Real astronomy and dated history, with sources. Documented traditions and folklore. Modern lunar astrology · symbolic, not predictive.

Chart basics · Advanced

Delta T

Also called ΔT, ΔT

The difference between the uniform time planets move in and clock time kept by Earth's slightly irregular spin.

About 69 seconds in 2026, and a few seconds in 1900. The Moon moves about half an arcsecond a second, so ignoring ΔT would shift it by around half an arcminute today. This site takes ΔT from the International Earth Rotation Service's measurements.

Kind: Astronomy, Calculation
Tradition: Astronomy
In this site’s birth chart: used

Swiss Ephemeris documentation (Astrodienst): house systems, nodes and calculation conventions (opens in a new tab) technical

Written for Cool Moon Facts in its own words. An astrology source documents what astrologers believe or practise; it does not establish that astrology works.

All terms · Your birth chart

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Delta T

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Delta T

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