Tuesday, April 29, 2003

Earth Will Eclipse the Moon on May 15 (2003)

Earth Will Eclipse the Moon on May 15 (2003)
by Dave Adalian

When the Moon comes up on the evening of May 15, it will be slipping into the shadow of Earth and a total lunar eclipse. There will be plenty to see and much to learn before it returns to normal just three hours later.

Every 30 days, Earth, the Moon and the Sun describe a line in space, and from Earth we see this as a full moon. Now and then, they align just so and for a few hours Earth upstages Luna, blocking its Sun. Although this is fairly rare, it will happen twice this year for us: May 15 and November 9. Of the two, May’s will probably be the better show.

The Moon rises at 7:40 p.m., but the Sierra will block our view for a few minutes. When the disk of the Moon shows itself, it will already be in the shadow’s lighter outer edge, the penumbra, and well into its darker center, the umbra. You won’t really notice much difference in brightness caused by the penumbral shadow, but the difference caused by the umbra will be striking--a blurry-edged curved line moving on the face of the Moon.

The umbra will continue to creep across until by 8:14 p.m. the entire face is covered. This is totality. The Moon inside the umbra looked dark when some part of the surface remained lighted. Now, it glows an eerie coppery crimson. The orange color reflected back during totality is red light passing through Earth’s atmosphere and bending into the path of Earth’s shadow. Sunlight is comprised of all different colors, and when it passes through Earth’s atmosphere the blue light is scattered. This is what makes the sky blue and the rising full moon bloody. If you could stand on the Moon during an eclipse, the effect would make Earth look like an absolutely black disk floating in a ring of fire.

While the Moon is dark is the time to look at the stars around it. The night of the eclipse, Luna is riding between the claws of Scorpius the Scorpion. Just below it is the head of the scorpion, and just below that is the red star Antares, a name that means rival of Mars. The scorpion’s tail is below the horizon during the eclipse, but will show itself as the Moon rises.

The height of totality comes at 8:40 p.m., and the Moon will start to move out of the umbra by 9:07 p.m. As it goes, take another look at the curved line of shadow. What you’re seeing is evidence the Earth is round, as the only spinning object that can cast a shadow like that is a sphere.

At 10:13 p.m., the Moon will have moved out of the umbra, and in another hour, as Luna passes out of shadow to become her familiar self again, the show will be over until autumn.


This column first appeared in the Visalia (Calif.) Times-Delta on April 29, 2003.

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