The Celestial Sphere

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The Celestial Sphere

• Locating Celestial Objects

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Describing the Location of Objects

• If you need to tell someone where something is,
  there are lots of ways you can do it
• You can point at it
• You can tell them what is near it
• You can describe its location using directions
• You can give them coordinates (an address)
• Each of these methods have pros and cons

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Terrestrial Coordinates

• Latitude
• Defined by distance N or S of the Equator

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Terrestrial Coordinates

• Longitude
• Defined as the distance E or W of the Prime
  Meridian (through Greenwich, England)

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Examples

• McKinney, TX is located at
• 331119N Latitude and 963753W Longitude
• Quito, Ecuador is located at
• -01322 Latitude and -783048 Longitude
• The North Pole is located at
• The South Pole is located at

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Homework!

• Use whatever resources you have available at home
  (globe, map, internet) to find the terrestrial
  coordinates (to the nearest degree) for the
  following locations
• New York City
• Sydney, Australia
• Johannesburg, South Africa
• Tokyo, Japan
• London, England

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Applying the Same Process to the Sky

• The earth is a sphere with us on the surface
• The sky can also be thought of as a sphere, but
  with us at the center
• This sphere is called the CELESTIAL SPHERE, and
  just like with terrestrial objects, there are
  several ways we can locate objects that exist
  on it

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The Horizon System

• Only useful if youre giving directions to
  someone who is with you
• Altitude The angle above the horizon, with the
  zenith existing at 90 degrees
• Azimuth The angle from north in the clockwise
  direction (to the east)

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The Equatorial System

• Does not change with the motion of the sky
• Declination The angular distance from the
  celestial equator
• Measured in deg, arcmin, arcsec
• Right Ascension The angular distance measured
  eastward from the vernal equinox
• Measured in hours, min, sec