Will the equinoxes and solstices switch places in 13,000 years
because of the precession of the Earth's rotation axis?
<TITLE> Archive of Dr. Magneto's Questions and Answers</title>
<body background=" amtile.gif" link=" #00FF00"
vlink=" #3399cc" text=" #FFFFFF">
<h2>Will the equinoxes and solstices switch places in 13,000 years because of
the precession of the Earth's rotation axis?
No, there will be no swapping of the seasons and the months of the year.
The precession of the equinoxes of the Earth is a motion that causes the axis
of the Earth's rotation to remain FIXED at an angle of 23.5 degrees, however,
it rotates along a great circle with a period of 26,000 years. The result is
that the two points where the equator of the Earth intersect the ecliptic
plane, the vernal and autumnal equinoxes, precess westward
along the ecliptic by 360
degrees per 25,800 years or 50.26 seconds of arc per year. This is also equal to
0.125 seconds of arc per day or 0.008 seconds of time, so that each day the
synchronization between sidereal and solar time slips a bit.
Currently, the vernal equinox which heralds the beginning of spring occurs in
the constellation of Pisces, but it is slowly moving towards the constellation
of Aquarius and will arrive there in a few hundred years or so.
The seasons of the year are produced by the tilt of the axis of the Earth,
and this tilt is not disturbed by the precession, but remains exactly the same
with respect to the ecliptic plane. Currently in the northern hemisphere, the
Earth is tilted TOWARDS the Sun by 23.5 degrees
when the Earth is at its farthest from the Sun ( aphelion ) in June, and we
experience summer. In the winter it is tilted AWAY from the Sun today. Because
our calendar year and its seasons are tied to when the equinoxes occur, it
automatically keeps up with the precession, so that in 13,000 years we will
have the following situation: The axis of the Earth will be tilted TOWARDS the
Sun by 23.5 degrees when the Earth is closest to the Sun ( perihelion) in the
northern hemisphere in JUNE, and tilted AWAY from the Sun when it is closest
to the Sun in December. Each day, our calendar is gradually 'precessing' in
time by 0.008 seconds to keep up with the new locations of the equinoxes and
solstices so no matter where we are in the precession cycle ,winter will
always happen in December, and Summer in June. BUT because in the northern
hemisphere in 13,000 years we will be closer to the Sun for our summer, and
farther for our winter, the severity of these seasons will be slightly
What will also change is the constellation that the summer solstice will be
in. In 13,000 years the summer solstice will travel 1/2 of a full
cycle around the zodiac. Will we still celebrate winter in December and summer
in June in the northern hemisphere? Yes, and we will also see Orion as a summer
constellation in 13,000 years. Precession affects the background
constellations against which the Earth-Sun motion plays itself out. It does
not affect the months during which the seasons occur, because these are
constantly being updated to keep the vernal equinox in March etc.
<a href=" http://bolero.gsfc.nasa.gov/~odenwald/ask/askmag.html#list" ><img src=" mdesk.gif" ></a>