terça-feira, 14 de junho de 2011

Eclipse total da Lua: amanhã!

The first lunar eclipse of 2011 occurs at the Moon's ascending node in southern Ophiuchus about 7° west of the Lagoon Nebula (M8). The Moon passes deeply through Earth's umbral shadow during this rather long event. The total phase itself lasts 100 minutes. The last eclipse to exceed this duration was in July 2000. The Moon's contact times with Earth's umbral and penumbral shadows are listed below.

Penumbral Eclipse Begins: 17:24:34 UT
Partial Eclipse Begins: 18:22:56 UT
Total Eclipse Begins: 19:22:30 UT
Greatest Eclipse: 20:12:37 UT
Total Eclipse Ends: 21:02:42 UT
Partial Eclipse Ends: 22:02:15 UT
Penumbral Eclipse Ends: 23:00:45 UT

At the instant of greatest eclipse [5] the umbral eclipse magnitude [6] will reach 1.6998 as the Moon's centre passes within 5.3 arc-minutes of the shadow axis. The Moon's southern limb will lay 32.8 arc-minutes from the edge of the umbra while the northern limb will lay 22.3 arc-minutes from the umbra's edge. Thus, the northern regions of the Moon will probably appear brighter than the southern regions that lie deeper in the shadow. Since the Moon samples a large range of umbral depths during totality, its appearance will change dramatically with time. It is difficult to predict the exact brightness distribution in the umbra so observers are encouraged to estimate the Danjon value at different times during totality (see Danjon Scale of Lunar Eclipse Brightness). Note that it may also be necessary to assign different Danjon values to different portions of the Moon (i.e. - north vs. south).

Nearly 30 years ago (1982 Jul 06), the author watched another total lunar eclipse with the Moon in the same part of the sky. I was amazed at how brilliantly the summer Milky Way glowed since it was all but invisible during the partial phases. Observers will have a similar opportunity during June's eclipse. In this case, the totally eclipsed Moon will lie in southern Ophiuchus just 8° northwest of the brightest Sagittarian star clouds. The summer constellations are well placed for viewing so a number of bright stars can be used for magnitude comparisons with the totally eclipsed Moon.

Antares (mv = +0.92v) is 15° to the west, Shaula (mv = +1.63) is 14° south, Epsilon Sgr (mv = +1.85) is 15° southeast, Arcturus (mv = -0.05) stands 55° to the northwest, and Altair (mv = +0.77) is 46° northeast of the Moon.

Figure 3 shows the path of the Moon through the penumbra and umbra as well as a map of Earth showing the regions of eclipse visibility. The entire event will be seen from the eastern half of Africa, the Middle East, central Asia and western Australia. Observers throughout Europe will miss the early stages of the eclipse because they occur before moonrise. Fortunately, totality will be seen throughout the continent except for northern Scotland and northern Scandinavia. Eastern Asia, eastern Australia, and New Zealand will miss the last stages of eclipse because they occur after moonset. Again, the total phase will be seen from most of these regions. Even observers in eastern Brazil, Uruguay and Argentina will witness totality. However, none of the eclipse will be visible from North America. At mid-eclipse, the Moon is near the zenith for observers from Reunion and Mauritius.

Table 3 lists predicted umbral immersion and emersion times for 20 well-defined lunar craters. The timing of craters is useful in determining the atmospheric enlargement of Earth's shadow (see Crater Timings During Lunar Eclipses).

The June 15 total lunar eclipse is the 34th member of Saros 130, a series of 71 eclipses occurring in the following order: 8 penumbral, 20 partial, 14 total, 22 partial, and 7 penumbral lunar eclipses (Espenak and Meeus, 2009a) spanning 1262 years.

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