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

earth/apsis.go

@@ -0,0 +1,32 @@
+package earth
+
+import (
+	"time"
+
+	"b612.me/astro/basic"
+)
+
+// ApsisInfo 轨道极值事件 / orbital distance extremum event.
+type ApsisInfo struct {
+	// Time 事件时刻，UTC / event time in UTC.
+	Time time.Time
+	// Distance 极值距离，单位 AU / extremum distance in AU.
+	Distance float64
+}
+
+// Perihelion 指定年份的地球近日点 / Earth perihelion in the given year.
+func Perihelion(year int) ApsisInfo {
+	return convertEarthApsisInfo(basic.EarthPerihelion(year))
+}
+
+// Aphelion 指定年份的地球远日点 / Earth aphelion in the given year.
+func Aphelion(year int) ApsisInfo {
+	return convertEarthApsisInfo(basic.EarthAphelion(year))
+}
+
+func convertEarthApsisInfo(event basic.ApsisEvent) ApsisInfo {
+	return ApsisInfo{
+		Time:     basic.JDE2DateByZone(event.JDE, time.UTC, false),
+		Distance: event.Distance,
+	}
+}

earth/apsis_test.go

@@ -0,0 +1,29 @@
+package earth
+
+import (
+	"math"
+	"testing"
+	"time"
+
+	"b612.me/astro/basic"
+)
+
+func TestApsisWrappersMatchBasic(t *testing.T) {
+	peri := basic.EarthPerihelion(2026)
+	periWrapped := Perihelion(2026)
+	if !periWrapped.Time.Equal(basic.JDE2DateByZone(peri.JDE, time.UTC, false)) {
+		t.Fatalf("perihelion time mismatch: got %s want %s", periWrapped.Time.Format(time.RFC3339Nano), basic.JDE2DateByZone(peri.JDE, time.UTC, false).Format(time.RFC3339Nano))
+	}
+	if math.Float64bits(periWrapped.Distance) != math.Float64bits(peri.Distance) {
+		t.Fatalf("perihelion distance mismatch: got %.12f want %.12f", periWrapped.Distance, peri.Distance)
+	}
+
+	aphe := basic.EarthAphelion(2026)
+	apheWrapped := Aphelion(2026)
+	if !apheWrapped.Time.Equal(basic.JDE2DateByZone(aphe.JDE, time.UTC, false)) {
+		t.Fatalf("aphelion time mismatch: got %s want %s", apheWrapped.Time.Format(time.RFC3339Nano), basic.JDE2DateByZone(aphe.JDE, time.UTC, false).Format(time.RFC3339Nano))
+	}
+	if math.Float64bits(apheWrapped.Distance) != math.Float64bits(aphe.Distance) {
+		t.Fatalf("aphelion distance mismatch: got %.12f want %.12f", apheWrapped.Distance, aphe.Distance)
+	}
+}

earth/earth.go

@@ -6,8 +6,10 @@ import (
 	"b612.me/astro/basic"
 )
 
-// EarthEccentricity 地球偏心率
-// 返回date对应UTC时间的地球偏心率
+// EarthEccentricity 地球轨道偏心率 / orbital eccentricity of Earth.
+//
+// 返回 date 对应绝对时刻的地球轨道偏心率，无量纲。
+// Returns Earth's orbital eccentricity at the instant represented by date; the value is dimensionless.
 func EarthEccentricity(date time.Time) float64 {
 	jde := basic.Date2JDE(date.UTC())
 	return basic.Earthe(basic.TD2UT(jde, true))