The Transit of Venus, one of the rarest of predictable astronomical events, occurs from 12:09 to 6:42 p.m. on June 5. It will take more than six hours for the black disc of the planet Venus to cross the blazing surface of the sun. Transits of Venus occur in pairs, eight years apart; the last transit of Venus was in June 2004. Between those pairs, however, you must wait for more than a century. After the June 5 transit, the next one will not occur until 2117. Hawaii missed the last Venus transit in 2004, since it occurred after sunset in the islands when neither the sun nor Venus was visible. In fact, the last transit visible in Hawaii occurred in 1874.

However, we are the best location in the 50 states to see the June 5 transit. We are in fact the only state to see the event from start to finish; on the mainland, the transit will still be in progress as the sun sets.

Warning: It is never safe to view the sun directly except during the extremely rare moments of a total solar eclipse. Bishop Museum’s Shop Pacifica sells inexpensive viewing glasses to observe the transit directly.

The museum will host a Transit of Venus Festival on June 5 to mark this event. Regular museum admission rates to apply to this event. We will be open from 9 a.m. to 5 p.m. on Tuesday (normally a day when we’re closed). For a full roundup of Bishop Museum’s offerings for the festival, go to staradvertiser.com.

The transit of Venus has a special place in the history of astronomy. By the start of the 17th century, astro­nomers knew the relative distances of the planets. They knew, for example, that Mars was about 1.5 times as far from the sun as the earth is. However, no one knew the actual distance to the objects in the solar system.

One solution to this mystery was proposed by Edmond Halley in 1716. His idea: time the start of the transit of Venus from two widely separated parts of the earth. Using the distance between those two spots on earth as the baseline, one could then use triangulation to get the distance from Earth to the sun. Since the relative distances were already known, getting the correct distance from the Earth to the sun would allow you to unlock the actual distances to all other objects in the solar system. For example: If you discover Earth was 100 million miles from the sun, you could figure out that Mars must be 150 million miles from the sun, since you already knew that Mars was 1.5 times as far from the sun as the Earth is.

As with the famous comet whose return he predicted, Halley did not live long enough to see the next transit of Venus in 1761. However, his idea drove a wide-flung series of expeditions in 1761 and 1769 to view the transit of Venus, since the Halley method required that the transit be watched from widely separated parts of the earth. The most famous of these expeditions was Captain Cook’s 1769 expedition to Tahiti. While there were complications that prevented the measurements from being as precise as desired, scientists were able to get the correct distance to the sun to within about 2 percent based on these 18th century transits.

Planets in June

Venus is lost in the sun at the start of June. It emerges as a morning star later in the month. Try to catch it as early as June 20, rising in the east at 3:30 a.m. By the end of June, Venus rises at 2:45 a.m. and is about 12 degrees above the horizon (roughly the width of a fist) at dawn. As it becomes a morning star, Venus will hang just below Jupiter.

At the start of June, Mars is halfway up in the western sky at dusk and sets at 12:45 a.m. By the end of the month, Mars is one-third of the way up in the west at dusk and sets by 11:30 p.m.

Jupiter returns to the morning sky in June. Look for it by the middle of the month, when it rises at 3:30 a.m. in the east-northeast. By the end of the month it rises at 2:15 a.m. and is about 15 degrees above the eastern horizon at daybreak. By late June, look for the lovely gathering of Jupiter with Venus just below it, shining in the predawn skies at 3:30 a.m. Jupiter is the higher of the two.

June is another good Saturn month. At dusk in early June, Saturn is due south, and about halfway up in the southern sky. Here in early June it sets at 2 a.m. By the end of June Saturn is a third of the way up in the southwest at dusk and sets by 12:15 a.m. Saturn remains close to the bright star Spica, which is slightly bluish; Saturn has a slight yellow color.

Look for Mercury low in the west for the last half of June, around 8:30 p.m.

Other June Events

» On the night of June 3-4 there is a partial lunar eclipse visible from the Hawaiian islands. During a partial lunar eclipse, part of the moon goes into the deep inner shadow of the earth. The moon looks like someone took a bite out of it. In Hawaii, stay up late on June 3; right after midnight, and around 12:02 a.m. on June 4 the partial phase will begin. At the peak of the partial eclipse, around 1 a.m., it will look like about a third of the moon is missing. This will end at 2:03 a.m.

» June 20 is the summer solstice. Summer for the northern hemisphere begins at 1:09 p.m. Hawaii time. This is the longest day of the year for the northern hemisphere and the shortest day for the southern hemisphere. In Honolulu, the sun rises at 5:50 a.m. and sets at 7:16 p.m., giving 13 hours and 26 minutes of sun.

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Mike Shanahan is director of Education, Exhibits and Planetarium. For more information, go to www.bishopmuseum.org/planetarium/planetarium.html