01 June 2011

Eclipse Season: Three Solar and Lunar Eclipses all in a row

For most people it is a surprise to learn that Solar and Lunar eclipses are quite frequent events. Every six months we have an "Eclipse Season" in which we have two or sometimes three eclipses over the course of a few weeks, depending on the exact geometry of the Sun-Earth-Moon trio. June is one of these months, starting with a Partial Solar Eclipse (today), then a Total Lunar Eclipse mid-month, and finishing with a Partial Solar Eclipse (actually in July, but just hours after the end of June!).

Eclipses are indeed common for Planet Earth, but for a given fixed location on the planet, eclipses are less common. For example, the first eclipse (Solar) of June is visible only from the very far north regions of the planet. The Total Lunar Eclipse mid-June will be visible primarily in the eastern hemisphere, so for those of us in San Francisco, it will take place during the day when we cannot see the Moon. And the final (Solar) eclipse of this eclipse season will be visible only in a small region of the globe deep in the southern hemisphere.

Eclipses come in "seasons" because they can only happen when the Moon is precisely positioned to cast its shadow on the Earth, or when the Moon passes precisely through the Earth's shadow. As the Moon's orbit is not exactly aligned with the Earth's orbit, the two orbits (and shadows) come into alignment for a few weeks every six months. The rest of the time, the shadows of the Moon and Earth miss each other and we are eclipse-free!

Since eclipses are such dramatic events, when they are visible in your area, you should go out of your way to see them. For us in California, the next good eclipse will be a Total Lunar Eclipse on December 10th. More on that when the date draws nearer.

Meanwhile, if you want to know more about upcoming eclipses, visit the excellent on-line resource from NASA. The NASA Eclipse Web Site is filled with detailed information about solar and lunar eclipses, including maps, charts, and exact timing for each event. Another excellent resource is the EarthView Eclipse Network. The image (above) is courtesy of the EarthView Eclipse Network.

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