Coordinates and Time

Coordinates

Alt-az System

Equatorial Coordinates

Observer-Based Azimuth and Consistent Altitude

No Permanent Description

Dec, RA, and Vernal Equinox

Permanent Description despite of Earth Rotation

Time

Other Coordinates

Ecliptic System

Galactic System

Conversion from one to another

Solar Time

Ture or Apparent Solar Time

Mean Solar Time

EqT = TST - MST

Dynamical Time

Univsersal Time (UT) is Greenwich Mean Time

Dynamical Time: TDT = UT + ΔT

Barycentric Dynamical Time

TAI

UTC: Leap Seconds

UT1

Sidereal Time

Sidereal Time is based on the Earth's rotation relative to the stars

Solar Day is 4 min or 0.986° longer than sidereal time

Julian Date

Calculate JD since 2000: JD=2451544.5 + 365 * (Y - 2000) + N + L

Began with January 1, 4713BC

Heliocentric Julian Date ( earth orbit motion considered)

Conparsion between Julian and Gregorian Calendar