Coordinate Transforms

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# Coordinate Transforms - PowerPoint PPT Presentation

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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## PowerPoint Slideshow about ' Coordinate Transforms' - hosea

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Presentation Transcript

z

x

y

Equatorial and Cartesian Coordinates

declination (δ)

Equator

right ascension (α)

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
• 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
• 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