Naked Eye Astronomy

1. Naked Eye Astronomy Summer Winter The Cycles of the Sun • The Sun (and everything else) rises in east and sets in west • At noon (in the northern hemisphere) it passes to the south • The angle it is at highest in the summer and lowest in the winter • This is responsible for the seasons • Seasons are not caused by changes in the Earth-Sun distance 2. What Causes Seasons?

2. The Cycle of the Stars • The Stars rise in the East and set in the West • They go around slightly faster than the Sun • Complete a cycle in one sidereal day – 23 hours 56 minutes • It looks like the stars are rotating uniformly around us on a sphere – the celestial sphere • In fact, this motion is caused by the Earth rotating once every sidereal day Constellations • Patterns in the heavens are given names – constellations • Originally these were associated with mythological stories • We now name portions of the sky after these

3. The Sun vs. the Stars • Compared to the background stars, the Sun follows a circle in the sky called the ecliptic • Over the course of the year, the Sun passes through thirteenconstellations – the basis of Sun-sign Astrology • Sun completes its apparent journey in 365.25 days – one year • The actual cause of this apparent motion is the motion of the Earth around the Sun Prof. Carlson Beats Up on Astrology • Only 12, not 13 constellations are used: Ophiuchus is omitted • The correspondences are nearly 2000 years out of date • Scientific tests have failed to confirm the claims of astrology

4. The Cycles of the Moon New First Quarter Third Quarter Full Q. 3: How Often is the Moon Full? • Entire cycle repeats every 29.5 days

5. The Cycles of the Moon • The Moon is illuminated by the Sun • The Moon is a sphere, not a flat disk • The Moon goes around the Earth, in the same direction the Earth spins • The Moon is much closer to the Earth than the Sun is

6. Solar Eclipses Q. 4: Types of Solar Eclipses