(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 mikes@bishopmuseum.org.)

Jupiter, king of planets, has been our constant evening companion for the last six months. Only Venus outshines Jupiter among the planets and stars, and Venus has not appeared in the evening since October.

Everything comes to an end, however, and March 2011 marks the end of Jupiter’s reign over our evening sky. Jupiter goes out with a bang, with a lovely conjunction between Jupiter and the planet Mercury in mid-March.

At the start of March, look for Jupiter around 7:15 p.m. low in the west. As long as you have clear weather in the west, you should have no problem finding it. Jupiter shines at minus 2 magnitude. Around dusk (7:15 p.m.) at the start of the month, Jupiter is about 15 degrees above the west horizon. Your fist at arm’s length is about 10 degrees in diameter; so Jupiter is about 1.5 fists above the west horizon at 7:15 p.m. Here March 1, Jupiter sets about 8:30 p.m.

Every night in early March, Jupiter will be a little lower at dusk. By March 10, Jupiter only 10 degrees above the horizon at 7:15 p.m. (one fist) and sets by 8 p.m.

Look for the early crescent moon just to the right of Jupiter on March 6.

By March 10, you may be able to see the planet Mercury down below Jupiter. On the 10th of March Mercury is very low at dusk, only about 4 degrees above the west horizon. That’s about the width of two fingers held at arm’s length. You’ll need a perfectly flat horizon, with no hills, trees, buildings (or clouds!) in your way to see Mercury.

That said, Mercury does shines much more brightly than usual, at minus 1.23 magnitude; so if you have that flat, clear horizon, you should be able to see this elusive planet.

From March 10 to 15, Mercury appears a little each higher each night at dusk, while Jupiter appears a little lower.

By March 15, the two planets will be side by side, low in the west at 7:15 p.m. Jupiter will be the brighter one, on the left, shining at minus 2 magnitude; Mercury will be on the right and shines that night at minus 0.9. The two planets will appear only two degrees apart from each other, or the width of a finger.

At 7:15 the planets are about seven degrees (3.5 fingers) above the horizon. Mercury and Jupiter will set simultaneously at 7:45 p.m. on March 15.

In the third week of March Jupiter will be a little lower in the sky each night at dusk. By March 25 Jupiter will be lost in the light of the setting sun, and its long-running appearance in our evening skies will be over.

Roughly a month later, in late April, Jupiter will reappear in the morning sky, heading for beautiful gathering with Venus in the morning skies in early May.

Mercury forges on

Mercury will remain in the March evening sky for the rest of the month. From March 15 to 25, Mercury will be roughly 10 degrees above the horizon in the west and will set around 8 p.m. With Jupiter taking a dive for the horizon, Mercury will be the most obvious dot of light in the sky at dusk in third week of March.

On the 22nd of March it reaches its greatest apparent distance from the sun.

From then on Mercury will fade. By the end of the month, Mercury is back to being only a few degrees above the horizon at dusk, and sets by 7:45 p.m. The also plunges in brightness; by March 31 Mercury shines at second magnitude, many times fainter than when it first appeared earlier in the month.

Planets appear to move against the background of the fixed stars. The closer a planet is to the sun, the faster it moves. Of all planets, Mercury appears to move the fastest, since it is the planet closest to the sun.

You can notice this speedy motion yourself if you track Mercury’s appearance is our dusk skies, night by night, this March. Perhaps due to its fast motion, Mercury was depicted in Greek mythology as the speedy, winged-footed messenger of Jupiter and the other gods.

NASA’s current mission to Mercury is also called MESSENGER. This March, as Mercury shines in our dusk skies, the Messenger spacecraft will go into orbit around the planet Mercury. We have received images of Mercury from Messenger, since it has made three flybys of the planet already.

Saturn joins the evening sky

Although Jupiter leaves the evening sky in March, Saturn has become an evening planet. Look for the planet rising almost due east at 9 p.m. at the start of March; in early March Saturn is halfway up in the east by midnight and halfway down in the western sky as day breaks. The planet shines at 0.4 magnitude. By the end of March, Saturn rises at sunset, is high overhead at midnight and sets at dawn. Look for the (just past) full moon next to Saturn on the night of March 19-20.

Venus blazes on

Venus remains the queen of the morning sky, though it’s now much lower at dawn than it was earlier this year. Venus rises around 4:30 a.m. throughout March. At the start of the month it’s twenty degrees above the horizon (two fists) at daybreak.

By the end of March its only 10 degrees (one fist) above the east horizon at daybreak. Venus remains brilliant at minus 4 magnitude. The month begins and ends with the lovely sight of a crescent moon next to Venus; looks for this on both March 1 and March 31.

Mars continues its long absence from the night sky. We lost sight of Mars in the December evening sky. It’s on the far side of the sun from us, and will not return to view till late April, when it pops into the predawn sky.

Spring returns

Spring begins at 1:21 p.m. March 20, Hawaii Standard Time (23:21 Universal time). This is called the “spring equinox,” which comes from Latin for “equal night.” Day and night are (roughly) equal on this day all over the world. In fact day and night would be exactly equal on the equinox (12 hours each) if earth, like Mercury and the moon, didn’t have an substantial atmosphere.

However, we do have air, of course, and that atmosphere bends the light of the sun. This means that we actually see the sun for a few minutes before it actually rises, and to see it for a few minutes after the sun actually sets.

For this reason, instead of exactly 12 hours of daylight on March 20, we get 12 hours and 9 minutes of sunlight March 20 in Honolulu; on that day the rises at 6:34 a.m. and sets at 6:43 p.m.

Spring forward (you continental types)!

Daylight Saving Time (DST) for most of the continental US and Alaska begins at 2 a.m. local time Sunday March 13. Hawaii of course does not observe DST, but it does affect us. As of that day, the east coast will be six hours ahead of Hawaii, and the west coast will be three hours ahead of us.

The March Sky Map

The map for March 2011 is good for 9 p.m. at the start of March, 8 p.m. in the middle of the month, and 7 p.m. at the end of the month. As always, hold this map over your head or the four directions will never line up!

The Big Dipper has returned! Look for it low in the Northeast. Called Nā Hiku (“The Seven”) in Hawaiian for its seven bright stars, this distinctive constellation has been missing from our evening sky maps since October. The “pointer stars” (the stars in the cup without a handle) provide the easiest way to point to the North Star.
The Big Dipper official astronomical name is Ursa Major, which is Latin for the Big Bear.

The closer you are to the equator, the less you see of the northern constellations. Both the Big Dipper and Cassiopeia spend a lot of time below the horizon here in Hawaii. The two constellations are on opposite sides of the North Star and you rarely see them at the same time. However, you can see them both in the March evening sky.

In the south, looks for the star Canopus. Called Kealiiokonaikalewa in Hawaiian – the chief of the southern skies – Canopus is the second brightest star in the entire sky. It’s also a good example of a star we can see from Hawaii, but which never rises above the horizon in most of the continental US.

This is the tradeoff of sky watching here: while the stars in the north are lower, we get to see southern stars that never rise above the horizon from places like New York or San Francisco.

Look for Orion the Hunter very high in the southwest, with its familiar hour-glass shape, distinctive belt of three stars, and brilliant stars Rigel and Betelgeuse. A modern Hawaiian term for the constellation is Ka hei hei on na keiki, or “the children’s cat’s cradle.”

Orion is a good guide for finding other constellations. The belt of Orion points up to Aldeberan, the bright star in Taurus the Bull. Take the belt of Orion the other way to find Sirius, the bright star in Canis Major (Big Dog). Sirius (Aa in Hawaiian, the fire star) is the brightest star in the sky.

Several distinctive constellations are just above Orion. These include the Gemini, marked by the twin bright stars Castor and Pollux. The Hawaiian term for this constellation, Nā Māhoe, also means “The Twins.” To the west of Gemini look for Auriga the Charioteer, with its brilliant yellow star Capella. The term Hokulei (“lei of stars”) is applied both to the star Capella and to the constellation Auriga as a whole. To the west of Auriga, in turn, is Perseus the Hero, whose shape looks somewhat like a night cap. The cluster of the Pleiades (in Hawaiian “Makalii” or “Little Eyes”) is at his feet.

In the east, look for Leo the Lion and, right on the eastern horizon, the planet Saturn.

Stars that aren’t on the map:

While we show the False Cross on this map, the real Southern Cross is missing from the evening sky. It will rise at midnight in early March and by 10 p.m. a the end of the month. In Hawaiian the Southern Cross is called Hanaiakamalama, which means “cared for by the moon.” Look very low in the south for the Southern Cross; you need to make sure there are no buildings or trees blocking your south horizon.

Its bottom star, Acrux, only gets about six degrees above the horizon at its highest point, or the width of two fingers at arms length. The Cross is due south at 2:15 a.m. at the start of February and 12:15 a.m. at the end. Look for the bright stars Alpha and Beta Centauri to the left of the Southern Cross; this can be your guide to point to the Cross itself.

Scorpius is also a morning constellation. Called Ka Makau Nui o Maui in Hawaiian, or “Maui’s Big Fishhook,” this massive constellation blazes brightly in the southeast at 3 a.m. at the start of March and 1 a.m. by the end of the month.

Moon phases
New Moon: March 4
First Quarter: March 12
Full Moon: March 19
Third Quarter: March 26

All dates are Hawaii Standard time.

— Find out more:
Bishop Museum Planetarium: www.bishopmuseum.org/exhibits/planetarium/planetarium.html
Hawaiian Astronomical Society: www.hawastsoc.org/