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Co-ordinate systems - Coggle Diagram
Co-ordinate systems
Equatorial Coordinates
Grid system mirroring geographical coordinates, but 'fixed' on the celestial sphere at a particular equinox
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Zero points
DEC - Defined via the celestial equator, goes from 0 degress to +- 90 deg at the celestial poles
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Declination
Dictates the max altitude above the local horizon, depending on your latitude
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Right Ascension
As the Earth rotates, we see that rotation mirrored in the sky
So as objects rise in the east and ascend, the move to the right
Now think of the meridian line due South as a clock hand, but it's the clock doing the rotating
If RA is measured in time units with 24hours going around the sky, the an object +1 hour in RA will cross the meridian roughly 1 hour of time later
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LST can be estimated.
The sun is at 0h RA on 21 march. At midnight the sun will be opposite the meridian, so it will be RA=12 hours at the Meridian = LST
The sun take 12 months to go once around the sky, so every 2 hours of RA per month
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Relative distances
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2
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If you go across zero-RA line, don't simply subtract
dalpha from 23h to 1 h is 2 hs, not 22
The celestial sphere
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Earths axis processes, 23.5%. This will change which object appears to be at north
Reference frames
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Epoch
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Important for solar system objects, nearby starts, (or M31 if you're using gaia)
Galactic co-ordinates
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Galactic longitude (I)
Defined as the apparent angular distance paralell to the galactic plane, zero point at Sgr A*.
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