Tuesday, December 21, 2010

Full Lunar Eclipse

Last night was a full lunar eclipse. Rather than try to sleep and then get up, I decided to work on the long-needed web page update for wwww.agatelady.com. I'll be sending the update today to my webmaster for uploading. At ten o'clock last night the skies were clear. Then, some high clouds started to form. At midnight the chances looked doubtful that we would be able to see the eclipse. The partial eclipse began at 1:33 a.m., which is around the time that friend, Renee, called. Although there were some thin clouds, you could still make out the outline of the moon, so Renee jumped in her car to come up to watch the eclipse at my house. Since I live out of town, there are no street lights or other sources of light pollution, so my house was a better viewing choice.

A lunar eclipse happens when the Earth gets in the way and blocks the sun's light from reaching the moon. The Earth always casts a shadow into space, and every now and then everything aligns just right so that the shadow falls on the moon. Lunar eclipses can only occur at full moon, that time each month when the moon is directly opposite Earth in relation to the sun. It's like you, representing Earth, standing in front of a bright light and casting a shadow on a child.

Since lunar eclipses occur always at full moon, it makes sense to ask why each full moon does not generate one. Eclipses are relatively rare because the plane in which the moon orbits around Earth is tilted 5 degrees compared to the plane of Earth's travels around the sun, a plane that astronomers call the ecliptic. The geometry of any eclipse — the relative positions of the sun, Earth and moon — is eventually repeated during a set of complex cycles that each last just more than 18 years (Saros cycle).

Solar eclipses are fairly numerous, generally two to five per year, but the area on the ground covered by totality is only a few tens of miles (kilometers) wide, so it’s rare to be in the path of a total solar eclipse. In any given location on Earth, a total solar eclipse happens only once every 360 years. Lunar eclipses are less frequent, but total lunar eclipses are visible everywhere that it is nighttime as the event takes place — essentially half the globe. Any given location can experience up to three lunar eclipses per year, as last happened in 1982. Some years there are none, as in 2005 and 2006.

During totality, the only light on the side of the moon we can see is reflected back from the Earth. In some cases, such as what happened early this morning, all the red light from the Earth's sunsets and sunrises combined to cast a red hue on the moon. Here is a diagram showing the geometry of a total lunar eclipse.

Just to clarify the difference, here is a diagram of a full solar eclipse.

Early this morning as the moon started to wane, the ice crystals in the upper atmosphere formed a large ring around the moon. Over the next half hour, the ring intensified. Then as the eclipse approached totality at around 2:41, the ring and all of the clouds disappeared. It was almost like the power of the eclipse blasted away the clouds.

During totality, scattered across the rest of the night sky, the stars appeared brighter than usual in contrast. Renee even saw a shooting star, but I missed it. The total eclipse ended at 3:53 a.m., and the partial eclipse ended at 5:01 a.m. I must admit that we didn't stay up for the duration.

Today is also the winter solstice, which is the shortest day of the year and marks the beginning of winter. The last time a full lunar eclipse took place on the solstice was long before any of our lifetimes. According to sources on the Internet the last time this happened was somewhere between 1544 and 1638!

First, here are a couple photos of the full moon. I enjoyed using the powerful zoom on my new camera. A tripod was definitely needed to steady the camera. I must admit that I took these two shots the night before, when there were no clouds.

The first three pictures taken during the waning period are a little fuzzy due to the high scattered clouds. The final two photos were taken with no remaining clouds, but the resolution is still not great. The camera was having a hard time focusing with so little light. The color of the moon in totality was a beautiful burnt orange.

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