Lunar Phases Eclipses

Apparent motion: The Moon’s orbit: The phases of the Moon Every object in the solar system is always _____________________________________ If we sometimes see the bright side of an object, and sometimes see the dark side, then the object will appear to go through ___________ This is what causes the phases of the Moon The Moon takes about 27.3 days to go once around the Earth - _________________ Because of Earth’s orbit the Moon takes 29.5 days to get back to the same place relative to the Sun - _________________ light on one side and dark on the other. phases Sidereal Period Synodic Period (Lunar Month)

Sidereal vs. Synodic Periods New 2.2 more days New 27.3 days

The Moon Moon phases cycle over a period of 29.5 days Always has the same “face” to Earth, which means it MUST _______ on its own axis! Moon phases - result of the _______, _____, and __________ positions relative to each other Moon rises later and later as the month goes on ________________ Plane of Moon’s orbit almost the same as Earth’s orbit - _______ rotate Moon Sun Earth 50 min/day 5o tilt

Rises at 3 p.m. Sets at 3 a.m.

Lunar Phases New Moon - ________________________________ ___________________________________ Waxing Moon – ________________________ Waning Moon – ________________________ Full Moon - ________________________________ ________________________________ Crescent – ________________________________ Gibbous – _______________________ The Moon is on the same part of the sky as the Sun and rises and sets with the Sun Increasing from day to day Decreasing from day to day The Moon is in the opposite side of the sky as the Sun and rises when the Sun sets and sets when the Sun rises concave/convex edges, ending in a point Rounded edges

Names/shapes of Moon phases (as seen from Northern Hemisphere) First _______ ~1 week ______ Moon ~1 week _______ Quarter ~1 week _____ Moon ~1 week ______ Moon _______ Crescent Waxing _______ _______ Gibbous Waning _______ New Waxing Full Waning Third New Quarter Gibbous Crescent light “creeps” across Moon from ______________ darkness “creeps” across Moon from ________________ right to left right to left

Phases of the Moon 1st Q. Wax. Gib. Wax. Cr. Full M. New M. Wan. Gib. Sun’s rays Moon’s orbit Wax. Gib. Wax. Cr. Earth N Full M. New M. Wan. Gib. Wan. Cr. 3rd Q.

The time the Moon rises and sets is correlated to its phase Moonrise/Moonset The time the Moon rises and sets is correlated to its phase Phase of the Moon Rise Zenith Set New Moon 6 am Noon 6 pm Waxing Half Moon Midnight Full Moon Waning Half Moon

Naming the Moon Blue Moon: Definition One: The second of two full moons in a single month. It is uncommon since the cycle of phases of the moon is 29.5 days (synodic month) which is almost a month. Definition Two: The third of four full moons occurring in a season. Again this is uncommon since the cycle of phases of the moon is 29.5 days and seasons are ~91 days (365/4=91.25). http://www.enchantedlearning.com/subjects/astronomy/moon/Phases.shtml

Naming the Moon Harvest Moon: The full moon that occurs closest to the autumnal equinox. This results in the near full gibbous moons and the full moon lighting the fields for harvest for a longer period.

Eclipses

Eclipses Eclipses occur when the Sun, the Earth and the Moon all lie along a straight line They must line up in all 3 dimensions + time the Moon’s orbit is tilted 5o with respect to the ecliptic, so there are only two times a year when the paths overlap

Eclipses Lunar Eclipse Earth positioned between the Sun and the Moon and casts a shadow ______________ Much more common than a solar eclipse Solar Eclipse Moon positioned between the Earth and the Sun, casting a shadow _______________ During a total eclipse the Sun’s Corona, normally invisible is visible Eclipses onto the Moon onto the Earth

Shadows ________ ____________ Umbra Penumbra dark cone of complete shadow ____________ lighter area of partial shadow Umbra Penumbra

Apparent motion: The Moon’s orbit: Eclipses When the Moon is in its Full Moon phase, it might pass through Earth’s shadow When this happens it will be at least partially blocked from our view This is known as a Lunar Eclipse Three kinds of lunar eclipse (of interest to us): Penumbral eclipse – _______________________ Partial eclipse - __________________________ Total eclipse – ___________________________ Moon in Earth’s Penumbra Moon in part of Earth’s Umbra Moon totally in Earth’s Umbra

Lunar Eclipses

Frequency of Lunar Eclipses One might expect a lunar eclipse to occur every month during full moon But the moon’s orbit is titled 5º to the Earth’s For a lunar eclipse, the moon phase must be full and the moon must be aligned with Earth’s orbit (at a lunar node) – every 5-6 months Partial eclipse – moon in penumbra where only some sunlight is blocked Total eclipse – moon is located in the umbra where all of the sunlight is blocked

Apparent motion: The Moon’s orbit: Eclipses When the Moon is in its New Moon phase, it might pass directly between us and the Sun When this happens it will at least partially block the Sun from our view This is known as a Solar Eclipses Three kinds of solar eclipse: Total eclipse – ___________________ Partial eclipse - _____________________ Annular eclipse – _____________________________ Total coverage Moon not covering all Sun Moon too far from Earth

Total Solar Eclipse of 21 June 2001 from Zimbabwe Bailey’s Beads See Richard Monk’s webpage on eclipses: www.williams.edu/ astronomy/IAU_eclipses/ Solar Corona “Diamond Ring”

Frequency of Solar Eclipses Similar to a lunar eclipse, the Sun, Moon, and Earth, must all be aligned in the same plane Much less frequent than lunar eclipses because the Moon is much smaller in size, and thus casts a much smaller shadow on Earth Because the moon is on a slightly elliptical orbit, it may be too far to cast a shadow on the Earth

Future Solar Eclipses If a solar eclipse occurs on a given day, another will occur in exactly 18 years and 11 1/3 days – saros cycle But the eclipse may change type and location during that cycle

Upcoming Solar and Lunar Eclipses Solar Eclipses: Mar 20, 2015 (Total) – Europe, N/E Asia, W/W Africa, West in North America, Atlantic, Arctic Sep 13, 2015 (Partial) – S in Africa, Atlantic, Indian Ocean Mar8/9, 2016 (Total) – SE Asia, NE Australia, Pacific, Indian Ocean Aug 21, 2017 (Total) – Much of North America Lunar Eclipses: Apr 4, 2015 (Partial) – Asia, Australia, Much of North Amer. and SA, Pacific, Atlantic, Indian Ocean, Arctic, Antarctica Sep 28, 2015 (Total) – Europe SE Asia, Africa, Much of NA and SA, Pacific, Atlantic, Indian Ocean, Arctic, Antarctic Mar 23, 2016 (Penumbral) Much Asia, Much NA and SA, Pacific, Atlantic, Indian Ocean, Arctic, Antarctic

Aug 21, 2017 (Total) – Much of North America

Motion of the Sun: Solar vs. Sidereal period Since the Earth moves in its orbit each day, the motion of (nearby) solar system objects is slightly different from stars. The Earth needs to revolve an additional 1 degree daily for the Sun to repeat its position (see diagram at right). This takes an additional 4 min This means that the Sun’s position repeats every 24 hrs. This is called the solar period.

Length of the Year It takes the Earth 365.242199 days to go from one vernal equinox to the next NOT an integer number But the extra is close to ¼ = 0.25 So every 4 years (leap year) we add an extra day to the calendar (Feb. 29) But this is too much (we’ve added 0.25!) So every 100 years (on the century) we don’t add the extra day (no leap year) But this isn’t right either, so every 4th 100 years, we do include the leap year This is why 2000 was a leap year

www.hep.fsu.edu/~tadams/courses/ spr04/ast1002-2/Lecture011404.ppt