Starry Monday at Otterbein Astronomy Lecture Series -every first Monday of the month- May 2, 2005 Dr. Uwe Trittmann Welcome to

Today’s Topics The Night Sky in May History of Astronomy

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The Night Sky in May The sun is getting higher -> shorter nights! Virgo contain lots of galaxies, Hercules some of the best globular star clusters Jupiter is bright, Saturn sets early

Moon Phases Today (Waning crescent, 33%) 5 / 8 (New Moon) 5 / 16 (First Quarter Moon) 5 / 23 (Full Moon) 5 / 30 (Last Quarter Moon)

Today at Noon Sun at meridian, i.e. exactly south

10 PM Typical observing hour, early May no Moon Pluto Jupiter Saturn

South Virgo and Coma with the Virgo-Coma galaxy cluster

Virgo- Coma Cluster Lots of galaxies within a few degrees

M87, M88 and M91

Zenith Big Dipper points to the north pole

East –Hercules –Corona Borealis –Bootes Globular Star Clusters: M 3 M 13 M 92

M13: Globular Cluster

South- West Spring Constellations - Cancer - Leo - Hydra Deep Sky Objects: - Beehive Cluster (M44)

A Short History of Astronomy Ancient (before 500 BC) Egyptians, Babylonians, Mayans, Incas, Chinese Classical Antiquity (500 BC-500 AD) Greeks, Romans: Plato, Aristotle, Ptolemy Middle Ages ( AD) Arabic astronomers Renaissance ( AD) Copernicus Baroque ( AD) Brahe, Kepler, Galilei, Newton

Ancient Astronomy Stonehenge, England Pyramids, Gizeh near Cairo, Egypt

The Babylonians Made systematic measurements as early as ~2000 BC By ~ 800–400 BC –State support for the calendar and astrology –Compiled the first star catalogs and began long- term records of planetary motions –Were able to predict lunar and solar eclipses May also have invented astrology

The Greeks Plato (428 BC) Introduces the celestial sphere. The stars are fixed to a sphere that rotates around the Earth introduces prejudice in favor of circles values theory over observation

The Greeks Aristotle (384–322 BC) –Argued that the planets move on spheres around the Earth (“geocentric” model) –Argues that the earth is spherical based on the shape of its shadow on the moon during lunar eclipses Aristarchus (310–230 BC) –Attempts to measure relative distance and sizes of sun and moon –Proposes, nearly 2000 years before Copernicus, that all planets orbit the Sun, including the Earth (“heliocentric” model)

The Greeks Eratosthenes (ca. 276 BC) –Measures the radius of the earth to about 20% (Works also between Detroit and Columbus)

The Greeks Hipparchus (~190 BC) –His star catalog a standard reference for sixteen centuries! –Introduces coordinates for the celestial sphere: Declination (dec) Right Ascension (RA) (analogous to latitude and longitude, respectively)

Ptolemy (~140 AD) Puts forth a complete geocentric model dominates scientific thought during the Middle Ages Longest lasting (wrong) theory ever: 1000 yrs Major Work: Almagest

Retrograde Motion

Epicycles Ptolemy’s explanation of retrograde motion About 40(!) epicycles necessary to explain all observations  complicated theory

The Medieval Setting Dominant Church 1000 years of relative stagnation Experimental research greatly reduced To answer a question: “Study the Bible or Aristotle!”

The Renaissance Setting Invention of the print (1450) by Gutenberg  Books widely available! (Think: Manuscripts vs Amazon.com ) End of Middle Age Church Domination Back to the roots (renaissance=rebirth) Study of Arabic astronomers Intellectual movement

Nicolas Copernicus (1473–1543) Rediscovers the heliocentric model of Aristarchus Planets on circles  needs 48(!!) epicycles to explain different speeds of planets Not more accurate than Ptolemy Major Work : De Revolutionibus Orbium Celestium (published posthumously)

The heliocentric Explanation of retrograde planetary motion See also: SkyGaze

The Scientific Method Systematized by Francis Bacon, Descartes and Galileo in the 17 th century Not the only way of knowing, but a very successful one A method to yield conclusions that are independent of the individual Conclusions are based on observation

Rene Descartes – The Rationalist Described the method to do science, known for his mind-body dualism Major Works: Discourse (1637) [full title: Discours de la méthode pour bien conduire sa raison et chercher la vérité dans les sciences, Discussion of the method for correct reasoning and for searching the truth in the sciences.] Meditations on first Philosophy (1641) Rene Descartes ( )

Rene Descartes’ Discourse Describes the method to do science in a straightforward way (see below) Major points: Science must be based on correct reasoning (logic) Science must be formulated in mathematical language Starting line: “Good sense is the most evenly distributed thing in the world, for all people suppose themselves so well provided with it that even those who are the most difficult to satisfy in every other respect never seem to desire more than they have.”

A Classical Example Aristotle observes that during lunar eclipses the Earth’s shadow on the moon is curved He assumes it will be curved for all eclipses A hypothesis that explains this: the earth is round A prediction of this theory is that the location of the stars in the sky should be different for observers at different latitudes This is confirmed by additional observations –E.g. Canopus is visible in Egypt but not further north

Scientific Theories Must be falsifiable –There must be some way the theory could fail Should make predictions –The more, the better! Theories that are very well tested and have the widest applicability are often known as “laws of nature” Always subject to revision or modification Occam’s Razor

Performing Experiments Experiments must be repeatable – requires careful control over variables Possible outcomes of an experiment: –The experiment may support the theory We then continue to make predictions and test them –The experiment may falsify the theory We need a new theory that describes both the original data and the results of the new experiment Since we cannot do every possible experiment, a theory can never be proven true; it can only be proven false

The Baroque Setting In the 1600s church through counter- reformation much stricter G. BRUNO (Italian; 1548) proposes that the Sun is just one star out of an infinite number  burned at the stake for heresy Years War ( ) between religions New inventions: telescope, air pump, etc.

Tycho Brahe – The Data Taker Key question: Where are things? Catalogued positions of planets in Uraniborg and Prague Working without telescope Data ten times as accurate as before Died at banquet binge drinking Tycho Brahe (1546–1601)

Tycho Brahe collects detailed and accurate (1-2’ accuracy) observations of stellar and planetary positions over a period of 20 years His research costed 5-10% of Danish GNP shows that comets and novas are extralunar contrary to Aristotle Shows that stars can change (Supernova of 1572) Tycho Brahe observing

Johannes Kepler–The Phenomenologist Key question: How are things happening? Major Works: Harmonices Mundi (1619) Rudolphian Tables (1612) Astronomia Nova Dioptrice Johannes Kepler (1571–1630)

Kepler’s Beginnings Astrologer and Mystic Tried to find “music in the skies” Tried to explain distances of the 5 known planets by spheres resting on the 5 mathematical bodies  pre-scientific

Johannes Kepler Manuscript: trying to disentangle The mystery of Mars’ orbit 

Kepler’s First Law The orbits of the planets are ellipses, with the Sun at one focus

Ellipses a = “semimajor axis”; e = “eccentricity”

Conic Sections From Halley’s book (1710)

Kepler’s Second Law An imaginary line connecting the Sun to any planet sweeps out equal areas of the ellipse in equal times

Kepler’s Third Law The square of a planet’s orbital period is proportional to the cube of its orbital semi-major axis: P 2  a 3 a P Planet Orbital Semi-Major AxisOrbital Period Eccentricity P 2 /a 3 Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto (A.U.)(Earth years)

Galileo Galilei – The Experimentalist Did experiments (falling bodies) rather than studying Aristotle Major Works Siderius Nuntius (1610) Dialogue concerning the Two Chief World Systems (1632) The latter discusses Copernicus vs Ptolemy  ban by Church (1633) –revoked by pope 1992 (1564–1642)

Siderius Nuntius (1610) Dialogo (1632)

Galileo Galilei (1564–1642) Astronomical observations that contradict Aristotle: –Observed mountains on the Moon, suggesting that the Earth is not unique –Sunspots; suggests that celestial bodies are not perfect and can change –Observed four moons of Jupiter; showed that not all bodies orbit Earth –Observed phases of Venus (and correlation of apparent size and phase); evidence that Venus orbits the Sun Also observed –the rings of Saturn –that the Milky Way is made of stars

Phases of Venus Heliocentric (observed) Geocentric (not observed)

Isaac Newton – The Theorist Key question: Why are things happening? Invented calculus and physics while on vacation from college His three Laws of Motion, together with the Law of Universal Gravitation, explain all of Kepler’s Laws (and more!) Isaac Newton (1642–1727)

Major Works: Principia (1687) [Full title: Philosophiae naturalis principia mathematica] Opticks [sic!] (1704) Major findings: – Three axioms of motion –Universal gravity

Law of Universal Gravitation Force = G M earth M man / R 2 M Earth M man R

Orbital Motion

Cannon “Thought Experiment” ets/newt/newtmtn.htmlhttp:// ets/newt/newtmtn.html

Mark your Calendars! Next Starry Monday at Otterbein: June 6, 2005, 7 pm (this is a Monday ) Web pages: – (Obs.) – (Physics Dept.)

Mark your Calendars II Physics Coffee is every Wednesday, 3:30 pm Open to the public, everyone welcome! Location: across the hall, Science 256 Free coffee, cookies, etc.