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Total Lunar Eclipse of February 20, 2008Decatur Area Astronomy Club, in cooperation with the Macon County Conservation District will host a public viewing session Wednesday, February 20, 2008 of the total lunar eclipse. This will be the last total lunar eclipse visible from the United States until until December 2010. Viewing begins at 7:00 pm at Rock Springs Center in Decatur Il. Introduction To The Lunar EclipseA total eclipse of the Moon occurs during the night of Wednesday, February 20/21, 2008. The entire event is visible from South America and most of North America as well as Western Europe, Africa, and western Asia. During a total lunar eclipse, the Moon's disk can take on a dramatically colorful appearance from bright orange to blood red to dark brown . An eclipse of the Moon can only take place at Full Moon, and only if the Moon passes through some portion of Earth's shadow. The shadow is actually composed of two cone-shaped parts, one nested inside the other. The outer shadow or penumbra is a zone where Earth blocks some (but not all) of the Sun's rays. In contrast, the inner shadow or umbra is a region where Earth blocks all direct sunlight from reaching the Moon. If only part of the Moon passes through the umbra, a partial eclipse is seen. However, if the entire Moon passes through the umbral shadow, then a total eclipse of the Moon occurs.
Times and Phases of the Total Lunar EclipseFrom start to finish, February's lunar eclipse lasts about three hours and twenty-six minutes (not including the penumbral phases which are very difficult to see). The partial eclipse begins as the Moon's eastern edge slowly moves into the Earth's umbral shadow. During the partial phases, it takes just over an hour for the Moon's orbital motion to carry it entirely within the Earth's dark umbra. The color and brightness of the totally eclipsed Moon can vary considerably from one eclipse to another. Dark eclipses are caused by volcanic gas and dust which filters and blocks much of the Sun's light from reaching the Moon. But since no major volcanic eruptions have taken place recently, the Moon will probably take on a vivid red or orange color during the total phase. After the total phase ends, it is once again followed by a partial eclipse as the Moon gradually leaves the umbral shadow. The total phase of a lunar eclipse is called totality. At this time, the Moon is completely immersed within the Earth's dark umbral shadow. During the February 20 eclipse totality will last just under 50 minutes. This is quite a bit less than the last total lunar eclipse ( August 28, 2007) which lasted 90 minutes. The major phases of the eclipse occur as follows (all times are GMT or Greenwich Mean Time). The partial eclipse commences with first umbral contact at 01:43 GMT. Totality begins at 03:01 GMT and lasts until 03:51 GMT. The partial phases end at 05:09 GMT. Eclipse times for time zones in the United States and Canada are shown in the following table.
The table above provides times of the major eclipse phases for North American time zones and Greenwich Mean Time (GMT). Eclipse times for other time zones can be calculated by taking the difference between local time and Greenwich and adding it to the tabulated GMT times.
Visibility of the Total Lunar Eclipse of February 20/21, 2008February's lunar eclipse is well-placed for North and South America as well as Europe and Africa. Observers along North America's west coast miss the early stages of the partial eclipse because it begins before moon rise. Alaskans in Anchorage and Fairbanks experience moonrise during totality but bright evening twilight will make it difficult for sourdoughs to view the event. Western Europe and northwest Africa also see the entire eclipse. Further to the east (east Africa and central Asia), the Moon sets before the eclipse ends. None of the eclipse is visible from eastern Asia or Australia. Preceding and following the eclipse are hour-long penumbral phases but these are faint and quite difficult to see. The more interesting and photogenic partial and total phases always take center stage to the penumbral phases.
The map above shows the geographic regions of visibility for each phase of the eclipse. The entire eclipse is visible from start to finish in the white (unshaded) portion of the map, while none of the eclipse can be seen from the dark gray areas. For anyone located in the blue shaded region labeled Eclipse at Moonset, this means that the Moon will set while some phase of the eclipse is already in progress. The contact curves labeled P1, U1, U2, U3, U4, and P4 represent each phase of the eclipse (see the key above). If you are east (right) of a particular curve, that phase occurs after moonset and you will not see it. However, if you are west (left) of a curve, that phase occurs before moonset and you will see it (weather permitting). For example, on the above map Turkey lies west (left) of the U3 curve (total eclipse end) and east (right) of the curve U4 (partial eclipse ends). This means that from this region, the Moon sets during the partial phases following totality. For observers located within the second blue shaded region labeled Eclipse at Moonrise, the situation is reversed. Here the Moon rises while some phase of the eclipse is already in progress. If you are west (left) of a particular curve (P1, U1, U2, U3, U4, or P4), that phase occurs before moonrise and you will not see it. However, if you are east (right) of a contact curve, that phase occurs after moonrise and you will see it (weather permitting). All total eclipses start with a penumbral followed by a partial eclipse, and end with a partial followed by a penumbral eclipse (the total eclipse is sandwiched in the middle). Since the penumbral phases of the eclipse are so difficult to see, we will ignore them.
Wonderful TotalityAt the instant of mid-totality (03:37 GMT), the Moon will lie in the zenith for observers in French Guiana. At this time, the umbral eclipse magnitude peaks at 1.1062. From the diagram above, it is clear that the northern (top) edge of the Moon will dip much deeper into the Earth's shadow than will the southern (bottom) edge. Since the Earth's umbral shadow is darker in the center than at the edge, the Moon's appearance will likely change dramatically with time. A large variation in shadow brightness can be expected and observers are encouraged to estimate the Danjon value at different times during totality ( Danjon Brightness Scale). Note that it may also be necessary to assign different Danjon values to different portions of the Moon at different times. This could be an excellent opportunity for budding astronomers and students to test their observing skills. Try recording your estimates of the Moon's brightness every ten minutes during totality using the Danjon Scale. Compare your results with your companions and classmates and discover how the Moon's appearance changes during the total eclipse. The brightness of the totally eclipsed Moon is very sensitive to the presence of volcanic dust in Earth's atmosphere. An eclipse of the Moon also presents a tempting subject to photograph. Since the Moon appears quite small in the sky, you'll need a fairly powerful telephoto lens (400 mm or more) or even a small telescope to attach to your camera. A typical ISO 400 speed (either digital or film) is a good choice. Unlike solar eclipses, lunar eclipses are completely safe to watch. Protective filters are not necessary and neither is a telescope. A lunar eclipse can be observed with nothing more than the naked eye. However, a pair of binoculars will magnify the view and make the red coloration brighter and easier to see. A standard pair of 7x35 or 7x50 binoculars is sufficient. During the eclipse, the Moon will be in Leo. Saturn and bright star Regulus are only 3 degrees east and west, respectively, of the Moon. Geminii, Orion, Taurus and other winter constellations will occupy the south and western sky for North American eclipse watchers. viewers. Although total eclipses of the Moon are of minor scientific value, they are remarkably beautiful events which do not require expensive equipment. They help to cultivate interest in science and astronomy in children and to provide a unique learning opportunity for families, students and teachers. To the nature lover and naturalist, the lunar eclipse can be appreciated and celebrated as an event which vividly illustrates our place among the planets in the solar system. The three dimensional reality of our universe comes alive in a graceful celestial ballet as the Moon swings through the Earth's shadow. Hope for clear skies, dress warmly and enjoy the show! |
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