The Cycles of the Moon The phases of the moon The tides Lunar eclipses Solar eclipses The Phases of the Moon 27.32 days The Moon orbits Earth in a sidereal period of 27.32 days . Moon Earth Fixed direction in space The Phases of the Moon (II) Fixed direction in space 29.53 days
Fixed direction in space
Fixed direction in space
Earth orbits around Sun => Direction toward Sun changes!
From Earth, we see different portions of the Moon’s surface lit by the sun, causing the phases of the Moon.
The moon orbits counterclockwise around Earth (viewed from the North). => It appears to move eastward against the background of the stars. => The waxing crescent is visible
New Moon → First Quarter → Full Moon
Full Moon → Third Quarter → New Moon
The Earth also exerts tidal forces on the Moon’s rocky interior.
→ It is rotating with the same period around its axis as it is orbiting Earth (tidally locked).
→ We always see the same side of the moon facing Earth.
0A total lunar eclipse
The Earth’s shadow consists of a zone offull shadow, the Umbra, and a zone ofpartial shadow,the Penumbra.
If the Moon passes through theUmbra, we see alunar eclipse.
If the entire surface of the Moon enters the Umbra, the lunar eclipse is total.
A total lunar eclipse can last up to1 hour and 40 min.
During a total eclipse, the moon has afaint, red glow, reflectingsun light scattered in the Earth’s atmosphere.
1 or 2
The Sun has approx. the sameangular diameterof~ 0.50as the Moon.
Thus, when the Moon passes in front of the Sun, it can cover it completely, causing a totalsolar eclipse.
Total Solar Eclipse
Chromosphere and Corona
Diamond Ring Effect
If the sun and the moon have the same angular diameter on the sky, does that mean that the sun and the moon actually have about the same size?
Apogee = position furthest away from Earth
Perihelion = position closest to the sun
Perigee = position closest to Earth
Aphelion = position furthest away from the sun
(Eccentricities greatly exaggerated!)
0What do you expect to see if at the time of a solar eclipse the moon is near apogee, and the Earth is near perihelion?
The angular sizes of the Moon and the Sun vary, depending on their distance from Earth.
When the Earth is near perihelion, and the Moon is near apogee, we see an annular solar eclipse.
Almost total, annular eclipse of May 30, 1984
0If the moon was orbiting around the Earth exactly in the plane of the ecliptic, …
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.
Eclipses occur in a cyclic pattern.
→ Saros cycle: 18 years, 11 days, 8 hours
Approximately 1 total solar eclipse per year