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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