Unit 3

Question 1

Earth’s location

Answer 1

– 150,000,000 km (93,000,000 mi.) 
from the Sun
– 385,000 km (239,000 mi.) from the 
moon
– 3rd planet from the Sun

Question 2

the sun

Answer 2

-where 99% of earth’s energy comes from
-The energy received at the
Earth’s surface drives all
weather and makes the planet
habitable

Question 3

rotation

Answer 3

– Spinning of Earth on its axis
• Axis is tilted 23.5 degrees 
• 1 rotation = 24 hours
– Earth rotates eastward (counter-
clockwise) if viewed from above 
North Pole
• Sun rises in the east, sets in the west
– Important Effects
1. Diurnal Pattern 
2. Tides
3. Coriolis Effect

Question 4

revolution

Answer 4

– A complete circling around the Sun
• 1 revolution = 365.25 days 
– Orbital path “nearly” circular
• Better defined as an ellipse 
– Due to the shape of orbit, distance 
from sun varies 
• Perihelion vs. Aphelion

Question 5

earth’s tilt

Answer 5

- reason of seasons 
• Earth revolves around the Sun on 
a geometric plane.
– Plane of the ecliptic
• Earth’s axis is tilted 23.5° from 
perpendicular to plane 
– Parallelism
• Axis always pointed in the same 
direction

Question 6

the tilt results in…

Answer 6

– 1) Day length
– 2) Spreading of the solar beam
– 3) Path length

Question 7

solstice

Answer 7

When the Earth’s rotational axis is pointed directly towards or away from the
sun

Question 8

summer solstice

Answer 8

– June 21 (NH) 
– North pole rotational axis pointed 
towards the sun 
– Sun directly overhead of Tropic of 
Cancer at noon (Solar Declination)
– Longest day (NH)
• 63 percent of Northern hemisphere 
is on lighted side of illumination 
• 66 N to North pole experiences 24 
hours of daylight

Question 9

winter solstice

Answer 9

– December 21 (NH) 
– North pole rotational axis pointed 
away from the sun 
– Sun directly overhead of Tropic of 
Capricorn at noon (Solar 
Declination)
– Longest night (NH)
• 37 percent of Northern Hemisphere 
is on lighted side of illumination
• 66 N to North pole experiences 24 
hours of darkness

Question 10

Equinoxes

Answer 10

– When the Earth’s rotational axis is 
directly perpendicular to the sun’s rays
– Length of day and night are equal at 
every latitude!
– Sun directly overhead of equator at 
noon (Solar Declination)

Question 11

spring equinox

Answer 11

march 20 (NH)

Question 12

fall equinox

Answer 12

september 22 (NH)

Question 13

Longer distance from equator =

Answer 13

more variation in day length 
throughout year
– Equator 
• 12 hours of light each day, year round
– Poles 
• 24 hours of light each day to 0 hours of 
light during a day

Question 14

solar declination

Answer 14

– Latitude at which the noon day sun strikes the Earth’s surface at 90 degrees
– 23.5 N –23.5 S

Question 15

solar altitude

Answer 15

– Angle of the sun above the horizon at noon
– Solar Altitude = 90 - latitude +/-Solar Declination
• + if in same hemisphere
• - if in opposite hemisphere

Question 16

Spreading of the solar beam

Answer 16

– Changes intensity of incoming solar

radiation (insolation)

Question 17

path length

Answer 17

– Amount of atmosphere insolation 
passes through changes 
– Atmospheric composition 
interferes with radiation 
• Reflects 
• Absorbs
• Scatters

Question 18

Milankovitch Cycles

Answer 18

• Changes in Earth’s motion
• Theory for why ice ages occur
• Three cycles

Question 19

ingredients for Milankovitch cycle

Answer 19

• 1) Axial Tilt 
– Ranges from 22° –24.5°
– 40,000 years
• 2) Orbital Eccentricity 
– Higher eccentricity = more elliptical
– Lower eccentricity = more circular
– 100,000 years
• 3) Axial Procession
– Wobbling on axis
– 25,000 years