In the tropics, the sun passes overhead twice during the year. On these two days, the sun will be exactly overhead at midday and an upright object such as a flagpole will have no shadow.

This phenomenon occurs only in the tropics; the sun is never overhead in any other part of the planet. As the only tropical state, Hawaii is the sole state to experience the overhead sun.

The “overhead sun” date varies depending on how far north or south you are in the tropics. The phenomenon occurs in mid-May in the southern end of the island chain. Thus, on Hawaii island, the overhead sun date occurs May 18 in both Hilo and Kailua-Kona, while in Lihue, the zenith sun day is on May 31.

In the islands, we describe the phenomenon as “Lahaina Noon,” the term selected by Bishop Museum in a 1990 contest to pick a name. The term “La haina” means “cruel sun” in Hawaiian, and while the sun in the islands is almost never cruel, it can be pretty intense as it shines directly down from the zenith.

Here are the overhead sun dates for both May and July, the two months each year when all of the main islands experience the phenomenon: Lihue, May 31, 12:35 p.m. and July 12, 12:42 p.m.; Kaneohe, May 27, 12:28 p.m. and July 15, 12:37 p.m.; Honolulu, May 26, 12:28 p.m. and July 16, 12:37 p.m.; Kaunakakai, May 25, 12:25 p.m. and July 16, 12:34 p.m.; Lanai City, May 23, 12:24 p.m. and July 18, 12:34 p.m.; Lahaina, May 24, 12:23 p.m. and July 18, 12:33 p.m.; Kahu- lui, May 24, 12:22 p.m. and July 18, 12:32 p.m.; Hana, May 23, 12:20 p.m. and July 18, 12:30 p.m.; Hilo, May 18, 12:16 p.m. and July 24, 12:27 p.m.; Kailua-Kona, May 18, 12:20 p.m. and July 24, 12:30 p.m.; South Point, May 14, 12:19 p.m. and July 27, 12:28 p.m.

May planets

Jupiter, the king of the planets, is a blazing light that you probably already noticed in April. Early in May, look for Jupiter about a third of the way in the eastern sky at dusk, shining at a blazing minus 2.4 magnitude. Jupiter will be high in the south at 11 p.m. and will set in the west by 4:45 a.m. By the end of the month, Jupiter is high in the east at dusk, is due south at 8:45 p.m. and sets at about 2:45 a.m.

Look for the waxing moon next to Jupiter on the nights of May 6 and 7.

Venus rises in the east at 4 a.m. in early May and is about 20 degrees up in the east (the width of two palms at arm’s length) at daybreak. In early May, Venus shines six times brighter than Jupiter. For the first week or so of May, if you have a flat horizon both to the west and to the east, you can compare these two brightest sky dots; Jupiter will be setting in the west around 4:30 a.m. as Venus rises in the east.

In the hours before dawn on May 22, look for the beautiful sight of a slender waning crescent moon just below Jupiter.

Saturn rises in the east by 10:30 p.m. in early May, is due south about 4 a.m. and is high in the west as day breaks. By the end of the month, Saturn is up at 8:30 p.m., due south at 1:30 a.m. and low in the west at dawn. Saturn shines as strong as a bright star and has a white-yellow color.

Mars has clung on in our western sky at dusk for months; this month, it comes to an end. In May, look for Mars about 10 degrees (the width of a palm) above the western horizon at dusk; through the month, it sets around 8:30 p.m. By mid-June we’ll lose the red planet.

For the last half of May, look for Mercury about 5 degrees (less than the width of three fingers) above the east horizon between 4:45 a.m. and dawn. The easiest morning to spot it will be May 23, where Mercury will be a mere 5 degrees to the left of a slender crescent moon.

May planets

Every year, May is the month when the great constellations of winter disappear into the light dusk, one after another. On May 1, the Pleiades are still visible low in the west at dusk; within few days, they are lost in the light of the setting sun. In early May, Orion is still striking, low in the west, at first darkness; by the middle of the month, Orion’s lost in the light of dusk as well. By the end of May, the brightest star, Sirius, and the constellation Auriga are also gone. Among the great winter constellations, only Gemini and Canis Minor shine on into early June, before they too plunge into the light of the sun.

May is the ideal time to look for the Cross, when it is due south and thus at its highest point in the sky. It’s still quite low as seen in the islands — about 6 degrees above the horizon as measured from the bottom (and brightest) star, Acrux, to the horizon. To locate the Cross, make sure you have a flat horizon such as the sea to view it. The Southern Cross will be visible, as every year, through the end of June; it returns to the predawn sky by early December.

Mike Shanahan is director of Education, Exhibits and Planetarium at the Bishop Museum. For more information, go to bishopmuseum.org.