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Celestial Sphere
- An imaginary, hollow dome surrounding the Earth
- It's essentially the sky we see when we look up
- Earth's coordinate system has been extended to the sphere
- It's what you see when you look up at the sky; you are at the center
- The path the Sun takes on the celestial sphere is called the ecliptic
- Apparent yearly path of the Sun
- Projection of the Earth's orbit onto the sky
- Tilted by 23.5 degrees with respect to the celestial equator
Coordinate System
- Declination
- Vertical position of an object
- Celestial equivalent of latitude
- Degrees, arcmin, arcsec
- Right ascension
- Horizontal position of an object
- Celestial equivalent of longitude
- Expressed as either degrees or units of time
- Starts getting counted at the vernal equinox
- Altitude
- Azimuth
- Horizontal position of an object
- Angle measured clockwise around observer's horizon from north
- Object due north has azimuth of 0Ëš
Relative to Viewer
- Zenith
- Point directly above your head
- Horizon
- Where the dome meets the Earth