The rare Transit of Venus is coming Tuesday 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.

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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.