The solar eclipse that will cross the continental U.S. this Aug. 21 will attract a huge audience — and rightly so. The millions of people who are expected to witness the astronomical event won't show up just because solar eclipses are exceedingly beautiful — they're also exceedingly rare. Here's why.
A solar eclipse occurs when the moon passes completely in front of the sun, casting a shadow that darkens a portion of the Earth. Since the moon takes roughly one month to complete a single orbit of Earth, solar eclipses could theoretically happen once a month, too. There are other variables at work, however, that ensure that they don't.
For one thing, the moon's orbit is inclined relative to the Earth's equator. That means that most of the time the moon eclipses the sun, the shadow it casts fall either above the Earth or below it. Here on the ground, the sun looks just as it always does. It's only when the moon passes the sun when it's in just the right spot in its orbit that the shadow reaches us. Read more....
A solar eclipse occurs when the moon passes completely in front of the sun, casting a shadow that darkens a portion of the Earth. Since the moon takes roughly one month to complete a single orbit of Earth, solar eclipses could theoretically happen once a month, too. There are other variables at work, however, that ensure that they don't.
For one thing, the moon's orbit is inclined relative to the Earth's equator. That means that most of the time the moon eclipses the sun, the shadow it casts fall either above the Earth or below it. Here on the ground, the sun looks just as it always does. It's only when the moon passes the sun when it's in just the right spot in its orbit that the shadow reaches us. Read more....