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
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Terms

• Vernal Equinox
  • Celestial equivalent of Prime Meridian
• Declination
  • Celestial equivalent of latitude
  • Degrees, arcmin, arcsec
• Right ascension
  • Celestial equivalent of longitude
  • Hours, mins, sec
• Altitude
  • Angle from the horizon to a point on the sphere
  • Zenith is 90˚
  • Altitude of Polaris with give you the latitude of where you are on Earth

Local Terms (Relative to Viewer)

• Zenith
  • Point directly above your head
• Horizon
  • Where the dome meets the Earth

Space Astronomy