Coordinate transforms
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Coordinate Transforms. z. x. y. Equatorial and Cartesian Coordinates. declination (δ). Equator. right ascension (α). Equatorial and Cartesian Coordinates. x = Rcosα y = Rsinα. y. α. R. x. right ascension (α). y. declination (δ). z. r = 1. δ. R = rcosδ z = rsinδ. R.

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Equatorial and cartesian coordinates

z

x

y

Equatorial and Cartesian Coordinates

declination (δ)

Equator

right ascension (α)


Equatorial and cartesian coordinates1
Equatorial and Cartesian Coordinates

x = Rcosαy = Rsinα

y

α

R

x

rightascension (α)

y

declination (δ)

z

r = 1

δ

R = rcosδz = rsinδ

R


Precession
Precession

  • Because the Earth is not a perfect sphere, it wobbles as it spins around its axis

  • This effect is known as precession

  • In the last lecture, I noted that the equatorial coordinate system relied on the idea that the Earth rotated such that only α, and not δ, was a time-dependent coordinate


The effects of precession
The effects of Precession

  • Currently, the star Polaris is the North Star (it lies roughly above the Earth’sNorth Pole at δ = 90oN)

  • But, over the course ofabout 26,000 years avariety of different pointsin the sky will truly beat δ = 90oN

  • The declination coordinateis time-dependent albeiton very long timescales

  • A precise astronomicalcoordinate system must account for this effect






Rotations and galactic coordinates
Rotations and Galactic Coordinates

NP of Galaxy

NP of

Earth