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Skywatch: Partial Solar Eclipse and Lahaina Noon highlight May viewing

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click on image for larger view. Image courtesy of NASA

(Sky Watch is a regular column written by Mike Shanahan, director of education and exhibits at the Bishop Museum in Honolulu. He can be reached at

Renovation of Watumull Planetarium starts in May

The Watumull Planetarium will be closed from May 10 – 25 inclusive to install a full-dome video system, Digistar 4, in our existing facility. Then, from May 26 through September 3 we’ll run the new Digistar system within our existing planetarium. Programs will include New Horizons (an overview of the planets and see by NASA’s robot probes) and Seven Wonders, which explores both the seven wonders of the ancient world and of the universe. We’ll also keep our popular Polynesian navigation show Explorers of Polynesia and Sky Tonight, enhanced with full dome visuals.

After Labor Day, September 3, we’ll close for three months and do a full renovation. These fall 2012 renovations will include a new Goto Chronos II star projector, new interior dome, lighting, seats, carpet and sound system, as well as the Digistar. Look for a spectacular, fully-renovated Watumull planetarium in December 2012.

Partial solar eclipse on May 20
As seen from the islands a small portion of the sun will be blocked by the moon on the afternoon on May 20. From Honolulu the first contact of moon and sun will occur at 2:03pm. By 3:15pm, the time of deepest eclipse, about 1/10th of the sun will be blocked by the moon. The eclipse will end at 4:12pm.

In parts of the continental US, this May 20 eclipse will be an annular eclipse. An annular eclipse occurs when the moon is unusually distant from the earth in its orbit around the earth. At times like this, the distant moon is too small to cover the entire disk of the sun. Even when the moon is dead-center in the middle of the solar disc, a ring of sunlight shines around the moon.

The annular eclipse will pass over the western US in the afternoon of May 20. The annular phase will touch the west coast in northern California near Eureka just after 5pm local time. In Redding, CA, the annular phase will start at 6:26pm and last for about four minutes. The path of the annular eclipse will proceed through the exact middle of Nevada, and then cross south Utah and Northern Arizona. It was cross the middle of New Mexico; Albuquerque is right in its path. The annular phase will start at 7:26pm on Albuquerque and last just over four minutes.

Please note that is never safe to view an annular or a partial eclipse without a proper filter. In preparation for the Transit of Venus less than three weeks later, Bishop Museum’s Shop Pacifica currently does have a good stock of inexpensive solar viewers, perfect for viewing solar eclipses and Venus transits safely.

(Editor’s note: The partial eclipse begins in Kailua-Kona at 2:18 p.m., is maximum at 3:18 p.m. and ends at 4:11 p.m. In Hilo the partial eclipse begins at 2:19 p.m., is maximum at 3:20 p.m. and ends at 4:14 p.m.

Detailed map of the eclipse path (PDF Document)

Lāhainā Noon in late May in the islands
In the tropics the sun passes overhead twice during the year. On these two days, at local noon, the sun will be exactly overhead and an upright object such as a flag pole will have no shadow. Lāhainā Noon only occurs in the tropics; the sun is never overhead in any other part of the planet. For Honolulu, the first of these “overhead noon” events occurs on May 26 at 12:28 p.m.

While sometimes called “shadowless noon,” “zenith noon” or “overhead noon,” there was no handy term for this phenomenon in the islands, so Bishop Museum had a contest in the early 1990s to name it. The winning term, “Lāhainā Noon,” means “cruel sun.”

Lāhainā Noon dates vary depending on your latitude. Here are the Lāhainā Noon dates and times for May 2012:

2012 Lāhainā Noon days and times

May 30 12:35 p.m.

July 11 12:42 p.m.


May 27 12:28 p.m.

July 15 12:37 p.m.


May 26 12:28 p.m.

July 15 12:37 p.m.


May 25 12:24 p.m.

July 16 12:34 p.m.

Lāna‘i City

May 25 12:24 p.m.

July 18 12:33 p.m.


May 23 12:23 p.m.

July 17 12:32 p.m.


May 23 12:22 p.m.

July 17 12:32 p.m.


May 23 12:20 p.m.

July 18 12:30 p.m.


May 18 12:16 p.m.

July 24 12:26 p.m.


May 18 12:20 p.m.

July 23 12:30 p.m.

Planets in May

Venus has been our bright evening light for months. That ends in May. At the start of May, Venus shines in the west at minus 4.5 magnitude, about one third of the way up from the horizon at dusk. In early May Venus sets around 10 p.m. Every night Venus will be a little lower in the west at dusk. By May 25, it will be only about 10 degrees above the horizon at dusk (the width of your hand at arm’s length) and will set by 8:30 pm. Venus will be completely lost in the sun’s light by the end of the month. Venus is heading for a rendezvous with the sun’s blazing disc; Venus will cross the sun on Tuesday June 5 for an extremely rare transit of Venus (see below).
Look for an early crescent moon next to Venus on May 22.

Mars shines high in the evening skies this May against the backdrop of Leo the Lion (see our May star map for exact location). At start of May, Mars is very high in the south at dusk and shines at 0 magnitude, several times brighter than the star Regulus in Leo. In early May, Mars sets by 2:45 a.m. By the end of the month, Mars has faded to 0.5 magnitude and shines high in the west at dusk and sets just after 1 a.m. Look for the waxing gibbous moon close to Mars on both May 1 and June 1.

Jupiter is lost in the sun all month.

May is another good Saturn month. Saturn shines at 0.3 magnitude. At dusk in early May Saturn is about 1/3 of the way up in the east, overhead at 11:30 pm, and sets at 5:15 am. By the end of the month Saturn is two-thirds of the way up in the east at dusk, halfway down in the west at midnight, and sets by 3:15 am.

What you’ll really notice is that Saturn appears twinned with the star Spica in Virgo, about 5 degrees to the right of Saturn. The two dots of light will remain about 5 degrees apart all month, and look like two eyes staring down at you. Saturn is slightly brighter than Spica. Saturn is slightly yellow and Spica is slightly blue.

On the night of May 1 and again on May 31, look for the waxing gibbous moon next to Saturn.

Mercury puts in a fleeting predawn appearance in the first few days of May. From May 1 through 7. Look for Mercury in the east around 5:20 a.m., about six degrees (three fingers) above the east horizon.

May star chart

click on image for larger view

click on image for larger view

The star map is good for 11 pm at the start of May and 9 pm at the end of the month.

In May we say farewell to the great constellations of winter. Canis Major, Orion, Auriga, Taurus and the Pleiades are all gone. With the winter stars gone, the first star of the summer triangle, Vega, rises in the east. In addition, the south is full of landmark late spring constellations. May is prime time for the Southern Cross, low in the south. The Southern Cross is officially know as “Crux” (Latin for “Cross”), and that’s how it’s labeled on the star map. Make sure you have a clear, flat horizon in the south if you want to have a chance of finding this small but famous constellation. Leaping over Crux is Centaurus the Centaur. Two brilliant stars, Alpha and Beta Centauri, mark his knees. Alpha and Beta Centauri are much easier to find that the Southern Cross, so find those two stars first; then go to the right and that will lead you to the Cross.

Scorpius, know here as Maui’s Fishhook, is just to the left of the Cross and has just cleared the horizon by the time of the May star map.

Arcturus is high overhead. You may know it better by its Hawaiian name, Hōkūle‘a (“star of gladness”); the famous voyaging canoe is named for the star.

In the north, both the bright Big Dipper and fainter Little Dipper are in prime location for viewing, though you’ll need a dark location to find the stars of the Little Dipper. Draco the Dragon winds between the dippers.

Transit of Venus Preview (June 5)
Mark your calendars for the Transit of Venus on Tuesday, June 5 2012. On that day, for the first time since 1874, viewers in Hawai‘i will be able to see the black dot of Venus cross the bright face of the sun.

Transits of Venus occur in pairs eight years apart. The “twin” of the 2012 transit occurred in June 2004. That 2004 transit occurred after sunset in the islands, so Hawai‘i missed it entirely. As if to make up for that, Hawai‘i is the best state in the US to view the 2012 transit. We will see the entire June 5 transit in Hawai‘i, weather of course permitting. The transit starts at 12:09 Hawai‘i Standard Time on Tuesday June 5 and runs over six hours, ending just before sunset at 6:42 p.m. This is the last transit of Venus till 2117, so this will be the only chance you will ever have observe this special event!

Bishop Museum will host a “Transit of Venus” festival on Tuesday June 5. The Museum and all its regular exhibit halls will be open from 9 am to 5 pm. Since the transit starts just after noon, members of the Hawaiian Astronomical Society will be on hand from noon to 5 pm to show the transit in their telescopes. The Watumull Planetarium, with its new Digistar 4 full-dome video system, will feature programs on Venus and other topics. We’ll also feature lectures on the transit of Venus and its importance to Hawai‘i; a live web cast of the transit; Science on a Sphere programs about Venus; and more!

Moon phases
Full Moon: May 5
Third Quarter: May 12
New Moon: May 20
First Quarter: May 28

All dates are Hawai’i Standard time.

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