/**
 * deltat.ts — ΔT = TT − UT1, the offset between uniform dynamical time and
 * Earth-rotation-based civil time.
 *
 * Ephemerides (DE440) are indexed by TDB; birth data is given in UT. Ignoring
 * ΔT shifts every body by its motion over ~60 s, which for the Moon is ~35″ —
 * far larger than everything else in this engine combined.
 *
 * Implementation: the Espenak & Meeus polynomial expressions published by NASA
 * (https://eclipse.gsfc.nasa.gov/SEcat5/deltatpoly.html), the same family of
 * fits Swiss Ephemeris uses outside its tabulated range. For 1600–2150 — which
 * covers all of de440s.bsp — these are accurate to ~1 s or better, i.e. under
 * 0.6″ of lunar motion.
 */
/** Last year covered by {@link OBSERVED_DELTA_T}. */
export declare const LAST_OBSERVED_YEAR: number;
/**
 * ΔT = TT − UT1 in seconds for the given Julian Day (UT).
 *
 * @param jdUT  Julian Day in UT
 */
export declare function deltaT(jdUT: number): number;
/**
 * Convert a Julian Day in UT to ephemeris seconds past J2000.0 TDB, as required
 * by the SPK reader.
 *
 * TDB − TT is periodic with amplitude < 1.7 ms (≈ 0.00002″ of lunar motion), so
 * TT is used directly.
 */
export declare function jdUTtoET(jdUT: number): number;