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Seeing the Sky

Seeing the Sky. Naked-Eye Astronomy. Naked-Eye Astronomy. Stars Planets (move relative to stars) Sun (disk about 1/2 degree) Moon (disk about 1/2 degree) Other (comets, meteors, UFOs, etc.). Angles.

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Seeing the Sky

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  1. Seeing the Sky Naked-Eye Astronomy

  2. Naked-Eye Astronomy • Stars • Planets (move relative to stars) • Sun (disk about 1/2 degree) • Moon (disk about 1/2 degree) • Other (comets, meteors, UFOs, etc.)

  3. Angles • Can only measure angles on the sky (circle spans 360 degrees; 1 degree = 60 minutes; 1 minute = 60 seconds) • Angular distance is the angle on the sky between two celestial objects • Use your fist (about 10 degrees at arm’s length)

  4. Sky Directions • Face South (sun at noon), then • North is to your back • West is to your right • East is to your left(Northern hemisphere!)

  5. Sky Motions • Only see angular speeds(angle covered per unit time-day, month, year) • Motions are relative with respect to some reference (stars, horizon) • Same object can have different motions at the same time relative to different references

  6. Stars • Patterns: “fixed” constellations (88 official); no visible change over human lifetimes • Daily: Rise in east, set in west(relative to horizon) • Seasonal: Different constellations visible at different seasons

  7. Moon • Daily: Rises in east, sets in west (relative to horizon) • Monthly: Cycle of phases; angle relative to the sun (opposition-full) • Monthly: Moves eastward relative to zodiacal stars • Eclipses can occur at new (solar) or full (lunar)

  8. Sun • Daily: Rise in east, set in west (relative to the horizon) • Due south at noon (northern hemisphere!); greatest angle (for the day) above horizon at noon • Seasonally: noon height varies (highest, summer, lowest winter); rising, setting points also vary

  9. Sun • Moves eastward relative to stars • Moves through constellations of the zodiac, about 360 degrees in one year (about 1 degree per day) • Path in sky relative to the stars defines the ecliptic

  10. Planets • Daily: Rise in east, set in west (relative to horizon) • Long-term: Move eastward relative to stars (zodiac) • In regular cycles, move westward relative to the stars (retrograde)

  11. Planets-Long term • Mercury, Venus stay near sun(morning, evening stars) • Mars, Jupiter, Saturn anywhere in zodiac relative to sun • Average angular speeds of eastward motion through zodiac: Mercury, Venus, Mars, Jupiter, Saturn

  12. Planets-Retrograde • Mercury, Venus retrograde only near sun (when moving from evening to morning “star”) • Mars, Jupiter, Saturn retrograde only when opposite the sun in the sky (opposition, 180 degrees apart)

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