The rare Transit of Venus is coming Tuesday (June 5, 2012) afternoon in the United States, and it’s a once-in-a-lifetime viewing chance for West Coast viewers. The next time this astronomical phenomena will happen is 2117.

At its heart, the exquisite show in the heavens is simple — Venus will cross paths between the sun and the Earth, and Earthlings will see a tiny dot floating across the surface of the sun over several hours.

How to view the Transit of Venus? You could buy a pair of solar glasses from a planetarium, like the Griffith Observatory in Los Angeles, which will sell them Tuesday after 12 p.m. for $2.99 a pair. An even better view, also at the Observatory, is seeing the transit magnified by a telescope, equipped with special solar filters.

You can also try buying No. 14 welder’s glass from a welder’s shop or home improvement store. Or use a pair of binoculars, preferably with more than seven times magnification, to project the sun’s light onto the sidewalk or a piece of paper. If you’re able to find an image of the sun, look for a tiny dot showing the image of Venus.

Don’t look at the sun directly. The sun’s rays are so bright it will obscure Venus, and you could damage your vision. If all else fails, watch a live NASA webcast from Hawaii.

This week’s viewing will be only the eighth time the Transit of Venus has happened since the telescope was invented, according to NASA’s Fred Espenak. It will begin at 3:06 p.m. Pacific Daylight Time, and hit the center of its journey at 6:25 p.m. The sun sets in Los Angeles at 8:02 p.m., but in points west — such as Alaska, Hawaii, Australia, eastern Asia, and most of Europe — the show will go on for two more hours. (The transit will occur on Wednesday for points west of the International Date Line.)

As long as clouds don’t interfere with the view, most of the world will be able to see at least part of the Transit of Venus, except for southeastern South America, western Africa, Portugal and Spain.

Entire lifetimes can go by with no one being able to see a Transit of Venus, but we’re living in a lucky time to see what Espenak calls one of the rarest of planetary alignments. The viewings occur only twice every 120 years. Since the telescope’s invention, Espenak says, it was only viewable in 1631, 1639, 1761, 1769, 1874 and 1882; the last viewable transit happened in 2004 but happened before sunrise in the western United States.

Some viewers have said the Transit of Venus looks as if there were a black hole punched in the sun, according to a NASA video.

The Transit of Venus has tantalized astronomers for centuries, and astronomers hoped that they could use the phenomenon to answer an enduring mystery — the distance between the Earth and Venus.

According to NASA, in the 18th century, astronomer Edmund Halley — whose name graces Halley’s Comet — theorized that if the Transit of Venus was observed from various locations on Earth, scientists could use that data to calculate the Earth’s distance to Venus.

European nations sent scientists on ships across the globe to observe the transit in 1769 in hopes of getting the data they needed. The British explorer James Cook was even dispatched to Tahiti to view Venus’ journey. But according to a NASA video, “bad weather, primitive optics and the natural fuzziness of Venus’ atmosphere prevented observers from gathering the data they needed.” According to this NASA article, it would take another century — when observers used photographs — for scientists to get the data to measure the size of the solar system.