The planet Venus is the black spot crossing the sun in 2004. It was photographed… (Geert Vanden Wijngaert…)
The transit of Venus sounds like a bus stop at some extraterrestrial outpost, but it's actually what happens in the sky when the planet Venus moves across the face of the sun. What NASA calls "the rarest of planetary alignments" will begin Tuesday afternoon until sunset -- and then won't be seen again for 105 years.
"In a way, you could call a solar eclipse a transit of the moon," says Tyler Nordgren, astronomer, author and associate professor of physics at the University of Redlands. "Venus will be moving in front of the sun's disk."
People can watch the transit for free between 3:06 and 8:01 p.m. in the coelostat (special solar telescope) and telescopes on the lawn at the Griffith Observatory in Los Angeles. Staff will be on hand to explain what's happening during the celestial phenom. The observatory's website notes the last transit of Venus that was visible in L.A. occurred in 1882.
But don't expect to see an impressive "ring of fire" like the one visible throughout the West during the May 20 annular solar eclipse. (But do expect to wear safety glasses to avoid eye damage if you plan to view the transit without a telescope.)
People with sharp vision should see a tiny black dot starting at 3:06 p.m. Pacific time Tuesday that will be visible until sunset around 8 p.m. Those with so-so vision should find a telescope at a star party to track Venus' movements. "The disk of Venus should be large enough to just make it out with the human eye," he says. "It's right at the limit of what the human eye can see."
It should be visible throughout the Unites States and northern South America on Tuesday and in Europe, eastern Asia and eastern Australia around sunrise Wednesday. NASA reports only seven transits of Venus have occurred since the invention of the telescope, in 1631, 1639, 1761, 1769, 1874, 1882 and 2004.