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)