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Watch the moon turn red during Dec. 20's lunar eclipse

By Mike Shanahan

Bishop Museum

POSTED:
LAST UPDATED: 09:06 p.m. HST, Aug 05, 2011

We'll see a spectacular total lunar eclipse from the Hawaiian Islands on the night of Dec. 20.

During a total eclipse the entire moon is in Earth's deep inner shadow. From about 9:45 to 10:50 p.m., the moon should turn a dark, eerie red.

While there is a lunar eclipse of some sort every six months, this is the first total lunar eclipse anywhere on Earth in three years.

Lunar eclipses can only occur during full moons. Only then do we have a straight line between sun, Earth and moon, with Earth in the middle. Earth blocks most of the sunlight and stops that light from hitting the moon.

As the sun's light passes by Earth on the way to the moon, our atmosphere blocks the shorter, blue wavelengths of light but allows the longer wavelengths of red light to pass through our atmosphere and continue onward to the moon. Thus, during lunar eclipses the moon does not turn black; it turns an eerie shade of dark red.

From Hawaii the lunar eclipse technically will start at 7:29 p.m. as the moon enters the faint outer shadow (penumbra) of Earth. However, you will not notice any darkening of the moon until at least 8:32 p.m., when the moon begins to enter Earth's deep inner shadow, or umbra. The moon will then be about one-third of the way up in the eastern sky.

By 9:42 p.m. the moon will be entirely in Earth's inner shadow as the total phase of this lunar eclipse begins. The moon will be about halfway up the eastern sky and should be dramatically darker and redder than usual. This total phase will last until 10:52 p.m. By the time the total phase ends, the moon will be almost exactly overhead, in the zenith of the sky.

As of 10:52 p.m. the moon will start to leave the umbra, and you will see the moon start to lighten. By midnight the moon will be out of that dark inner shadow and will look like a regular full moon. Technically this eclipse ends at 1:03 a.m. on Dec. 21 as the moon leaves Earth's outer shadow completely.

Lunar eclipses are safe to view. All you really need to view this event is clear skies. More information is available at eclipse.gsfc. nasa.gov/eclipse.html.

 

WINTER SOLSTICE

Winter officially begins at 1:38 p.m. Dec. 21 in Hawaii. This marks the shortest day of the year for the Northern Hemisphere. In Hawaii the sun rises at 7:05 a.m. and sets at 5:55 p.m., still giving us nearly 11 hours of daylight. Perhaps more striking, the sun is much lower in the sky this time of year. While the sun passes overhead in Hawaii in summertime, the highest it gets on Dec. 21 is about 45 degrees above the southern horizon at noon.

 

GEMINID RETURNS

The Geminid shower is a consistent meteor shower that comes by every mid-December. This year the peak is the night of Dec. 13 and into the early morning hours of Dec. 14. Meteor showers are always better after midnight; and on Dec. 14 the moon will set at 12:05 a.m., leaving the coast clear for good meteor hunting. Under dark skies this shower can produce 100 meteors an hour. While the night of the 13th is the peak, it's worth hunting for Geminids on the day before and the day after, as well.

As with any meteor shower, find clear skies, a clear horizon and a place where you can look up comfortably. Focus on the eastern sky. The constellation Gemini, which is where the shooting stars seem to come from, is about two-thirds of the way up in the east at about 12:30 a.m.

 

DECEMBER PLANETS

You should have no problem finding Jupiter next month; at minus 2.5 magnitude it's the brightest dot in the evening sky. Look for Jupiter high in the sky at about 7 p.m. at the start of December; it sets at about 1 a.m. in early December. By the end of December, Jupiter is about two-thirds of the way up in the southwest when it gets dark at 7 p.m., and sets at 11:30 p.m.

Venus is now a blazing morning star. It rises in the east just before 4 a.m. all month. It's about a third of the way up in the east by daybreak. At minus 4.9 magnitude, it outshines everything else and is impossible to miss (unless clouds get in the way). Saturn has also popped into the morning sky. At the start of December, Saturn rises just before 3 a.m. and is halfway up the sky as day breaks. By the end of the month, Saturn rises at 1 a.m., due south as day breaks.

On Dec. 7 you can use the crescent moon to find Mercury: It will be the dot just below the moon.

 

DECEMBER STARS

The map for this December is good for 9 p.m. at the start of the month, 8 p.m. in the middle and 7 p.m. at the end. Hold the map over your head or the four directions will not line up.

Familiar constellations of winter have returned. Look for Orion the Hunter rising in the east. Other winter constellations on the map include Auriga, Gemini and Taurus. The brightest object on the map is Jupiter, marked on this map by a large round dot in the southern portion of the sky.

The Southern Cross returns to our morning sky as it does every December. It rises in the southeast at 6 a.m. in early December, when you have a few minutes to catch it before daybreak. By the 15th it's up by 5 a.m., and you have an hour until daybreak. By the end of the month, the Cross rises at 4 a.m., and you have two hours prior to dawn to spot it.


Mike Shanahan is director of education, exhibits and planetarium at Bishop Museum. Reach him at mikes@bishopmuseum.org. A longer version of this article can be found at www.bishopmuseum.org/planetarium/planetarium.html.






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