Classical Astronomy - Homeschool Blogger

What's Up With That Leap Second?

Wed, 31 Dec 2008 10:03:00 -0600

In case you hadn't heard, a leap second will be added to the calendar at midnight on December 31, 2008. Modern timekeeping will hang in limbo for a whole second between the end of 2008 and the start of 2009. Like most people, you won't even notice or give it a second thought.

For most of us, the leap second is something to laugh at -- a trivial bit of minutia of interest only to pedantic scientists and utterly irrelevant to everyone else. How could anyone possible care whether or not we bother with a second at the end of the year?

It turns out that such precision in timekeeping is extremely important to the modern world. We live in an age of computers where a second is like a century worth of processor cycles. Global telecommunications depend on precise timekeeping. We all know how awkward it can be to have a dropout or a delay of one second when talking on the phone. Timekeeping and navigation are interdependent, and the precision accuracy of GPS systems is a function of accurate time measurement. Indeed, our modern world would have major problems without that leap second!

Atomic Time

We read that the LORD created the Sun, Moon and stars for time measurement (Genesis 1:14). For millennia of human history, the luminaries were sufficient for man's timekeeping needs. Down through history, the second was defined as 1/86,400 of a solar day. This was more than enough for telling time from a sundial, or even a wind-up mechanical clock that corresponded to the solar day.

It's only in our breakneck, high-paced modern world that God's timekeepers have been deemed to be inadequate. Perhaps the LORD never intended us to live as we do today. On the other hand, the LORD did give us the minds to study His handiwork to learn the rules of His creation, and fashion devices to serve our needs. As we all know, modern technology can be a blessing or a curse, depending on how it is used. These are questions best discussed at home or with your pastor.

For better or worse, since the 1950s our modern world functions on a system of International Atomic Time (TAI) in which the second is defined as 9,192,631,770 oscillations of a certain electron orbital in a Cesium-133 atom. TAI is periodically adjusted to result in Universal Coordinated Time (UTC) which is the basis of our standard system of civil timekeeping. Atomic timekeeping is maintained through a time service of professional scientists working through the U.S. Naval Observatory and other agencies in the USA and abroad.

The Unruly Earth

Our modern method of atomic timekeeping does not exactly correspond to the rotation of the Earth. Though our world spins around each day at more or less the same speed to complete a 24 hour day, it so happens that the Earth's rotation is slowing by a very tiny amount. This amount is not in any way discernable to human perception, but factors in heavily with atomic time.

To make matters worse, this slowing does not occur evenly. Sometimes the Earth's rotation slows by a greater amount and sometimes by a lesser amount. Scientists suspect that there are "inhomogenieties" within the Earth, that there might be magma or something "sloshing around" inside our planet, though there is no way to know anything with certainty. In spite of everything that we have learned about our world, we only live on the thin skin of a sphere 8000 miles in diameter, and we actually know very little about what might lie thousands of miles under our feet.

Anyway, to account for the irregular slowing of the Earth's rotation, the professional time service inserts a leap second to TAI every couple years as needed, in order to bring the unruly Earth into the precise harmony of UTC-based civil time. A leap second was added on December 31, 2005 and another for December 31, 2008.

To accommodate the addition of the leap second, I've noticed over the years that the television broadcasts from Times Square in New York tend to start the countdown one second late, so that midnight arrives at the time everyone would expect!

At the present time, there is discussion as to whether our system of atomic time should be modified to eliminate the leap second. Depending on the outcome of that, we may not hear about these leap seconds in years to come.

The Slowing of the Earth Rotation

In addition to whatever internal "sloshing" that makes the Earth's spinning uneven, a smooth, regular, predictable slowing of the Earth's rate of rotation has been observed. This has been found to be the result of the tides raised by the Moon.

The Moon's gravity acts upon the level of the oceans, and raises the tide along the coastlines of the Earth. As the Earth rotates, the tide is like a wave continually moving west and colliding with the coast, resulting in a continual friction between land and sea. It is this friction that slows down the Earth's rotation by a very small amount each day.

As shown by Isaac Newton in A.D. 1687, for every action there is an equal and opposite reaction, and this is also true in the case of the Earth's slowing rotation. Remarkably, as a result of this tidal interaction, the Moon is actually moving farther away from the Earth! As the Earth's rotation slows down, the orbit of the Moon grows larger. This is a result of conservation of angular momentum, since the momentum lost from the Earth's rotation appears in the Moon's motion in its orbit.

This is similar to a skater who twirls faster as her arms are drawn closer, and twirls slower again as her arms are extended. It seems strange to me that energy can be transferred from the Earth to the Moon without any direct physical contact, yet this energy is in fact transferred through the gravitational field that connects our world with its satellite.

The Receding Moon

This Earth-Moon tidal interaction was known theoretically since the 1870s. It was finally proved by Apollo 11 in 1969. Astronauts Neil Armstrong and Buzz Aldrin set up a laser ranging reflector on the Moon. A laser beam is fired from the Earth and reflected back to the Earth. This ranging reflector is a corner-cube reflector similar to our traffic signs that return light beams back in the same direction down the same path. In this way, a measurement can be made from the Earth to the Moon a quarter-million miles away.

By precisely measuring the travel time to the reflector, the exact distance from the Earth to the Moon can be measured. From this, it has been found that the Moon is moving away from the Earth by about three centimeters a year, about an inch and a half! The last I heard, the Apollo 11 lunar ranger reflector was still functioning and this measurement is continually being maintained nearly 40 years later.

The Other Darwin's Theory

The tidal interaction between the Earth and Moon was theoretically deduced in 1878 by George Darwin, the son of proto-evolutionist Charles Darwin. Like father like son, the younger Darwin following in the family tradition of making long inferential leaps from skimpy scientific evidence. George Darwin proposed the "fission theory" of the Earth-Moon system.

Upon realizing that the Moon was receding from the Earth, Darwin taught that, once upon a time, the Earth and Moon must have been part of the same ball of glop. Darwin figured that the mass of the Moon mst have flown off away from the Earth to form its own body in space. Darwin proposed that the crater formed by the escaping Moon resulted in the Pacific Ocean, which happens to be just about the right size to fit the Moon.

The fission theory was contended during Darwin's lifetime. Basically, if the Earth was spinning fast enough to throw off the Moon, how would it have formed as a single mass in the first place? There is too much angular momentum in the Earth-Moon system to form a single stable body. Darwin's theory was ultimately debunked by Apollo 11 and the other Apollo missions which brought back lunar samples that proved that the Earth and Moon were not made of the same stuff and thus could not have arisen from the same body.

The "fission" or "ejection" theory and other secular creation myths is touched on in this Update article, The Face on the Moon. If nothing else, the failed theory of Darwin, Jr. encapsulates the whole problem with his father's methodological approach to science -- that small, isolated observations can be extrapolated to produce a grand, all-encompassing universal theory of science. It's unfortunate that the science mainstream refuses to acknowledge this simple point as continually made by creation scientists.

Apollo 8 - 40th Anniversary

Mon, 22 Dec 2008 15:10:00 -0600

This week marks the 40th anniversary of the flight of Apollo 8, the first manned mission to venture forth from the Earth to visit another world. The linked article includes several cool YouTube videos, so please gather your family and friends around to share this together.

Click this link to read more.

The Winter Solstice

Sat, 20 Dec 2008 16:39:00 -0600

I thank Thee, Lord! The whiteness
Of winter on my heart
Shall keep some glint of brightness
Though sun and stars depart.

-- William James Linton (from The Old Farmer's Almanac, 1903)

During December, the Sun passes through the stars of Sagittarius the Teapot. This constellation is therefore not visible at this time, hidden behind the Sun's bright glare. The Sun is now in the southernmost portion of its annual path through the zodiac constellations, and thus rises and sets far to the south.

(from Signs & Seasons: Understanding the Elements of Classical Astronomy)

On about December 21 each year, the Sun reaches the southernmost extent of its annual cycle. This day is known as the winter solstice and is traditionally regarded as the official "first day of winter" for observers in the northern hemisphere.

On this day, the Sun is at its lowest point of the year in the noon sky as seen from the northern latitudes. The Sun never gets too high off the ground at noon as seen from the temperate zone. On this day you can measure the longest noon shadows of any day of the year.

After reaching its most southerly declination on the winter solstice, the Sun will appear to head north again, following its annual cycle through the seasons. In the coming months following December, keep your eye on the noon shadows, and notice how the they get shorter as Sun moves higher to the north in the noon sky, until reaching its northern maximum on the summer solstice in June.

On the winter solstice, since the Sun rises and sets very far to the south, it is not in the sky for very long. For this reason, the winter solstice is also "the shortest day of the year" since the length of daylight is shortest for people living north of the equator.

Here in Cleveland, the daylight on the shortest day lasts about 9 hours. Cleveland is near latitude 40 degrees North, along with many other large American cities, such as New York, Washington DC, Chicago, and San Francisco. So the length of daylight is about the same for these cities as well.

However, the length of winter daylight is even less for places further north. At the Arctic Circle, the Sun rises directly in the south at noon and immediately sets. In Alaska and Iceland, daytime is simply an extended twilight on either side of the noontime sunrise/sunset, and the Arctic nights of early winter are long and dark.

(from Signs & Seasons: Understanding the Elements of Classical Astronomy)

Meanwhile, December 21 is the summer solstice and thus the longest day of the year for people in the southern hemisphere. Folks in New Zealand, Australia, and South America are enjoying warm days and late sunsets we northerners shiver in the dark! But please don't envy them, they get their payback in June since their shortest day of the year is our longest!

The solstices and other aspects of the Sun's annual cycle are explained in detail in Chapter 5 of our Signs & Seasons astronomy curriculum. Remember, S&S isn't just for homeschool students! An increasing number of parents (especially the dads) are reporting that they are also learning a lot!

What Was The Star of Bethlehem?

Thu, 18 Dec 2008 14:44:00 -0600

One of our most frequently asked questions, especially around this time of year, is "what was the Star of Bethlehem?" I don't like this question and always wince every time it comes up. Thr truth is, I don't know the answer, and in fact, no one else does either, in spite of what you might hear. If there was a clear-cut answer to this question, everyone would already know the answer and wouldn't have to ask.

Whenever people ask about the Star of Bethlehem, they apparently want to know if there was an actual recorded astronomical event that accompanied the birth of Jesus. But one of the many problems with trying to answer is that we do not know for sure exactly when Jesus was born. Also, even if we suppose a range of years when Jesus might have been born, there are no clear cut astronomical events within that range that would meet all the requirements of the Star of Bethlehem according to Scripture, science, and secular history.

Thus, there are a number of theories that attempt to give a rationalistic, naturalist explanation of the Star of Bethlehem, and it seems that new popular theories make the rounds all the time. After pondering the evidence and the various theories over the years, I've concluded that the Star of Bethlehem must have been a supernatural event, not a natural occurrence of astronomy. We'll look at some of that evidence in this article.

When Was Jesus Born?

Ironically, though Jesus is the most important person in history, there is not a lot of specific information about His life outside the Gospels, and Scripture does not provide a great amount of detail. Modern chronology can give us accurate dates for the births of Julius Caesar, Caesar Augustus, and a great number of other ancient personages, but not of Jesus himself.

The Bible gives us many clues but none that can be specifically correlated with recorded historical events. For example, Luke 2:1-2 indicates "a decree from Caesar Augustus that all the world should be taxed" which occurred "when Cyrenius was governor of Syria." Scholars debate back and forth when this might have been, based on the sketchy records that have survived of the early Roman empire.

Matthew 2:1 states that "Jesus was born in Bethlehem of Judaea in the days of Herod the king." Traditionally, Jesus' birth is dated to 4 B.C based on a clue recorded by Flavius Josephus, the first century Jewish historian. Josephus wrote of the execution of two seditionists, both named Matthias, stating "and that very night there was an eclipse of the moon." Modern astronomy has dated this eclipse to the night of March 13, 4 B.C.

Since Josephus indicates the death of Herod as being soon thereafter, many scholars infer that Jesus must have been born sometime in that year. It also happens that since 4 B.C. was the 750th anniversary of the founding of Rome, and the 25th year of Caesar Augustus' rule, scholarship concludes that this was a likely time for Caesar to order a census. If all this sounds like a stretch, it should at least indicate the difficulties in trying to draw conclusions from scanty historical evidence.

So what was the Star of Bethlehem?

In addition to the chronological problems with dating the birth of Jesus, we then must determine whether there are historical records of any astronomical events that meet the requirements. Also, no one is sure exactly what sort of celestial event would have signified the birth of the "King of the Jews" to "wise men from the east," traditionally regarded as Persian astrologers.

Over the years, people have tried to say that the Star of Bethlehem was a supernova, a comet, or the latest popular notion -- a triple conjunction of Jupiter and the star Regulus. Let's consider each of these:

Supernova

From time to time in history, a nova was seen in the night sky, a "new star," from the Latin word for "new." Modern science defines a supernova as an exploding star, which shines very brightly for a short time and then goes away. Throughout history, a number of novae have been observed in the night sky. Ancient Chinese astronomers kept a careful record of such new stars, though no such records survive in any Greek, Roman, or other western sources.

It would be very tempting to suppose the Star of Bethlehem would have been a supernova. Such a unique occurrence is very rare and would be a very conspicuous sign in the sky that would attract a lot of attention. The problem is, there is no historical or scientific evidence of such a supernova. The Chinese did not record any new stars within the suitable period of time.

Also, supernovae leave behind a remnant in the form of a nebula that can be seen through telescopes on the Earth. The most famous example is the Crab Nebula in the constellation Taurus, the remnant of a supernova that the Chinese observed in A.D. 1054. If there were a supernova that was visible over the latitude of Bethlehem in or around 4 B.C., a remnant nebula should be visible in a certain region of the sky. However, no such object can be found.

Triple Conjunction of Jupiter and Regulus

One theory that has been popular in recent years is the notion that the Star of Bethlehem was a very rare triple conjunction of the bright planet Jupiter with the star Regulus in the constellation Leo. In this astronomical event, Jupiter would have had a retrogradation in Leo such that it would have passed this bright star three times. This theory is compelling in that it is full of astrological symbolism that might indicate to a Persian magus that a king was born in Judaea.

Such a triple conjunction event did actually occur over a span from September, 3 B.C. through May, 2 B.C. Blazingly bright Jupiter, which signifies kingship, passed three times very closely to the brightest star of Leo, which might signify Judah (as from the Blessing of Israel, Genesis 49:9). No doubt this was at least a spectacular sight to anyone who saw it at the time. A planetary alignment similar to this was depicted in the recent movie, The Nativity Story.

The triple conjunction theory makes the rounds every Christmas, and is explained in detail in a DVD from http://www.bethlehemstar.net/. Though a compelling case is made, this triple conjunction event is not a "star" per se (astera, as stated in the Greek text of Matthew 2:2) but rather an alignment of a well known star and planet. This triple conjunction is a series of close approaches of these objects spread out over an eight month period. For these reasons, I personally find this to be an unsatisfying explanation to account for the Star of Bethlehem.

Also, this conjunction series occurs after the traditionally accepted date of the death of Herod in 4 B.C. as suggested by Josephus. However, scholars are constantly debating over the skimpy facts, so a strong element of guesswork is involved in any of these chronologies or Star theories.

Comet

Over the years, one popular idea is that the Star of Bethlehem was a comet, a celestial object with a long tail that passes through the solar system for a short time. This theory has been around since at least about A.D. 250, with the Christian writer Origen, who wrote:

The star that was seen in the east we consider to have been a new star, unlike any of the other well-known planetary bodies, either those in the firmament above or those among the lower orbs, but partaking of the nature of those celestial bodies which appear at times, such as comets, or those meteors which resemble beams of wood, or beards, or wine jars, or any of those other names by which the Greeks are accustomed to describe their varying appearances.

One popular notion that One popular notion that made the rounds for a while was that the Star of Bethlehem was an appearance of Halley's Comet. It was the astronomer Edmund Halley who, in A.D. 1715, discovered that a number of the famous comets of history were actually reappearances of the same comet. One such reappearance was in A.D. 1305. This reappearance might have been observed by the Italian artist Giotto di Bondone. That very year, Giotto painted a famous fresco entitled Adoration of the Magi, which included a very comet-like depiction of the Star of Bethlehem. However, the arithmetic of the cycle of Comet Halley indicates that it would have revisited the Earth in A.D. 12, much too late to have been within the lifetime of King Herod.

Another comet theory is explained by astronomer Colin Humphreys who considers a number of historical sources and scientific data, including Chinese observations of comets from the period, concluding that the Star of Bethlehem might indeed have been a comet.

So What Was The Star of Bethlehem Anyway?

In my opinion, all the above theories are in the category of "maybe, maybe not." They all have their compelling arguments and yet none fit all the available facts of science, history and Scripture. However, as far as I'm concerned, all rationalistic, naturalistic theories to locate a celestial object as the Star of Bethlehem suffer from one major problem: the Star of Bethlehem as described in Scripture does not behave like a natural celestial object. The text of Matthew 2:9 states:

When they had heard the king, they departed; and, lo, the star, which they saw in the east, went before them, till it came and stood over where the young child was.

So after their audience with Herod in Jerusalem, the star "went before" the wise men, and "stood over" the place where Jesus was. The distance from Jerusalem and Bethlehem is about six miles, maybe a three or four hour walk. So the wise men could have reached Bethlehem the same night.

However, natural celestial bodies rise in the east, reach their highest at the meridian, and set toward the west. However, Bethlehem is nearly due south of Jerusalem. Any natural star would pass to their left or right as the wise men headed south from Jerusalem, and would not have "went before" as Scripture indicates.

Also, for a star to have "stood over" a place, it would have to pass through the zenith, otherwise it would appear off to the north or south. There are no visible supernova remnants that pass through the zenith at the latitude of Bethlehem, and neither Jupiter nor Regulus pass overhead at Bethlehem's latitude. A comet could have passed overhead at the latitude of Bethlehem, but there's still a Scriptural problem that every natural celestial body cannot overcome....

Even if a star passes overhead at the latitude of Bethlehem, the text clearly states that the Star of Bethlehem "stood over where the child was." After talking to Herod, the wise men knew they were going to Bethlehem, but the text suggests that the Star led them to the actual location of Jesus, not just the city.

The text of Matthew 2:9 clearly describes an object that "went before" the wise men and "stood over" a precise location. This is not a description of a natural celestial body. Also, any natural object would pass briefly through the zenith, but would not "stand over" a place, at least not for longer than a moment. A "star" as described in Scripture would have to move around in space, and hold a geosynchronous position in the sky against the apparent motion of the sky due to Earth's rotation.

As mentioned many times in the Update and in our Signs & Seasons curriculum, Classical Astronomy was well understood for centuries before the New Testament period, and anyone reading the text at that time would likely understand that the object that led the wise men to young Jesus was not a natural celestial object.

Scholars and other modern "wise men" can sort all this out by bogging down with semantics or creatively interpreting the passage. Either way, as we've seen, Scripture does not supply very much detail, secular history does not offer much support, and science does not offer a plausible naturalistic explanation.

Given all the above, I just choose to stick with a simple acceptance of the Biblical text and don't attempt to reconcile it with naturalistic speculations. As for me and my house, we choose to understand the Star of Bethlehem to be a supernatural event that guided the wise men, like the angelic hosts that directed the shepherds to the manger.

The Sky This Month for July, 2008

Thu, 3 Jul 2008 10:45:00 -0500

Continuing our astronomy animation series, here is the latest installment, featuring some of the astronomy events you can observe in July, 2008. Tell all your friends! For more information, please visit www.ClassicalAstronomy.com.

The Sky This Month for June, 2008

Fri, 6 Jun 2008 11:53:00 -0500

For everyone interested in astronomy, here is a Flash animation depicting some of the astronomy events you can observe in June, 2008. Tell all your friends! For more information, please visit www.ClassicalAstronomy.com.

See Saturn in the constellation Leo

Mon, 14 Apr 2008 10:56:00 -0500

(From the Classical Astronomy Update newsletter)

Saturn in Leo in the Spring of 2008

It's once again that time of year when "the Lion is higher than Orion"! After proclaiming the glory of God through the winter months, the awesome constellation Orion is once again sinking toward the sunset as the days of spring grow warmer and longer. In this month, the constellation Leo is high in the evening sky after sunset.

Unlike a lot of constellations, Leo actually looks like the object it is supposed to represent. Its trapezoidal shape looks like a big cat in mid-jump, and a faint "sickle" of stars is reasonably recognizable as a head.

In the current season, Leo is joined by the planet Saturn, which is the brighter "star" nearby the star Regulus in Leo. If you've been observing Leo and Saturn throughout this winter, you have had an excellent opportunity to observe the "retrograde motion" of this planet.

In the weeks before the Earth "passed" Saturn back in February, the Earth's motion has caused a change in the line of sight between Saturn and the more distant background stars, causing the ringed planet to appear to move backwards.

Consequently, Saturn appears to be moving west and approaching Regulus. Since Saturn's position on the night of the lunar eclipse in February, Saturn has moved quite a noticable distance to the west. These two bodies will make their closest approach at its "station" on May 3, when Saturn will be only a couple Moon diameters away from Regulus. After that time, Saturn will resume its regular eastward motion and will draw away from Regulus.

The waxing gibbous Moon will pass near Regulus and Saturn on the evening of Tuesday, May 15, 2008. Though this will be visible from North America, these bodies will appear very close to the Moon as seen from the meridians of Europe and Africa. The meridian of Jerusalem will be especially favored for this conjunction, and the Moon will appear very close to Regulus. Observers to the south in Madagascar will be able to see an occultation of Regulus by the Moon, in which the Moon will pass in front of this star, covering it from view for a time. Wherever you are, this lunar conjunction should be a pretty sight for everyone in the world.

Backyard Compass - Winter Solstice

Wed, 19 Dec 2007 13:08:00 -0600

Further to our previous Backyard Compass entries, we were blessed with some clear noon skies this week to create the last installment. Here's a snap of my son Happy showing his shadow around noon near the Winter Solstice. Note how long his shadow is, especially compared to the previous summer and autumn shots.

Noon shadows around the shortest day of the year are nealy twice as long as the height of the persons or objects casting them. This is because the Sun is very low in the noon sky at this time.

The pic was snapped on December 17, which is close enough to the actual solstice so that any difference would be very small. Happy needed to stand in the Sun next to the actual standing stone, since the pine tree in our backyard covered the compass. The standing stone and the "North" marker stone are indicated with red circles to make them more clear, since we had a big snow storm the day before. (BTW, these shots were taken from our second storey bedroom window, overlooking our backyard in Cleveland, Ohio.)

The seasonal changes in the shadows are among the many thing your homescholar can learn from Signs & Seasons, our Christian homeschool astronomy curriculum.

Backyard Compass - The Autumnal Equinox

Wed, 26 Sep 2007 21:58:00 -0500

Following our last Backyard Compass entry, here's a snap of my son Happy showing his shadow around noon on the Autumnal Equinox. Note how much longer his shadow is, and also how different the noon sunlight looks when the Sun is at a slanting angle and not directly overhead. LORD willing we'll have clear skies around the Winter Solstice so we can show how long the shadows are on that day.

These are all the sorts of things your homescholar can learn from Signs & Seasons, our Christian homeschool astronomy curriculum.

Backyard Compass

Fri, 3 Aug 2007 10:28:00 -0500

In Signs & Seasons, our first field activity is to make a "backyard compass" that will help orient the observer to the compass points while making observations of the Sun, Moon, and stars. Here's a pic of my 13yo son Happy standing in the backyard compass he and his younger brothers made.

The boys made it their little busy project, which is always a lot of fun for their Mom to watch. They did a fine job. The compass is slightly off from true north and south, but it does the trick. We had a hard time finding enough round paver stones so we used bricks for the intercardinal points, NE, NW, SE and SW.

Note that Happy's shadow is very short. This shot was taken on about June 17, very close to the summer solstice. If we come back on the equinox, his shadow will be about his height, and on the winter solstice his shadow will be twice as long as that.

Also note that his shadow is slightly pointed to the west. This tells you that it's not quite "High Noon," which occurs at about 1:30PM in our longitude during daylight savings.

Let us know how it goes if your kids make a backyard compass. Send us a pic and we'll post it.