What’s Your Sign? OR How The Zodiac Came To Be

On January 13, 2011, Minneapolis Community and Technical College astronomy instructor Parke Kunkle caused a stir by announcing that horoscopes are wrong because the zodiac has shifted. Not only do most people ‘belong’ to the sign immediately before the one they are traditionally assigned to, but there is a 13th ‘sign,’ Ophiuchus.

This then, is an ideal time to tell the story of what the zodiac is and how it came to be.

The Story of the Solar System
The Earth orbits the sun once a year.  This orbit defines a plane in space.  That plane, projected against the background stars, is a line in our sky which astronomers call the ecliptic.  The plane of Earth’s orbit contains the sun, so the Sun always appears on the ecliptic in our sky.

The solar system itself formed from a spinning disk of dust that flattened out as it spun.  As a result, the solar system today is so flat that all planets orbit almost (although not exactly) in the same plane.  The planet with the greatest inclination (deviation from the plane of Earth’s orbit) is Mercury, and it’s off by just seven degrees.  All planets, therefore, always appear near the ecliptic in our sky.

The best theory for the moon’s formation posits that shortly after Earth had formed, a Mars-sized body dubbed Theia crashed into Earth, throwing off debris which formed the moon.  Theia, like most everything else in the solar system, had been orbiting near Earth’s orbital plane.  As a result, our moon orbits within about five degrees of Earth’s orbital plane.  In our sky, then, the moon always appears within about five degrees of the ecliptic.

Can’t see the video? Click here.

With our sun, moon, and all planets near the same plane, only a small set of stars–those aligned with the ecliptic–can ever appear near them in the sky.

The First Astrologers
Patterns formed from these stars were therefore of great importance to observers of antiquity.   Those that we use today go back to Mesopotamia, particularly Babylonia, in about 1370 BCE.  It was about that time that Babylonians created a text called MUL.APIN, which lists all of their constellations as well as the times of year when each constellation rose with the sun. (MUL.APIN, meaning ‘The Plough,’ is the name of the first constellation listed.)

Tablet 1 of MUL.APIN also includes a list of all constellations near the path of the moon in the sky–a forerunner of our zodiac.  The 18 (or 17) star patterns on that path are:

1)  The Star Cluster                                      (The Pleiades)

2) The Bull of Heaven                                 (Taurus)

3) The Loyal Shepherd of Heaven        (Orion)

4) The Old Man                                             (Perseus)

5) The Scimitar                                             (Auriga)

6) The Great Twins                                      (Gemini)

7) The Crayfish                                             (Cancer)

8) The Lion                                                     (Leo)

9) The Seed Furrow                                    (Virgo)

10) The Scales of Heaven                         (Libra)

11) The Scorpion                                         (Scorpius)

12) Pabilsag (a Babylonian god)           (Sagittarius)

13) The Goat-Fish                                       (Capricornus)

14) The Great One                                       (Aquarius)

15) The Tails                                                 (Pisces–one of its fish)

16) The Great Swallow                              (part of Andromeda and Pisces–the other fish)

17) Anutitum (a goddess)                        (part of Andromeda)

18) The Hired Man                                       (Aries)

There is some disagreement as to whether patterns 15 and 16 represent one or two constellations, hence the uncertainty as to whether the list has 17 or 18 members.

The Ancient Greeks, by about the sixth century BCE, had modified that list and produced a zodiac more like the one we use today.  They did so by leaving out stars in Orion, Perseus, Auriga, and Andromeda, which are a bit off the ecliptic itself (although the moon, which deviates by up to 5 degrees, can pass through them).

The Greeks also treated the Pleiades and Taurus as one constellation.  Virgo, the Virgin, is nearly always depicted with a stalk of wheat in her left hand, revealing her association with agriculture, like the furrow.  Babylonians had depicted Pabilsag as a composite creature armed with a bow and arrow; the Greek centaur shooting an arrow which we call Sagittarius is a simplification of this.

Babylonians often associated the Hired Man with Dumuzi, a legendary shepherd.  This may have influenced the change from ‘Hired Man’ into Aries, the Ram. The Ancient Greeks made the Babylonian ‘Scales’ constellation into the claws of Scorpius, the Scorpion, but the Romans reintroduced the Scales, putting the zodiac in its current form.


Of all the objects to appear only in the zodiac, by far the most important was the sun.  By noting which zodiacal constellations rose just before the sun and set just after the sun, early observers could use the changing position of the Sun against the background stars as a guide to the seasons.

Early lists of Babylonian patterns listed in MUL.APIN, possibly reflecting incipient stages in its formation, typically include the Bull, possibly indicating plowing season, the Lion, perhaps a symbol of the oppressive summer sun, since the sun rose with these stars in summer, the Scorpion, an emblem of death representing autumn, and the Water Bearer, representing the rains of winter.  Also often appearing on these early partial lists are the farrow and the goat/fish.  The former could represent the harvest season which follows the oppressive heat represented by the lion.  The latter is likely to represent Ea, Babylonian god of the waters, as the goat and the fish are animals associated with him.

When astrologers began using the positions of the planets, sun, and moon to describe people’s personalities, they focused on the sun.  The zodiac sign behind the sun (and thus not visible at night) on someone’s birthday was supposed to be most influential in determining that person’s character and destiny.  Although no evidence has established any connection between the apparent position of the sun and personality, belief in ‘sun signs’ continues to this day.

However, the stars’ positions in the 21st century are not the same as in antiquity.
As Earth orbits the sun, it wobbles.  After all, Earth could spin without wobbling only if no other forces whatsoever were acting on it, which is not the case.  However, Earth’s wobble is not as chaotic as it might be because we have a Moon relatively large for a planet as small as Earth.

With the Moon as a ‘counterweight,’ the Earth’s wobble becomes a more orderly precession in which the Earth’s axis describes an apparent circle on the sky once every 26,000 years.  This same precession causes the position of the sun on a given date to shift slightly–by about one degree every 72 years.  Since millennia have passed since Babylonians created the zodiac (about 1370 BCE) and since Romans finalized it (about 1 CE), the sun no longer aligns with the same patterns during the same seasons.

This brings us back to Kunkle’s announcement a few weeks ago.
It turns out that the dates traditionally associated with the ‘sun Signs’ are valid only for about the year 1 CE.  In general, the constellation actually behind the sun on your birthday is the one immediately before your traditional ‘sign.’  For example, astrologers would call me a Gemini, but the sun was in fact aligned with the stars of Taurus, the Bull, on my birthday.  You can compare the traditional dates and the actual constellations here. (The table is towards the bottom of the page).

Under the Milky Way
Creative Commons License photo credit: jurvetson

This is not a new discovery.
The ancient Greek astronomer Hipparchus noted that the stars Spica and Regulus were in slightly different positions in his time than on his predecessors’ star maps.  From this, he was able to deduce in the second century BCE that precession was occurring.  Astronomers have thus known of this effect for over two millennia.

So have astrologers, who maintain that they can still cast horoscopes because their ‘signs’ refer to fixed sectors of the sky and not to constellations.  As it happens, the traditional dates do roughly reflect when the sun would have aligned with the constellations about 2000 years ago.  Astrologers fail to explain why the constellations’ positions of 2,000 years ago might be magically relevant, however.

In 1930, astronomer Eugène Delporte helped fix the official constellation boundaries used by the International Astronomical Union.  These boundaries place a sizable chunk of the ecliptic in the constellation of Ophiuchus, a legendary healer who holds a large snake (Serpens) and stands on top of Scorpius, the Scorpion.  His stars are not on the Path of the Moon in MUL.APIN, although stars at some distance from the ecliptic, such as those in Orion or Perseus, are.  However, Ptolemy included this pattern in his list of 48 constellation in the Almagest.  Traditional skymaps of antiquity usually show the ecliptic passing through the Scorpion’s upper claw and legs, with Ophiuchus superimposed on Scorpius and standing on the ecliptic as if balancing on a high wire.  This is what may have influenced Delporte to assign most of that section of the ecliptic to Ophiuchus.

The idea of Ophiuchus as the ’13th sign’ is not new either.
Astronomers have been using Ophiuchus to point out the arbitrariness of astrology for at least 40 years.  Ophiuchus has been standing on the ecliptic for millennia, his right foot much closer to the planets than Scorpius’ stinger.  If the band of the ecliptic has powers over us, why doesn’t Ophiuchus partake of that power?  Several other constellations come near (but are not on) the ecliptic, including Cetus the Whale and Sextans, the Sextant.  The Moon and planets, which deviate by a few degrees from the ecliptic, can appear in them.  Should we factor them in as well?

Astrology vs. Astronomy
The ‘new’ dates for the zodiac signs and the ’13th sign’ Ophiuchus serve to underscore the difference between astrology and astronomy.

Astronomy is a science.  Astronomers study real planets, stars, and galaxies to learn about the real universe around us.

Astrology is myth-making.  The real positions of the stars do not matter to astrologers because astrology has more to do with mankind’s psychological needs. These include the need to see patterns and impose meaning and order onto the world and the need to feel in control of our surroundings.  Astrology thus offers the comfort of feeling that apparently random events might be predictable and controllable.

But since the astrologer’s predictions are ‘..not in our stars, but in ourselves,” as Shakespeare might say, astrology offers none of the wonder and excitement that comes from seeing the celestial bodies as they actually are, apart from our needs and desires for influence.  For that, I recommend astronomy. 

Partial Eclipse of the Eclipse: Report from Shanghai

In July 2009, I had a rare opportunity to travel with an HMNS sponsored tour group to the path of a solar eclipse. That eclipse occurred the morning of July 22, 2009, and was visible in Asia and the Pacific. Unfortunately, clouds marred the event as seen from our location just outside Shanghai. But since the clouds did not completely hide the eclipse, we were able to witness some of its effects.

Eclipsed? Not totally.
Creative Commons License photo credit: James Jordan

Solar eclipses occur when the Moon passes between the Sun and the Earth and casts its shadow on the Earth.  The shadow itself, called the umbra, is the region in which the Moon completely blocks the Sun.  Anyone in the Moon’s umbra experiences a total eclipse of the Sun.  As the Moon passes in front of the Earth, its shadow traces a path across the Earth’s surface; this is the ‘path of totality’.  To see a total solar eclipse, one must travel to a place on the path of totality.  As it happens, last month’s path covered parts of India, the Himalayas, China, and the open Pacific.

In an interesting coincidence, the Moon is about 400 times smaller than the Sun and about 400 times closer.  Thus, the Moon and Sun appear to be about the same size (just over 1/2 degree across) in our sky.  However, the Moon had been at perigee (closest approach to Earth) on July 21, making it slight larger than usual in our sky.  Further, every year in early July (July 3 in 2009) the Earth is as far as possible from the Sun (called aphelion).   These factors combined to make the New Moon of July 22 8%  larger than the Sun in our sky.  Thus, this is the longest eclipse of the 21st century, lasting 6 minutes and 39 seconds when seen on the centerline at local noon.

This was the latest eclipse in Saros cycle 136.  Astronomers in ancient Babylon noticed that similar solar and lunar eclipses recurred every 18 years, 10, 11, or 12 days, and 8 hours.  This corresponds to 223 lunations.  (One lunation is the period from one New Moon to the next–about 29.5 days).  The 10, 11, or 12 days depend on how many leap years are in the 18 year period.  In 1691, Edmund Halley applied the name ‘saros’ to this cycle, based the ‘SAR,’ a Babylonian unit of measure.  It turns out that the unit for keeping track of eclipses in Babylon was not the SAR, but Halley’s term stuck.  Cycle 136, then includes the eclipses of  July 11, 1991, June 30, 1073, and June 20, 1955.  Future eclipses in this cycle will occur on August 2, 2027, August 12, 2045, and so on.  As eclipses of cycle 136 occur further and further from aphelion, they won’t be quite as long as this year’s.  There won’t be a longer total solar eclipse until June 13, 2132.  That’s when a different saros cycle, #139, begins to occur near aphelion.

The Shanghai Tourism Administration estimates that over 13,000 overseas visitors traveled to Shanghai to watch the eclipse.  Along with hundreds of other eclipse chasers, our group left Shanghai proper to observe the eclipse from the Yangshan Deep Water Port, a small island southeast of the city itself.   To understand why, refer again to the July 2009 path of totality.  Drawn on the eclipse path on that map is a black Sun with small rays, indicating a point on the open water southeast of Japan.  This is the point of maximum eclipse, where the eclipse occurred at local noon and lasted the full 6 minutes and 39 seconds.  At other places on the path, totality was slightly shorter.  A few folks actually sailed the Pacific in order to be near that point.  We, however, opted for the convenience of observing on land.  Shanghai was the place in the path of totality closest to the point of maximum eclipse while still on the Asian mainland.

Also, note the blue line drawn down the middle of the path of totality.  Observing on that line, as opposed to the northern or southern edges of the path, gives you a longer eclipse.  Shanghai, although well within the path, is somewhat north of the blue centerline.  Moving from Shanghai itself to Yangshan island to the southeast put us closer to the centerline.  This gave us 5 minutes, 57 seconds of totality as opposed to about 5 minutes even in Shanghai.

eclipse 1
Photo from Shanghai, 2009 solar eclipse

As it turns out, there was another benefit from observing from Yangshan.  July 22, 2009 was rainy in Shanghai.  At Yangshan, however, it was simply overcast.  And just when we were beginning to think we’d miss the entire event, the clouds began to thin out in spots, allowing us occasional glimpses of the partially eclipsed Sun.

Unfortunately, those thinner clouds were not with us during totality.  We missed seeing the beautiful corona around the totally eclipsed Sun.  We could not see the planets and the brighter stars against the mid-day twilight sky.  And we could not watch the Moon’s shadow approach and then leave us  making shadow bands on the ground as it did so.  However, we did notice how much darker and cooler it got during totality.  After all, an overcast sky at night or in twilight is much darker than an overcast sky in broad daylight.  Cheers and whistles rose from Yangshan as darkness fell at 9:37 am and lasted until 9:43 am local time.

eclipse 2
Photo from Shanghai, 2009 solar eclipse

Literally seconds after totality was over, the clouds once again became thin enough for us to see the Sun through them.  As we watched the Sun come out of eclipse, we gave thanks for having avoided the rain and for being able to see as much as we saw, although we wished the clouds had thinned a little earlier to give us a glimpse of totality.

Would you like to have a similar experience?  Well, the path of the next total solar eclipse, on July 11, 2010, scarcely touches land at all, although it does pass over exotic Easter Island.  On November 13, 2012, totality is visible from northern Australia.

Can’t afford to leave the country to see an eclipse?  The Moon’s shadow crosses the United States on Monday, August 21, 2017.  The path of totality for that eclipse passes roughly from Salem, Oregon to Charleston, South Carolina.  How about a total eclipse right here in Texas?  Mark April 8, 2024, on your calendars.  On that date the Moon shadow first touches land near Mazatlan, Mexico, then sweeps right across the center of Texas before heading off to the northeast.  Folks in Dallas, Austin, and the western part of the San Antonio area see a total eclipse on that date; Houston experiences a deep partial eclipse.  The really young can look forward to May 11, 2078.  On that date, the Moon’s shadow passes just south of the upper Texas coast on its way to New Orleans and Atlanta.  Houstonians again experience a very deep partial eclipse.

The Moon’s shadow, then, will visit North America several times in the 21st century.  Maybe you can go observe the rare and beautiful spectacle of a solar eclipse, with better luck than I had in Shanghai. 

Send help now!

In theory, archaeologists set out on their digs with specific goals in mind. They want to find out when a site was occupied and what people were doing at that time. They also want to know the bigger picture: how did people at the site they are digging interact with those living elsewhere?
In practice this does not always mean that they know what they will unearth.  In that regard, I have often compared archaeology to fishing; people tend to go where they think they will catch (or, in the case of archaeologists, find) something.  The discovery described below is a good example of this.

untitled
Creative Commons License photo credit: procsilas

Cambridge University  professor John MacGinnis recently commented on one of his finds, a small clay tablet with cuneiform writing on it. The tablet, which dates back to the final years of the Assyrian Empire, was found at the site of Tushan in Southeast Turkey. This site is known today as Ziyaret Tepe; several archaeological teams have undertaken excavations there.

 The tablet contains a message written by an Assyrian army commander facing imminent danger from invading Babylonian forces.  His message is a raw plea for help. “Death will come out of it! No one will escape! I am done!” 
 
What is this all about?
The year is 630 BC and Tushan, considered to have been the administrative capital of the northern province of the Assyrian Empire, is threatened by the Babylonians. From the brief cuneiform text, it appears that the citizens knew all too well this was happening. Many fled, among those specialists in weapons manufacturing. This is what caused the commander to lament: “Nobody mentioned in this letter, not one of them is here! How can I command?”  His premonitions proved to be correct: the city fell.

Assyrian door gaurd
Creative Commons License photo credit: glyn_nelson

Yet the Assyrians had had a great run for a long time. Centered on the capital city of Ashur (Assur), located on the west bank of the river Tigris in northern Mesopotamia, the Empire’s roots date back to 1800 BC. Its zenith occurred during the 13th century BC, during the reign of king Tukulti-Ninurta I (1244–1208 B.C.). As with all empires, decline eventually set in and by the time we reach 630 BC, the Assyrian Empire was but a shadow of its former self.  The Babylonians were systematically conquering them.

Through this tablet, we get a glimpse of what people experienced at that time. Archaeologists  value this highly: when we read history, we often forget that real people were part of these events and that to them these developments were more than just of academic interest. To me, this cry for help still packs a punch, even after more than two and a half millennia have gone by.

The world’s oldest alternative energy source

As oil reaches a new record of $143 per barrel today, I think it’s safe to say that energy – and possible alternatives to fossil fuels – are topics on everyone’s mind. Before the development of fossil-fuel based energy technology, wind-power wasn’t an alternate form of energy – it was just the way things were done.

Julian Lamborn, Master Docent for the Wiess Energy Hall, has been kind enough to share the history of wind technology as well as share his case for developing wind energy today, in this two-part post.

Shakespeare had it right when he penned: “Blow, blow thou winter wind, thou art not so unkind.”

The winds of the world today bring with them the promise of low cost, renewable and sustainable electricity which will help feed the world’s insatiable demand for energy. One perk of using wind energy is it has a low atmospheric pollution potential.

In 2007, the globally installed capacity of electricity generation from wind increased by some 26.6% over 2006.

Ontario Turbines (2)
Creative Commons License photo credit: JoshMcConnell

The global capacity of wind-generated electricity is currently equivalent to some 1.3% of the world’s electricity needs with Germany producing the most wind power.  In fact, Germany has 22,247 megawatts of installed wind generating capacity which meets between 5% and 7% of the country’s electricity needs. 

Here in the USA (which, at 16,818 MW, is second only to Germany in installed, wind-generating capacity) about 1% of our electricity needs are met by wind generation and in Texas particularly, this number rises to 3%. Texas is also the state that uses the most wind energy.

Blood Hill Wind Farm, West Somerton, Norfolk

Creative Commons License photo credit: .Martin.

It’s all very well talking about a megawatt of wind generated power, but what can it actually do for you in your home?  In very round numbers, one megawatt of wind generating capacity typically will satisfy the electricity needs of 350 households in an industrial society, or roughly 1,000 people per year.  Although wind generators are placed in windy areas and designed to run optimally at wind speeds between 25 and 35 mph, wind does not blow all the time.  In the USA wind generators work at about 30.5% of their capacity.

But, of course, this is the modern story. 

IMG_3163
Creative Commons License photo credit:
Wouter de Bruijn

The first windmills were developed to automate the tasks of grain-grinding and water-pumping. The earliest-known design is the vertical axis system developed in Persia about 500-900 C.E. (although there is some suggestion that King Hammurabi of Babylon in c 1760 B.C.E used wind driven scoops to move water for irrigation).   The first known documented design of a Persian windmill is one with vertical sails made of bundles of reeds or wood which were attached to the central vertical shaft by horizontal struts. 

Windmills as we know them today from paintings by the Dutch Masters first appeared in the late Middle Ages, although it took another 500 or so years for the highly efficient mills of the Dutch to be fully developed. 

However, by the late 19th century, all the technology was in place to allow the design of the first power-generating wind-mill. This first use of a large windmill to generate electricity was a system built in Cleveland, Ohio, in 1888, by Charles F. Brush. Compared to today’s behemoths producing up to 3.6 MW or more, Bush’s machine was a lightweight producing just 12 KW!

The modern wind powered generating devices, such as those near Abilene, typically each produce 1.5 to 2 MW of power at around the same 4.5 cent cost per kilowatt-hour as electricity from coal but without the co-production of greenhouse gases