1. Chapter 3:
Cycles of the Sky

2. A Total Lunar Eclipse (II)
A total lunar eclipse can last up to 1 hour and 40 min.
During a total eclipse, the moon has a faint, red glow, reflecting sun light scattered in the Earth’s atmosphere.

3. Typically,
1 or 2
lunar eclipses
per year.

4. Solar Eclipses (I)
The angular diameter of the moon (~ 0.5o) is almost exactly the same as that of the sun.
This is a pure chance coincidence. The moon’s linear diameter is much smaller than that of the sun.

5. Total Solar Eclipse
The moon’s shadow sweeps across the Earth, over points from where we can see a solar eclipse.

6. Total Solar Eclipse
During a total solar eclipse, the solar chromosphere, corona, and prominences can be seen.

7. The Diamond Ring Effect
The Diamond Ring Effect

8. Earth’s and Moon’s orbits are slightly elliptical:
Apogee = position furthest away from Earth
Earth
Perihelion = position closest to the sun
Moon
Perigee = position closest to Earth
Sun
Aphelion = position furthest away from the sun
(Eccentricities greatly exaggerated!)

9. Annular Solar Eclipses
The angular sizes of the Moon and the Sun vary, depending on their distance from Earth.
Apogee
Aphelion
Perigee
Perihelion
When the Earth is near perihelion, and the Moon is near apogee, we see an annular solar eclipse.

10. Almost total, annular eclipse of May 30, 1984

11. Approximately 1 total solar eclipse per year

12. Very Important Warning:
Never observe the sun directly with your bare eyes, not even during a partial solar eclipse!
Use specially designed solar viewing shades, solar filters, or a projection technique.

13. Conditions for Eclipses (I)
The Moon’s orbit is inclined against the ecliptic by ~ 50.
A solar eclipse can only occur if the Moon passes a node near New Moon.
A lunar eclipse can only occur if the Moon passes a node near Full Moon.

14. The Origin of Modern Astronomy
Chapter 4:
The Origin of Modern Astronomy