When the Moon's penumbral shadow strikes Earth, we see a partial eclipse of the Sun from that region. Total solar eclipses are visible from within the umbral shadow. Partial solar eclipses are visible from within the penumbral shadow.The Moon's shadow actually has two parts: Unfortunately, this doesn't happen because the Moon's orbit around Earth is tilted 5 degrees to Earth's orbit around the Sun.Īs a result, the Moon's shadow usually misses Earth as it passes above or below our planet at New Moon.Īt least twice a year, the geometry lines up just right so that some part of the Moon's shadow falls on Earth's surface and an eclipse of the Sun is seen from that region. Since New Moon occurs every 29 1/2 days, you might think that we should have a solar eclipse about once a month. If the Moon's shadow happens to fall upon Earth's surface at that time, we see some portion of the Sun's disk covered or 'eclipsed' by the Moon. Geometry of the Sun, Earth and Moon During an Eclipse of the Sun The Moon's two shadows are the penumbra and the umbra.Īn eclipse of the Sun (or solar eclipse) can only occur at New Moon when the Moon passes between Earth and Sun. When the Moon is New, it rises and sets with the Sun because it lies very close to the Sun in the sky.Īlthough we cannot see the Moon during New Moon phase, it has a very special significance with regard to eclipses. The New Moon phase is uniquely recognized as the beginning of each calendar month just as it is the beginning on the Moon's monthly cycle. The Hebrew, Muslim and Chinese calendars are all lunar calendars. In fact many calendars are synchronized to the phases of the Moon. To many early civilizations, the Moon's monthly cycle was an important tool for measuring the passage of time. The rest of the phases are familiar to all of us as the Moon cycles through them month after month.ĭid you realize that the word month is derived from the Moon's 29.5 day period? The phase known as New Moon can not actually be seen because the illuminated side of the Moon is then pointed away from Earth. Waning Gibbous > Last Quarter > Old Crescent > New Moon (again)
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