TWO TOTAL LUNAR ECLIPSES

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

As you may know, the earth's shadow (like many other shadows) is actually composed of two parts: a dark central region called the umbra (Latin for "shadow") and an outer fringe portion called the penumbra (" almost a shadow"). Their passage over the face of the moon causes the eclipse to progress in three phases. Let's follow the sequence of events that'll make up the summer eclipse in order to see those separate stages in action.

AND THE SHOW BEGINS
On July 6 the moon will move into the earth's penumbra at about 12:22 a.m. Eastern Daylight Time. By 1:00 a.m. EDT, the shadow should be visible, but only as a slight darkening near the moon's left (east) edge. The first truly exciting moment of the eclipse, however, takes place at 1:33 a.m. EDT. At that point, observers will begin to see a very distinct dark stain on the left side of the celestial body, which signals the beginning of the partial phase (stage one) of the event . . . when the moon enters the umbra.

If you watch the movement of this shadow with binoculars or a small telescope, you can see whole craters and mountains being engulfed by the moving wave of darkness. But naked-eye observation will reveal something equally intriguing: You'll be able to notice that the edge of the umbra is curved. This phenomenon, naturally, proves that the earth is truly round (just in case you had any doubts!). When you watch a partial lunar eclipse, then, you're seeing the shape of the world on which you stand, projected onto a rocky "screen" a quarter of a million miles away!

As more and more of the moon's mass is shrouded in umbral shade, you'll soon become aware of the effect that the eclipse has on the surrounding sky. If clouds are scarce and you're not in the midst of a large city, you'll likely notice that crowds of "new" stars are appearing, while the commonly seen constellations seem to be brighter than usual ... all thanks to the absence of that overpowering lunar luminance.

A SIGHT TO SEE
When the umbra has almost fully covered the moon, the sphere will glow dimly with a ruddy, copper-colored light. At 2:38 a.m. EDT, total eclipse will begin (stage two) as the entire lunar face is covered by the umbra. Although the sight of a reddish moon is indeed a beautiful one, it also confuses many people. If the solid mass of the earth is preventing sunlight from reaching the moon, such folks reason, how can our lunar satellite continue to shine?

The answer to that question becomes obvious if we imagine ourselves standing on the moon during this phase of the eclipse. From that vantage point, we'd see the huge, dark disk of earth move into sight and then—as it completely hid the far more distant sphere of the sun—become encircled by a stunning ring of light . . . which is the sun shining through the earth's atmosphere. The same phenomenon produces the moon-glow we see during an eclipse. Because the light has to pass through the earth's atmosphere, to the moon, and back through the atmosphere to our eyes, its short wavelengths are almost completely scattered . . . leaving only the longer red wavelengths of light visible.

RSS | Comments | E-mail | Print