Week 2
Earthly Phenomena:
Seasons
Lunar Phases
Solar and Lunar Eclipses
Tides
Reading: E2, E3, 5.2 (12 pages)
Quick Quiz
1) If new Moon fell on March 2nd, what is the Moon's
phase on March 14th?
A) waxing crescent
B) first quarter
C) waxing gibbous
D) full
E) waning crescent
2) Only people in the Moon's umbral shadow can see a
total solar eclipse. T/F
3) What will occur when the full Moon is on the ecliptic? )
A) a total lunar eclipse B) a total solar eclipse
C) a partial solar eclipse D) an annular lunar eclipse
E) a partial lunar eclipse if the Moon is at perigee
• Rotation of the Earth
• Revolution (orbit) of the Earth
• Revolution (orbit) of the Moon
• Rotation of the Moon
Rotation of the Earth
Earth’s rotation around its axis:
• Causes night and day (Solar day = average
time between consecutive “noontimes”).
• Causes (apparent) motion of the stars
Rotation of the Earth
Earth’s rotation around its axis:
• Causes night and day (Solar day = average
time between consecutive “noontimes”).
• Causes (apparent) motion of the stars
Revolution (Orbit) of the Earth
• The revolution of the Earth around the Sun
defines the year (365.2425 days).
• Earth’s motion around the
Sun traces a path on the
Celestial Sphere called the
ecliptic.
• The Earth’s revolution
around the Sun also causes
the seasons. How?
TPS: What causes the seasons?
A. The changing distance between the Earth
and the Sun?
B. The 23.5 degree tilt of the Earth’s axis?
Hint: Although it is Winter in the Northern Hemisphere
right now, it is Summer in the Southern Hemisphere.
Spring in Northern Hemisphere
Fall in Southern Hemisphere
Winter in Northern Hemisphere
Summer in Southern Hemisphere
NP
SP
Summer in Northern Hemisphere
Winter in Southern Hemisphere
Fall in Northern Hemisphere
Spring in Southern Hemisphere
Why exactly?
The Sun is lower in the sky in the Winter.
The light from the Sun is diluted.
Short Winter days mean less overall light shining on
that part of the Earth.
Summer
Winter
Earth as Seen from the Sun
North American
Summer
North American
Winter
Equinoxes – Sun crosses the celestial equator (twice –
Spring and Fall)
Solstices –
Sun’s farthest
northerly or
southerly
position
(Summer or
Winter)
Ecliptic –
Path that the
Sun follows
in the sky
Seasons
• Ecliptic is plane of Earth’s path around Sun; at 23.5° to
celestial equator
• Northernmost point (above celestial equator) is summer
solstice; southernmost is winter solstice; points where path
cross celestial equator are vernal and autumnal equinoxes
Seasons
• Combination of day length and sunlight angle gives seasons
• Time from one vernal equinox to next is tropical year
“Path of the Sun”
Revolution of the Moon
The Moon’s revolution around the Earth causes:
• Lunar phases
• Eclipses
• Tides
Lunar Phases
What causes the phases of the Moon?
Is this crescent Moon caused by
A. Sunlight shining mostly on the
“far side” of the Moon?
B. The shadow of the Earth?
Months
The Moon takes about
29.5 days to go
through whole cycle of
phases – synodic
month
Phases are due to
different amounts of
sunlit portion being
visible from Earth
Time to make full
360° around Earth,
sidereal month, is
about 2 days shorter
First quarter
Waxing gibbous
Waxing crescent
Full Moon
New Moon
Waning gibbous
Third quarter
Waning crescent
First quarter
Waxing crescent
New Moon
Waning crescent
First quarter
Waxing gibbous
Waxing crescent
Full Moon
New Moon
Waning gibbous
Third quarter
Waning crescent
Name of Phase
Fraction Illuminated
(Apparent) Side Illuminated
Rises
Sets
New Moon
0
None
6am
6pm
Waxing Crescent
¼
West (Right)
9am
9pm
First Quarter
½
West (Right)
Noon
Midnight
Waxing Gibbous
¾
West (Right)
3pm
3am
Full Moon
1
All
6pm
6am
Waning Gibbous
¾
East (Left)
9pm
9am
Third Quarter
½
East (Left)
Midnight
Noon
Waning Crescent
¼
East (Left)
3am
3pm
Lunar Phases Movie