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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 viceversa. 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=90epsilon. This is near the NEP.
so what's near the SEP? RA=6h, Dec=epsilon90.
why would you care? most SS stuff is near the ecliptic.
High eclip latitudes mean fewer asteroids, less SS dust.
Now some altazequ.
from northern hemisphere: (phi>0)
altaz a=0 A=0 is due north at the horizon. H=12h, dec=90phi
altaz a=0 A=180 is due south at horizon. H=0h, dec=phi90
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=phi90
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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 Spring '09
 Fernandez
 Astronomy

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