When viewed from the Earth, a solar eclipse happens when the Moon passes between the Sun and Earth so the Moon blocks the Sun. If the Moon only blocks part of the Sun, then it is a partial solar eclipse. If the Sun is fully obscured by the Moon, then it is a total solar eclipse. Total eclipses are rare at any one location, because the Moon fully blocks the Sun along only a narrow path on the Earth’s surface traced by the Moon’s shadow.
According to the National Aeronautics and Space Administration (NASA), a partial solar eclipse will occur on May 20, 2012. This is the first solar eclipse to happen in the United States since 1994. In San Francisco, this eclipse will begin at 5:15 pm and end at 7:40 pm. The maximum eclipse will occur at 6:32 pm when 85% of the sun will be obscured. This partial eclipse will look the like the Moon has a ring of fire surrounding it.
Although it is tempting, you shouldn’t view a solar eclipse with the naked eye. Your eye-lens will concentrate the sun’s light onto your retina, and this can cause permanent eye damage. You can safely view a solar eclipse wearing inexpensive solar glasses (with a “CE” label), which have filters that block out 99.99% of the sun’s light and 100% of the harmful ultraviolet rays. Don’t have solar glasses? You can also safely view a solar eclipse by indirect projection – projecting the image of the sun onto a white piece of paper using a pinhole camera. The San Francisco Exploratorium has directions on how to make a pinhole camera.