Download History of Astronomy Notes

Babylonians (~2000 BC under Hammurabi, well
documented by 1800 B.C.)
 Created the earliest known astrological system
People who learned how to use this system became known as Magi
(wise men), which is where we get our word “magic”.
TRADITIONAL
ASTROLOGICAL DATES
Constellation
Date Span
Days
ACTUAL ASTRONOMICAL DATES
TODAY (c. 2000 C.E.)
Constellation
Date Span
Days
Aries
21 Mar - 19 Apr 30
Aries
19 Apr - 13 May 25
Taurus
20 Apr - 20 May 31
Taurus
14 May - 19 Jun
37
Gemini
21 May - 20 Jun 31
Gemini
20 Jun - 20 Jul
31
Cancer
21 Jun - 22 Jul
Cancer
21 Jul - 9 Aug
20
Leo
23 Jul - 22 Aug 31
Leo
10 Aug - 15 Sep
37
Virgo
23 Aug - 22 Sep 31
Virgo
16 Sep - 30 Oct
45
Libra
23 Sep - 22 Oct 30
Libra
31 Oct - 22 Nov
23
Scorpio
23 Oct - 21 Nov 30
Scorpius
23 Nov - 29 Nov 7
Ophiuchus
30 Nov - 17 Dec 18
32
Sagittarius
22 Nov - 21 Dec 30
Sagittarius
18 Dec - 18 Jan
32
Capricorn
22 Dec - 19 Jan 29
Capricornus
19 Jan - 15 Feb
28
Aquarius
20 Jan - 18 Feb 30
Aquarius
16 Feb - 3/11
24-25
Pisces
19 Feb - 20 Mar 30-31
Pisces
12 Mar - 18 Apr
38
Aristotle (384-322 BC)
Considered the greatest general authority in antiquity. Aristotle wrote about virtually everything known at his time.
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Crystalline concentric spheres (spheres within spheres)
Geocentric and Geostatic. The Earth was a sphere, fixed and
unmoving at the center of the Cosmos because it was too big to move
in any way.
All other spheres were in unceasing, uniform circular motion
because the Heavens are naturally “perfect”. (No speeding up or
slowing down, no changing directions, etc.)
Comets, “shooting stars”, etc, must be “terrestrial” phenomena
because the heavens are perfect.
Eratosthenes (~240 BC)
 Calculated circumference of earth using shadows and proportions.
Claudius Ptolemais (Ptolemy - c. 150 AD)
Astronomer and Geographer based at Alexandria, a colonial outpost of the Roman Empire at the time. Wrote the Mathematical
Syntaxis (called the Almagest in Arabic).
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Ptolemy introduced the Epicycle, “circles on circles” to explain
changes in observed speed and especially retrograde motion.
Epicycle demonstrating retrograde motion
Successes of Ptolemy’s System :Epicycles
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Explains retrograde motion.
Explains apparent changes in brightness for some planets.
Explains some of the observed non-uniform motions of the Sun,
Moon, and Planets.
Can fine-tune the model by adding epicycles.
Failures of Ptolemy’s System: It was really, REALLY complicated.
 Had to introduce the “Equant” and the “Eccentric Deferent” in
order to preserve the appearance of circular motion.
Nicolaus Copernicus (1473-1543)
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The Sun, not the Earth, is at the center.
The Earth rotates around its axis, producing the daily motions of
celestial bodies.
The Earth revolves (orbits) around the Sun, producing the annual
motions.
Tycho Brahe (1546-1601)
 Built giant astronomical
instruments to record the
movement of stars and
planets.
 Collected 20 years of very
precise data on over 700
stars within 1-2 arcminutes
of precision
 Left his data to his assistant,
KEPLER, after he died.
Johannes Kepler (1571-1630)
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Had a genius for analyzing data.
Created the first 3 laws governing celestial motion.
1. The Law of Elliptical Orbits
2. The Law of Equal Areas
3. The Law of Distance and Orbital Period
The 1st Law of Planetary Motion
The orbits of the planets are ellipses with the Sun at
one focus.
Click on the image to view full size (8Kb)
The 2nd Law of Planetary Motion
The line joining the Sun and the planet sweeps out
equal areas in equal times.
Click on the image to view full size (10Kb)
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Planets move fastest at Perihelion (closest to the Sun)
Planets move slowest at Aphelion (farthest from the Sun)
The 3rd Law of Planetary Motion
The square of a planet's orbital period is proportional to the cube of the orbital
radius.
Expressed Mathematically:
T 2 α r3
where P is the planet's orbital period measured in years, and r is the radius along the semimajor
axis of the planet's orbit measured in AUs.
Kepler's Third Law applied to the Planets
Planet
r (AU)
P (yr)
Mercury 0.3871 0.2408
r3
P2
P2/r3
0.0580
0.0580
1.0000
Venus
0.7233 0.6152
0.3785
0.3785
1.0000
Earth
1.0000 1.0000
1.0000
1.0000
1.0000
Mars
1.5237 1.8808
3.5373
3.5376
1.0001
Jupiter 5.2034 11.8626 140.8810 140.7216 0.9989
Saturn 9.5371 29.4475 867.4510 867.1551 0.9997
The Third Law applies to all bodies orbiting the Sun: planets, comets, rocks, &
spacecraft!
Galileo Galilei (1564-1642)
Galileo Galilei was the first modern astronomer.
Galileo made his own telescope based on a description
he heard in 1609.
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His was better than the original.He solved many technical problems, and came up with a design that
produced good-quality images with a magnifying power of 20x.
This is printed in 8 pt type.
20 x
With his telescope, Galileo found
1) Found craters and mountains on the Moon:
https://pauljwillett.files.wordpress.com/2014/10/img_1873-small.jpg
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Moon was not a smooth, perfect sphere as taught by the Aristotle and Ptolemy.
Surface was "... rough and uneven, and just like the surface of the Earth itself..."
Galileo was able to measure the heights of lunar mountains using their shadows.
Conclusion: The Moon was another world like the Earth.
2) Galileo noted spots on the rotating Sun:
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Bright surface of the Sun had dark spots (imperfections) that changed and moved across its surface.
Observed solar rotation.
Conclusions: The sun is huge, imperfect and rotating. If the sun rotates, why not the Earth?
3) Galileo discovered 4 moons orbiting Jupiter:
Conclusion: The Earth is not the center of all motion in the Universe.
4) Venus goes through phases like the Moon:
Order of phases and change in diameter proved conclusively
that Venus orbited the Sun. Ptolemaic theory predicted the
opposite behavior.
Conclusion: The Sun was also a center of motion.
Eppur si muove (and still, it moves)
Galileo died, blind and under house arrest, on January 8, 1642.
On Christmas Day of that same year, Isaac Newton was born in Woolsthorpe England.
Isaac Newton (1642-1727)
“If I have seen farther than other men, it is because I have stood on the shoulders of giants.”
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Invented the integral and differential calculus.
Developed the binomial theorem.
Started fundamental work on optics. (Named the colors of the rainbow.)
Formulated his laws of motion & gravitation.
Did not discover gravity. Discovered the mathematical formula describing gravity and proved it was universal.
Universal Law of Gravitation
Anything, anywhere in the universe
is attracted to
every other thing, everywhere in the universe.
F = G m1 m2 / d2
Inverse squared law
G = 6.67 x 10-11 N (m/kg)
Albert Einstein (1879-1955)
Revolutionizes astronomy with General Theory of Relativity which
re-defines gravity: Gravity is a curve in space.
Speed of light is the universal speed limit, and gravity bends space
and time!
https://www.youtube.com/watch?v=4yyb_RNJWUM
Edwin Hubble (1889-1953)
Discovered the first galaxy outside our own.
Georges Lemaitre (1894-1966)
Belgian Jesuit Priest & astronomer/physics professor
Big Bang Theory
https://www.youtube.com/watch?v=xhLQ_b3bKdI
Discovered evidence of Expanding Universe.
(Doppler shifts)
Neil Tyson De Grasse, 1958 -
Carl Sagan, 1934-1996
Stephen Hawking, 1942 -
Determined temp of surface of planets.
Worked with NASA to land probes.
Promoted Nuclear Winter Theory and
published claims that Kuwait Oil Fires
would create temporary global cooling.
Hawking Radiation from black holes
Popular figures that promoted astronomy