Galileo Galilei's observations of Venus, Jupiter, and the Moon provided strong evidence supporting Copernicus' heliocentric model of the solar system. Galileo observed phases of Venus similar to Earth's Moon, proving that Venus orbits the Sun. He also discovered four moons orbiting Jupiter, showing that other celestial bodies can orbit something other than Earth.

2. 4.6: The Wanderers
• The word planet is from the Greek planete , meaning “wanderer” . All
of the known planets moved against the background stars; the
historically-known planets included Mercury, Venus, Mars, Jupiter,
and Saturn (and Earth, of course).

3. •The rare celestial shot (pictured) was captured by Martin Dolan over Stephens Castle in Dorset. It is the first time in 11 years the five neighbouring planets have been vis

4. • Mercury and Venus stayed close to the Sun. Mars, Jupiter, and Saturn could be tracked as they
moved across the sky. But occasionally the planets were observed to move backwards against the
stars.

5. • This phenomenon is called retrograde .At the time, the thinking was
that the Earth was the center of the Solar System and even the
Universe. So the Sun, Moon, and known planets revolved around
Earth – called the Geocentric Solar System ; Geo means Earth. How
could this retrograde motion occur if Earth was the center of the Solar
System and even the Universe? Thus, the planets presented problems.
•

6. • Geocentric Solar
System :

7. Retrograde Motion
Retrograde Motion
(the "current" iteration
referred students to their
textbook, but the next iteration
will replace that with a proper
discussion)

8. 4.7: Claudius Ptolemy
• Another ancient Greek astronomer and philosopher, Claudius
Ptolemy (100-170 AD), developed a Geocentric Solar System which
placed the “stellar” universe on a crystal sphere. Earth stood still
(didn’t rotate) and the Sun orbited Earth, producing our day and night
cycles.

9. GEOCENTRIC MODEL VS. HELIOCENTRIC MODEL OF THE SOLAR SYSTEM

10. epicycles on the orbits
• To account for the retrograde of the planets, Ptolemy used looping
small circles called epicycles on the orbits. It was an ingenious system
accepted, as Law… except a Geocentric Universe was wrong! Even
though Ptolemy was Greek, he was born in Egypt.
eliocentric model of Aristarchus?

11. Perseusisdescribedas‘nebulosa
Apagefromthe1515printingoftheAlmagest,
showingtheendofthestarcataloguefor
Cassiopeia(toptwolines)andthestartofthe
listingofstarsinPerseus.Notethatthefirstentry
inPerseusisdescribedas‘nebulosa’,i.e.
nebulous.Thisisinfactthetwinstarcluster
knownastheDoubleCluster,visibletothe
nakedeyeunderclear,darkskies.

12. Ptolemy’s“Almagest”
• All of his observations and work was
done from Alexandria, Egypt. He
was also a geographer and
mathematician, and
Ptolemy’s“Almagest” (1515) is one
of the most influential scientific
texts of all times.
•

13. why do we see
Retrograde Motion?
• If Ptolemy’s Geocentric Universe is incorrect,
why do we see Retrograde Motion? Each
planet orbits the Sun at a different velocity;
the closer the planet to the Sun, the faster it
orbits. Earth catches up then passes planets
further away from the Sun, giving the illusion
that the planet is moving backwards for a
while. The planet does retrograde, but due to
the two bodies’ orbital motions.

15. Geocentric Solar System
• The correct solution would ultimately come nearly 1,500 years later.
However, the Geocentric Solar System was deemed Scientific Law –
and in some cases Church Law; no one could challenge the Geocentric
Solar System until overwhelming evidence made accepting it
impossible.

16. Claudius Ptolemy

17. 4.8: Astronomy and Astrology
• Historically Astronomy and Astrology went hand-in-hand, but is there
scientific evidence to support this theory? No. Astronomy is the
scientific examination of the Universe, whereas Astrology attempts to
predict one’s future due to the positions of specific celestial bodies.
The premise of astrology is that celestial objects affect us here on
Earth.

18. unknown forces the arrangement of celestial
objects
• First, do celestial objects affect us here on Earth? Yes, for example,
the Sun and the seasons, daylight, the Moon and tides, asteroids, and
comets affect us on Earth. What does astrology claim? Basically
through unknown forces the arrangement of celestial objects can
determine human characteristics and fates.

20. Do youfeel the pull yet?
Doyoufeelthepullyet?
Let'scalculate:Jupiteris318timesmoremassivethanEarthand410
millionmilesaway.AccordingtoNewton'sLawofUniversalGravitation,
Jupiterpullsyouup34milliontimeslessthanEarthpullsyoudown.
Jupiter's"pull" isutterlyfeeble.
Soit'sallin yourmind.Butdon'tletthatstopyou:give intothepull!

21. Astrology today
• Astrology today is based primarily on the influence of the planets on
individual lives. Yet the planets are so far away that their gravitational
influence is nil. For example Jupiter’s gravitational influence on Earth
raises our tides 0.0001 inch! Why not include closer-by asteroids?
And why do astrologers now include Uranus, Neptune and Pluto
when they were not included prior to their discovery? And for Pluto:
a planet or dwarf planet?

22. Sun-Sign Astrology
• Sun-Sign Astrology is the most-popular form; this is based on the
Sun’s position in the sky relative to background stars. What is your
Sign? Capricorn, Aquarius, Leo, Sagittarius, Ophiuchus? Astrologers
claim you are born under the sign in which the Sun is in that
constellation. However the Sun is not in that constellation due to the
Earth’s precession.

23. Have

24. Precession
• Precession is the circular motion of a planet’s tilted axis, much like a
top or a gyroscope. For Earth this is a slow process– 26,000 years to
complete one precession.
•

25. • Earth Wobbles.
•

26. 4.9: The Birth
of Modern
Astronomy

27. Copernican Revolution
• The Copernican Revolution was based on the works of four men —
Copernicus, Brahe, Kepler, and Galileo.
• Nicolaus (or Nicolas) Copernicus was a Polish astronomer who
believed there were too many errors in the Ptolemaic Geocentric
Universe. Copernicus noted, as did some others, that Ptolemy’s
“retrograde” was too complicated. So Copernicus developed a Sun-
Centered Solar System, that is, a Heliocentric Solar System .
•

28. 4.10:
Observations
of Motion:
Brahe, Kepler,
and Galilei

29. • Tycho Brahe made numerous measurements of the positions of
astronomical objects until his death in 1601. His measurements were
accurate to better than 1/100 of a degree.
•

30. • Johannes Kepler was Tycho’s assistant. Kepler tried to obtain Tycho’s
data to fit the Copernican Heliocentric Solar System Model. (Kepler’s
and Tycho did not get along.) But Tycho’s data did not exactly work for
a Heliocentric Solar System! So Kepler looked for a new model, and
from that he developed Kepler’s Laws

31. Kepler’s First Law
• Kepler’s First Law
• The planets travel around the Sun in elliptical orbits. Copernicus
thought the planets moved in perfect circles, whereas Kepler defined
these as ellipses, based on Brahe’s data.
•

32. The orbital eccentricity
The orbital eccentricity of a planet
or of an astronomical object is a
parameter that determines the
amount by which its orbit around
another body deviates from a
perfect circle. A value of 0 is a
circular orbit, values between 0
and 1 form an elliptical orbit

34. Kepler’s Second Law
As a planet orbits the Sun, it sweeps out
equal areas of its ellipse in equal periods
of time. The closer the planet to the Sun
(or its star), the faster it moves.
Kepler’s Second Law is stated as:
Where:
•v is the orbiting object’s velocity
•a is the semimajor axis of the object’s orbit
•P is the sidereal period of revolution
•r is the distance between the orbiting object and the body being orbited,
such as Earth orbiting the Sun, or the Moon orbiting Earth

35. • Kepler’s second law, imagine a planet on an elliptical orbit with a line
joining it to its parent star. As the planet moves the line sweeps out
an area that is the same at all times.

36. because of the eccentricity,
• Yet because of the eccentricity, when a planet is closer to its star the
line between the two is shorter. This means the area it traces is
shallower. Thus, to map out the same area in the same amount of
time, the planet must move more quickly

37. Kepler’s Third law
Kepler’s Third law
A relationship exists between the planet’s
period and its distance from the Sun.
Kepler’s Third Law is stated as:
Where:
•a is the orbiting object’s semimajor axis
•P is the orbiting object’s period to orbit
•r is a constant, referred to as Kepler’s
constant

38. Kepler demo
• https://www.starhop.com/blog/2020/6/10/at-home-stem-activities-
keplers-laws-of-planetary-motion

39. Kepler’s third
law
• .

40. Kepler’s third law
• The orbits are ellipses, with focal points F1 and F2 for the first planet
and F1 and F3 for the second planet. The Sun is placed at focal point
F1.
• The two shaded sectors A1 and A2 have the same surface area and the
time for planet 1 to cover segment A1 is equal to the time to cover
segment A2.
• The total orbit times for planet 1 and planet 2 have a ratio

41. improved the model
• Kepler’s laws improved the model of Copernicus. If the eccentricities
of the planetary orbits are taken as zero, then Kepler basically agreed
with Copernicus:
• The planetary orbit is a circle with epicycles.
• The Sun is approximately at the center of the orbit.
• The speed of the planet in the main orbit is constant.

42. Kepler's laws fit the observations
• The eccentricities of the orbits of those planets known to Copernicus
and Kepler are small, so the foregoing rules give fair approximations
of planetary motion, but Kepler's laws fit the observations better than
does the model proposed by Copernicus. Kepler's corrections are:
1. The planetary orbit is not a circle with epicycles, but an ellipse.
2. The Sun is not near the center but at a focal point of the elliptical
orbit.
3. Neither the linear speed nor the angular speed of the planet in the
orbit is constant, but the area speed (closely linked historically with the
concept of angular momentum) is constant.

43. 4.11: Observations of
the Heavens: Galileo
• Italian astronomer and
physicist Galileo Galilei..

44. Italian astronomer and physicist Galileo Galilei
• Italian astronomer and physicist Galileo Galilei first used the telescope
astronomically in 1609. He was the first to see such wonders as
sunspots, which he described as blemishes on the Sun, and features
on the Moon like Mare —seas or bodies of water.
• Galileo’s observations of the planets were monumental.
•

45. • Galileo Galilei's observations that Venus appeared in phases -- similar
to those of Earth's Moon -- in our sky was evidence that Venus
orbited the sun and contributed to the downfall of the centuries-old
belief that the sun and planets revolved around Earth. Also sketched
here are Jupiter, Saturn and Mars.

46. Venus appeared in phases

48. How did Galileo's
observations of Jupiter
and Venus support
Copernicus's model?
• Before Copernicus most
people were thinking
that the Earth is at center
of universe.

49. Explanation:
• Explanation:
• In 1609 Galileo observed sky through his home made telescope.
He found 4 moons orbiting Jupiter..It was a proof that bodies are
orbiting other planets Not earth alone.
He found the crescent shape of Venus through his telescope.This
could happen only if Sun is at center,

50. 4.12: The Mathematical Finish: Newton
• The next major leap was that of Sir Isaac Newton, an English physicist
and mathematician. Newton is credited with developing the Laws of
Motion, Law of Universal Gravitation , building the first Reflecting
Telescope (still called the Newtonian Reflector), and developing a
Theory of Color .
•

51. The Theory of Color
• The Theory of Color was based on Newton’s observations that a prism
breaks sunlight into component colors. Newton also shares credit for
the development of Calculus with Gottfried Leibniz, as well as
developed other ideas in physics, including an empirical law of
cooling, studies the speed of sound, and the idea of a Newtonian
fluid.

52. • Before Newton, standard telescopes provided magnification, but with
drawbacks. Known as refracting telescopes, they used glass lenses
that changed the direction of different colors at different angles. This
caused “chromatic aberrations,” or fuzzy, out-of-focus areas around
objects being viewed through the telescope

53. • After much tinkering and testing, including grinding his own lenses,
Newton found a solution. He replaced the refracting lenses with
mirrored ones, including a large, concave mirror to show the primary
image and a smaller, flat, reflecting one, to display that image to the
eye.

54. Newton’s new “reflecting telescope”
• Newton’s new “reflecting telescope” was more powerful than
previous versions, and because he used the small mirror to bounce
the image to the eye, he could build a much smaller, more practical
telescope. In fact, his first model, which he built in 1668 and donated
to England’s Royal Society, was just six inches long (some 10 times
smaller than other telescopes of the era), but could magnify objects
by 40x.

56. Newton’s First Law of Motion
• An object remains at rest or in motion at a constant velocity unless
acted upon by an outside force. A force is any influence that can
change the speed or direction of motion of an object.
•

57. Newton’s Second Law of Motion
• Newton’s Second Law of Motion is stated as:
• F = ma
• Where:
F is force, m is the mass, a is acceleration
• Units in the Metric System:
• Mass is kilograms, kg, Acceleration is meters per second squared; m/s
2
• f = kg-m/s 2 = Newton (N)

58. gravitational pull
• An object’s weight is the force with which the object is attracted by a
body’s gravitational pull.
• F = ma w = mg
• Where:
• w is the object’s weight
• m is the mass
• g is acceleration due to gravity, 9.8 m/s 2 (metric system) or 32 ft/s 2
(English system)

59. Earth, the Moon,
• This module will overview movements of Earth, the Moon, and other astronomical
bodies and the effects these movements have on what we observe from here on Earth.
• Objectives
• Upon completion of this module, the student will be able to:
• Define motions of objects, including rotation, revolution, and precession
• Identify parts of the points on the Celestial Sphere, such as the celestial poles, meridian,
zenith, celestial equator, and ecliptic
• Identify measurement systems used by astronomers
• Explain why we experience seasons, and the descriptions used to discuss seasons
• Explain why the Moon goes through its phases, and the terminology used to explain the
phases of the Moon
• Identify types of eclipses
• Explain why eclipses occur

60. The Motion of the Moon in the Night Sky
• This is a good time to talk about the motion of the Moon; you can
check it out over the next several nights. This week, the Moon is in
the night sky, approaching the full phase. Look at your textbook
(Chapter 9) with one of the illustrations of the orbital motion of the
Moon about the Earth.
•

61. the properties of the Moon’s orbit about the
Earth.
• The following are the main points of the properties of the Moon’s
orbit about the Earth.
• The moon orbits the Earth-Moon Barycenter , which is the center of
mass of the Earth-Moon system.
• The average distance of the Moon from the Earth is 384,000
kilometers (240,000 miles, or 60 Earth radii.

62. the properties of the Moon’s orbit about the
Earth.
• The orbit is not circular; at its closest, the Moon is only 356,400 km,
and at its most distant, 406,700 km. This means that the angular size
of the Moon changes during the month.
• From Earth we only see the illuminated part of the Moon, which
varies during the course of the month from 0 % to 100 %. These are
called the phases of the Moon.

63. the properties of the Moon’s orbit about the
Earth.
• There is a correspondence between the place the Moon is in its orbit
and the phase we see it. You will never see the full moon on the
meridian at sunset.
• The Moon undergoes synchronous rotation. This means that it turns
on its axis once in the time that it orbits the Earth. As a result, we
always see the same hemisphere of the Moon. This is illustrated in
Figure 9.2 of the textbook.

64. • The sidereal period of the Moon’s orbit, or time it takes to complete
a path across the sky relative to the background stars, is 27.32
days. The period determined by the phases, or times between
successive full (or new) moons is 29.53 days.

65. Think about why it is that these two periods
are different.
• The plane of the Moon’s orbit is nearly the plane of the ecliptic. The
inclination angle of the Moon’s orbit to the plane of the ecliptic is 5
degrees. This means that the Moon also moves along the ecliptic, and
is seen only in the constellations along the ecliptic.

67. The properties of the Moon’s orbits
• The properties of the Moon’s orbits discussed here allow us to understand
the properties of eclipses.
•
• There are two kinds of eclipses, lunar eclipses like we saw last November
• http://antwrp.gsfc.nasa.gov/apod/ap031121.html
•
• and solar eclipses. A total eclipse of the Sun has not been seen in Iowa in
my lifetime
• http://antwrp.gsfc.nasa.gov/apod/ap010408.html
•

69. In a lunar eclipse,
• In a lunar eclipse, the Moon moves into the shadow cast into space
by the Earth. In a solar eclipse, the Moon moves between the Sun
and Earth, and cuts off the light of the Sun.

70. a total lunar eclipse before dawn on May 26,
2021
• One of the top astronomical happenings of 2021 will unfold in the early
morning sky on Wednesday as the Earth, moon and sun align perfectly to
create a total lunar eclipse.
• This will be the first event of its kind since 2019, when stargazers braved
the cold wintry weather on the night of Jan. 20, to witness the moon turn
red over North America.
• There have been several lunar eclipses since the early 2019 eclipse,
including four penumbral lunar eclipses in 2020, but these have been far
less impressive than what is set to take place during the last week of May.
•

71. penumbral lunar eclipse,
• During a penumbral lunar eclipse, the moon only passes through part
of the penumbra, Earth’s outer, brighter shadow. It can be very
difficult to spot the different between a penumbral eclipse and a
normal full moon even with the help of a telescope.
• This month’s total lunar eclipse will be much more eye-catching as the
moon passes through the umbra, Earth’s inner, darker shadow.
•

72. penumbral lunar
eclipse,
.

73. Why don’t eclipses happen every month?,
• Why don’t eclipses happen every month?, you would think that a
lunar eclipse would happen every month at the time of full
moon, and an eclipse of the Sun would occur every month at new
moon. But that doesn’t happen. We typically see a lunar eclipse
every 18 months of so, and an eclipse of the Sun happens
somewhere on Earth about as often.

75. • Tycho Brahe made numerous measurements of the positions of
astronomical objects until his death in 1601. His measurements were
accurate to better than 1/100 of a degree.
• Johannes Kepler was Tycho’s assistant. Kepler tried to obtain Tycho’s
data to fit the Copernican Heliocentric Solar System Model. (Kepler’s
and Tycho did not get along.) But Tycho’s data did not exactly work for
a Heliocentric Solar System! So Kepler looked for a new model, and
from that he developed Kepler’s Laws
•