feat: 完善时标与天象几何计算并扩展输出接口

- 新增时标、ΔT 模型、质心时间与 UT1 支持
- 改进日月食、月掩、行星事件及路径边界计算
- 完善恒星三维自行与动态距离传播
- 扩展 SVG、GeoJSON、KML 输出与底层距离换算工具
- 整理中英文手册、示例资源及回归测试

timescale.go

@@ -0,0 +1,87 @@
+package astro
+
+import (
+	"time"
+
+	"b612.me/astro/basic"
+)
+
+// TimeScale 导出时间标签的时标，零值为民用 UTC / output-label time scale, defaulting to civil UTC.
+type TimeScale int
+
+const (
+	// TimeScaleUTC 默认民用时标 / default civil time scale.
+	TimeScaleUTC TimeScale = iota
+	// TimeScaleUT1 UT1 读数，输出 Location 须为 nil 或 UTC / UT1 reading; output Location must be nil or UTC.
+	TimeScaleUT1
+)
+
+// LabelIn 把民用时刻换成该时标下的时刻值 / converts a civil instant to a value in one scale.
+func LabelIn(scale TimeScale, date time.Time) time.Time {
+	if scale == TimeScaleUT1 {
+		return UT1FromUTC(date)
+	}
+	return date
+}
+
+// UT1FromUTC 民用时刻转 UT1 读数，以 UTC Location 承载 / converts a civil instant to a UT1 reading in a UTC Location.
+func UT1FromUTC(date time.Time) time.Time {
+	return utcLabel(basic.UTC2UT1(basic.Date2JD(date.UTC())))
+}
+
+// UTCFromUT1 是 UT1FromUTC 的逆 / inverts UT1FromUTC.
+func UTCFromUT1(ut1 time.Time) time.Time {
+	return utcLabel(basic.UT12UTC(basic.Date2JD(ut1.UTC())))
+}
+
+// TTFromUTC 民用时刻转 TT，按实例的 UTC 时刻取值 / converts a civil instant to TT.
+func TTFromUTC(date time.Time) time.Time {
+	return utcLabel(basic.UTC2TT(basic.Date2JD(date.UTC())))
+}
+
+// UTCFromTT 是 TTFromUTC 的逆 / inverts TTFromUTC.
+func UTCFromTT(tt time.Time) time.Time {
+	return utcLabel(basic.TT2UTC(basic.Date2JD(tt.UTC())))
+}
+
+// DUT1 返回民用时刻的 UT1−UTC，单位秒 / UT1−UTC in seconds.
+func DUT1(date time.Time) float64 {
+	return basic.DUT1Seconds(basic.Date2JD(date.UTC()))
+}
+
+// TCGFromTT 地球时转地心坐标时 / converts TT to TCG.
+func TCGFromTT(tt time.Time) time.Time { return utcLabel(basic.TT2TCG(basic.Date2JD(tt.UTC()))) }
+
+// TTFromTCG 是 TCGFromTT 的逆 / inverts TCGFromTT.
+func TTFromTCG(tcg time.Time) time.Time { return utcLabel(basic.TCG2TT(basic.Date2JD(tcg.UTC()))) }
+
+// TCBFromTT 地球时转太阳系质心坐标时，采用地心近似 / converts TT to TCB using a geocentric approximation.
+func TCBFromTT(tt time.Time) time.Time { return utcLabel(basic.TT2TCB(basic.Date2JD(tt.UTC()))) }
+
+// TTFromTCB 是 TCBFromTT 的逆 / inverts TCBFromTT.
+func TTFromTCB(tcb time.Time) time.Time { return utcLabel(basic.TCB2TT(basic.Date2JD(tcb.UTC()))) }
+
+// TDBFromTT 地球时转太阳系质心力学时，采用地心近似 / converts TT to TDB using a geocentric approximation.
+func TDBFromTT(tt time.Time) time.Time { return utcLabel(basic.TT2TDB(basic.Date2JD(tt.UTC()))) }
+
+// TTFromTDB 是 TDBFromTT 的逆 / inverts TDBFromTT.
+func TTFromTDB(tdb time.Time) time.Time { return utcLabel(basic.TDB2TT(basic.Date2JD(tdb.UTC()))) }
+
+// TCBFromTDB 质心力学时转质心坐标时 / converts TDB to TCB.
+func TCBFromTDB(tdb time.Time) time.Time { return utcLabel(basic.TDB2TCB(basic.Date2JD(tdb.UTC()))) }
+
+// TDBFromTCB 是 TCBFromTDB 的逆 / inverts TCBFromTDB.
+func TDBFromTCB(tcb time.Time) time.Time { return utcLabel(basic.TCB2TDB(basic.Date2JD(tcb.UTC()))) }
+
+// TCGMinusTT 返回 TT 时刻的 TCG−TT，单位秒 / TCG−TT in seconds for a TT instant.
+func TCGMinusTT(tt time.Time) float64 { return basic.TCGMinusTTSeconds(basic.Date2JD(tt.UTC())) }
+
+// TCBMinusTT 返回 TT 时刻的 TCB−TT，单位秒 / TCB−TT in seconds for a TT instant.
+func TCBMinusTT(tt time.Time) float64 { return basic.TCBMinusTTSeconds(basic.Date2JD(tt.UTC())) }
+
+// TDBMinusTT 返回 TT 时刻的地心 TDB−TT 近似值（秒）/ geocentric TDB−TT approximation in seconds at a TT instant.
+func TDBMinusTT(tt time.Time) float64 { return basic.TDBMinusTTSeconds(basic.Date2JD(tt.UTC())) }
+
+func utcLabel(jd float64) time.Time {
+	return basic.JD2DateByZone(jd, time.UTC, false)
+}