Dr. Lee T. Shapiro, Director
Morehead Planetarium
CB #3480 Morehead Bldg.
University of North Carolina
Chapel Hill, NC 27599-3480
Planetarian, Spring 1977
[see note at bottom]
Sooner or later anyone involved with astronomy has contact
(or conflict) with astrology or someone interested in astrology.
To a great extent the response from the astronomical and planetarium
community has been defensive, denying the validity of astrology
when asked. There have been some attempts to go on the offensive,
such as the recent publication Objections to Astrology
(Prometheus Books, 1975). However, such clearly antiastrology
publications are probably only read by those who already are nonbelievers.
To put astrology in the proper perspective, we can do two things
to try to remedy the situation. First we must stop spreading astrological
information. Yes, I believe all of us have done this even though
unintentionally. The prime example and major point of this article
is in reference to the band of the zodiac. Consider just the ecliptic.
How often have you referred to the twelve constellations that
the sun passes through during a year? The number twelve is correct
only if one is using astrological constellations. There are thirteen
astronomical constellations that cross the ecliptic. Whenever
you refer to the zodiac use the number thirteen and name the constellations
of the ecliptic (see Table #l). If someone complains that these
are not the right constellations, just point out that all constellations
are arbitrary and strictly artificial. The ones we use are the
official constellations of the International Astronomical Union.
In addition to ceasing our propagation of astrological information,
we can also give the public further astronomical information that
will hopefully have the effect of raising questions about astrological
belief and practice. Table #1 also includes the dates for which
the sun is in each constellation of the ecliptic and the number
of days it spends in each constellation. If someone asks you what
constellation the sun is in on a particular date, use this information
and mention that the answer you are giving is the astronomical
constellation the sun is in on the date in question. If you cross
check between the dates listed here and the standard astrological
dates, you will find there are approximately only four dozen dates
in common.
Then there is a question of the definition of the zodiac itself.
In a quick survey through about ten basic astronomy texts, the
definition given was either 8° or 9° on either side of
the ecliptic. To be on the conservative side, Table #2 lists those
constellations that come within 8° of the ecliptic. (Venus
is the only naked eye planet that reaches more than 8° away
from the ecliptic. ) You can quickly see that there are not 12
constellations of the zodiac but 24. At the appropriate times
you can list the nontraditional constellations in which the sun,
moon, or planets can be found. The current American Ephemeris
& Nautical Almanac and the Atlas Coeli (or some
other suitable stellar atlas with constellation boundaries marked)
are all that are needed for producing this type of list.
If you include the orbit of Pluto which is tilted at 17° to
the ecliptic, then the zodiac also includes the constellations
Bootes, Coma Berenices, Eridanus, and Leo Minor. Using this information,
you can have an interesting time incorporating it into shows or
creating public displays. If and when astrologers complain, your
interest is promoting astronomy, not astrology.
However, there is one caution I would like to mention. If someone
asks you whether you believe in astrology, ask them what they
mean before you reply. If someone gives me a definition such as
"the belief and study of cosmic influences on the earth and
its creatures", I can agree that such influences do exist.
However, I point out that while it is obvious there are cosmic
influences, especially from the sun and the moon, there is no
evidence that positions of the heavenly bodies can be used to
predict the actions or characteristics of individuals.
Table # 1
Astronomical Constellations of the Ecliptic
Constellation Dates # of d
Sagittarius Dec 18 Jan 18 32
Capricornus Jan 19 Feb 15 28
Aquarius Feb 16 Mar 11 24
Pisces Mar 12 Apr 18 38
Aries Apr 19 May 13 25
Taurus May 14 Jun 19 37
Gemini Jun 20 Jul 20 31
Cancer Jul 21 Aug 9 20
Leo Aug 10 Sep 15 37
Virgo Sep 16 Oct 30 45
Libra Oct 31 Nov 22 23
Scorpius Nov 23 Nov 29 7
Ophiuchus Nov 30 Dec 17 18
Dates may fluctuate plus or minus a day from year to year.
Table # 2
Astronomical Constellations of the Zodiac
Aquarius Cetus Libra Scorpius
Aries Corvus Ophiuchus Scutum
Auriga Crater Orion Serpens
Cancer Gemini Pegasus Sextans
Canis Minor Hydra Pisces Taurus
Capricornus Leo Sagittarius Virgo
Reprinted from the Planetarian, Vol 6, #1, Spring 1977.
Copyright 1977 International Planetarium Society. For permission
to reproduce please contact Executive Editor, Sharon Shanks.
John Mosley of the Griffith Observatory and the Belgian astronomer
Jean Meeus investigated this question in 1999 and found that the
planets (minus Pluto) actually pass through these 21 constellations
(using IAU boundaries):
