CoordinatesAST443, Lecture 2Stanimir Metchev2Administrative• Classes– MW, 8:20–10:10pm– ESS 450 + ESS 437A (UG astro lab)• Office hours– MW, 1–2pm, ESS452• Keys to ESS 437A– see Owen Evans (ESS 255, 2-8061)– $25 refundable deposit3Angles• Circle: 360º = 2π radians• 1º = 60′ (arc minutes) = 3600″ (arc seconds)• 1 rad = 57.2958º = 206265″4Celestial Coordinates• horizoncoordinates– altitude/elevation (a),azimuth (A)– zenith, zenith angle(z)• observer’s latitude– angle PZ5Celestial Coordinates• equatorialcoordinates– right ascension• R.A., α– declination• DEC, δ• cf., Earth’s longitude,latitude• meridian, hour angle(HA)6Celestial Coordinates• ecliptic coordinates– ecliptic longitude (λ)– ecliptic latitude (β)• vernal equinox (ϒ)– Earth passes throughecliptic on Mar 20/21– origin of equatorial andecliptic longitude• Earth’s axial tilt:–ε = 23.439281º– a.k.a., “obliquity ofthe ecliptic”7Celestial Coordinates• galactic coordinates– galactic longitude (l; letter“ell”)• l = 0 approx. towardgalactic center (GC)• definitionlNCP = 123º (B1950.0)– galactic latitude (b)• NGP definition (B1950.0)α = 12h 49mδ = 27.4º– Sagittarius Al = 359º 56′ 39.5″b = –0º 2′ 46.3″8Celestial Coordinates• galactic coordinates– galactic longitude (l; letter“ell”)• l = 0 approx. towardgalactic center (GC)• definitionlNCP = 123º (B1950.0)– galactic latitude (b)• NGP definition (B1950.0)α = 12h 49mδ = 27.4º– Sagittarius Al = 359º 56′ 39.5″b = –0º 2′