foundations of astronomy the scientific method-winning...
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Foundations of AstronomyFoundations of AstronomyThe scientific methodThe scientific method--winning or winning or
losing?losing?•Geodorno Bruno•Warned to stop teaching “heretical” sun-centered solar system of Copernicus.•Failed to heed church warnings during inquisition…•Was burned at the stake for continuing to teach earth orbited the sun.
Reasons for early interestReasons for early interestStars as navigational aids.Stars as navigational aids.Mediterranean traders could sail to correct Mediterranean traders could sail to correct latitudelatitude…….Using north star as a guide.Using north star as a guidethen sail east or west at the same latitude until they then sail east or west at the same latitude until they spotted familiar landmarks. spotted familiar landmarks.
Altitude of PolarisAltitude of PolarisNote: the altitude of Polaris above the horizon equals Note: the altitude of Polaris above the horizon equals the observers latitude. the observers latitude. Here is Polaris as seen from San Francisco, latitude 37 Here is Polaris as seen from San Francisco, latitude 37 degrees.degrees.
Astrological and religious beliefs Astrological and religious beliefs
image from: http://www.kprf.ru/clipart/misc/astrology.jpg
We are connected to the stars
The sun does appear in front of the zodiacal constellations
Humans were a bit confused about the other details till recently!
Precession of the EquinoxesPrecession of the Equinoxes• The Earth’s axis precesses (wobbles) like a top, once about every 26,000 years.• Precession changes the positions in the sky of the celestial poles and the equinoxes. ⇒ Polaris won't always be the north star.⇒ The spring equinox, seen by ancient Greeks in Aries, moves westward and is now in Pisces!
Need for a Calendar Need for a Calendar
especially related to agriculture.
When to Plant? When to Harvest? When to Migrate?
The Nile Flood was an especially important, yearly event.
The Search for Meaning…
• With no street lights and no alarm clocks…• The Night sky was a great glowing
question…• Who are we? (no answer yet?)
• Why are we here (not clear on that one either…?)
• Where are we?• Humans have been working on that one
for a long time!
Early CosmologyEarly Cosmology
models of the relation between the Earth and Celestial bodies
How to explain the observations?
Why did some celestial objects move on the celestial sphere?
Why did most celestial objects stay in their places?
Retrograde MotionRetrograde Motion
Like the Sun, planets usually Like the Sun, planets usually appear to move eastward appear to move eastward relative to the stars.relative to the stars.But as we pass them by in But as we pass them by in our orbit, they move west our orbit, they move west relative to the stars for a few relative to the stars for a few weeks or months.weeks or months.Noticeable over many nights; Noticeable over many nights; on a single night, a planet on a single night, a planet rises in east and sets in rises in east and sets in westwest……
29 Images of Mars taken one week apart (Tunc Tezel, apod060422)
The The ““rationalistsrationalists”” of Greeceof Greece
Plato (428Plato (428--348 BC)348 BC): Heavens were perfect and that the most : Heavens were perfect and that the most perfect geometric object was the circle. perfect geometric object was the circle.
Socrates (469Socrates (469--399 BC)399 BC)——form and perfectionform and perfection
Plato’s ideas derived from Socrates study of forms…
image of "Plato" a Plate, from: http://www.vidrioyarte.com/proddos.htm
AristotleAristotle (384(384--322 BCE)322 BCE)
Plato's student Plato's student ––founded founded Lyceum in AthensLyceum in AthensPrivate Tutor to Private Tutor to Alexander the GreatAlexander the GreatAristotle's interest didnAristotle's interest didn’’t t end with astronomy! end with astronomy!
Image from: http://clendening.kumc.edu/dc/pc/Aristotle.jpg
Aristotle Favored "GeoAristotle Favored "Geo--Centric" Centric" model of the Universe. model of the Universe.
Why?Why?Evidence and Logic! Evidence and Logic! Observed no stellar parallaxes Observed no stellar parallaxes no winds no winds spinning Earth would hurl its inhabitants into spinning Earth would hurl its inhabitants into space. space. Had Pre Galilean/Newtonian view of Motion. Had Pre Galilean/Newtonian view of Motion. DidnDidn’’t have t have ““privilegedprivileged”” view of Earthview of Earth
Parallax AngleParallax AngleApparent shift of a star’s position due to the Earth’s orbiting of the Sun
The nearest stars are much farther away than the Greeks thought.
So the parallax angles of the star are so small, that you need a telescope to observe them.
Aristotle got some things correct!
••demonstrated that the Earth demonstrated that the Earth was spherical:was spherical:••Earth's shadow on the moon Earth's shadow on the moon was always circular was always circular
Practice Quiz
1. Who was the only astronomer executed for teaching what he believed was true?
2. What did he teach?3. For a person traveling the globe, what
does the altitude of Polaris tell them?4. List two other reasons why ancient
people were interested in the motions of the stars and planets
Practice Quiz continued
5. What is the term describing the apparent “backward” motion of a planet on the celestial sphere? Draw a picture illustrating this phenomena.
6. Describe in one sentence what shapes Plato favored for describing orbital motion and why he favored them
7. List Three things Aristotle is famous for
Practice Quiz-last page!
8. List one reason why Aristotle favored a geocentric model—explain his reasoning in one sentence
9. List another reason why Aristotle favored a geocentric model—explain his reasoning in one sentence
10. Describe one thing Aristotle was correct about!
Quiz answers1. Who was the only astronomer executed for teaching
what he believed was true? Geodorno Bruno2. What did he teach? The Heliocentric Model (Helios =
sun) 3. For a person traveling the globe, what does the altitude
of Polaris tell them? Their latitude! 4. List two other reasons why ancient people were
interested in the motions of the stars and planetsNavigation, As a calendar for Agriculture, Astrology,
Religion
Answers continued5. What is the term describing the apparent “backward”
motion of a planet on the celestial sphere? Draw a picture illustrating this phenomena. Retrograde motion
6. Describe in one sentence what shapes Plato favored for describing orbital motion and why he favored them. Regular geometric solids (platonic solids), especially the sphere because heavens are perfect, and the higher the symmetry, the more perfect a shape is. (…wait till you meet Kepler)
7. List things Aristotle is famous for Theory of motion, bio-medicine, Geocentric Model (including epicycles), proof that the Earth is round, and many more…
And more answers…8. List one reason why Aristotle favored a
geocentric model—explain his reasoning in one sentence: no parallax of stars, no winds, not flung off earth..didn’t have modern concept of inertia, gravity, and distance to stars.
9. List another reason why Aristotle favored a geocentric model—explain his reasoning in one sentence..pick from above
10. Describe one thing Aristotle was correct about! Demonstrated that the Earth was round by shadow on Moon during eclipse.