Presentation on theme: "The Cycles of the Moon The phases of the moon The tides Lunar eclipses"— Presentation transcript:
1The Cycles of the Moon The phases of the moon The tides Lunar eclipses The Cycles of the MoonThe phases of the moonThe tidesLunar eclipsesSolar eclipses
2The Phases of the MoonFrom Earth, we see different portions of the Moon’s surface lit by the sun, causing the phases of the Moon.
3The Moon orbits Earth in a sidereal period of 27.32 days. The Phases of the Moon27.32 daysThe Moon orbits Earth in a sidereal period of days.MoonEarthFixed direction in space
4Is the moon going to show the same lunar phase after one sidereal period? Yes.No, it will not have completed a full cycle of phases.No, it will have completed more than a full cycle of phases.
5Earth orbits around Sun => Direction toward Sun changes! The Phases of the MoonFixed direction in space29.53 daysEarthMoonEarth orbits around Sun => Direction toward Sun changes!The moon’s synodic period (to reach the same position relative to the sun) is days (~ 1 month).
6The moon orbits counterclockwise around Earth (viewed from the North) 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 visiblein the morning sky.in the evening sky.the whole night, from sunset to sunrise.only around midnight.never.
7New Moon → First Quarter → Full Moon The Phases of the MoonNew Moon → First Quarter → Full MoonEvening Sky
8Full Moon → Third Quarter → New Moon The Phases of the MoonFull Moon → Third Quarter → New MoonMorning SkyWaning
9The TidesThe tides are caused by the difference of the Moon’s gravitational attraction on the water on EarthBetween the near side and the center of the EarthBetween the center and the far side of the Earth→ 2 tidal maxima→ 12-hour cycle
10On the day of full moon, high tides occur … around noon and 6 p.m.around noon and midnight.around 6 a.m. and 6 p.m.around 6 p.m. and midnight.Impossible to tell. The times of tides are not correlated with the phases of the moon.
11Spring and Neap TidesThe 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 tidesNear first and third quarter, the two effects work at a right angle w.r.t. each other, causing neap tides.Spring tidesNeap tides
12The Tidally Locked Orbit of the 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.
14A total lunar eclipse …is a high-performance moon vehicle built by Mitsubishi.occurs when the moon disappears behind the sun.occurs when the moon becomes invisible because it is too close to the sun.occurs when the moon moves through Earth’s shadow.occurs when the moon disappears behind Mars.
15Lunar EclipsesThe Earth’s shadow consists of a zone of full shadow, the Umbra, and a zone of partial shadow, the Penumbra.If the Moon passes through the Umbra, we see a lunar eclipse.If the entire surface of the Moon enters the Umbra, the lunar eclipse is total.
17A 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.
18Typically, 1 or 2 lunar eclipses per year. Typically, 1 or 2 lunar eclipses per year.
19The Sun has approx. the same angular diameter of ~ 0.50 as the Moon. Solar EclipsesThe Sun has approx. the same angular diameter of ~ 0.50 as the Moon.Thus, when the Moon passes in front of the Sun, it can cover it completely, causing a total solar eclipse.
20Total Solar EclipseChromosphere and CoronaProminences
23If 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?Yes.No because the sun is much farther away, but also much larger than the moon.No, because the sun is much farther away, but also much smaller than the moon.No because the moon is much farther away, but also much larger than the sun.No, because the moon is much farther away, but also much smaller than the sun.
24Earth’s and Moon’s orbits are slightly elliptical: Apogee = position furthest away from EarthEarthPerihelion = position closest to the sunMoonPerigee = position closest to EarthSunAphelion = position furthest away from the sun(Eccentricities greatly exaggerated!)
25What do you expect to see if at the time of a solar eclipse the moon is near apogee, and the Earth is near perihelion?A regular total solar eclipse.No solar eclipse at all.A partial solar eclipse with a crescent appearance.A partial solar eclipse with a ring-like appearance of un-occulted parts of the sun.A lunar eclipse.
26Annular Solar Eclipses The angular sizes of the Moon and the Sun vary, depending on their distance from Earth.PerigeeApogeeAphelionPerihelionWhen the Earth is near perihelion, and the Moon is near apogee, we see an annular solar eclipse.
28If the moon was orbiting around the Earth exactly in the plane of the ecliptic, … lunar and solar eclipses would occur once every day.lunar and solar eclipses would occur once a week.lunar and solar eclipses would occur once a month.lunar and solar eclipses would occur once a year.lunar and solar eclipses would never occur.
29Conditions 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.
30Conditions for Eclipses (II) Eclipses occur in a cyclic pattern.→ Saros cycle: 18 years, 11 days, 8 hours