St
Definition
St, usually written ST, commonly abbreviates sidereal time in astrological tables, chart calculations, and older technical texts. Sidereal time measures Earth’s rotation relative to the stars rather than the Sun. Greenwich sidereal time may be adjusted for longitude to obtain local sidereal time, a value used when calculating the angles and houses of a horoscope. Because abbreviations vary, the source’s notation key should always be checked.
Astrological Meaning
ST is a calculation factor rather than a planet, sign, aspect, or interpretive symbol. Astrologers use local sidereal time to determine which degree of the zodiac is crossing the eastern horizon and which is culminating at the meridian for a particular time and place. These points become the Ascendant and Midheaven, while the remaining house cusps depend on the selected house system. In traditional hand calculation, sidereal-time tables helped astrologers construct charts before software automated the process.
Why It Matters
Understanding ST clarifies how birth time and geographic location shape a chart’s angles and houses. Even a small timing difference can alter cusp degrees, especially near a sign boundary, although its interpretive importance depends on the chart and method used. Recognizing the abbreviation also makes historical ephemerides, tables of houses, and calculation manuals easier to read accurately.
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