# ls2 - AST 3722C summary for lecture on tuesday january 15,...

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AST 3722C summary for lecture on tuesday january 15, class #2. warning: this is not supposed to be a substitute for reading the textbook. Textbook Chapter 8: Lecture Part A: -some handy conversions: generally you want to be able to know where certain coordinates are with respect to RA and Dec and vice-versa. Why? because RA and Dec are the most commonly given coords. first think about the Sun: The Sun moves along the ecliptic over the course of the year. Mar 21 - ecliptic beta=0 lambda=0 is RA=0 Dec=0. Jun 21 - ecliptic beta=0 lambda=90 is RA=6h Dec=+epsilon. Sep 22 - ecliptic beta=0 lambda=180 is RA=12h Dec=0. Dec 20 - ecliptic beta=0 lambda=270 is RA=18h Dec=-epsilon. Note that RA is expressed in hours -- you can multiply by 15 here to get RA in degrees if you want. Note also that this can get you quickly an estimate of where the Sun is at any time --- how many hours of RA does the Sun move per month? one more ecliptic: RA=18h, Dec=90-epsilon. This is near the NEP. so what's near the SEP? RA=6h, Dec=epsilon-90. why would you care? most SS stuff is near the ecliptic. High eclip latitudes mean fewer asteroids, less SS dust. Now some altaz-equ. from northern hemisphere: (phi>0) altaz a=0 A=0 is due north at the horizon. H=12h, dec=90-phi altaz a=0 A=180 is due south at horizon. H=0h, dec=phi-90 from southern hemisphere: (phi<0) altaz a=0 A=0 is due north at the horizon. H=0h, dec=90+phi altaz a=0 A=180 is due south at horizon. H=12h, dec=-phi-90 at equator: phi = 0 altaz a=0 A=0 is due north at the horizon. H=anyth, dec=90 altaz a=0 A=180 is due south at horizon. H=anyth, dec=-90 other things: altaz a=0 A=90 is due east at horizon. H=18h(-6h), dec=0. altaz a=0 A=270 is due west at horizon. H=6h, dec=0.

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## ls2 - AST 3722C summary for lecture on tuesday january 15,...

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