December 20-21: The Night of the Red Moon
Friday, December 17 3:29 pm
Astronomer Joe Rao and colleagues will be celebrating the final night of the autumn season at the Hayden Planetarium Winter Solstice Party on Monday, December 20, with observations of celestial objects on the Arthur Ross Terrace (weather permitting) and a preview of the total lunar eclipse in the Hayden Planetarium Space Theater. Below, Rao shares a few interesting facts about the coming full lunar eclipse.
Parts of four continents will be treated to a view of a total eclipse of the Moon early on the morning of December 21, and Hayden Planetarium astronomers say the show will be the best of its kind New Yorkers will see until the year 2014.
Eclipse Timetable
In the New York area, the eclipse will officially begin on December 21 at 12:29 am as the Moon begins to enter Earth’s outer, or penumbral, shadow. But even in clear weather sky watchers will not notice any changes in the Moon’s appearance until about 1:15 am, when a slight “smudge” or shading begins to become evident on the upper left portion of the Moon’s disk. The first definitive change in the Moon’s appearance will come on the Moon’s upper left edge. At 1:33 am the partial phase of the eclipse will begin as the Earth’s dark shadow–called the umbra–starts to slowly creep over the face of the full Moon. At that moment the Moon will be roughly two-thirds of the way up in the sky as measured from the southwest horizon to the point directly overhead.
At 2:41 am the eclipse will reach totality, but sunlight bent by our atmosphere around the curvature of the Earth should produce a coppery glow on the Moon. At this time, the Moon, if viewed with binoculars or a small telescope, will present the illusion of seemingly glowing from within by its own light.
At 3:17 am the Sun, Earth and Moon will be almost exactly in line and, assuming clear skies, the light of the Moon will appear at its dimmest. Totality ends at 3:53 am, and the Moon will completely emerge from the umbra and return to its full brilliance at 5:01 am. By then the Moon will have descended to a point about one-quarter up from above the west-northwest horizon.
A Sight for the Billions
The entire 72-minutes of total eclipse will be visible from all of North and South America, the northern and western part of Europe, and a small part of northeast Asia including Korea and much of Japan. Totality will also be visible in its entirety from the North Island of New Zealand and Hawaii.
In all, an estimated 1.5 billion people will have an opportunity to enjoy the best part of this lunar show. In other parts of the world, either only the partial stages of the eclipse will be visible or the eclipse will occur when it’s daytime and the Moon is not above their local horizon. Portions of western Africa and central Europe can catch the opening stages of the eclipse before the Moon sets below their horizon, while the eastern-third of Asia and central and eastern Australia can catch the closing stages just after moonrise.
Generally speaking, about half of the world’s population–about 3 billion people–will be able to view at least a part of this eclipse.
A Shady Drama
Unlike an eclipse of the Sun, an eclipse of the Moon presents no hazards to the viewer. No precautions to protect the eyes are needed. A lunar eclipse occurs whenever the Moon passes into the umbral shadow of the Earth. This dark shadow extends in the shape of a cone which on December 21 will measure about 844,000 miles into space (the Moon will be 231,000 miles from Earth that day). A total lunar eclipse occurs only when a full Moon, the Earth and the Sun are in a direct line and allows the Earth’s shadow to fall on the face of the full Moon. In most cases, however, the full Moon passes above or below the shadow cone every month.
For any one location, total lunar eclipses occur at an average frequency of four or five times per decade. The last total eclipse of the Moon seen in New York occurred on February 20, 2008, and there won’t be another until April 15, 2014.
The Earth, when it comes between the Sun and Moon, casts a shadow large enough to embrace the entire Moon, sometimes for nearly two hours. In contrast, in the case of the most ideal set of circumstances for a total eclipse of the Sun, the Moon casts a shadow onto the Earth’s surface that’s rarely more than 167 miles wide, and totality lasts no more than 7½ minutes.
Solar eclipses attract numerous scientific expeditions because they offer ways to study the Sun that are unavailable at other times.
In contrast, a lunar eclipse is of far less scientific value.
Only the Shadow Knows the Moon’s Color
Although astronomers do not expect to gain new astronomical insights from the eclipse, lunar eclipses vividly reflect the overall state of the Earth’s atmosphere. Under normal weather and atmospheric conditions, as the Moon slides into the shadow of the Earth, its normal yellow-white color changes into a still-visible but dull coppery-red at the height of the eclipse. Since the Sun’s rays are bent by Earth’s atmosphere so that some still reach the Moon, the Moon is still visible in an eclipse. However, because of the recent eruptions of an Icelandic volcano last spring and the Mt. Merapi volcano in Indonesia in October, one and possibly two clouds of ash and dust are currently floating high above the Earth. As a result, the Moon may appear darker than usual during this eclipse. So during totality, parts of the Moon might even become black and invisible.
Or…the Moon might wear its normal eclipse cloak of a deep red or a coppery-hue or take on still other colors (orange, chocolate brown or gray). Hayden Planetarium astronomers say that the color possibilities are unpredictable and that it is impossible to tell exactly how much light the Earth’s atmosphere will refract as its shadow creeps across the Moon. Cloud cover and other atmospheric conditions may also affect the visibility and coloration of the Moon.
In short: we’ll all just have to wait for eclipse night and see what actually happens.
