Packages/MoonriseKit/Tests/SkyEngineTests/EclipsePathTests.swift

 1import Foundation
 2import Testing
 3@testable import SkyEngine
 4
 5/// Distance in km between two points on a sphere.
 6private func km(_ a: (lat: Double, lon: Double), _ b: (lat: Double, lon: Double)) -> Double {
 7    let r = Double.pi / 180
 8    let h = pow(sin((b.lat - a.lat) * r / 2), 2) + cos(a.lat * r) * cos(b.lat * r) * pow(sin((b.lon - a.lon) * r / 2), 2)
 9    return 2 * 6371 * asin(h.squareRoot())
10}
11
12@Test func totalEclipse2027Path() throws {
13    // NASA (Espenak): greatest eclipse 2027-08-02 10:07 UT at 25.5° N, 33.2° E,
14    // totality 6 m 23 s, path 258 km wide; the path crosses southern Spain and Luxor.
15    let path = try #require(EclipsePath.compute(near: Date(timeIntervalSince1970: 1_817_201_220)))
16    #expect(path.kind == "Total")
17    #expect(abs(path.greatest.lat - 25.5) < 0.3 && abs(path.greatest.lon - 33.2) < 0.3)
18    let duration = try #require(path.centralDuration)
19    #expect(abs(duration - 383) < 5)
20    #expect(path.points.count > 100)
21
22    func nearest(_ place: (lat: Double, lon: Double)) -> Double {
23        path.points.map { km($0.center, place) }.min()!
24    }
25    #expect(nearest((25.69, 32.64)) < 40) // Luxor, close to the centre line
26    #expect(nearest((36.01, -5.60)) < 120) // Tarifa, inside the path
27
28    let middle = path.points.min { abs($0.date.timeIntervalSince(path.peak)) < abs($1.date.timeIntervalSince(path.peak)) }!
29    #expect(abs(middle.widthKm - 258) < 20)
30}
31
32@Test func noPathForPartialEclipse() {
33    // 21 September 2025 was partial only.
34    #expect(EclipsePath.compute(near: Date(timeIntervalSince1970: 1_758_483_660)) == nil)
35}
36
37@Test func localCircumstances2027() throws {
38    let peak = Date(timeIntervalSince1970: 1_817_201_220)
39    let luxor = try #require(LocalEclipse.at(Observer(latitude: 25.69, longitude: 32.64), near: peak))
40    #expect(luxor.kind == "Total")
41    let begin = try #require(luxor.centralBegin), end = try #require(luxor.centralEnd)
42    #expect(end.timeIntervalSince(begin) > 360)
43    let madrid = try #require(LocalEclipse.at(Observer(latitude: 40.42, longitude: -3.70), near: peak))
44    #expect(madrid.kind == "Partial" && madrid.centralBegin == nil)
45    #expect(madrid.obscuration > 0.8 && madrid.obscuration < 0.95)
46    #expect(LocalEclipse.at(Observer(latitude: 41.88, longitude: -87.63), near: peak) == nil) // Chicago: night
47}
48
49@Test func moonMatchesHorizonsFrame() {
50    // Artemis I from JPL Horizons (geocentric, J2000 ecliptic, km) at 12:47 UTC on 21 November 2022,
51    // ten minutes before its closest approach, about 130 km above the Moon.
52    let craft = SIMD3<Double>(-337_632.7, -172_437.2, 9_689.0)
53    let moon = SkyEngine.geocentricMoonEcliptic(at: Date(timeIntervalSince1970: 1_669_034_820))
54    let d = ((craft - moon) * (craft - moon)).sum().squareRoot()
55    #expect(d < 3_000)
56}