Presentation on theme: "Seasons Review Earth’s rotation axis is tilted 23.5 degrees; tilt remains the same as it orbits the sun Therefore, different parts of the Earth receive."— Presentation transcript:
1Seasons ReviewEarth’s rotation axis is tilted 23.5 degrees; tilt remains the same as it orbits the sunTherefore, different parts of the Earth receive different amounts of daily sunlight throughout the year, as Earth orbits the Sun.If Sun is higher in the sky throughout the day, incident sunlight is more concentrated, heating more efficient summerIf Sun is lower in the sky throughout the day, incident sunlight is more dilute, heating less efficient winter
2Seasons ReviewEquinoxes: Sun is on equator (ecliptic and celestial equator intersect); rises due East, sets due westMarch: moving northSeptember: moving southEqual daylight / night timeSolstices: Extreme North and South positions for SunJune: farthest North (Tropic of Cancer, latitude +23.5), longest dayDecember: farthest South (Tropic of Capricorn, latitude -23.5), shortest day
3Seasons ReviewAntarctic circle (lat. = -( ) = receives no sunlight on June SolsticeArctic circle (lat. = +( ) = receive no sunlight on December Solstice
4Phases of the MoonThe Phases of the Moon are the variations in the Moon’s appearance as the Moon orbits the Earth.They are due to the changing Sun-Earth-Moon angle through each month.The following is the cycle of lunar phases: new, waxing crescent, first quarter, gibbous, full, gibbous, third quarter, waning crescent, newTo see a time-lapse movie of the Moon going through a complete cycle of Lunar PhasesGo to
5Moon Phases The Moon orbits the Earth in about one month (29.5 days) Over one orbit the appearance and rise and set times change with the cycle of Lunar Phases.The figure is not to scale
6Light & DarkWe only see the Moon because sunlight reflects off its surface.At any one time, half the Moon is always lit and half is in darkness.The amount of the illuminated half we see from Earth depends on the position of the Moon in its orbitThe time of day the Moon is visible also depends on its phase.How the Earth and Moon wouldlook high above Earth’s North Pole.The figure is not to scale.
7Example: Observing the Moon Between September 10-11, at dusk, the Moon will be visible in its waxing crescent phase.The first night it appeared close to the Sun. Subsequent nights it will appear higher in the sky (farther from the Sun) and the lit portion appeared to be growing larger.What do you think you would see the next night? How about a week later?
9Lunar Phase Terms The cycle of Lunar Phases starts at the New Moon. At New Moon the Moon is not visible to us on Earth.From New Moon to Full Moon the illuminated fraction of the Moon we see from Earth grows. It is said to be waxing.After Full Moon the fraction of the illuminated Moon visible from Earth shrinks. It is said to be waning.In this figure if we were standing on the Earth looking up at the moon we would seeonly a small part of the illuminated side of the Moon,the Moon would appear to us as a crescent.We can only see the half of theMoon above and to the right of thediagonal line drawn on the Moonin the figure above.
10The Cycle of Lunar Phases The Lunar cycle is split into quartersNew Moon1st QuarterFull Moon3rd (or Last) QuarterSince the whole cycle lasts about a month each quarter lasts about a week.Since our calendar is not perfectly aligned with the cycle of Lunar Phases the phases will never be at exactly the same day each month.See for more months.
11As you view the moon from different directions (relative to the Sun) its appearance changes.
12sunlight sunlight crosses meridian at sundown crosses meridian at about 9:00 pmcrosses meridianat about 3:00 pmsunlightcrossesmeridianat midnightcrossesmeridianat noonsunlightRemember the meridian is the line that goes through your zenith, the North Celestial Poles and the North and South points on the horizon. The times given are only approximate.Does the appearance of the Moon at each phase (the figures in the black boxes) make sense considering that the Sun is to the right in this figure?Do the online exercise “Lunar Phases Web Tool” located atcrosses meridianat about 9:00 amcrossesmeridianat about 3:00 amcrosses meridianat dawn