Although this is the third total eclipse in the past 12 months, it’s the first visible from all of North America. The previous two favoured only half the continent. As a bonus this time, Saturn lies near the eclipsed Moon.
Understanding what causes a lunar eclipse is easy once you grasp the three-dimensional arrangement of the Sun, Earth, and Moon. The Sun radiates lots of light throughout the inner solar system, and our opaque planet casts a shadow into space. Typically, a Full Moon passes untouched to the north or south of this shadow, but not so this month. The Moon plows right into the shadow, where direct sunlight can’t reach.
Earth’s dark shadow creeps across the lunar surface starting at 8:43 P.M. Eastern Standard Time this evening (February 20). Along the East Coast, the Moon already stands more than 30° high in the dark eastern sky then. For West Coast observers, the Moon rises minutes after the partial eclipse begins, just as the Sun sets. If you’re on a hilltop with a clear view of both the western and eastern horizons, you might get a unique opportunity to briefly see both the Sun and eclipsed Moon…and if you try really hard you might be able to make shadow puppets on the moon!Earth’s shadow takes 78 minutes to envelop the Moon completely. Once totality starts, our orbiting companion takes on a reddish-orange hue. The Moon isn’t totally dark because sunlight sneaks through Earth’s atmosphere, which acts like a lens and bends red rays into the shadow. This bathes the lunar surface in an eerie ruddy light. The shadow’s darkness depends largely on the amount of dust in Earth’s atmosphere – the more dust, the darker the Moon appears.As totality progresses and the sky grows darker, the surrounding stars of Leo the Lion pop into view. The constellation’s brightest star, Regulus, appears just 3° above the eclipsed Moon.
Meanwhile, Saturn lies 4° to the Moon’s lower left. Notice the Moon and Saturn edging closer as the eclipse advances. When the eclipse begins, they lie 4.4° apart; by eclipse end, the gap is down to 3.5°.Look at the subtle colors across the totally eclipsed Moon. The northern limb should appear darker than the southern limb because it lies deeper in Earth’s shadow. Take photographs, either through a telescope or with a camera on a tripod. If you want to capture a wide-field view, try to include interesting foreground objects. Totality lasts 51 minutes, wrapping up at 10:52 P.M. EST. The Moon then leaves the shadow over the following 78 minutes.
Get your camera’s ready to see this total lunar eclipse – the next one won’t come until December 20/21, 2010.