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Intense Frames of Scientific Instruction, Analysis, Comparing
and Contrasting, Description, and for Some Vocabulary.
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ASTRONOMY
ORBITAL MECHANICS:
A History
OBJECTIVES
By the end of this presentation, students will
be able to
• Explain the origins of astronomy.
• Describe four observations that show the
earth is a sphere.
Origins Of Astronomy
As early as 2800 B.C. massive structures
were constructed as calendars using
star and sun positions to keep track of
– when migratory birds would arrive for
hunting;
– when berries would ripen;
– what season babies will be born;
– when farmers should plant and harvest;
– when to shelter livestock.
Origins Of Astronomy
Societies that had these structures had
astrologer-priests, who observed,
recorded, kept track of and announced
when these events were about to take
place.
Some Astrologer-Priests asserted these
events to be controlled by the motions
of the stars.
Origins Of Astronomy
Some Astrologer-Priests turned the
structures into temples and their
announcements became religious
ceremonies.
– Stonehenge (Scotland)
– Woodhenge (St. Louis)
– Casa Grande (Arizona)
– Myan Ruins (Yucatan, Mexico)
– Temple of Amen-Ra (Karnak, Egypt)
Origins Of Astronomy
Other Astrologer-Priests tried to
improve their observations, be more
accurate with their records.
They believed that if they could better
understand these motions, they could
better their predictions for these
events.
Origins Of Astronomy
One such philosopher used records
dating back 800 years and discovered
a periodic cycle for eclipses.
An eclipse should occur every 173
days, yielding an eclipse year every
346 days, completing the entire cycle
every 223 lunar months, or 19 eclipse
years (Saros Cycle).
Early GREEK Astronomy
Thales (624-546 B.C.)
– Rejected mythological explanations for
natural phenomena
– Developed the Saros Cycle
– Correctly predicted the solar eclipse of
585 B.C.
Early GREEK Astronomy
Anaximander (611-547 B.C.)
– Developed a model for the cosmos
– Coined the term “Celestial Sphere”
– Placed the earth at the center
Early GREEK Astronomy
Pythagoras (540-497 B.C.)
– Developed advances in geometry
– Proposed a spherical earth
• Viewing ships sailing over the horizon,
the mast is the last to disappear.
• Sailors view different constellations in
the sky as they sail from south to
north.
Early GREEK Astronomy
Philolaus (470-385 B.C.)
– First proposed ten concentric spheres
on which the sky, planets, moon and
earth revolve around a “central fire.”
Anaxagoras (500-420 B.C.)
– Deduced the true nature of eclipses
– Speculated that the sun was larger than
all of Greece.
Early GREEK Astronomy
Eudoxus (408-355 B.C.)
– Developed a model
representing the motion
of the planets with
combinations of 27
rotating spheres
– Each sphere pivoted
on two opposing points
on the next-inner sphere.
Late GREEK Astronomy
Aristotle (384-322 B.C.)
– Proved the earth to be a sphere
• Viewing the shadow of the earth on
the moon during an eclipse.
Late GREEK Astronomy
Aristarchus of Samos (310-280 B.C.)
– First to calculate and quantify distances
and sizes of the earth, moon, sun, and
celestial sphere.
– Rejected the Geocentric view owing to
the size of the bodies and the vast
distances he calculated.
– Values were far from accurate and
lacked detail; thus, they were rejected.
Late GREEK Astronomy
Eratosthenes (384-322 B.C.)
– First to measure the circumference of
the earth.
s = C_
q 360⁰
q
s
q
Radius, R
Late GREEK Astronomy
Hipparchus (160-127 B.C.)
– Invented and developed trigonometry.
– Devised a system for categorizing stars
by brightness.
– Made extensive observations with great
accuracy.
– Catalogued over 850 stars by position
and brightness
Late GREEK Astronomy
Hipparchus (160-127 B.C.)
– First to observe the precession of the
poles and explained them with eccentric
circles as planetary orbits; thus…
– Agreed with Aristarchus’ heliocentric
view.
– To avoid criticism, he explained the
precession from a geocentric view using
epicycles and deferents.
Late GREEK Astronomy
Claudius Ptolemy (A.D. 90-168)
– Expanded the catalogue of Hipparchus to
1022 stars and agreed with his heliocentric
conclusion.
– Refined Hipparchus’ model of the
Celestial sphere, which became popular
until the time of Copernicus (A.D. 1500).
Late GREEK Astronomy
Claudius Ptolemy (A.D. 90-168)
– Model of the Celestial Sphere. Epicycles
– The deferents explain
retrograde motion of
the planets
Deferents
MIDIEVAL Astronomy
As the Greek civilization declined and
Rome captured Egypt, interest in
science dwindled and died.
Muhammad al Battani (c. A.D.900)
– compiled tables of the positions of the
sun, moon, and planets, recalculated
the precession and predicted eclipses.
MIDIEVAL Astronomy
Arab astronomers introduced Ptolemaic
model of the Celestial Sphere to
European astronomers.
By 1130, European astronomers
understood Ptolemy’s model to be of
“what is” and not of “what is seen”.
MidIEVAL Astronomy
King Alfonso, 1252, supported a tenyear project to calculate predicted
planetary positions. The result were
the Alfonsine Tables, the basis for all
planetary predictions for the next
three centuries
Revolutionary Astronomy
Nicolas Copernicus (1473-1543)
– In 1504, observed a conjunction
between all five known planets –
something the Alfonsine Tables did not
predict.
– Determined the Ptolemaic model was
too complex to produce reliable results.
– Developed a simpler, more reliable
model:
Revolutionary Astronomy
Nicolas Copernicus (1473-1543)
– Developed a simpler model
• Placed the sun at the center of the
celestial sphere.
• Placed the planets, including the earth,
in their correct order from the sun
outward.
• Made the celestial sphere so big, the
distances to the planets was negligible.
Revolutionary Astronomy
Michael Servetus
– Adamantly agreed with Copernicus.
– Burned at the stake in 1533.
Giordano Bruno
– Vigorously defended Copernicus.
– Burned at the stake in 1600.
Revolutionary Astronomy
Tycho Brahe (1546-1601)
– Catalogued nearly 800 stars, their
positions and brightness.
– Catalogued precise positions of the
planets, moon and sun each night from
1576 – 1596.
– viewed positions of seven comets
– viewed a nova (new star) for 16 months.
• It out shined Venus for several weeks.
Revolutionary Astronomy
Tycho Brahe (1546-1601)
– Hired to make observations for King
Frederick II of Denmark.
– Built “Uraniborg” for the purpose of
making very precise, naked-eye
observations.
– Fired by the King’s successor and forced
to move to Prague to study his
observations until the day he died.
Revolutionary Astronomy
Johannes Kepler (1571-1630)
– Studied Tycho’s data after Tycho died
– Tried to fit the data to many versions of
the Ptolemaic model.
– Found the data to fit closely to the
Copernican model.
– Developed 3 laws describing the motions
of the planets:
Revolutionary Astronomy
Johannes Kepler (1571-1630)
– Developed 3 laws describing the motions
of the planets
Plane of
• Law of Ellipses – Every planet
Earth’s
orbit
moves around
the sun in an
star
elliptical orbit
Orbital
Planet
(near circular
Orbit
Radius
oval) with the
Planet
sun at one focus.
Revolutionary Astronomy
Johannes Kepler (1571-1630)
– Developed 3 laws describing the motions
of the planets
• Law of Areas – A line drawn from
the sun to a
r A1
planet will
star
sweep out equal
A1 = A2
areas of space
A2
in equal times.
Planet
Revolutionary Astronomy
Johannes Kepler (1571-1630)
– Developed 3 laws describing the motions
of the planets
• Law of Harmony – The ratio of the cube
of the average orbital radius to the
square of its period is a constant.
T2 = K
a3
• More on this later.
Revolutionary Astronomy
Galileo Galilei (1564-1647)
– Agreed with Aristotle’s principles of
mechanics, but set out to prove them
experimentally
– Pointed the telescope to the stars and
found evidence to prove Aristotle’s
Celestial mechanics was flawed.
• Viewed lines on Mars, “ears” on Saturn,
moons orbiting Jupiter, spots on the sun,
mountains and depressions on moon.
Revolutionary Astronomy
Isaac Newton (1643-1727)
– Developed 3 laws to explain all motion
– Developed the universal law of gravity
• Proved that the force that pulls an
apple to the ground is the same force
that keeps the moon in orbit.
• Provided the explanation for Kepler’s
Laws that Kepler lacked.
RENAISENCE Astronomy
Edmund Halley (1656-1742)
– Expanded the use of Newton’s Laws
and Kepler’s Laws to comets.
– Published data on 24 comets, noting
that three were so similar they had to be
the same comet.
– Predicted it reappearance in 1758.
– George Palitzsch identified the comet in
its predicted position in 1758.
RENAISENCE Astronomy
Johann Bode (1747-1826)
– Popularized a relationship between the
planets and their relative distances from
the sun.
• Begin with a series of 4’s – one for
each planet
• add to each 4 the corresponding number
in the sequence 0, 3, 6, 12, 24, 48, 96...,
then divide the result by ten.
RENAISENCE Astronomy
Johann Bode (1747-1826)
– Popularized a relationship between the
planets and their relative distances from
the sun.
Planet # 1
2
3
4
5
6
7
8
4
4
4
4
4
4
4
4
+ 0
3
6 12 24 48 96 192
4
7 10 16 28 52 100 196
RENAISENCE Astronomy
Johann Bode (1747-1826)
– Popularized a relationship between the
planets and their relative distances from
the sun.
Planet # 1
2
3
4
5
6
7
8
4
7 10 16 28 52 100 196
10 10 10 10 10 10 10 10
Dist. = 0.4 0.7 1.0 1.6 2.8 5.2 10.0 19.6
Mer. Ven. Earth Mars
Jup.
Sat.
RENAISENCE Astronomy
Giuseppe Piazzi (1746-1826)
– Discovered the “missing planet” from
Bode’s Rule (1851). Its orbit was
between Mars and Jupiter.
– Named it Ceres.
– Many others were discovered (110 by
1900), and the “missing planets” formed
a ring of “minor planets”.
– Now over 650,000 minor planets.
RENAISENCE Astronomy
William Herschel (c.1738-1822)
– Discovered Uranus (1781) while making
deep sky observations; called it
“Georgian Star”.
– Mapped the “universe” (1790).
• disk-shaped
• Stars at varying distances from our own
• The sun was at the center.
– Called the “Minor Planets” asteroids.
RENAISENCE Astronomy
John Couch Adams (1819-1892)
– Using the data on the orbit of Uranus,
applications of Newton’s Laws and
discrepancies from Bodes’ Rule,
predicted the existence of another planet.
– Planet later discovered by Galle (1846)
and was named Neptune.
MODERN Astronomy
JC Kapteyn (c.1910)
– expanded the size of Herschel’s universe
to about 55,000 ly.
Harlow Shapley (c.1920)
– expanded the size of Herschel’s universe
to about 300,000 ly.
HP Robertson (c.1924)
– placed the sun away from the center of
the galaxy.
MODERN Astronomy
Edwin Hubble (c.1925)
– Proved the existence of objects beyond
our own galaxy.
• Viewed 45,000 other galaxies, which
were at such tremendous distances
away from the near-by stars.
• Measured their velocities and
determined them to be expanding
away from a common center.
MODERN Astronomy
Clyde Tombaugh (c.1930)
– Using the data on the orbit of Neptune,
applications of Newton’s Laws and
discrepancies from Bodes’ Rule,
predicted the existence of another
planet.
• Called the planet Pluto.
ASTRONOMY
ORBITAL MECHANICS