Hawaii's Sky Tonight

(Reprinted from the Bishop Museum Website)
Skywatch Article
March 2008
By Carolyn Kaichi, Bishop Museum

SPRING SKIES

March brings in the spring season with the vernal equinox, the moment when the sun crosses the celestial equator on the way up to the northern hemisphere. This is also the beginning of “cross season”, or the time you can view the Southern Cross in the evening sky. The Southern Cross, also known as Crux, is the smallest of the 88 officially recognized constellations.

Here in Hawaii, this constellation is known as Hanaiakamalama, or “cared for by the Moon” and is part of the modern Polynesian navigational “star line” called Ka Iwikuamo’o, “The Backbone”. In Polynesian navigation this is one of the four reference lines of stars that runs from the north sky to the south. The Backbone starts with the North Star, Hokupa’a, through Ursa Major, Hokule’a (the star Arcturus), Hikianalia (Spica) in Virgo, Me’e (the constellation Corvus), finally to the Southern Cross.

You can start looking for the Southern Cross just before midnight looking out over the ocean on the Leeward side. There are four bright stars that make up the kite shape with a smaller fifth star between the second and third bright star (if you count the top star as number 1, then go clockwise). You can see the Southern Cross on the flags of many countries of the southern hemisphere, like Australia, Samoa and Papua New Guinea since this constellation is more prominent in the southern skies.

The Southern Cross was visible at least 5,000 years ago at higher latitudes in North America and Europe. According to one historian the Southern Cross was seen in Jerusalem at the time Christ was crucified. But because of precession, the “wobbling” of the Earth’s axis, the Cross is no longer visible at higher latitudes in the northern hemisphere.

Even here in Hawaii at 20 degrees north of the equator, the Southern Cross does not get very high above the horizon. Standing completely upright, the top star (Gacrux) is only a mere 12 degrees. In fact, the distance between the top and bottom stars of the upright Cross is the same distance as the bottom star (Acrux) to the horizon—another navigational feature. In the southern hemisphere, draw an imaginary line between the top and bottom stars and they will point the way to the South Celestial Pole. In the northern hemisphere, the North Star conveniently marks the North Celestial Pole but there is no equivalent star in the south.

Because the Southern Cross is so low in the sky and close to the South Celestial Pole, its path in the sky is short. From the time it rises to the time it begins to set it is only in the sky for around six hours, whereas objects that rise closer to due east and set due west takes approximately 12 hours to traverse the sky. In other words, don’t expect to see the Southern Cross in the sky all evening long!

Earlier in the evening you will still see the signature stars and constellations of the winter—Orion, Taurus, Gemini and Auriga are some of the more famous. Orion’s dog, Canis Major (translated as “Big Dog”, not too original but descriptive) has the distinction of having the brightest star as seen from the Earth. Sirius’ status as the brightest star has more to do with its closer proximity rather than its properties—there are many larger and luminous stars in our skies but they are just farther away. Low in the south under Sirius is Canopus in Carina, the second-brightest star in our sky.

Looking to the east of Canopus, you can see another cross-like shape—surprise, you found the “False Cross”! The False Cross is actually made up of stars from two separate constellations that are low in the southern skies. The stars of Vela the sails, and Carina the keel, comprise the False Cross. Those two constellations along with Pyxis the compass and Puppis the stern make up pieces of the ship Argo that carried Jason and the Argonauts on great adventures in Greek mythology.

The “real” Cross will be visible in the sky until around July, when it will then begin to set by the time darkness falls. To find the real Southern Cross, remember that Orion and pals are low in the west by the time the Cross starts to rise and look for the two “pointer stars” to the east of the constellation that point to the top star of the Cross. These stars are Alpha and Beta Centauri in the constellation Centaurus.

The Planets

Earth:

The Vernal Equinox falls on March 19 here in Hawaii, 7:49 P.M. HST. This is the earliest spring date since 1896. Also, Daylight Savings Time begins Sunday, March 9. ADD an hour to most times on the mainland.

Mercury:

Mercury and Venus spend the month huddled in the eastern morning sky just before the sunrise. On March 5 a very thin crescent Moon will join the pair. Neptune and eventually Uranus are also in the vicinity (Uranus comes close to Venus in the last half of the month), and Jupiter is also high in the sky at the time. You will need a telescope to view Neptune and Uranus.

Venus:

Venus rises around 5:30 A.M. at the beginning of March, close to neighbor Mercury. By the end of the month it is getting very close to the sunrise and more difficult to see, rising only around 45 minutes before the sun. Venus is making its way back to the evening sky and will pass in back of the sun (superior conjunction) in June.

Mars:

As we get closer to the summer months the sky darkens later, so although Mars is high in the sky by 7:00 P.M. it will be hard to spot right away. We are already leaving Mars behind after passing by in December last year, and as the Red Planet recedes it looks smaller and dimmer in our night sky. Throughout March Mars sits above the horns of Taurus next to the legs of the brother Castor in Gemini.

Jupiter:

Jupiter rises by 3:45 A.M. in early March right off the handle of the Sagittarius “teapot” asterism. Until Venus rises two hours later, Jupiter commands the sky as the brightest object aside from the Moon.

Saturn:
Saturn was in opposition last month and is already in the eastern sky at dusk. The planet is in Leo the Lion and sits to the east of the lion’s heart, the star called Regulus, which Saturn easily outshines. On March 18 the almost-full Moon (three days short) passes right next to the pair.

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