Drew astronomy chap 4

Sun spot

discovered by Galileo, proving the sun is not perfect

Galielo's observations of the gibbous phase of Venus proved

that Venus orbits the sun

Planets move around the sun on ___ paths, with ___ velocities.

Elliptical; non-uniform

Eudoxus

(409 - 356 B.C.): Model of 27 nested spheres

A line from ___ to ___ sweeps over equal areas in equal intervals of time.

A planet; the sun

Almagest (Ptolemy)

2nd-century Greek-language mathematical and astronomical treatise on the apparent motions of the stars and planetary paths

Aristotle

384 - 322 B.C.), major authority of philosophy until the late middle ages: Universe can be divided in 2 parts: Imperfect, changeable Earth, Perfect Heavens. He expanded Eudoxus' Model to use 55 spheres.

Stonehenge

Alignments with locations of sunset, sunrise, moonset and moonrise at summer and winter solstices

Winter Solstice

December 22, when the sun is at its southernmost point (newgrange, Ireland, may have been a temple)

Ptolemy

Further refinements, including epicycles

Moons of Jupiter

Galileo discovered; Io, Europa, Ganymede, Callisto

Phases of Venus

Galileo's observations of phases of Venus prove that it orbits the Sun and not Earth.

Tycho Brahe (1546-1601)

High precision observations of the positions of stars and planets; Measurement of the nightly motion of a "new star" (a supernova) showed no parallax; Evidence against Aristotelian belief of "perfect", unchangeable heavens

When Tycho observed the new star of 1572, he could detect no parallax. Why did that result undermine belief in the Ptolemaic system?

In the Ptolemaic model, the celestial sphere is perfect and changeless. A new star, therefore, must be an object not of the celestial sphere but has to lie closer to Earth than the moon. Objects closer to Earth than the moon show a detectable daily parallax relative to the distant stars. Not observing such a parallax indicates that the new star is further away than the moon and probably as distant as the stars.

Perfect Heavens

Motions of all celestial bodies described by motions involving objects of "perfect" shape, i.e., spheres or circles.

Hipparchus

Placed the Earth away from the centers of the "perfect spheres"

A planet's orbital period (P) squared is proportional to its average distance from the sun (a) cubed

Py2 = aAU3 (Py = period in years; aAU = distance in AU)

Chaco Canyon, New Mexico

Slit in the rock formation produces a sunlit "dagger" shape, indicating the day of summer solstice

What did Galileo see on the moon?

Surface structures; first estimates of the height of mountains on the moon

Explain how each of Galileo's telescopic discoveries contradicted the Ptolemaic theory?

The moon has mountains and valleys, much like Earth. The Ptolemaic model describes a perfect moon, i.e. a perfectly smooth sphere. The Copernican model does not specify the surfaces of the planets but suggests the bodies are like Earth. (b) The discovery that the Milky Way is made of stars too faint to be seen with the naked eye doesn't support or argue against either model. (c) The discovery of new "planets" orbiting Jupiter shows that at least four objects do not orbit Earth. It supports the Copernican model by determining that Jupiter, like Earth, has satellites. It also indicates that moons will not be left behind if the planet they orbit is moving. Sunspots show the sun is not perfect, as held in the Ptolemaic model, but "blemished." The spots also indicate that the sun is a sphere that rotates on its axis. (d) Observations of Venus prove that it goes through phases of illumination much like the moon and that these phases only make sense if Venus orbits the sun.

Kepler's laws of planetary motion

The orbits of the planets are ellipses with the sun at one focus;

Johannesburg Kepler (1571-1630)

Used the precise observational tables of Tycho Brahe to study planetary motion mathematically. • Planets move around the sun on elliptical paths, with non-uniform velocities. • Found a consistent description by abandoning both circular and uniform motion. Rudolphine tables; designed the AU

Does Tycho's model of the universe explain the phases of Venus that Galileo observed? Why or why not?

Yes. In Tycho's model all planets except Earth orbit the sun, and the sun orbits Earth once each day. In this model Venus shows a full set of phases.

Epicycles

a small circle whose center moves around the circumference of a larger one

Why did Copernicus have to keep small epicycles in his model?

because he used uniform circular motion instead of elliptical motion.

Eratosthenes (200 BC)

calculated the diameter of Earth using the distance between Alexandria and Syene and the angle of the sun at noon relative to the zenith on the summer solstice.

Copernicus (1473 - 1543)

came up w/ Heliocentric Universe model (Sun in the Center); der revolution

Geocentric Theory

in the Middle Ages, the earth-centered view of the universe in which scholars believed that the earth was an immovable object located at the center of the universe

retrograde motion

the apparent westward motion of the planets with respect to the stars; occurs when the Earth passes the planet. Demonstrated through Ptolemy's epicylces; the Ptolemaic system was considered the "standard model" of the Universe until the Copernican Revolution.

Galileo Galilei (1564-1642)

the dialogue; four moons of jupiter • Greatly improved on the newly invented telescope technology (But did NOT invent the telescope!) • Was the first to meticulously report telescope observations of the sky to support the Copernican Model of the Universe

Velocity

the speed of an object in a particular direction