Almost all of us know our birthsign, but not all of us know why it's our birthsign.
In it's yearly orbit around the Sun, the Sun appears to cross different star patterns. The Sun follows a path along the these star patterns ( the celestial sphere) called the ecliptic. Most of the other planets also stay along this path. The belt in the sky, about 18 degrees wide and centered on the ecliptic is called the Zodiac.
When early astronomers looked up into the night sky they noticed that some of the "stars" moved from night to night. These wandering "stars" always moved over the same fixed stars. These wandering stars where in fact the planets, the word planet comes from a Greek word meaning "wanderer". The background stars that the planets moved across where catagorized and named as constellations. Most are figures of animals, this is the Zodiac (The word is again derived from the Greek, the same word that gives us zoo, zoology etc.).
The zodiac is divided into 12 zones, each zone has a constellation. When you are born the Earth projects the Sun onto one of these zones and that is your birthsign. The Zodiac lines on a Sundial show this apparent movement from one sign to the next.
The dates for Zodiac change over time. We live in a Universe where everything is moving and on a planet that wobbles. Because of this the dates that the Sun enters the different Zodiac vary. I was born in late March, my sign is Aries however in the year I was born the Sun was in Pisces. If I was born 1000 years from now the Sun would be in Aquarius.
The Zodiac lines on a sundial are usually labled with the accepted signs. Aries at the Vernal Equinox (first day of spring), Cancer at the Summer Solstice (first day of summer), Libra at the Autumnal Equinox (the first day of fall), and Capricorn at the Winter Solstice (the first day of winter).
The Zodiac lines on a Sundial are based on the declination of the Sun. The ecliptic is at an angle of about 23.5 degrees with the celestial equator. The Sun appears north of the celestial equator half the year and south of it the other half. The dates that the Sun crosses the celestial equator it has a declination of 0 degrees. Because of this day and night are of equal length. These are Spring/Fall Equinox (from the latin meaning equal night). When the Sun reaches its maximum northen or southern declination, about +/-23.5 degrees, these are the Solstices.
The declination of the Sun varies from day to day. The declination values can be found in an Astronomical Ephemeris or calculated. It is because of this that a sundial can be built with anniversary lines on it.
Below is a graph which shows how the declination of the Sun varies with the date. These values are used to calculate the Zodiac lines on a sundial.
Below is a chart that shows that data used in Sundial (Zodiac Lines) development.
The Equinox (Spring, Fall) and the Solstice (Summer, Winter) are not usually associated with 'holidays', however the mid-points between were used by ancient people (the Celts) and have become 'modern' holidays.
The chart below shows a graphical representation of the Equinox (Spring/ Fall) and the Solstice (Summer/Winter) and the 'mid-points'.
The U.S. tradition that a groundhog emerges from his burrow after a long Winter sleep to look for his shadow. If the shadow is seen he runs back to his burrow to sleep for six more weeks, If no shadow is seen he stays above ground and Spring will soon follow.
In England this day is Candlemas; an old English song:
If Candlemas be fair and bright,
Come, Winter, have another flight;
If Candlemas bring clouds and rain,
Go, Winter, and come not again.
The festival of Spring also an important holiday in Europe honoring workers.
The Celtic and Anglo-Saxon end of Summer and the start of a new year. The souls of the dead were supposed to revisit their homes on this day and needed to be 'scared' into returning to the nether-world. Bonfires and costumes were used to frighten the evil spirits.
A related 'modern' holiday is unknown to me, please email an opinions to the address below.
The above list (and diagram) shows the 'Holiday', date, Cardinal (or semi- cardinal) direction, and the name of the 'Wind' (Greek) associated with the direction.
(c) 1998 P. Field I/O Asso.
The zodiac Taurus is of particular interest. It has been attributed to the Mesopotamians (around 6000 years ago). Some scholars believe that the Mesopotamians may have borrowed the bull figure from earlier people.
In Southwest France is the Lascaux cave, a cave that has many paintings and animal figures. These figures have been dated to 15000 BC and one in particular has caught the attention of stargazers. The painting shows a bull with a cluster of dots over his shoulder. The Pleiades (the sisters) is a star cluster that is associated with the constellation Taurus. The constellation of Taurus is easily identified as a V. It is interesting to note that the cluster of "dots" on the cave painting is in the general position of the Pleiades (with respect to the V). The brightest star in Taurus is Aldeberan (the eye of the Bull), look carefully at the painting and note that there seems to be a collection of "dots" in the shape of a V around the eye of the bull.
The image on the left is from the cave in Lascaux, the image on the right is how the constellations appeared in the South of France in 15000 BC
For more information about Lascaux (and other palaeoastronomy subjects) please visit : INFIS
It is important not to confuse Astronomy with Astrology. What is discussed here is Astronomy.