Anxious Astrologers Re-Discover Precession!

   Astronomers, and even some astrologers, have known for centuries that due to the precession of the earth’s axis, the constellation in which the Sun resides on a given day of the year slowly changes over the millenia. Because the codification of astrology was over two thousand years ago, the "Sun Sign" attributed to any given birthday by the Sunday paper or in various astrology guide-books is usually wrong -- literally out of date.   My contribution to this knowledge is that I developed a new way to use a common star map, known as a star wheel or planisphere, to show people where in the real starry sky the Sun actually resided on their birth date.  I have discovered how to show anyone their "Real Sun Sign" on a star map.

   With an August 23^rd birthday, I grew up believing my sign to be Virgo, when actually the Sun was centered in Leo on my birth date.  In mid-2011 these facts were noticed by the general public, via social networking on the Internet, and people everywhere found their astronomy superstitions challenged.

   Well, that was fun to learn. Many of us, even astronomers, may use astrology as a topic of conversation, an excuse to talk about who we are, even if only to explain why astrology is nonsense. I have found that showing people their real Sun Sign opens the door to teaching bona fide astronomy. People are fascinated to learn about precession, the ancient historical nature of their Sun Sign, and most of all, that it may not be what they have been told. 

   For years I used a corrected, that is modern, table of dates to show my astronomy students, both adults and children, at schools, scout camps, historical re-enactment events, and star parties, which constellation the Sun actually occupied on the date they were born. However, many people do not know what a constellation looks like, have never seen a star map, and do not understand how the planets and Sun move along the ecliptic. I wanted something more visual, and more fun, than a simple table of dates.

   Then one day, while playing with a planisphere, the solution came to me. What is the one time of day when we always know where the Sun is in the sky? The answer is Noon. Ignoring for now a small variance due to the equation of time*, the Sun is always due south at midday. This insight allows me to show people where among the stars the Sun actually resided on the day they were born:  their Real Sun Sign.

   I ask my “student” what their birthday is, telling them that the year does not matter, unless they are hundreds or thousands of years old. “Are you an immortal or a vampire? No? Then the year of your birth will not matter.” I set their birthday opposite Noon on the planisphere. The sun is then due south in the sky, on the ecliptic, which is astronomer-speak for the path of the Sun and planets in the sky. The Sun is then correctly placed among the stars of the Zodiac. When students see their Real Sun Sign for the first time, the effect is often dramatic. My favorite response is “That explains everything!"

   The viewer begins to appreciate that their “Sun Sign” is derived from astronomical observations, that the sun moves through the sky, not just every day, as the Earth spins, but also more slowly against the background stars, as the Earth travels around the Sun. Even after 50+ years as an astronomer, I still find this to be wonderful, to see the sky as Copernicus and Galileo saw it, as a fresh discovery.

   Repeated and predictable patterns in the sky probably contributed to the evolution of human intelligence, and later became fundamental to the development of culture. Whether viewed by early naturalists or shamans and priests, the study of the sky helped early man become us.

   A long time ago, some genius realized that between the first constellation visible in the west, after the Sun sets, and the last constellation in the east, just before sunrise, existed the star pattern, the constellation, wherein must lie the Sun, invisible but still present, behind our Sun. This intuition, this triumph of imagination, ranks as one of the Great Ideas, right up there with taming fire and harnessing the wheel.

   No wonder the discovery of the hidden-but-inferred stars behind the Sun lead to the magical thinking of astrology. We still do this today with the more mysterious aspects of cutting edge scientific thinking. As astronomers discovered that stars are suns like ours, probably harboring planets, popular culture explored the idea of aliens. Growing understanding of stellar spectra gave us Superman, born under a red sun. The challenging light speed barrier inevitably spawned space operas about FTL travel and galactic empires.

   The mystery of invisible but frightening atomic radiation helped Stan Lee ask the question, "What would happen if a radioactive spider bit a teenager?"

   For most people these novel uses of new scientific knowledge are simply entertainment. But for others new scientific ideas and theories imply actual magic which affects their daily lives. Nearly everyone has encountered an adventure story featuring aliens (think Star Wars). A few people are certain that aliens walk among us, while a tiny minority believe they have been abducted!

   Naturalists and scientists generally understand the practical applications of new discoveries. I suspect that fewer scientists  notice the effect that science may have on culture, art, and superstition.

   I play with that connection via my Real Sun Sign party trick. After showing my students their own Sun Sign constellation, I point out that each zodiacal constellation is a different size, and that many of them overlap. For the astrological true believer, this revelation is eye-opening, and may hint that they have not been given the whole story. Some are pleased, some are worried or angry!

   The more science minded listener is just as interested as the astrology believer, but more as a discovery of new details to fill in what they already may have suspected. This person often knows that astrological signs were based on astronomy, and after my demonstration, they can visualize this more clearly, and perhaps ask questions. “Why doesn’t the year of my birth matter?”  “Why doesn’t my newspaper publish this information along with the daily astrological advice?” Good questions! 

   These days I bring my planisphere to New Year’s parties as well as star parties, science fiction conventions, medieval re-enactment tournaments and all sorts of events where people are enjoying themselves. When the opportunity presents, I ask “What’s Your Sign?” and then answer my own question by using the planisphere. Generally, a crowd soon gathers. Nearly everyone, the superstitious and the skeptic, loves this astronomical party game.

   Readers of Sky & Telescope may want to include a correction for the equation of time should you try this teaching technique for yourself, although the adjustment makes only a slight difference in the graphical representation on a planisphere. You can use the following table to make your demonstration of your listeners’ Real Sun Sign more precise. Using the date in the table closest to your student’s birthday, set the indicated time opposite that same birthday.

   For example, if your listener tells you that her birthday is April 5^th, set 12:04 opposite April 5^th. 

* Correction for the Equation of Time.

Michael Kauper teaches astronomy, especially to children, in Minneapolis and elsewhere. Childcareguy47@yahoo.com

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