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AS 2001 Galactic Astronomy
Galactic coordinates
• α : Right ascension l : Galactic longitude • δ : Declenation b : Galactic latitude
• How do we transfer between coordinate systems?
NCP NGP
Equatorial Galactic
celestial equator α
δ
Galactic equator
b l GC
Motivated by Earth’s rotation
Motivated by Galactic rotation
AS 2001 Galactic Astronomy
Galactic latitude, l
AS 2001 Galactic Astronomy
Galactic Longitude l=0=Gal. centre
Galactic Latitude b=0=in plane
b & l
AS 2001 Galactic Astronomy
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AS 2001 Galactic Astronomy AS 2001 Galactic Astronomy
Cosine/sine rules of spherical trig.
cos(c)=cos(a).cos(b)+sin(a).sin(b).cos(C)
sin(a) sin(b) sin(c) sin(A) sin(B) sin(c)
Use Cosine rule twice and sine rule once to solve independently for l & b
= =
see over…
AS 2001 Galactic Astronomy AS 2001 Galactic Astronomy
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AS 2001 Galactic Astronomy
Examples
• See Q 2 of tutorial sheet 1
or compare to:
• http://nedwww.ipac.caltech.edu/forms/calculator.html