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Total lunar eclipse on Wednesday, Oct. 27 to be visible from North America

– There will be a total lunar eclipse on Wednesday, October 27, 2004, visible from North America!

The full moon will gradually enter Earth's shadow (the "umbra"), becoming dark and (during the total eclipse phase) quite colorful. Here in California the eclipse will begin just as the full moon is rising at sunset, so the first part will be in a rather bright sky and low over the east/southeast horizon --- not very favorable for viewing. However, the moon will be substantially higher above the horizon, and the sky will be dark, during most of totality. The second partial phase (after totality) will occur when the moon is very high in the sky. East of California, conditions will be favorable even during the first part of the eclipse.

The partial eclipse begins at 6:14 pm PDT (i.e., just before sunset, which will be at 6:21 pm in the San Francisco area). Totality will be reached at 7:23 pm PDT, when the sky is relatively dark and the moon is well above the horizon and hence easily visible. Totality will last a long time (about 81 minutes), ending at 8:44 pm, when the moon will be quite high in the sky. The second partial phase will end at 9:53 pm PDT, when the moon will be very high in the sky. [By "partial phases" above, I mean "umbral" -- the penumbral partial phases last longer, but are difficult to see.

Those of you east of California: be sure to watch, but at the time appropriate for your time zone! For example, the partial phase begins at 9:14 pm EDT (the equivalent of 6:14 pm PDT). Totality will be reached at 10:23 pm EDT (7:23 PDT), and will last until 11:44 pm EDT (i.e., 8:44 pm PDT). The second partial phase will end at 12:53 am EDT (i.e., 9:53 pm PDT).

Total lunar eclipses look reddish for the same reason that sunsets do. Earth's atmosphere refracts the red light, but blue and green are absorbed and scattered.


The fully eclipsed moon is not completely dark. The reason for this is that although Earth blocks most of the light, sunlight passing through the Earth's atmosphere along the "edges" gets bent (refracted) slightly, allowing some of the light to reach the moon. Most of the blue and green parts of sunlight get absorbed by dust in the atmosphere, or scattered away by air molecules, and the remaining light is largely yellow, orange, and red. Thus, I expect the totally eclipsed moon to appear orange or reddish. The moon will be passing through the Earth's shadow somewhat above center, so we will probably see a brighter upper portion of the moon during totality (more of the bent rays of light can reach that part of the moon).

To view the eclipse, especially the initial stages, you will need to find a place having a clear east/southeast horizon, with no hills, buildings, or trees in the way. Later during the eclipse, when the moon will be quite high in the sky, you won't require such a clear eastern horizon, although it must still have relatively low obstructions. How low do they need to be for you to see the first part of totality (around 7:30 pm)? Well, stretch out your (adult) arm horizontally, open your hand as wide as possible, and rotate it so that the thumb is below the pinky. If hills, trees, and buildings toward the east rise above the horizon by an amount smaller than the width of your hand (i.e., smaller than the space between the tip of your thumb and the tip of your pinky), you will see the fully eclipsed moon. By 8:30 pm, while the moon is still totally eclipsed, obstructions can be as high as two hand-widths as described above, roughly speaking. Different people have a range of hand-widths, of course, so if in doubt you might want to walk or drive to a clearer location.

Lunar eclipses are totally safe to watch, and no optical aid is needed. Telescopes and binoculars can provide even better views, but are not necessary. I encourage you to find a suitable location and enjoy the eclipse, at least for a short time.

Good luck, and have fun!

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