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Consider the dome of the sky over our heads….

Consider the dome of the sky over our heads…. mixing bowl. Consider the dome of the sky over our heads…. inverted mixing bowl …. Celestial Sphere: Extension of the Earth’s Coordinates. celestial sphere N/S celestial poles celestial equator. Like a salad bowl over your head!.

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Consider the dome of the sky over our heads….

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  1. Consider the dome of the sky over our heads…. mixing bowl

  2. Consider the dome of the sky over our heads…. inverted mixing bowl ….

  3. Celestial Sphere: Extension of the Earth’s Coordinates • celestial sphere • N/S celestial poles • celestial equator Like a salad bowl over your head!

  4. The Ecliptic • The sun appears to move along a plane in the sky referred to as the ecliptic. • The other planets also appear to move close to the ecliptic.

  5. The Zodiac throughout the Year Example: In Winter sun in Sagittarius, Gemini at night sky;in summer sun in Gemini, Sagittarius at night sky

  6. Earth’s Seasons

  7. Seasons Earth is tilted 23.4 degrees on its axis

  8. “On Earth”, we observe changes over the course of the year due to the tilt of the Earth on its axis Sunrise southeast northeast due east Notice the sun only rises and sets due East and West on the equinoxes!

  9. Zodiacal signs vs. Constellations • “Constellation” is a modern, well-defined term • - Some constellations are big, some are small on the celestial sphere • “Zodiacal sign” is the old way of dividing the year and the Sun’s path into 12 equal parts • zodiacal sign is exactly 30 degrees “long”

  10. Tropic of Cancer Tropic of CapricornArtic CircleAntarctic Circle

  11. Hipparchus • Lived about 150 BC • 850 Star Positions • Defined Magnitudes • Discovered Precession Cataloger of the Heavens

  12. Precession of the rotation axis

  13. Precession causes the north celestial pole to drift among the stars, completing a circle in 26,000 years.

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