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Leap Year     February 22, 2004


This is a Classical Astronomy Update, an email newsletter especially for Christian homeschool families (though everyone is welcome!)  Please feel free to share this with any interested friends. 

If you or a friend would like to be added to the list for future emailings, please drop a line to -- If you wish to removed from the list, please send an email to .


  "Seasonal Skies"
  "Dance of the Planets"
     * Venus *
     * Lunar Occulation of Mars *
  "Signs and Seasons (Gen 1:14)"
     * Leap Year *
     * The Dominical Letter *

"If sometimes, on a bright night, whilst gazing on the inexpressible beauty of the stars, you have thought of the Creator of all things; if you have asked yourself who it is that has dotted heaven with such flowers, and why visible things are even more useful than beautiful; if sometimes, in the day, you have studied the marvels of light, if you have raised yourself by visible things to the invisible Being, then you are a well prepared auditor, and you can take your place in this august and blessed amphitheater."
-- Basil the Great, Archbishop of Caesarea (330-379 A.D.), from his "Hexaemeron"      

Hello Friends,

It's been over a month since the last Update.  We've had a busy winter, full ski lessons, Cub Scout events and home maintenance projects.  But also, we've been very busy with redesigning the Classical Astronomy web site.  Rather than being simply a newsletter archive as it is now, the new site will be updated frequently and will feature timely information about sky events.  Also, many new features are being added that will make everyone wish to visit the site regularly, in the hopes of establishing an online community for readers of the Update.  

Among other things, we'd like to include articles and columns from you, the readers.  And not just astronomy topics, but also on homeschooling, faith and just about any other topic of interest to the readers.  We plan on relaunching the site sometime soon.  If you'd like to contribute an article to be posted on the site, please drop us a line to propose a topic.  Please understand however that this is all "volunteer work" on our end, so we can't offer payment at this time for any submissions.  But we'd be very grateful if you'd still like to be involved!


* Christian Astronomy *
We recently were pleased to find out about CASE, the Christian Association of Stellar Explorers.  This is an amateur astronomy club and member of the Astronomical League, founded by Patrick Carr and based in Siloam Springs, Arkansas.  If you're from that part of the country, be sure to visit this club some starry night.  The club web site is:

Even more exciting is the Christian Astronomer's Network, a national organization formed to be a resource to Christian camps, schools or home eduation associations.  The Network has created a curriculum that enables amateur astronomers with their own telescopes to combine classroom lessons in astronomy with outdoor telescope sessions. 

We know that several amateur astronomers read the Update.  We hope that this Network can provide an excellent vehicle for you to promote astronomy in your area, from a Christian perspective, to the many Christian schools and Christian camps who would be interested in utilizing this resource. 

But we're most excited that a Network has been founded around which astronomically-minded Christians may gather.  We hope that the Christian Astronomer's Network may enable Christian amateur astronomers from all over the world to come in contact to share ideas and fellowship, and co-labor to help teach God's starry sky to the next generation.  The web page for the Christian Astronomer's Network is at:

* Astronomy Cartoon Museum Exhibit *
For folks who live in California near the Bay Area, there is an exhibit of my educational astronomy cartoons currently on display at the Chabot Space and Science Center in Oakland.  The exhibit is called "SkyWise: Picturing Astronomy" and features 16 of the 54 SkyWise comics strips that I created for Sky & Telescope magazine from 1997 through 2001.  More info, including a link to the SkyWise web site, can be found at:

This is actually old news, but I've kept forgetting to mention it in the Update since its debut last October.  If you live in the Bay Area, try to catch this exhibit before it's gone.  But this is a traveling exhibit that may appear in museums around the USA, so perhaps this will someday come to a science museum near you.  If the exhibit does move on to another museum, we'll announce it in a future Update.

"Seasonal Skies"

* Orion *
During February and into March, the evening sky is dominated by that wonderous constellation, Orion the Hunter.  As we've seen in past Updates, Orion is the brightest constellation in the night sky, and perhaps the best known star pattern after the Big Dipper.  Orion includes several "first magnitude" stars, among the brightest in the celestial sky. 

Orion is easily found by the three stars of "Orion's Belt."  These three stars are of equal brightness, equally spaced apart and lying almost directly in a line.  Orion's Belt defines the middle of Orion, and it's easy to see two bright stars above the Belt, and two below that form general shape of a man.  In this way, Orion is easily visible from just about everywhere, even from locations under the bright city lights. 

As seen from a rural, dark-sky location, other stars can be seen that give the appearance an extended arm, as if holding a shield, and another arm, appearing to hold a club.  The constellation Orion is seen facing off in a neverending battle against the constellation Taurus the Bull.  This constellation is seens as a distinct triangle of stars including the bright star Aldebaran, the reddish "eye" of the Bull. Taurus is seen to the northeast of Orion (the upper right as seen from the northern hemisphere, and the lower left as seen from the lands of the southern hemisphere.)

In my opinion, Orion's Belt is evidence in the sky of the existence of a Creator God.  There are about 6000 stars visible to the unaided eye in the entire sky.  Of these, there are only about 70 stars that are brighter than the stars of the Belt.  And these three stars are so obviously similar in brightness and so perfectly spaced and lined up.  I'm no statistician, but it seems highly unlikely to me that three stars would present themselves in this way, assuming the strictly random presumptions of science!  And there are other unlikely star patterns, but that is another story....

In our era, Orion's Belt lies nearly directly on the Celestial Equator, the mid-circle in the sky between the North and South Celestial Poles.  In this way, Orion's Belt would pass directly overhead as seen from the Earth's Equator.  And for this reason also, Orion is the only prominent constellation of which at least a portion can be seen from everywhere on the Earth, from the North Pole to the South Pole. 

Just as the stars of Orion's Belt are no coincidence, it's also no coincidence that remarkable Orion is one of the few constellations named in the Bible:

"Seek him that maketh the seven stars and Orion, and turneth the shadow of death into the morning, and maketh the day dark with night: that calleth for the waters of the sea, and poureth them upon the face of the earth: the LORD is his name." -- Amos 5:8 

For more about Orion, check out last year's Update, also posted at .

"Dance of the Planets"

* Venus *
The bright planet Venus is currently shining brightly, high in the western sky at sunset.  Even though we've mentioned Venus in recent Updates, we still have received several emails asking, "what is that bright object in the western sky in the evening?"  You need ask no more!!  Yes folks, that's not an airplane, it's the bright planet which is our closest neighbor in the solar system!

People are always amazed at the incredible brightness of Venus.  It is in fact the brightest object in the sky after the Sun and Moon, shining a whopping fifteen times brighter than the brightest star in the sky!  Most everyone has seen Venus at some time, even if they didn't know what it was.  Most folks probably think it's an airplane and don't give it a second glance.  But those who do look closely notice that Venus doesn't move across the sky like an airplane, but hovers in one spot, moving only with the slow daily rotation of the sky.  For this reason, police departments everywhere always report an increase in UFO sightings when Venus is a bright evening star!

We will be closely following Venus in 2004, as an historic event involving Venus will occur on June 8.  In the next couple months, Venus will begin to overtake the Earth its orbit.  We will see in the Spring that Venus will again drop down lower in the sky, closer toward the sunset with each passing week.  By late May, Venus will vanish into the Sun's glare as it swings past the Earth in its orbit. 

But on June 8, the disc of Venus will pass in front of the Sun, an event known as a "transit," a type of "planetary eclipse" that we can see from the Earth.  Transits of Venus are very rare, occurring in pairs about every 130 years.  This event will be the first since the "horse-and-buggy days."  Scientists around the world will be studying this.  And we are currently working on some things to help you all observe this yourselves!  We'll keep you posted in future Updates.    

The crescent Moon will pass near Venus on the evening of Monday, February 23.  A fairly close conjunction will be visible from the longitudes of North America.  This event will not favor the far east longitudes of Australia and New Zealand.  But wherever you live, you can't go wrong by also taking a look on the evenings before and after, so as to observe the monthly motion of the Moon in its orbit around the Earth.

* Lunar Occulation of Mars *
Our friends in the southern hemipshere get their turn later in the week, on the night of Thursday, February 26 (local time).  On this evening, there will be an extremely close conjunction of the Moon with the planet Mars.  If you've been following Mars since last Summer's historic opposition, it's quite plain that Mars has decreased considerably in brightness.  Mars is now at about first magnitude, about the same as the bright stars in Orion -- still very bright but not like the blowtorch of last August!

Anyway, the Moon will be very close to Mars on the evening of Thursday, February 26.  The southern hemsiphere is favored, especially New Zealand, and a little red Mars will be seen grazing very near the edge of crescent Moon.  But the main event will be over the South Pacific Ocean.  If you're floating in a rubber raft somewhere in the South Pacific, you would see the Moon pass in front of Mars, and completely hide the red planet.  This type of event is called an "occulation," from the Latin word "occultare," which means "to hide."  Lunar occultations of the planets don't happen all the time, but you can catch them every couple years.  Too bad no will probably see this one.

Here in the North America, we can also expect to see a very close conjunction of the Moon and Mars, but on the evening of Wednesday, February 25, local time.  Remember, New Zealand and Australia are on the other side of the International Date Line, so it's "tomorrow" in New Zealand when it's "today" in North America! (Of course, from the New Zealand point of view, it's always "yesterday" in the USA!)  The further west you live, the closer the conjunction you'll see on Wednesday evening.  So California and the rest of the West Coast will be favored for this event. 

"Signs and Seasons (Gen 1:14)"

During February, the Sun is passing in front of the faint stars of the constellation "Aquarius the Water Bearer."  The Sun's zodiacal path along the Ecliptic is leading into declinations further and further to the North.  So therefore, the days are growing increasingly long for observers in the northern hemisphere, signaling the coming of Spring for the winter-weary north-temperate latitudes.  And on the flipside, the days are now growing shorter for folks in the southern hemisphere, the harbinger of colder, darker days ahead in the lands Down Under.  

* Leap Year *
We all learn early on in life that there are 365 days in a year.  This is one of those commonplace facts of life, like 24 hours in a day, and seven days in a week.  But the number of hours and days are the same for every day and every week.  However, this is not so for year, since every fourth year has 366 days.  These years are called "leap years."  2004 is a leap year, and this year will have a February 29, an extra day at the end of this month.

The idea of leap year can be puzzling to people.  Some people wonder why every year doesn't have the same number of days as every other year, why we need to mess around with adding this extra day every four years.  This would surely be easier, but it wouldn't be correct, since the length of days and years is determined by astronomical cycles.  The standard "solar day" of 24 hours is measured as the average time for a complete cycle of the Sun across the sky, for example, from Noon to Noon. 

However, the standard "tropical year" is a totally separate astronomical cycle, the time required for the Sun to complete a full cycle of seasons.  This is observed in the sky as the time taken by the Sun to follow a circle of the Zodiac from any seasonal point and return to the same point, for example, from one March Equinox to the next March Equinox.  The length of the day is mostly determined by the rotation of the Earth on its axis, while the year is defined by the revolution of the Earth around the Sun. 

To keep an orderly accounting of the days, every civilization in the world has observed the cycles of the Sun and Moon to develop a "calendar."  This area of study has always been very important for determining the proper times of planting and harvest of crops, to insure the food supply.  And most other human affairs are also regulated by the seasonal cycles of the "Luminaries," the Sun and the Moon.  As we read, this is the purpose for which the LORD created these bodies:

"And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days and years." -- Genesis 1:14 

* Julian Calendar *
In ancient Rome, the calendar was in disarray.  Roman politicians had changed the calendar around to suit their own interests, adding and subtracting days to the point where the Roman calendar no longer agreed with the seasons.  When Julius Caesar became dictator of Rome, he sought to reform the Roman calendar, and this is perhaps his most enduring contribution to world history. 

Caesar consulted with a Greek-Egyptian astronomer named Sosigenes, from whom he learned that the tropical year was 365 1/4 days in length, or 365 days, 6 hours.  In implementing the Julian Calendar, Caesar decreed that an "intercalated" day would be added to the regular 365 days every fourth year.  And this has been the practice in western civilization ever since the time of Caesar.  

In the original Julian Calendar, the intercalated day was added on "Sextilis Kalendarus Martiarum," or "The Sixth Kalends of March," a day that corresponds to our February 24.  The intercalated day was regarded a second instance of the 6th Kalends, called the "bissextilis."  So for many centuries of history since, the leap day had been called "Bissextile," even though the Roman reckoning of months had passed out of usage. 

And just was we say "Leap Year" to identify the entire year of the extra day, the word "Bissextile" was once a commonly synonym for the entire year.  Most of the Colonial and Early American Almanacks would indicate the current year as being "the second year after Bissextile," and so forth.

After centuries of careful measurement, the length of the year, that is, the time between March Equinoxes, has been precisely measured as being 365 days, 5 hours, 48 minutes and 42 seconds in length.  This precision is reflected in the current "Gregorian Calendar," the updated version of the calendar of Julius Caesar, in current use around the world today.

For more information on the Gregorian Calendar, check out the article "The Astronomy of Easter" from the following Update, also posted at

* The Dominical Letter *
You may notice that there are five Sundays in February, 2004.  This is a rare occurrence, since a regular February only has 28 days, and as such, only four Sundays.  A month like this can only happen in Leap Years where February begins on a Sunday.  The frequency of this type of February is determined by the seven-day cycle of the weekdays combined with the four-year cycle of the leap year.  It works out that a Five Sunday February only occurs every 28 years (4 x 7).  The last one was in 1976, and the next one will be in 2032. 

In doing this sort of figuring, there are many variations for which to account.  The months do not all have the same number of days, and the 12 month cycle of the year doesn't divide perfectly into the seven day cycle of the week.  It can be mind-boggling to try to figure all that out, even without adding in a leap day every four years. 

But in spite of all that, there are recurrent patterns that can be observed in the dates.  Many of us have learned the old Mother Goose rhyme:

"Thirty days hath September,
"April, June and November,
"All the rest have thirty-one,
"Excepting February alone,
"And that has twenty-eight days clear,
"And twenty-nine in each leap year."

My Mom, Mrs. Ryan, also shared a pneumonic that helps recall the lengths of the months.  If you count on your fists, count the knuckles as "long months" and the spaces between the knuckles as "short months":

One hand:
January - knuckle
February - space
March - knuckle
April - space
May - knuckle
June - space
July - knuckle

Other hand:
August - knuckle
September - space
October - knuckle
November - space
December - knuckle

Since these numbers don't change from year to year, we can find a mathematical progression in the days of the months.  And since the days of the week also don't change from week to week, we can combine these cycles into a mathematical progression for finding the day of the week for any month of any year. 

If you have a wall calendar for the entire year, try to notice the relationships between months and the days of the week.  For 2004, January, April and July all begin on a Thursday.  February and August both begin on Sunday.  September and December both begin on a Wednesday.  There are different rules for non-leap years, but all these rules have already been figured out and are very useful.

These mathematical progressions are embodied in the "Dominical Letter."  This is a device used by calendrists to keep track of the weekdays.  The Dominical Letter is a letter A, B, C, D, E, F, or G used to indicate the day of the week of January 1 for each successive year.  The Dominical Letter is usually given in almanacks and other detailed calendar materials.

A Dominical Letter of "A" indicates that January 1 of a given year lands on a Sunday.  But just to make it extra confusing, the other letters indicate a reverse-order of the weekdays.  That is, the letter "B" indicates that January 1 is a Saturday, letter "C" indicates that January 1 falls on a Friday, and so on.  Like many topics from astronomy, the Dominical Letter scheme is a "legacy" system inherited from centuries past, and is somewhat counter-intuitive.

Dominical Letters are used to create a "perpetual calendar" in which any weekday for any year can be predicted well in advance.  This was especially important to the medieval church, for the purpose of calculating the date of Easter and other dates in the church calendar. 

The regular tropical year has a length of 52 weeks, and one day, since 7 days times 52 weeks equals 364 days.  So in general, each new year begins one weekday after the previous year, and the Dominical Letter generally moves back one letter each year.  For example, the year 2001 had a Dominical Letter of "G," indicating that January 1 fell on a Monday.  2002 began on a Tuesday, and thus had a Dominical Letter of "F."  The year 2003 had a Dominical Letter of "E," indicating that January 1 fell on a Wednesday.    

However, it is common to assign two Dominical Letters to leap years.  Since 2004 is a leap year, the Dominical Letters for this year are DC.  This indicates that January 1, 2004 was a Thursday.  However, when the extra day is added at Sunday, February 29, this shifts the weekday sequence back by another day.  The remainder of the 2004 proceeds as though January 1, 2004 was a Friday.  So the rest of 2004 is regarded as having a Dominical Letter of "C."

After 2004, the Dominical cycle continues in its reverse-alphabetical order.  The next January 1 falls on a Saturday, so 2005 has a Dominical Letter of "B."  And 2006 begins on Sunday, so its leter is "A."  And 2007, a "G" year, thus begins on a Monday, and 2008, the next leap year, has the letters "FE. 

From this sequence, some straightforward relationships can be reckoned between the weeks and months:  In a regular year, January and October begin on the same weekday, and all their subsequent dates fall on the same days of the week.  Likewise, in a regular year, February, March and November begin on the same day of the week.  However, in a leap year, January, April and July begin on the same weekday, as do February and August.  In any given year, September and December follow the same weekdays.  And in any year, May and June never line up with other months, and always begin on their own days of the week.

Thanks to my buddy Mike Doherty for inspiring this topic.  More info on perpetual calendars can be found at these web sites:

As the current season winds down, we hope that the LORD blesses your families.  And as we approach this special Paschal season, we pray that you all continue to walk in the path of our LORD Jesus!

Til next time, God bless and clear skies!



The Ryan Family
Cleveland, Ohio, USA

"When I consider thy heavens, the work of thy fingers, the moon and the stars, which thou hast ordained, what is man that thou art mindful of him? and the son of man, that thou visitest him?"

-- Psalm 8:3,4, a Psalm of David

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For more information about topics from Classical Astronomy, please check out Signs & Seasons, a homeschool astronomy curriculum!

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