Every May, the Hawaiian Islands experience the first of the two "overhead sun" days for the year.

This phenomenon is unique to the tropics; so, like seeing the Southern Cross, Hawaii is the only state where you can experience the overhead sun.

While people sometimes think that the sun is always overhead at noon, it’s never overhead unless you live in the tropics, and even there, it’s overhead on only two days of the year. On those two days, at local noon, the sun will be exactly overhead and an upright object such as a flag pole will have no shadow.

Our "overhead sun" dates vary depending on how far north or south we are in the tropics. Thus, for Lihue, the May "zenith sun"day occurs on May 31. Further south, on Hawaii island, the overhead sun date occurs nearly two weeks earlier, on May 18.

Here in the islands a term we often use for zenith noon is "Lahaina Noon." This is a modern term, selected by Bishop Museum in a 1990 contest held to select a name for the zenith noon phenomenon. 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. The other "Lahaina Noon" days occur in July.

Here are the dates and times for "Lahaina Noon" throughout the islands this May: Lihue, May 31, 12:35 p.m.; Kaneohe, May 27, 12:28 p.m.; Hono­lulu, May 26, 12:28 p.m.; Kaunakakai, Molokai, May 25, 12:25 p.m.; Lanai City, May 24, 12:24 p.m.; Lahaina, May 24, 12:23 p.m.; Kahului, May 24, 12:22 p.m.; Hana, Maui, May 23, 12:20 p.m.; Hilo, May 18, 12:16 p.m.; Kailua-Kona, May 18, 12:20 p.m.; and South Point, Hawaii island, May 15, 12:19 p.m.

May planets

Throughout May, look for Venus appearing in the west about 20 minutes after sunset. Venus looks as bright as an airplane. As it gets dark enough to see it, Venus will about a third of the way up in the west. The bright planet sets around 10 p.m. in early May and around 10:20 p.m. at month’s end.

Throughout May, as it gets dark enough to see Venus, look high overhead for Jupiter.

At the start of May, Jupiter is almost exactly overhead at dusk and spends the evening working its way down the western sky, setting in the west at 1:15 a.m. By the end of the month, look for Jupiter halfway up in the west at dark, in the same general part of the sky as Venus, but much higher up in the west. Jupiter will set around 11:30 p.m. at the end of the month.

Saturn is now in the early evening sky as well. The planet rises in the southeast at 8:45 p.m. in early May, is halfway up in the south around 2 a.m., and is low in the west as day breaks. By the end of the month, Saturn appears low in the southeast at dusk, is due south at midnight, and sets at dawn.

One big help in finding Saturn this year: Saturn is currently in the claw of Scorpius the Scorpion. This famous constellation has four stars that mark off the claw of the scorpion (or the top of the fishhook if you see it as Maui’s Fishhook).

At the start of May, Saturn is a fifth dot of light in that claw (or that fishhook-top), just above the other four, and whitish-yellow compared with the bluish-white of the four actual claw stars. Saturn does move against the starry background, like any planet; as May goes on, the planet will move slowly away from the four claw stars. By the end of May, look for Saturn in front of the uppermost of the four claw stars, about 2 degrees to the right of that star (that’s about four times the diameter of the moon).

In early May, look for Mercury low in the west at dusk (around 7:30 p.m.), just above where the sun went down. The planet will be about 10 degrees (the width of your palm) above the horizon, and sets by 8:15 p.m. On May 6, the planet will be about 13 degrees above the western horizon at dusk, setting at 8:30 p.m. After that, it will become harder to catch Mercury, and it will be gone by mid-month.

Other sky events

The Eta Aquarid Shower peaks on the evening of May 5-6. Viewing should be best early on May 6, in the hours before dawn. The meteors appear to come from the constellation of Aquarius, which rises above the horizon around 3:45 a.m. Expect about 10 to 30 meteors an hour. That said, there is a bright moon in the sky this year, just two days past full, that will interfere with the viewing of this shower.

This shower is one of two caused by debris from Halley’s comet, along with the Orionids in October.

May sky map

The map is good for 10 p.m. at the start of May, 8 p.m. at the end. A highlight of the May map is that Venus, Jupiter and Saturn are all in the sky at the same time. Venus is setting in the west, Saturn is rising in the southeast, and Jupiter is high overhead.

The last of the winter constellations, Gemini and Auriga, are now low in the west. Orion the Hunter is gone and will not reappear until August. His nemesis, Scorpius, rises in the east.

May is the ideal time in the islands to catch the Southern Cross, officially call "Crux" (Latin for "Cross"). If you want to see the Southern Cross, make sure you have a flat horizon (looking over the water is a good idea), since Crux never gets far above the south horizon.

Mike Shanahan is the director of visitor experience and planetarium at Bishop Museum. For more information, go to www.bishopmuseum.org/planetarium/planetarium.html.