Climate and Latitude Sun’s rays –spread over large area = cooler –concentrate in small area =...

Climate and Latitude

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• 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• 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

No!

Cause of Seasons• 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

Yes

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cooler

cooler

warmer

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Zen

ith Zenith

Horizon

Hor

izon

Cause of Seasons - Part 2• 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

Yes

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 shadowat noon? Note that the position of the Sun’sshadow at noon on the Winter and Summer Solstices are shown.a) ab) bc) cd) de) e

Motions and Phases of the Moon

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Composite Image Credit: T.A. Rector, I.P. Dell'Antonio, NOAO, AURA, NSF

Motion of Moon• Daily Motion Like Stars

– 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

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Moon Phases• New = all black

• Full = all white

• Crescent < half white

• Gibbous > half white

• Quarter = half white

• Waxing = growing

• Waning = shrinking

crescent

crescent

gibbous

gibbous

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QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.1st quarter

full

3rd quarter

Wax

ing

Wan

ing

D --> O --> C

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) noneb) less than halfc) halfd) more than halfe) all

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

• Which phase of the Moon rises at noon?a) Waning gibbousb) Third quarterc) First quarterd) Waxing crescente) None of the above

Solar & Lunar Eclipses

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Eclipses

• Solar– Moon’s shadow

falls on Earth

• Lunar– Moon moves into

Earth’s shadow

Earth and Moon Shadows

A. Umbra

B. (and C) Penumbra

D. Umbral Extension

Earth and Moon Shadows

A B C D

Appearance

of Sun

Observer location

TotalType of Eclipse Partial Annular

Solar Eclipse

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Lunar EclipseQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

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• When the Moon appears to completely cover the Sun (a solar eclipse), the Moon must be at which phase?

a) fullb) newc) first quarterd) 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) fullb) newc) first quarterd) 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

•Generally move from W to E

•Retrograde motion - time when planet appears to move backwards from E to W

E 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)