1. Astronomy from Earth’s
Perspective:
Before the invention of technology that
enable humans to leave earth’s
perspective, astronomers relied solely on
their observations of the heavens to
make inferences about earth’s motions.

2. Models of the Solar
System
 Based upon observations of the
apparent motion of celestial objects.
 Before our current understanding
that the planets revolve around the
sun, people actually believe that
the sun and other planets revolved
around earth.

3. Explain the difference
between
the geo- and helio-centric
models of the solar system.
Earth-
centered
Sun-
centered

4. Models of the Solar
System
Geocentric Model – Earth is the center
of the solar system, and all objects
revolve around it.
 Used epicycles (small sub-orbits) to
explain retrograde (backward) motion
of planets

5. Models of the Solar
System
 Heliocentric Model – The Sun is at
the center, and the planets revolve
around it

6. Geocentric vs. Heliocentric

8. Coordinates in the Sky
On earth we use latitude
and longitude to locate
places. In astronomy we use
_______________ and
__________________.
Altitude
Azimuth

9. Coordinates in the Sky
Altitude is the angle above the
horizon in degrees. (Horizon:
imaginary boundary between
the sky and the ground)

10. Coordinates in the Sky
90°
Zenith
The highest angle of altitude
is ________ and that is the
point directly over the
observers head called
_______

11. Coordinates in the Sky
0° 360°
Azimuth is direction broken
down into degrees from
_______ to _______
Altitude and azimuth together
form a coordinate grid for
locating objects in the sky.

12. We draw this grid on a dome
model of the sky called a
celestial sphere.
•Zenith- directly above
90°

14. Is the Earth Perfectly
round?
 The Earth is NOT a perfect sphere
 It is an oblate spheroid.
 It is flattened at the poles and
bulges at the equator
 Earth is slightly out of round or
OBLATE.

15. The Oblate Sphere
 The difference is small
 We can not see it with the naked eye
 It still appears like a sphere
 Be careful on multiple choice

16. Why is the earth not
perfectly round?
 Earth’s rotation causes…
Bulging at equator
Flattening at the poles

17. Why do observations of
Polaris help determine the
Earth’s shape?????
 The North Star appears lower and
lower in the sky as you travel toward
the equator because of earth’s
spherical shape, where the North
Star is just visible at the horizon.
The latitude of the equator is 0°.

18. Ships appear to sink gradually
below horizon

19. Lunar Eclipse
 Only a sphere can cast a shadow that
appears round. During a lunar eclipse,
the earth casts its shadow on the moon
during the full moon phase.

22. What proof is there that we
are slightly oblate?
 Gravity measurements. Gravity is the
force of attraction between any 2 objects.
Increase mass of objects = increase
gravity Decrease distances =
increase gravity
 If Earth were a perfect sphere, it would
be expected to exert an equal force on
objects at equal distances from the center
of earth.

23. Weight!!! – measure of
gravitational force
 We are further from the center of
the Earth at the equator – gravity is
less
 This means we weigh LESS!!!
 We are closer at the poles…
 We weigh MORE!!!!

24. The least amount of gravity is
farther from the center of
Earth
High Mountains farther from the center of earth – gravity is less

25. Summary: How did they
prove the Earth to be
round?
 Ships appear to sink GRADUALLY below the
horizon as they travel away from observer
 Polaris (North Star) changes altitude (angle
measured in degrees above earth’s surface)
directly with your latitude
ALT OF POLARIS = LAT OF OBSERVER
 Lunar Eclipses - Earth’s shadow on the moon
 Satellite Imagery – absolute proof

26. Gillism #1: “It’s all a matter of
perspective! When you change
the way you look at things the
things you look at change!”

27. Celestial Observations
 celestial object: any object in space
(outside of earth’s atmosphere)
examples: Moon, planet, stars, sun
 The apparent daily motion of celestial
objects (like stars) have enabled
scientist to create theories about
earth’s motions: Rotation and
Revolution

29. How long is one rotation of
Earth?

30. Rising and Setting
of the Sun
Rising and Setting
of the Moon
The Seasons
Changing
Constellations
Movement of Stars
through the sky

31. Earth’s axis is tilted 23.5° from the
perpendicular. Earth’s axis is always tilted in
the same direction this is called parallelism.
AXIS – the imaginary line through the planet
from the North Pole to the South Pole

32. The earth rotates counterclockwise when
looking down from the north pole. Or from
west to east when looking at a side view of
earth

33. Tilt of the axis always stays
the same – 23.5° from a line
perpendicular to the ecliptic
plane: Parallelism

34. One rotation = 360°
Time for one rotation = 24 hours
360° ÷ 24 = 15°/hr

35. Regents Question
Earth’s rate of rotation is
approximately
(1)1
○
per day (3) 180
○
per day
(2)15
○
per day (4) 360
○
per day

36. Regents Answer
(4)360
○
per day

38. Polaris
North Star
This is the
star that
lies in space
practically
over the
geographic
North Pole
of the earth.

Polaris

39. Since it is located above our
axis of rotation– Polaris is a
fixed point in our sky above
the North Pole.
90º

40.  Anyone in the
Northern
hemisphere can
see Polaris but
where it appears
on the observer's
celestial sphere
depends on their
latitude.

 If you stood at
the North Pole,
Polaris would be at
your zenith
(directly
overhead).
Polaris

41. An observer on the equator
would find Polaris along the
horizon
Any observer in between
would find Polaris has an
altitude equal to their
latitude. So for NYS, Polaris
will have an altitude of
approximately 41°.

42. Polaris – Fixed Point above
the North Pole
 Because of this, in the Northern Hemisphere,
the altitude (angle measured in degrees above
the horizon) of Polaris tells observer his latitude
position.
 If observer’s latitude changes in the Northern
Hemisphere, the altitude of Polaris will exactly
match observer’s latitude.
ALT OF POLARIS = LAT OF OBSERVER

44. Locating Polaris – our latitude
is 41°N , Polaris’ altitude
will be 41°

45.  To find Polaris, look for
the Big Dipper.
 Draw an imaginary line
from the two end
‘pointer’ stars.
 They will point
approximately to the
last star in the handle
of the Little Dipper…
Polaris!

46. Am I pointing to Polaris?
How can you check to be somewhat sure?
To Polaris
Zenith = 90° above
the observer
Horizon
42 Degree Angle…
Pretty close to 41
Degrees

49. Apparent Daily Motion
 An apparent motion is a motion an
object appears to make
 An apparent motion can be real or an
illusion
 Celestial objects appear to move in
the sky
 This is due to the earth’s rotation

50. Apparent Motion
 Celestial Objects appear to move
15° per hour, because Earth rotates
360° in 24 hours.

51. Apparent Motion
 The apparent daily motions of stars
changes when the observer’s Latitude
on earth changes.
 Therefore, at the poles (90° N or S)
stars do not rise or set but at the
equator (0° ) all stars rise and set

52. Apparent Motion
 At 41° N (New York state) some
stars, like the sun appear to rise in
the east and set in the west making
an arc across the celestial sphere.
Other stars such as ones part of
circumpolar constellations never set
but instead trace out giant circles
daily around the poles.

53. Apparent Motion
Using a time-lapse camera we can
document this phenomenon. We call
these images Star Trails

54. Apparent Motion
 Stars are so far away they appear
stationary (not moving). Why do they
have this pattern? Earth is Rotating!

55. Circumpolar
New York State
Mid October
3
4
2
1
2
3
4

56. Since earth is spherical as it rotates
greater distances are covered at the
equator than at the poles for every
degree the earth turns.
 Rotational speed at Poles: 1 cm/day
 Rotational speed at Equator: 1000
miles/hour
 The Earth is moving faster at the
equator than at the poles

57. How many degrees did the stars move
from diagram 1 to
diagram 2?
30° (2 hours x 15°)

58. How can you find
Polaris?
It’s the only one that didn’t move

59. What hemisphere
must you be in?
Why?
Northern
Because Polaris can only been seen in
the North

60. What direction must
you be looking?
North

61. What direction do
the stars appear to
move?

62. What causes the
stars appear to move?

64. 1. Evidence of Earth’s
Rotation
 1851, Foucault’s pendulum will appear to
change in a predictable way.
 Why is this evidence? There is no force
acting on the pendulum to make its plane of
oscillation rotate or go around its own axis
 It would continue to swing in the original
path if Earth did not rotate.

65. No force that makes pendulum rotate
– must be earth that is rotating!!!

67. 2. Evidence for Rotation
 Coriolis Effect – the tendency of objects moving
over the earth (air, water, planes, projectiles) to
be deflected (curve away) from a straight line
path. The French scientist, Gaspard Coriolis, first
explained the deflection of objects moving over
the surface due to Earth’s rotation
 The deflection is to the right in the Northern
Hemisphere and to the left in the Southern
Hemisphere.
 This deflection occurs because Earth’s surface is
rotating with respect to the objects.

73. Rising and Setting
of the Sun
Rising and Setting
of the Moon
The Seasons
Changing
Constellations
Movement of Stars
through the sky

74. Regents Question

75. Regents Question
The diagram below shows how Earth is
illuminated [lighted] by the Sun as viewed
from above the North Pole.
In which orbital position would Earth be
illuminated as shown?
(1)A (3) C
(2)B (4) D

76. Regents Answer
(1)A

77. Regents Question
In the Northern Hemisphere, planetary
winds blowing from north to south are
deflected, or curved, toward the west.
This deflection is caused by the
(1)unequal heating of land and water
surfaces.
(2)movement of low-pressure weather
systems.
(3)orbiting of Earth around the Sun.
(4)spinning of Earth on its axis.

78. Regents Answer
(4) spinning of Earth on its axis.

79. Apparent Solar Motion
 The sun appears to move across the sky,
like all celestial objects.
 The sun’s apparent path in the sky
varies by latitude and season.

80. Four Seasons
Name the four seasons and
their starting date.
•Summer Solstice– June 21
•Autumn Equinox–
September 21
•Winter Solstice– December
21

81. What changes do we
observe during seasons?
Sun’s
altitude
changes
with the
season.
Highest – June 21, Lowest – Dec.
21, But NEVER overhead at our

82. What changes do we
observe during seasons?
Sun rise and
Sun set
positions
change with
the seasons.
South of
E/W in fall
and winter. North of E/W in
spring and
Sun rise in DC

83. What changes do we
observe during seasons?
Day length
– Duration
of
Insolation
Longest on Summer Solstice, June
Shortest on
Winter Solstice,
Dec. 21
12 hours on
Equinox for
all.

84. What changes do we
observe during seasons?
What to know about the Summer So
1.June 21, longest day of the
year.
2.Sun at highest altitude at
noon.
3.24 hrs of daylight at North
Pole.

85. What changes do we
observe during seasons?
What to know about the Winter
Solstice.
1.Dec. 21, shortest day of the
year.
2.Sun at lowest altitude at noon.
3.24 hrs. of darkness at North
Pole.
4.Direct sun ray at 23.5° south

86. What changes do we
observe during seasons?
What to know about the Equinox.
1.Sept. 21 and March 21.
2.12 hrs of daylight, 12 hrs of
night.
3.Direct sun ray at Equator.
4.Sun rise – E, Sun set – W.

87. How long is one revolution of Earth?

88. Regents Question
Which observation provides the best
evidence that Earth revolves around the
Sun?
(1)The constellation Orion is only visible in
the night sky for part of the year.
(2)The North Star, Polaris, is located above
the North Pole for the entire year.
(3)The sun appears to move across Earth’s
sky at a rate of 15
○
/hr.
(4)The Coriolis effect causes Northern
Hemisphere winds to curve to the right.

89. Regents Answer
(1)The constellation Orion is
only visible in the night sky
for part of the year.

91. Regents Question
If Earth’s axis were tilted less
than 23.5
○
, which seasonal
average temperature change
would occur in New York State?
(1)Spring and fall would be cooler.
(2)Spring and fall would be warmer.
(3)Winter would be cooler.
(4)Summer would be cooler.

92. Regents Answer
(4)Summer would be cooler.

93. Is distance important to
seasonal change?
NO!
Farthe
st
away
on
July
4,
Closest
on
Earth’s orbit is an

94. Reasons for the Seasons Video Clip

95. Regents Question

96. Regents Question
Which position of Earth
represents the first day of
summer in the Northern
Hemisphere?
(1)A (3) C
(2)B (4) D

97. Regents Answer
(3) C

98. Regents Question

99. Regents Question
How many degrees will the
Sun’s vertical rays shift on
Earth’s surface as Earth
travels from position C to
position D?
(1)15
○
(3) 47
○
(2)23.5
○
(4) 365
○

100. Regents Answer
(2) 23.5
○

101. Constellations are groupings of stars that make an
imaginary image in the night sky. They have been named
after mythological characters, people, animals and objects.
In different parts of the world, people have made up
different shapes out of the same groups of bright stars. It is
like a game of connecting the dots. In the past
constellations have became useful for navigating at night
and for keeping track of the seasons.

102. 661/20N
661/20 S
231/20N
231/20S
00
900N
900S
Orbital
Plane

105. Long Island
1
2
3
4
9:00 pm
2
3
4

106. Summer
Autumn
Winter
Spring
Scorpio, Sagittarius,
Capricorn
Aquarius, Pisces, Aries
Taurus, Gemini, Cancer
Leo, Virgo, Libra

107. Regents Question
Which object is closest to Earth?
(1)The Sun (3)the moon
(2)Venus (4)Mars

108. Regents Answer
(3)the moon

109. The Moon

110. The Moon
 The Moon is Earth’s only natural
satellite
 It is estimated to be about 4.5 billion
years old

112. Features
 The Moon’s interior is thought to
have layers, similar to earth
 The Moon’s surface is covered with
craters, caused by meteor impacts.

113. The Moon’s Surface
 Dark areas called Maria (from Latin
mare, meaning sea). These are
ancient lava flows.
 Light areas are Lunar Highlands,
which are mountain ranges made of
lighter color rocks.

114. Moon Rocks
 Rocks on the Moon are made of
minerals similar to those on Earth.

115. Rotation and Revolution
 The Moon’s periods of rotation and
revolution are both 27.33 days. The
result is that the same side of the
Moon always faces Earth (the near
side).
 However, it takes 29.5 days for the
Moon to completely revolve around
the Earth

116. Why Two More Days?
Moon’s
orbit
Earth
moving
around
Sun.
Eart Moon
Moon has to
revolve for 2
more days to
get back to
the new moon
phase.
This occurs
because the
Earth is revolving
around the Sun.

117. Dark Side/Light Side

118. Changes in Shape

120. Phases
 Moon Phases are apparent changes in shape
due to the position of the Moon in its orbit.
 Phase names:
– New
– Crescent
– Quarter
– Gibbous
– Full
 Waxing – becoming more visible
 Waning – becoming less visible

121. Phases Of The Moon

123. ESRTs p15

124. Regents Question
Which sequence of Moon phases could be observed
from Earth during a 2-week period?

125. Regents Answer

127. because as the Earth
rotates, the moon
revolves

129. How many hours is the
moon visible each day?
Approximate Times of Moonrise and Moonset
moonrise moonset
new moon 06:00 AM 06:00 PM
waxing crescent 09:00 AM 09:00 PM
first quarter 12:00 PM 12:00 AM
waxing gibbous 03:00 PM 03:00 AM
full moon 06:00 PM 06:00 AM
waning gibbous 09:00 PM 09:00 AM
third quarter 12:00 AM 12:00 PM
waning crescent 03:00 AM 03:00 PM
new moon 06:00 AM 06:00 PM

138. Moon’s Effect on Tides
 Tides are the periodic rise and fall of
the ocean surface
 Tides are caused by the gravitational
attraction of the Moon and the Sun
on ocean water
 High tide will occur when the Moon is
overhead, as well as on the opposite
side of the Earth.

139. Tides
Eart
h
Hig
h
High
Low
Low
Caused by
Moon’s gravity
pulling Earth’s
water.
Two of each
because the
Earth
rotates.
Tides always
High in line
with Moon.

140. Regents Question
The change in the tides as shown
on the graph is primarily the
result of
(1) Earth’s rotation and the Moon’s
revolution
(2) Earth’s rotation and revolution
(3) The Moon’s rotation and Earth’s
revolution
(4) The Moon’s rotation and revolution

141. Regents Answer
(1) Earth’s rotation and the Moon’s
revolution

145. Phases and Tides
 The alignment of the Moon with the Sun
affect tides.
 At the full and new moon phase, both are in
line, causing a higher high tide and a lower
low tide. This is called the Spring Tide.
 At the quarter phases, the Sun and Moon
work against each other, resulting in
weaker tides, called Neap Tides.

146. Spring and Neap Tides
Eart
h
Earth
Sun
Sun
Neap Tide
Spring Tide
Quarter Phase
– not a large
change from
high to low
tide.
New and Full
Phase – big
change from
high to low tide.
Water
being
pulled in
two
directions.
Moon and Sun’s gravity pulling in one
direction.

149. Regents Question
What is the main reason that the
gravitational attraction between
Earth and the Moon changes each
day?
(1) Earth’s axis is tilted at 23.5○
.
(2) Earth’s rotational speed varies
with the seasons.
(3) The moon has an elliptical orbit.
(4) The moon has a spherical shape.

150. Regents Answer
(1) The moon has an elliptical
orbit.

152. Eclipses and Conclusions Video Clip

153. Eclipses
 An eclipse occurs when the Sun’s light
is blocked from either the Earth or
the Moon.
 Since the orbit of the Earth and the
Moon are along different planes,
eclipses don’t happen frequently.

154. What’s the
difference between
solar and lunar eclipses?
Earth goes
into moon’s
shadow
moon goes
into Earth’s
shadow

155. Solar Eclipse
 Solar Eclipse – occurs when the Moon
blocks the Sun’s rays from reaching Earth.
It occurs only at new moon phase.

156. Solar Eclipse
Sun’s Rays
Penumbra
Umbra
•Only occurs during the new moon phase.
•Only total eclipse if in the umbra. Only a few
people see it.
•Moon blocks light to the Earth. Occur less often
Solar Eclipse
Photo

157. Lunar Eclipse
 Lunar Eclipse – occurs when the Earth
blocks the Sun’s rays from reaching the
Moon. Only occurs at full moon phase.

158. Lunar Eclipse
Umbr
a
Penumbra
Sun’
s
Rays
•Can only occur during the full moon
phase.
•Earth blocks light to the moon.
•Moon must be in Umbra for a Total Lunar
Every one
on the
night side
sees the
eclipse.

163. Why don’t we have
solar and lunar eclipses
every month?
The moon’s orbit is
tilted 5° from the
Earth’s orbit.

164. Are We Alone?

165. Home Sweet Home
You are here!