Moon Sign Tracker Screensaver

In astrology the zodiac is a band of twelve equal sectors of thirty degrees each, measured along the ecliptic, the Sun’s apparent path across the sky. The Moon’s sign is simply the sector that contains it, measured by its ecliptic longitude. This saver uses the tropical zodiac, whose zero point (0° Aries) is the March equinox, the convention in Western astrology. Sidereal systems, used mainly in Indian astrology, correct for the precession of the equinoxes and sit more than twenty degrees away from the tropical signs.

The Moon moves faster across the sky than any other major body, averaging a little over thirteen degrees a day against the stars. It circles all twelve signs in about 27.3 days, so it spends roughly two and a quarter days in each, though its speed varies because its orbit is not circular. Its position is calculated from lunar theory, using many periodic terms that correct a simple orbit for the pull of the Sun and other perturbations.

The astronomy is precise, but the astrological meaning is a matter of tradition. Practitioners usually associate Moon signs with moods or emotional tone, but scientific testing has not found support for astrology’s predictions about behaviour or events. The position shown is geocentric, as seen from the centre of the Earth. An observer on the surface sees the Moon displaced by up to about a degree, so the moment of a sign change differs slightly depending on where you stand.