Precession of the
Earth's Rotation Axis
The Earth's rotation axis is not fixed in space. Like a rotating toy top, the
direction of the rotation axis executes a slow precession with a period of
26,000 years (see following figure).
Pole Stars are Transient
Thus, Polaris will not always be the Pole Star or North Star.
The Earth's rotation axis happens to be pointing almost exactly at Polaris now,
but in 13,000 years the precession of the rotation axis will mean that the
bright star Vega in the constellation Lyra will be approximately at the North
Celestial Pole, while in 26,000 more years Polaris will once again be the Pole
Precession of the Equinoxes
Since the rotation axis is precessing in space, the orientation of the
Celestial Equator also precesses with the same period. This means that the
position of the equinoxes is changing slowly with respect to the background
stars. This precession of the equinoxes
means that the right ascension and declination of
objects changes very slowly over a 26,000 year period. This effect is
negligibly small for casual observing, but is an important correction for
The Dawning of the Age of Aquarius (Almost)
Because of the precession of the equinoxes, the vernal equinox moves through
all the constellations of the Zodiac over the 26,000 year precession period.
Presently the vernal equinox is in the constellation
Pisces and is slowly approaching Aquarius.
The Vernal Equinox
This is the origin of the "Age of Aquarius"
celebrated in the musical
Hair: a period when according to astrological mysticism and related
hokum there will be
unusual harmony and understanding in the world. We
could certainly use a dose of
harmony and understanding in this old world; unfortunately, it is unlikely to
come because of something as irrelevant as the position of the vernal
equinox with respect to the constellations of the Zodiac.