AstroLab-2 Locating Stars in the Sky

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AstroLab-2Locating Stars in the Sky

• Merav Opher-Fall 2004

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Motion of the Night Sky

• Motion of the stars across the night sky (from
  east to west) (due to the earth rotation from
  west to east.

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Ecliptic-The Path of the Sun along the Sky

• The Earth equator is inclined by 23 1/2 degrees
  to the plane defined by the Earths orbit around
  the Sun

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Ecliptic, Equinoxes and Solstices

• Ecliptic apparent annual path of the Sun as
  projected in the Celestial Sphere
• Because of the 23 1/2 tilt the ecliptic
  intersects the celestial equator in two points
  called equinoxes.

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The Suns Daily Path Across the Sky

• The sun rises in the east and set in the west.
• During summer in the northern hemisphere, the Sun
  reaches its northernmost position at the summer
  solstice. It reaches its southernmost position at
  the winter solstice

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Celestial sphere

• Its the apparent sphere of the sky. The
  celestial equator and poles are projections of
  the Earths equator and axis of rotation out in
  space.

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View from 35 North Latitude

• Viewed from North America the north celestial
  pole is always above the horizon. From an
  observer at 35 north latitude (Los Angeles) the
  north celestial pole is 35 degrees above the
  horizon
• Stars within 35 south and north rise in the east
  and set in the west

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Celestial Coordinates

• Right ascension and Declination (latitude and
  longitude)
• Right ascension is measured from Vernal Equinox
  (late March) eastward
• Units hours and minutes7u!!! (corresponds to the
  time required for the celestial sphere to rotate)

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Apparent Solar Time

• Horizon
• Meridian
• Zenith

Altitude (height above or Below the
horizon) Azimuth zero at the North pole!!!