Slide 1 The Motion of the Planets The planets are orbiting the sun almost exactly in the plane of the Ecliptic. Jupiter Mars Earth Venus Mercury Saturn The Moon is orbiting Earth in almost the same plane (Ecliptic).

Slide 2 Inferior planets are visible only at small angular distances from the Sun

Slide 3 The Motion of the Planets Mercury appears at most ~28° from the sun. It can occasionally be seen shortly after sunset in the west or before sunrise in the east. Venus appears at most ~46° from the sun. It can occasionally be seen for at most a few hours after sunset in the west or before sunrise in the east.

Slide 4 The Cycles of the Moon Chapter 3

Slide 5 I. The Changeable Moon A. The Motion of the Moon B. The Cycle of Phases II. The Tides A. The Cause of the Tides B. Tidal Effects III. Lunar Eclipses A. Earth's Shadow B. Total Lunar Eclipses C. Partial and Penumbral Lunar Eclipses Outline

Slide 6 IV. Solar Eclipses A. The Angular Diameter of the Sun and Moon B. The Moon's Shadow C. Total Solar Eclipses V. Predicting Eclipses A. Conditions for an Eclipse B. The View From Space C. The Saros Cycle Outline (continued)

Slide 7 The Phases of the Moon (1) From Earth, we see different portions of the Moon’s surface lit by the sun, causing the phases of the Moon.

Slide 8 Lunar Phases

Slide 9 The Phases of the Moon (2) The Moon orbits Earth in a sidereal period of days days EarthMoon Fixed direction in space

Slide 10 The Phases of the Moon (2) The Moon’s synodic period (to reach the same position relative to the sun) is days (~ 1 month). Fixed direction in space Earth Moon Earth orbits around Sun => Direction toward Sun changes! days Synodic period defines the cycle of lunar phases

Slide 11 Tides Newton’s law of gravitation

Slide 12 Integrate over the mass distribution In the Earth’s body Tides

Slide 13 The Tides Caused by the difference of the Moon’s gravitational attraction on the water on Earth  2 tidal maxima Excess gravity pulls water towards the moon on the near side Forces are balanced at the center of the Earth  12-hour cycle Excess centrifugal force pushes water away from the moon on the far side

Slide 14 Spring and Neap Tides The Sun is also producing tidal effects, about half as strong as the Moon. Near Full and New Moon, those two effects add up to cause spring tides. Near first and third quarter, the two effects work at a right angle, causing neap tides. Spring tides Neap tides

Slide 15 Effects of tides Slow down the rotation of earth Seabed slips under the water bulges Friction slows down the rotation The day was 18 hours long 900 million yr ago

Slide 16 The Tidally-Locked Orbit of the Moon The Earth also exerts tidal forces on the moon’s rocky interior that slow down its rotation.  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.

Slide 17 Acceleration of the Moon’s Orbital Motion Earth’s tidal bulges are slightly tilted in the direction of Earth’s rotation. Gravitational force pulls the moon slightly forward along its orbit.

Slide 18 Effects of tides 1. Synchronization of the rotational and orbital period 2. Tides cause the heating of the interiors of the interacting bodies 3. If the bodies are too close to each other, they can be disrupted by tides (Roche limit).

Slide 19 Modulated by ellipticity of the Earth’s and Moon’s orbits Tides - reality

Slide 20p. 28 Eclipses

Slide 21 Why not every new and full moon??

Slide 22 Moon’s orbit is tilted by 5 o from the ecliptic

Slide 23Fig. 3-15, p The moon should be at one of the nodes – crossing the plane of the earth’s orbit 2.The line of nodes should point at the sun For an eclipse to occur,

Slide 24 Conditions for Eclipses A solar eclipse can only occur if the moon passes a node near new moon. The moon’s orbit is inclined against the ecliptic by ~ 5 0. A lunar eclipse can only occur if the moon passes a node near full moon.

Slide 25 Lunar Eclipses Earth’s shadow consists of a zone of partial shadow, the Penumbra, and a zone of full shadow, the Umbra. If the moon passes through Earth’s full shadow (Umbra), we see a lunar eclipse. If the entire surface of the moon enters the Umbra, the lunar eclipse is total.

Slide 26

Slide 27 A Total Lunar Eclipse (1) Note a circular shadow: from this observation Aristotle concluded that Earth is a sphere!

Slide 28 Lunar Eclipses: Typically, 1 or 2 lunar eclipses per year.

Slide 29 How come that the Moon can eclipse the Earth?? Solar Eclipses Accidentally, they have almost the same angular sizes! Earth-Moon system to scale

Slide 30 Angular diameter (rad) = Linear diameter Distance 180 degrees =  radian  (rad) = L/D  (deg) =  (rad)  180/ 

Slide 31  radian = 180 degrees  D L Convert from radian to arcseconds: 1 deg = 60 arcmin = 3600 arcsec Note units!! Small Angle Formula

Slide 32  radian = 180 degrees  D L Convert from radian to arcseconds: 1 deg = 60 arcmin = 3600 arcsec Note units!! Exact Formula

Slide 33 Small Angle Formula (SLIDESHOW MODE ONLY)

Slide 34 Moon:  = 3476 km km = rad = 0.5 deg Sun:  = 1.4  10 6 km 1.5  10 8 km = rad = 0.5 deg Very close!

Slide 35 Solar Eclipses The sun appears approx. as large in the sky (same angular diameter ~ ) as the moon.  When the moon passes in front of the sun, the moon can cover the sun completely, causing a total solar eclipse.

Slide 36 Umbra is below 270 km in diameter It moves at 1600 km/hr Total eclipse lasts for not more than 7.5 min

Slide 37 Total Solar Eclipse Prominences Chromosphere and Corona

Slide 38 Solar Atmosphere Revealed

Slide 39 Diamond Ring Effect

Slide 40 Moon’s orbit is elliptical -> when the moon is in apogee, umbra does not reach the earth -> annular eclipse

Slide 41 Annular Solar Eclipses The angular sizes of the moon and the sun vary, depending on their distance from Earth. When Earth is near perihelion, and the moon is near apogee, we see an annular solar eclipse. Perigee Apogee Perihelion Aphelion

Slide 42 Solar Eclipses: Approximately 1 total solar eclipse per year

Slide 43 The Saros Cycle Saros cycle: 18 years, 11 days, 8 hours Repeats in one place every 3 cycles, or ~ 54 yr 1 month