// Package planet provides the low-level entry points of the built-in ephemeris models: the semianalytic tables (default) and the VSOP87/ELP2000-82 legacy series; jde is a TT Julian day, angles are degrees and distances are AU.
// 求值接口的 N 后缀是 n 变体:n < 0 取完整级数;半解析模型下所有 n >= 0 使用同一张快速表;Legacy 按 n 截断。
// The N suffix marks an n-variant: n < 0 uses the full series, every n >= 0 uses one fast table under the semianalytic model, and Legacy truncates by n.