19 December 2010
RARE LUNAR ECLIPSE: The lunar eclipse of Dec. 21st falls on the same date as the northern winter solstice. Is this rare? It is indeed, according to Geoff Chester of the US Naval Observatory, who inspected a list of eclipses going back 2000 years. “Since Year 1, I can only find one previous instance of an eclipse matching the same calendar date as the solstice, and that is Dec. 21, 1638,” says Chester. “Fortunately we won’t have to wait 372 years for the next one…that will be on Dec. 21, 2094.”
WHEN TO LOOK: The total eclipse lasts more than an hour from 02:41 am to 03:53 am EST on Tuesday morning, Dec. 21st. Any time within that interval is a good time to look. For other time zones, consult Shadow & Substance’s animated eclipse.
ALL-CLEAR IN THE STRATOSPHERE: Earth’s stratosphere is as clear as it’s been in more than 50 years. University of Colorado climate scientist Richard Keen knows this because he’s been watching lunar eclipses. “Since 1996, lunar eclipses have been bright, which means the stratosphere is relatively clear of volcanic aerosols. This is the longest period with a clear stratosphere since before 1960.” Consider the following comparison of a lunar eclipse observed in 1992 after the Philippine volcano Pinatubo spewed millions of tons of gas and ash into the atmosphere vs. an “all-clear” eclipse in 2003…
[Richard Keen’s Power Point presentation is at this link.]
Keen explains why lunar eclipses can be used to probe the stratosphere: “At the distance of the Moon, most of the light refracted into the umbra (Earth’s shadow) passes through the stratosphere, which lies 10 to 30 miles above the ground. When the stratosphere is clear, the umbra (and therefore, the eclipsed Moon) is relatively bright. On the other hand, if the atmospheric lens that illuminates the Moon becomes dirty enough, light will be blocked and the eclipse will appear dark.”
This is timely and important because the state of the stratosphere affects climate; a clear stratosphere “lets the sunshine in” to warm the Earth below. At a 2008 SORCE conference Keen reported that “The lunar eclipse record indicates a clear stratosphere over the past decade, and that this has contributed about 0.2 degrees to recent warming.”
What will the eclipse 21st eclipse look like? “The stratosphere is still fairly clear, and the December 2010 eclipse should be normally bright,” predicts Keen. “I welcome any and all reports on the brightness of future lunar eclipses for use in my volcano-climate studies. While actual brightness measurements (in magnitudes) made near mid-totality are most useful, I can also make use of Danjon-scale ratings of the eclipse. Please be sure to note the time, method, and instruments used in your reports.” Submit your observations here.
more eclipse resources:
Solstice Lunar Eclipse — from Science@NASA
Visibilty map — North America is favored
Live webcast — from the Coca-Cola Space Science Center
CAJ note: What events were taking place in 1638-39? Information from Answers.com has some historic facts. One of our favorites:
Clergyman Thomas Hooker tells the Connecticut General Court that people have a God-given right to choose their own magistrates (see Hooker, 1636). Although he has no thought of separating Church and state and prefers the more autonomous Congregational style of governance to Presbyterianism’s more hierarchical structure, he insists that the privilege of voting should be exercised according to the will of God, a view that will cause some later historians to call him “the father of American democracy.”
In January 1639:
The Connecticut General Court promulgates Fundamental Orders that will be recognized by some as the first written constitution in America. Neither wholly democratic nor entirely antitheocratic, it embodies many of the ideas of Hartford clergyman Thomas Hooker and is an advance over general Puritan thinking.
Undated in 1639 (via wikipedia):
The first printing press in North America is started in Cambridge, Massachusetts.
And, back to 1638:
Honeybees will be introduced into the American colonies in the next few years, will soon escape from their domestic hives, and will establish wild colonies. Native Americans will call honeybees “the white man’s fly,” and as the bees move westward many pioneers will be led to believe that the bees are indigenous (see Irving, 1835).
