By David Ward
We do not usually think about Earth having a shadow, even though we live in it half the time. Our shadow extends almost a million miles into space, and every now and then when the sun, Earth and the moon line up perfectly, the moon travels through it.
We call this event a lunar eclipse and it is one of the coolest astronomical sights to see. The ancient Greeks noticed the curve of the Earth’s shadow on the moon during an eclipse, and correctly surmised that our planet was round — a fact that was forgotten for over 1,000 years until rediscovered by Copernicus and Galileo.
The Greeks also used lunar eclipses to deduce the sun was larger than the moon and much further away. They did not get their calculations quite right and underestimated the vast distance between us and the sun.
This time the action will start at 11 p.m. on April 14, when the full moon traveling eastward in its orbit around Earth enters the darker part of the planet’s shadow called the umbra. For the next hour, watch the moon slowly disappear. At 12:07 a.m., totality begins when the moon is completely immersed in our shadow.
The moon will usually take on a striking reddish or even a coppery hue due to the atmosphere of the Earth refracting some of the sun’s light on the surface of the moon. The color of every lunar eclipse is different due to the amount of dust or clouds in our air. If you were standing on the moon looking at Earth you would see a completely darkened orb surrounded by a thin fiery ring, the combined sunrises and sunsets all around our world.
Before and after the eclipse, the moon’s glare is so intense it washes out all but the brightest stars and constellations. During the total phase of the eclipse, however, all the constellations pop into view. The moon is right in the middle of Virgo the virgin, and that bright star just below it is Spica. Notice how its white light contrasts with the reddish, fully eclipsed moon.
To the right, or westward, Mars shines at nearly its peak brightness for the year. We will have reached our closest approach to the red planet just a week before. The bright star Arcturus glows above the eclipsed moon and Saturn shines to the left. At 1:25 a.m. the moon starts to leave Earth’s shadow. Over the next hour it will grow larger until it exits the shadow and goes back to being a normal full moon.
If you get to see this eclipse, congratulations — you have witnessed a beautiful demonstration of the mechanics of our solar system. Stay up for another couple of hours to see brilliant Venus rising just before dawn in the east.
Sorry about the late night timing of this eclipse. I will try to arrange the next one earlier in the evening so you do not have to stay up so late.
There is still plenty to see just after dark. Take a last look at all those brilliant winter stars and constellations like Orion the hunter, Taurus the bull, and Sirius the dog star. They are all drifting westward into the sunset glow. Jupiter is the really bright one in the west. It will be visible most of the spring but will vanish into the west just before summer arrives.