Definition: [Ancient Astrological Concepts] An
imaginary sphere of stars surrounding the Earth and rotating around it.
In astrology we generally represent
the stars and constellations as lying on this single sphere. We tend to think
of the planets as lying between this sphere and the Earth and - whilst mostly
moving along with the celestial sphere - possessing much smaller but
independant motions of their own. [This is why the ancients called the planets
the Wanderers.] This, essentially, was the view of the night skies held
by the Classical astrologers, such as
who defined much of modern astrology.
However, this view of the
night skies isn't actually true in two important respects:
(1) In the celestial
sphere view of the skies, the Earth stays still and the sphere rotates around
it. This is the opposite of what really happens: in reality, the stars stay
still and the Earth spins on its axis giving the illusion of stellar movement.
Those small idependent movements of the planets relative to the stars that we
can see happen each night are because they - and we on Earth - are orbiting the
The Rotating Celestial Sphere This way
of thinking about the night sky can be confusing for we astrologers as it's not
reality. The movement of the stars through the sky each night is because of the
Earth's spin, not the movement of the stars around us. [West on the above
sphere is to the right.] ©
The Rotating Earth This is the reality:
the Earth rotating around its axis once each day and producing the illusion of
the movement of the stars through the night sky. The Earth spins west to east,
giving the illusion of the stars moving from east to west, parallel to the
celestial equator, each night. The stars
seem to rise in the east and set in the west. In the daytime, so does the Sun.
Again, this is simply an illusion caused by the Earth's spin. This is a view of
the Earth at Equinox, so the light and dark portions of the Earth are the same
(2) The celestial
sphere implies that the stars are all the same distance away from us; this is
not correct. In fact, there can be huge differences in the distances from the
stars to the Earth of the stars within a single constellation.
A Renaissance Celestial Sphere
Illustration from Opera Mathematica, Johannes Schoner, Nuremberg 1551.
The two dashed black and white lies mark that can be seen mark the great
circles of the Ecliptic [upper line] and the Celestial Equator [lower line].
[Click on the above diagram for a complete version,
Circles of the Celestial Sphere: In a tradition
going back at least as far as Manilius in the first century BC, Classical
astrologers used Great Circles to mark out the boundaries celestial sphere.
Shown below are the Ecliptic and the Celstial Equator within the celestial
Shown right is a drawing of
sixteenth century celestial sphere. These were often produced as globes, for
rich patrons and working astrologers, often made as pairs with globes of the
A Static View of the Celestial Sphere
The Celestial Equator is the horizontal plane in the centre. A second plane
tilted with respect to the Celestial Equator marks the Ecliptic. Where these
two meet are the Equinoxes and where they lie furthest from each other are the
Solstices. You could also draw a Great Circle between the Vernal Equinox and
through the Celestial Poles. This marks the right vertical border on our star
maps, the line of zero Right Ascension.
© Dr Shepherd Simpson, Galactic Astrologer
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