Thursday, May 1, 2014

Solar Eclipses

Solar eclipses have been documented throughout history as peculiar natural phenomena. One can easily imagine how confused and alarmed people in the past were when the Sun unexpectedly disappeared. As a line from Homer’s The Odyssey stated, “The Sun has perished out of heaven, and an evil mist has overspread the world,” with a time of doom being prophesied for Earth. Eclipses were strange happenings that greatly frightened the public.

As technology advanced and research was further developed, scientists were able to extensively examine these special events. These rare episodes occur when the Moon aligns between the Sun and Earth, blocking the Sun’s light and creating a shadow on the Earth. During an eclipse, the day turns into night. In partial and annular eclipses, only part of the Sun is blocked, but in a total eclipse, the entire disk of the Sun is covered by the Moon. Although the process of a total eclipse takes about an hour, the state of totality lasts for at most seven and a half minutes. The only part of the Sun that is visible to the human eye is its corona, which is the normally unnoticed outer atmosphere that shines in the darkness. As the Sun begins to reappear, the diamond ring effect takes place, which is associated with the phenomenon of Baily’s beads. In approximately an hour, daylight is reestablished.

Total eclipses are fascinating phenomena that many people want to experience. Unfortunately, these only happen during a new Moon phase, which is when the Moon moves to the side of Earth facing the Sun. Because the Moon orbits Earth at an angle of 5 degrees relative to the Earth’s orbit around the Sun, the three spheres only align periodically. During a solar eclipse, the line of nodes, which is the intersection of the orbital planes, points to the Sun and the Moon lies on that line. Having both occur at the same time accounts for the rarity of solar eclipses. Total eclipses occur every one or two years, but because they are only visible from a small area on Earth, the chance of experiencing a total eclipse is less than once in a lifetime.

The second type of solar eclipse, the annular eclipse, occurs when the Moon’s orbit carries it too far from Earth that it cannot completely block the Sun. From Earth, this eclipse appears as a blackened circle surrounded by sunlight. Total and partial eclipses together average about two and a half occurrences per year. 

On Tuesday April 29, 2014, a partial solar eclipse took place. As the first solar eclipse of the year, it transformed the Sun into what is popularly known as, the “ring of fire.” It was classified as a non-central annular eclipse, a rare event, because the central axis of the Moon’s shadow missed Earth entirely while the shadow’s edge just barely grazed the planet. The Moon crossed the Sun’s disk at 3 in the morning in Australian time. The next eclipse that will be visible in Pittsburgh is estimated to be on October 8, 2014.
Clara Lee