Climate and Latitude Sun’s rays spread over large area = cooler concentrate in small area = warmer Warmest where sun directly overhead (at noon) cooler warmer cooler

Seasons What do we observe? Warm in Summer; Cold in Winter Yearly cycle Linked to Sun’s location on ecliptic (Spring = Vernal Equinox, Summer = Summer Solstice; etc) Sun is heat source Seasons in N and S hemispheres opposite N summer = S winter Seasons near Equator less severe

Cause of Seasons No! Changing distance to Sun? Orbit is ellipse; distance changes Good idea, BUT Orbit almost circular Trivial change in distance little change in heating Closest to sun in January Predicts summer in January Both N and S hemispheres at same distance Predicts seasons same in N and S hemispheres

Cause of Seasons Yes Tilt of Earth’s Axis? Location where sun overhead (at noon) Vernal & Autumnal Equinoxes (Mar 21, Sept 21) Overhead at Equator Summer Solstice (Jun 21) Overhead on Tropic of Cancer (23.5º N) Warmer in N hemisphere; cooler in S hemisphere Winter Solstice (Dec 21) Overhead on Tropic of Capricorn (23.5º S) Warmer in S hemisphere; cooler in N hemisphere cooler warmer cooler Zenith Horizon

Cause of Seasons - Part 2 No!! Changing distance to Sun? Earth’s axis tilted N hemisphere closer in summer; farther in winter Opposite for S hemisphere BUT Trivial change in distance Predicts little change in heating

Cause of Seasons - Part 2 Yes Tilt of Earth’s Axis? Path of Sun in sky Summer Solstice (Jun 21) Sun farthest north Transits high at noon Days are long Winter Solstice (Dec 21) Sun farthest south Transits low at noon Days are short Large amount of heating Small amount of heating

For an observer in the continental U. S For an observer in the continental U.S., which, if any, of the x’s (a – e) in the figure below correctly shows the position of the Sun’s shadow at noon? Note that the position of the Sun’s shadow at noon on the Winter and Summer Solstices are shown. a) a b) b c) c d) d e) e

Motions and Phases of the Moon Composite Image Credit: T.A. Rector, I.P. Dell'Antonio, NOAO, AURA, NSF

Motion of Moon Daily Motion Like Stars Moon Orbits Earth Rise in East; Transit in South; Set in West Moon Orbits Earth Moon slips on Celestial Sphere 13 degrees per day = 1 lunar diameter per hour Sidereal Period = Orbital Period 27.3 days Time from full moon to full moon 29.5 days (similar to sidereal day vs. solar day) Moon rises roughly 50 min later each day

Rotation of Moon Always see same side Moon rotates once per month Non-rotating moon Rotating moon

D --> O --> C Moon Phases New = all black Full = all white crescent Moon Phases Waxing 1st quarter New = all black Full = all white Crescent < half white Gibbous > half white Quarter = half white Waxing = growing Waning = shrinking gibbous full gibbous 3rd quarter Waning D --> O --> C crescent

Phases of Moon

Phases of Moon Not caused by Earth’s shadow! Cause: Changing view of illuminated side (as Moon orbits Earth) “Back Side” sometimes called “Dark Side” Back side not dark Back side has night and day (just like front side)

Workbook Exercise: Cause of Moon Phases (pages 23-25 in workbook)

During the full moon phase, how much of the Moon’s surface is being illuminated by sunlight? a) none b) less than half c) half d) more than half e) all

CHALLENGE QUESTION You look up at a 1st Quarter moon and see that the crater where you built your retirement home is on the terminator (the dividing line between light and dark). What time of day is it there? Sunrise Noon Sunset Midnight

Workbook Exercise: Predicting Moon Phases (pages 27-28 in workbook)

Which phase of the Moon rises at noon? a) Waning gibbous b) Third quarter c) First quarter d) Waxing crescent e) None of the above

Solar & Lunar Eclipses

Eclipses Solar Lunar Moon’s shadow falls on Earth Moon moves into Earth’s shadow

Earth and Moon Shadows Umbra (and C) Penumbra Umbral Extension

Earth and Moon Shadows A B C D Total Partial Annular Appearance of Sun Observer location A B C D Type of Eclipse Total Partial Annular

Solar Eclipse

Lunar Eclipse

Eclipse Requirements Why not every new/full moon? Moon’s orbit tilted Moon usually crosses above (or below) Sun Eclipses require: Moon crossing ecliptic Sun at crossing point

Eclipse Seasons Twice each year Eclipses occur in sets when sun near lunar crossing Eclipses occur in sets “two’s” or “three’s” alternate lunar, solar (separated by 2 weeks) Frequency of eclipses: solar same as lunar Lunar visible from half of Earth Solar only dramatic if total Total Solar only visible from small region

When the Moon appears to completely cover the Sun (a solar eclipse), the Moon must be at which phase? a) full b) new c) first quarter d) last quarter

When the Moon moves through the Earth’s shadow, causing it to appear to darken (a lunar eclipse), the Moon must be at which phase? a) full b) new c) first quarter d) last quarter

Motion of the Planets Diurnal motion like fixed stars Rise in “east” Transit “high/low in south” Set in “west” Position on celestial sphere slowly “slips” from day to day (similar to sun and moon)

Planet Motion E W Generally move from W to E Retrograde motion - time when planet appears to move backwards from E to W

Planets Planet = Greek for “wanderer” 5 visible planets (others too faint) Mercury, Venus, Mars, Jupiter, Saturn Total of 7 wandering objects (including Sun and Moon)

Planet Location Planets always found in Zodiac 18º wide belt centered on ecliptic Mercury and Venus always close to sun Mars, Jupiter, Saturn seen everywhere (in Zodiac) Sometimes near sun (conjunction) Sometimes opposite to sun (opposition)

Where (and at what time) would you look to see a planet rise when it is in retrograde motion? a) Near the eastern horizon at sunrise b) Near the western horizon at sunrise c) Near the eastern horizon at sunset d) Near the western horizon at sunset

Workbook Exercise: Understanding Retrograde Motion (pages 47-48 in workbook)

A planet moving in retrograde motion will, over the course of one night, appear to a) move east to west b) move west to east c) not move at all, as planets do not move with the stars d) move randomly, as planets move differently than the stars

A planet is moving in retrograde motion A planet is moving in retrograde motion. Over the course of several nights, how will the planet appear to move relative to the background stars? a) east to west b) west to east c) It will not move at all, as planets do not move with the stars d) It will move randomly, as planets move differently than the stars

A planet is moving in normal motion A planet is moving in normal motion. Over the course of several nights, how will the planet appear to move relative to the background stars? a) east to west b) west to east c) It will not move at all, as planets do not move with the stars d) It will move randomly, as planets move differently than the stars