It’s a spectacle that won’t repeat for another century — the sight of Venus slowly inching across the face of the sun — and people in Hawaii will have front-row seats.

So unless scientists discover the fountain of youth, none of us alive today will likely ever witness this celestial phenomenon again, dubbed a "transit of Venus."

It’s so unique that museums and schools around the globe are hosting Venus viewing festivities — all for a chance to see our star sport a fleeting beauty mark. Even astronauts aboard the International Space Station plan to observe the event.

The drama unfolds Tuesday afternoon from the Western Hemisphere.

Skygazers who want the full experience are flocking to Hawaii, considered one of the prime viewing spots since the whole transit will be visible. From Waikiki Beach to the summit of Mauna Kea, eclipse glasses will be passed out so people can safely see Venus crossing without damaging their eyes.

Just remember to have patience.

"There’s no one big climactic moment. It takes longer to happen" than a solar or lunar eclipse, said Larry O’Hanlon, who does outreach at the W.M. Keck Observatory on Mauna Kea.

Venus will appear as a small black dot gliding across the disk of the sun. As in a solar eclipse, do not stare directly at the sun; wear special protective glasses.

The entire transit, lasting six hours and 40 minutes, will be visible from the western Pacific, eastern Asia and eastern Australia.

Skywatchers in the United States, Canada, Mexico, Central America and the northern part of South America will see the beginning of the show before the sun sets. Europe, western and Central Asia, eastern Africa and western Australia will catch the tail end after sunrise. Those who don’t want to leave their homes can follow live webcasts by NASA and various observatories.

The second planet from the sun between Mercury and Earth, Venus is about the same size as Earth. It appears as one of the brightest objects in the night sky because its thick clouds reflect much of the sunlight back into space.

There will be no obvious change to the brightness of the sky during the event; Venus blocks out only a tiny fraction of the sun.

Venus is the third celestial show to grace the sky in less than a month. Just a day earlier a partial lunar eclipse will be visible from western North America, South America, Australia and eastern Asia. And there was the much-hyped "ring of fire" solar eclipse May 20.

Unlike eclipses, Venus transits are truly rare. They come in pairs, separated by more than 100 years. The last one occurred in 2004; the next pair will be in 2117 and 2125.

Since the German astronomer Johannes Kepler first predicted it in the 17th century, only six have been observed. The upcoming one will be the seventh.