feat: 扩展天文计算能力

- 新增日食、月食、本地可见性、中心线、半影区域、SVG 图示与沙罗周期信息
- 新增行星冲合、留、方照、物理星历、视直径、相位、亮肢角、轨道节点等计算
- 新增木星伽利略卫星位置、现象与接触事件计算
- 新增恒星星表、星座判定、自行修正与观测辅助能力
- 新增 coord、formula、orbit、sundial、lite/sun、lite/moon 等扩展包
- 完善农历年号、月相英文别名、视差角、大气质量、折射、日晷与双星计算
- 增加 NASA、JPL Horizons、IMCCE 等回归测试数据与基线测试
- 重构基础算法文件组织，补充大量公开 API 注释和语义回归测试
- 更新中文和英文 README，补充示例、精度说明、SVG 配图

coord/coord.go

@@ -0,0 +1,129 @@
+// Package coord 坐标工具包 / coordinate utility package.
+//
+// 本包面向用户提供常用坐标变换、恒星时、岁差、站心和地平坐标封装。
+// 所有角度输入和输出默认使用度；恒星时输出使用小时。
+// date 按绝对时刻使用，内部会转换为 UTC 后计算。
+package coord
+
+import (
+	"time"
+
+	"b612.me/astro/basic"
+)
+
+// Ecliptic 黄道坐标 / ecliptic coordinates.
+type Ecliptic struct {
+	Lon float64 // 黄经，单位度 / ecliptic longitude in degrees.
+	Lat float64 // 黄纬，单位度 / ecliptic latitude in degrees.
+}
+
+// Equatorial 赤道坐标 / equatorial coordinates.
+type Equatorial struct {
+	RA  float64 // 赤经，单位度 / right ascension in degrees.
+	Dec float64 // 赤纬，单位度 / declination in degrees.
+}
+
+// Horizontal 地平坐标 / horizontal coordinates.
+type Horizontal struct {
+	Azimuth   float64 // 方位角，正北为0，顺时针增加 / azimuth from north clockwise, degrees.
+	Altitude  float64 // 高度角，单位度 / altitude in degrees.
+	Zenith    float64 // 天顶距，单位度 / zenith distance in degrees.
+	HourAngle float64 // 时角，单位度 / hour angle in degrees.
+}
+
+func jdeUTC(date time.Time) float64 {
+	return basic.Date2JDE(date.UTC())
+}
+
+// EclipticToEquatorial 黄道坐标转赤道坐标 / converts ecliptic to equatorial coordinates.
+func EclipticToEquatorial(date time.Time, lon, lat float64) Equatorial {
+	ra, dec := basic.LoBoToRaDec(jdeUTC(date), lon, lat)
+	return Equatorial{RA: ra, Dec: dec}
+}
+
+// EquatorialToEcliptic 赤道坐标转黄道坐标 / converts equatorial to ecliptic coordinates.
+func EquatorialToEcliptic(date time.Time, ra, dec float64) Ecliptic {
+	lon, lat := basic.RaDecToLoBo(jdeUTC(date), ra, dec)
+	return Ecliptic{Lon: lon, Lat: lat}
+}
+
+// Precess 岁差修正 / precesses equatorial coordinates from one date to another.
+func Precess(from, to time.Time, ra, dec float64) Equatorial {
+	nextRA, nextDec := basic.Precess(ra, dec, jdeUTC(from), jdeUTC(to))
+	return Equatorial{RA: nextRA, Dec: nextDec}
+}
+
+// EclipticObliquity 黄赤交角 / ecliptic obliquity.
+func EclipticObliquity(date time.Time, nutation bool) float64 {
+	return basic.EclipticObliquity(jdeUTC(date), nutation)
+}
+
+// Nutation2000B IAU 2000B 章动 / IAU 2000B nutation.
+func Nutation2000B(date time.Time) (longitude, obliquity float64) {
+	return basic.Nutation2000B(jdeUTC(date))
+}
+
+// Nutation1980 IAU 1980 章动 / IAU 1980 nutation.
+func Nutation1980(date time.Time) (longitude, obliquity float64) {
+	return basic.Nutation1980(jdeUTC(date))
+}
+
+// MeanSiderealTime 平恒星时，单位小时 / mean sidereal time in hours.
+func MeanSiderealTime(date time.Time) float64 {
+	return basic.MeanSiderealTime(jdeUTC(date))
+}
+
+// ApparentSiderealTime 真恒星时，单位小时 / apparent sidereal time in hours.
+func ApparentSiderealTime(date time.Time) float64 {
+	return basic.ApparentSiderealTime(jdeUTC(date))
+}
+
+// HourAngle 时角 / hour angle.
+//
+// ra 为瞬时赤经；observerLon 为观测者经度，东正西负。
+// ra is apparent right ascension; observerLon is east-positive longitude.
+func HourAngle(date time.Time, ra, observerLon float64) float64 {
+	return basic.StarHourAngle(jdeUTC(date), ra, observerLon, 0)
+}
+
+// EquatorialToHorizontal 赤道坐标转地平坐标 / converts equatorial to horizontal coordinates.
+//
+// ra/dec 为瞬时赤经赤纬；observerLon/observerLat 为观测者经纬度，东正西负、北正南负。
+// ra/dec are apparent coordinates; observerLon/observerLat are east-positive and north-positive.
+func EquatorialToHorizontal(date time.Time, ra, dec, observerLon, observerLat float64) Horizontal {
+	jde := jdeUTC(date)
+	altitude := basic.StarHeight(jde, ra, dec, observerLon, observerLat, 0)
+	return Horizontal{
+		Azimuth:   basic.StarAzimuth(jde, ra, dec, observerLon, observerLat, 0),
+		Altitude:  altitude,
+		Zenith:    90 - altitude,
+		HourAngle: basic.StarHourAngle(jde, ra, observerLon, 0),
+	}
+}
+
+// TopocentricEquatorial 地心赤道坐标转站心赤道坐标 / converts geocentric to topocentric equatorial coordinates.
+//
+// distanceAU 为目标天体到地心距离，单位 AU；height 为观测者海拔，单位米。
+// distanceAU is geocentric distance in AU; height is observer elevation in meters.
+func TopocentricEquatorial(date time.Time, ra, dec, observerLon, observerLat, distanceAU, height float64) Equatorial {
+	topRA, topDec := basic.TopocentricRaDec(ra, dec, observerLat, observerLon, jdeUTC(date), distanceAU, height)
+	return Equatorial{RA: topRA, Dec: topDec}
+}
+
+// TopocentricEcliptic 地心黄道坐标转站心黄道坐标 / converts geocentric to topocentric ecliptic coordinates.
+//
+// distanceAU 为目标天体到地心距离，单位 AU；height 为观测者海拔，单位米。
+// distanceAU is geocentric distance in AU; height is observer elevation in meters.
+func TopocentricEcliptic(date time.Time, lon, lat, observerLon, observerLat, distanceAU, height float64) Ecliptic {
+	topLon := basic.TopocentricLo(lon, lat, observerLat, observerLon, jdeUTC(date), distanceAU, height)
+	topLat := basic.TopocentricBo(lon, lat, observerLat, observerLon, jdeUTC(date), distanceAU, height)
+	return Ecliptic{Lon: topLon, Lat: topLat}
+}
+
+// AngularSeparation 角距离 / angular separation.
+//
+// 输入为两组赤道坐标，单位度；返回角距离，单位度。
+// Inputs are two equatorial coordinates in degrees; return value is in degrees.
+func AngularSeparation(ra1, dec1, ra2, dec2 float64) float64 {
+	return basic.StarAngularSeparation(ra1, dec1, ra2, dec2)
+}