse, it is nonetheless a literal ‘once-in-a-lifetime’ event (or twice if you saw the transit of 2004),” according to the U.S. Naval Observatory’s website.

The transit should begin at approximately 5:04 p.m. in Columbia. This is the moment that Venus touches the outer edge of the sun, called ingress exterior. At 5:22 p.m., Venus should be fully inside the solar disc, called ingress interior. The planet will continue to cross the sun well after sunset at 8:29 p.m.

As of Friday, the National Weather Service predicted sunny conditions for Tuesday and mostly clear skies for Tuesday evening. If clouds get in the way, NASA’s webpage for the transit has a list of webcasts available

Supervising editor is Jake Kreinberg.

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