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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Coordinate Transforms

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Coordinate transforms

Coordinate Transforms


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


Equatorial coordinates and equinoxes

Equatorial coordinates and equinoxes


Equatorial coordinates and equinoxes1

Equatorial coordinates and equinoxes


Equatorial coordinates and equinoxes2

Equatorial coordinates and equinoxes


Rotations

Rotations


Rotations and galactic coordinates

Rotations and Galactic Coordinates

NP of Galaxy

NP of

Earth


Idl tasks

IDL tasks


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