The History of Astronomy
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The History of Astronomy
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The History of Astronomy. A Grand Tour of the Heavens. Measurements Scientific Notation How big is…? Scientific Method. Measuring Things. For us to communicate “how much” something is, we must use units. - PowerPoint PPT Presentation
Transcript of The History of Astronomy
The History of Astronomy
A Grand Tour of the Heavens
MeasurementsScientific Notation
How big is…?Scientific Method
Measuring Things
• For us to communicate “how much” something is, we must use units.
• What if I were to offer a job to you that pays an annual salary of 60,000 per year? Would you accept the job?
• Three fundamental units used in the SI system (SI is the most common system of units used in science)– unit of mass, kilogram (kg)– unit of distance, meter (m)– unit of time, second (s)
Prefixes
prefix meaning power of 10
micro one-millionth 10-6 1/1,000,000
milli one-thousandth 10-3 1/1000
centi one-hundredth 10-2 1/100
kilo one thousand 103 1000
mega one million 106 1,000,000
giga one billion 109 1,000,000,000
tera one trillion 1012 1,000,000,000,000
Scientific Notation
• There is an easier way to express numbers so that we don’t have to count all those digits and commas.
9850 kg = 9.85 x 103 kg = 9.85 x 106 g
299,792, 458 m/s = 2.99792458 x 108 m/s
384,403 km = 3.84403 x 106 km = 3.84403 x 109 m
• The mass of the earth is 5.97 x 1024 kg. Do you really want to write that number without using scientific notation?
Mass
• a measure of inertia (how much net force is needed to accelerate an object)
• independent of location in the universe• a measure of how much “stuff” an object is
made of and what kind of “stuff” it’s made of; it depends on the atomic composition of which an object is made
Powers of Ten
The following 9 minute video was made in 1968.
Yes, that may seem old, but it gives us a great perspective on the limits of our Universe.
Mass and Weight
• mass is NOT the same thing as weight!– near a large body such
as a planet or moon or star, w = mg where g is the local acceleration due to gravity.
– g depends on the mass of the large body
Bodyg
(m/s2)weight
(N)weight(lbs)
Earth 9.8 800 180
Moon 1.6 130 29
Jupiter 25 2050 460
Mars 3.7 300 67
Pluto 0.1 8 1.8
Masses of a few common objects
Object mass (kg)
1 liter of water 1
Earth 5.97 x 1024
Moon 7.36 x 1022
Sun 1.99 x 1030
me 90
universe ~1050
hydrogen atom 1.67 x 10-27
Distance
• “how far” one point is from another point.• need to define the two points
– distance of the center of the moon from the center of the earth
– distance of the center of the moon from the center of the sun
• need a standard– a meter, as defined by the length of a meterstick, is too
arbitrary– a meter should be based on another unchanging and
unarbitrary value.
What about Light?
• Albert Einstein made a presupposition that the speed of light is the same in all reference frames (i.e. no matter how fast you are traveling and no matter what direction you’re traveling in, you will measure the same value for the speed of light).
• Einstein also proposed that nothing travels faster than the speed of light in a vacuum.
• The speed of light is a universal speed limit!• The speed of light is a universal constant!
c
• c = 299,792,458 m/s and is DEFINED to be this value.
• Therefore, in one second, light travels 299,792,458 meters.
• 1 m = the distance light travels in 1/299,792,458 second
Light Year (ly)
• 1 light year is the distance light travels in one year.
• 1 ly = 9.46 x 1015 m• It takes about 8.3 minutes for light from the
Sun to reach Earth.
distance to the Sun / speed of light = 500 seconds = 8.3 minutes
The Second
• Throughout history, time has been measured in various ways.
• Astronomy has long been important in defining time.• A month was originally measured by lunar phases, the day
is measured by the earth’s rotation about its axis, and the year is measured by the earth’s motion about the sun.
• A day is broken into hours, hours into minutes, and minutes into seconds.
• But what are some problems with using this method to define a second?
The Second
• The time duration for Earth to rotate once about its axis (a day) is not necessarily constant. Earth’s rate of rotation is slowing down.
• A day cannot be measured as precisely as we would like.• We now define a second in terms of the frequency of the
light emitted by excited electrons in cesium atoms. The electrons emit light at a frequency of 9,192,631,770 Hz. Thus, one second is the time required for this light to make 9,192,631,770 oscillations. The official clock of the United States is the cesium fountain clock, NIST-F1, at NIST.
• The uncertainty of NIST-F1 is so low that it will neither gain nor lose a second in 20 million years!
• http://leapsecond.com/great2005/tour/
The Nature of Science
• Science is the systematic enterprise of gathering knowledge about the world and organizing and condensing that knowledge into testable theories.
• You will notice four important things in this definition– observing (i.e. experimenting)– developing a model for understanding and predicting– testing the model– doing this in a systematic way
History of Astronomy
Five Eras of Astronomy
• Ancient (Dawn of History to fall of Roman Empire ~ 5th Century)
• Medieval (5th to 15th Century)
• Renaissance (Copernican Revolution to middle of 17th Century)
• Modern(Newton’s Gravitation to end of 19th Century)
• 20th Century and Beyond(Einstein’s relativity until now)
Ancient Astronomy
• Primitive Astronomy
– Sun, Moon, and changing seasons observed and studied.
– Belief that the Earth was flat.
– Solid Earth with a watery underworld.
Ancient Astronomy
• Babylonians and Chaldeans
– First to study skies and associate legends and myths.
– The quest for divine knowledge developed astrology.
Ancient Astronomy
• The Chinese– First to take records
of observations– Understanding was
lacking
Ancient AstronomyStonehenge (2000 B.C.)
Ancient Astronomy
• Eratosthenes of Cyrene (now Shahhat, Libya) measures the circumference of the Earth with extraordinary accuracy by determining astronomically the difference in latitude between the cities of Syene (now Aswan) and Alexandria, Egypt.
Ancient Astronomy
• Greeks– Thought Earth was flat with a rotating
crystalline sphere above.– Anaximander was first philosopher to
suggest a round Earth to explain effects of the horizon.
– Plato and Aristotle furthered the idea of a spherical Earth using lunar eclipse observations.
Ancient Astronomy
– Ariatarchus proposed that the Earth was not the center of the Universe, but was not accepted because it made the Earth inferior.
– Hipparchus catalogued over 100 stars noting position and motion.
– Ptolemy was an Earth-centered (geocentric) man.
• Epicycles described variation in motions. Explains retrograde.
• System became part of the church doctrine.
Medieval Astronomy
• Status Quo• Observations, data collections, better
estimations of size.
Renaissance
• 1473, Copernicus was born.– Tried to prove Ptolemy’s system that seemed to
have a few inaccuracies.– Determined that it was truly a heliocentric solar
system.– Knew ideas would not be accepted by church so
waited until the year he died (1543) to publish.
Renaissance
• Tycho Brahe– Danish astronomer, born in 1546– Enormous amounts of data and observations
made.– Lost nose in a duel with a fellow student.– Believed in geocentric theory.– After he died, his assistant looked through
all his work, Johannes Kepler.
Renaissance
• Kepler– All data fit the
heliocentric theory– Three laws of
planetary motion revolutionizing astronomy
First Law: all orbits are elliptical
Second law: a line that connects a planet to the sun
sweeps out equal areas in equal times.
Third law: the square of the period of any planet is
proportional to the cube of the semi-major axis of its orbit.
Renaissance
• Galileo Galilei, born 1564
– Conflict with church
– Used telescopes to look at Moon, Venus, Sun, and Jupiter
– Forced to recant his view by the church.
Modern Astronomy
• Sir Isaac Newton– Laws of
Gravitation, Physics, Mathematic
– Principia Mathematica
Modern Astronomy
– Halley predicts return of comet– Charles Messier catalogs– Herschel discover Uranus (1784)– First dwarf planet discovered, Ceres– Galle found discovered Neptune (1846)– Telescope advancement.
20th Century Astronomy
– New theories of gravity– Flight– Edwin Hubble proves galaxies besides our
own and discovers the universe is expanding.
20th Century Astronomy
– Artificial satellites– Manned space flight– Man on Moon– Space Exploration (probes to Moon and solar
system objects)– Hubble Space Telescope (1986)– Discovery of dark energy (1999)
20th Century Astronomy– Current missions: Curiosity (Mars rover), Opportunity (Mars rover), Voyager 1 & 2 (leaving solar system), New Horizons (Pluto in 2015), Dawn (asteroids Vesta and Ceres), Cassini (Saturn), Kepler (exoplanets), Chandra (X-ray sources), Herschel (infra-red sources), Mars Odyssey (Mars orbiter), Mars Reconnaissance Orbiter (Mars), Messenger (Mercury), GALEX (x-ray sources), Juno (Jupiter bound), Planck (microwave sources), Spitzer (infrared sources), SOHO and STEREO (Sun) and… a multitude of Earth-orbiting satellites.
21st Century Astronomy…?????
20th+ Century Astronomy
Lake Mary High School
Astronomy Class
Three Cool Dudes & a Comet
