Announcements

Classical Astronomy at the Midwest Homeschool Convention - March 27-29 
Attention homeschoolers in Ohio, Kentucky and Indiana!  We'll be attending the Midwest Homeschool Convention in Cincinnati, Ohio the weekend of March 27-28.  Formerly known as the Cincinnati Homeschool Convention, this new convention is the most fun, happening homeschool event in this part of the country.  There will be a top lineup of homeschool speakers such as Jessie Wise, Jeannie Fulbright and my ubiquitous pal Todd Wilson.  I'll be doing three workshops on "The Biblical Purpose of Astronomy." 

This the only convention we have planned for 2008 (though we might also attend the CHEO convention in Columbus, Ohio.)  So if you're attending this convention, please drop by and say hi.  For more info, visit:

http://www.cincinnatihomeschoolconvention.com/   

Signs & Seasons Reviews
We recently received some very kind reviews for our astronomy curriculum Signs & Seasons from some prominent homeschool websites....     

Knowledge House
Signs & Seasons provides a serious study of astronomy, and yet it is enjoyable to read and doesn't seem like a textbook at all. Even the introduction and appendix are interesting! It is suitable for a high school level astronomy class or as a self-study guide to the sky for homeschoolers, college students, and adults. While the recommended age level for Signs & Seasons is 13 and up, the whole family can benefit from this book.  (Read the Full Review)

HomeschoolChristian.com
Signs & Seasons is a fascinating book. Its beautiful cover will grab children's interest immediately, and the descriptive illustrations will allow parents with no knowledge of the subject to grasp it quickly. The activities are plentiful so a family can pick and choose. Not only will Signs & Seasons put you more in touch with God's creation as the author suggests, but also it will bring your family closer as you gaze at the heavens together.  (Read the Full Review)

Many thanks to these reviewers for their kind words!  You can read more at our Endorsements page, including the nice reviews from the homeschool magazines.  Include Signs & Seasons with your homeschooling plans for 2008!  

As we've seen in previous eclipse coverage, a lunar eclipse occurs when the Full Moon lines up with the Earth and the Sun in such a way that the Moon passes behind the Earth and into its shadow.  

The first stage of an eclipse is the penumbral stage, when the Moon passes through the Earth's "penumbra" or partial shadow.  This stage is not very noticable since only a subtle darkening of the Moon occurs.  

The next stage is the partial stage, when the Moon begins to enter the "umbra" or full shadow of the Earth.  At this point, the curved shadow of the Earth can be seen to "take a bite" out of the Moon's face. 

Totality begins when the Moon fully enters the Earth's umbra.  During totality, the Moon can look very dark.  At other times, a ruddy glow can be seen on the Moon's surface, as red sunlight filtered through the Earth's atmosphere shines onto the Moon, giving it a reddish-orange color.    

This total eclipse is very well placed for observers in North America.  The penumbral stage will begin at 7:34 PM eastern standard time (EST), and everyone east of the Mississippi will be able to see the entire eclipse.  The partial stage will begin at 8:42 PM EST, and the Moon will be slowly gobbled up by the Earth's shadow until totality begins at 10:00 PM EST.  This time around, totality will only last until 10:51 PM EST since the Moon is only grazing through the edge of the Earth's shadow.  After totality, partial eclipse will past until 12:09 AM EST as the Moon leaves the Earth's umbra. 

Observers in western North America will see this eclipse at earlier local times.  The Moon will rise in the penumbral stage as seen from west Texas through Alberta.  People on the west coast in northern California and Oregon will see the Moon rising in partial eclipse. 

The eclipse will be visible over Europe and Africa and western Asia, but this will be more for night owls and early birds!  Totality begins at 3:00 AM on Thursday morning in the United Kingdom, and even later at points east.  The Moon will be setting at various stages of eclipse as seen from as far east as Afganistan!  So if you or a missionary friend is in that part of the world, be sure to wake up and check out this eclipse before sunrise on Thursday morning, February 21! 

Be sure to catch this one folks, this is the last total lunar eclipse visible over North America until 2010!  As before, if you have a nice view of this eclipse, please send along a detailed report.  We're looking for colorful descriptions folks, so please, tell us a story!  Also, please share any nice pix of this eclipse and we'll include them in the next Update.  I'm expecting solid clouds over Cleveland, so this is the most our family might see! 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Eclipses - Why Not Every Month?
When I was a kid in school, we were taught very little practical astronomy, and what we were taught was mostly confusing.  I remember hearing that a Full Moon occurred when the Moon was "behind" the Earth, as seen from the Sun.  I also remember learning that a lunar eclipse occurred when the Moon was "behind" the Earth so as to fall into the Earth's shadow. 

Similarly, I was taught that a New Moon occurred when the Moon was near the Sun, but a solar eclipse was caused by the Moon passing in front of the Sun so that the Moon's shadow passed over the surface of the Earth.  Hearing these explanations, I was puzzled as to why we didn't have eclipses every month.  The New Moon and Full Moon are monthly events, yet eclipses were relatively rare and made the news. 

What I did not learn as a kid was the orbit of the Moon is slightly "tilted."  The Moon's orbit is inclined 5.2 degrees to the Plane of the Ecliptic, which is the plane of the Earth's orbit around the Sun.  As a result of this inclination, the Moon wanders over a large area of the sky, sometimes passing through the plane of the Earth's orbit, other times passing high above.  This creates many interesting phenomena of the Moon, from changes in its appearance to variations in the the tides.  It also affects the timing and circumstances of lunar and solar eclipses.

Most of the time, the New Moon passes high above the Sun or far below, and does not cross over the face of the Sun.  Similarly, the Full Moon usually passes above or below the Earth's shadow, and does not pass directly into it.  However, at two times in each lunar month, the Moon does cross the plane of the Earth's orbit.  At these times, the Moon appears to cross the ecliptic, which the apparent path of the Sun's motion through the constellations of the zodiac.

The Nodes
The points where the Moon's orbit crosses the ecliptic are called the nodes of the Moon's orbit.  The ascending node is the point where the Moon is moving north of the ecliptic, while the descending node is the point where the Moon is moving south of the ecliptic.

In most months, the Moon crosses the ecliptic in any old waxing or waning phase, and is far from the Sun.  However, a couple times a year, the Sun, Earth, and Moon will line up in such a way that one of the Moon's nodes is very near the Sun.  At such times, the New Moon crosses the ecliptic in proximity to the Sun so that an eclipse occurs.  Similarly, the Full Moon crosses the ecliptic within the Earth's shadow.  It is for this reason that the path of the Sun through the stars is called the ecliptic, since this is where eclipses occur.

The Moon's nodes are not always seen in the same zodiac constellations at all times.  In fact, the nodes are constantly moving toward the west in a cycle that takes about 18.6 years.  This is called the regression of the nodes.  So if a lunar eclipse is seen in the constellation Gemini, a year and a half later another lunar eclipse will be seen in Taurus.  For this reason, over a long enough period of time, solar and lunar eclipses can be seen on just about any date of the year from any place in the world.

The phenomena of eclipses and nodal regression was a baffling mystery down through all history.  However, following the revolutionary law of universal gravitation of Isaac Newton, the science of celestial mechanics showed that the complex motions of the Moon were the result of the combined gravities of the Sun and Earth tugging on the Moon and continually diverting its orbit, but allowing very precise prediction of future eclipses. 

As a result, we understand that a solar eclipse is followed by a lunar eclipse and that eclipse pairs are found about six months apart.  In 2008 eclipses are seen at the New and Full Moons of February and August.  However, such eclipse pairs do not always result in total eclipses, nor eclipses that can be seen in the same parts of the world.  But they can be predicted for centuries forward and backward in time. 

Using these techniques, calculations of known historical eclipses have been used to assign exact dates to many events in history where no actual dates have been recorded.  For example, a lunar eclipse over Jerusalem reported by the historian Flavius Josephus was used to estimate the birth of Jesus as being in 4 B.C.

The Names of the Nodes
For much of history, Classical Astronomy was extensively used by sailors to navigate their way from port to port and eventually around the world.  Anyone who has read any books on the Age of Exploration or who has seen any of these pirate movies will know that the seafarers of old were a very colorful bunch and used a lot of quaint jargon of the sea.  This also applies to their use of astronomy.  Everyone out there worried about "pagan influences" in astronomy will be interested to know that the old mariners referred to the Moon's  ascending node as "the head of the Dragon" and the descending node as "the tail of the Dragon"!

The head of the Dragon is the place where that the Moone dothe come over the line Ecliptick, from the South part, unto the North part: and the Tayle of the Dragon is, where the Moone passeth over the line ecliptick from, the Northe part unto the South part.  The use of the head and tayle of the Dragon, is to know, when that there is any eclipse of the Sunne or Mone: and of what quantitie or greatnesse the eclipse is.  -- William Bourne, A Regiment For the Sea (A.D. 1574)

This colorful perspective allows us to interpret the following old woodcut, which is from an Austrian publication in A.D. 1534.  It shows the Dragon's head engulfing an eclipsed Moon in the constellation Leo.  The Sun is shown at the Dragon's tail with a black circular edge indicating a partial eclipse, in the constellation Aquarius, on the opposite side of the sky from Leo.



The modern techniques of eclipse calculation reveal that there was in fact an eclipse pair that meet this exact description.  A partial solar eclipse at the descending node was visible over Europe on January 14, 1534.  This would have occurred in the part of the sky traditionally associated with the constellation Aquarius.  Later that month, on the night of January 29-30, a total eclipse of the Moon near the ascending node was seen over Europe.  Compare the picture of the Sun in the woodcut above to this animation of the solar eclipse showing the appearance as seen from Vienna in 1534.   

This woodcut is quite remarkable as being carved nine years before Mikolaj Kopernik published his heliocentric theory, and more than 150 years before Isaac Newton's famous work was published.  It might have been carved based on an eyewitness account, since the astronomy of eclipse prediction was very rough at that time.  But this should illustrate the precision available today to modern science. 

I find it remarkable that the LORD created such a remarkable order in the heavens and that He gave Man the mind to observe and develop the mathematics to make such a precise model.  Compare this remarkable piece of practical, quantitative "here and now" science with the speculative, inferential explanations used to prop up evolutionary beliefs.   

Though not much about eclipses is discussed, you can learn basic information about the Moon's cycle and the ecliptic from Signs & Seasons, our homeschool astronomy curriculum.