Announcements

Please pick up HW#1, due next Friday

On problem 7, should be p. 61, not p. 71

Extra Credit in this case is more mathematical, help is available

Another EC opportunity: Jan 27th, 7 pm, planetarium show on the Solar System. Please sign up at the link on Carmen

Next reading assignment posted to Carmen

Please turn off all electronic devices

What can you conclude about A vs B?

a) A has a larger physical size than B

b) B has a larger physical size than A

c) A has a larger angular size than B

d) B has a larger angular size than A

e) a and c are both true

A

B

The Heliocentric UniverseThe Heliocentric Universe

Astronomy 1143 – Spring 2014Astronomy 1143 – Spring 2014

Key Ideas:Nicolaus Copernicus – revived the heliocentric theory

in De revolutionibus orbium celestium• Better explanation for structure of solar system• Still complicated & did not predict positions

more accurately than geocentric

Heliocentric model attractive because of the shift away from the views of Aristotle/Ptolemy

Tycho Brahe – great observer• Observer the changing heavens• Most accurate naked-eye positions for planets

Key Ideas:Galileo Galilei -- first modern astronomer

Important Discoveries with the telescope:• Moons of Jupiter• Phases of Venus• Craters & Mountains on the Moon• Sunspots

Galileo’s observations clashed with the ideas of perfection of the heavens and the center of motion being the Earth. They undermined the foundations of the geocentric model.

Nicolaus Copernicus

The Heliocentric System

Heliocentric = Sun-Centered

Alternative viewpoint to Geocentric:• Puts the Sun, not the Earth, at the center.• The Earth rotates & revolves around the Sun.• Stars are on an outermost celestial sphere.

Complex non-uniform & retrograde motions are a consequence of viewing the planets from a moving Earth.

It too was proposed in ancient Greece

The Heliocentric System Revived

Revived Aristarchus’ Heliocentric system, which he knew only through Archimedes’ description in The Sand Reckoner.

• The Sun, not the Earth, is at the center.

• The Earth rotates around its axis, producing the daily motions.

• The Earth revolves around the Sun, producing the annual motions.

Copernicus’ Solar System

Scientific Objections

Requires very large speeds:

• Speed of rotation at equator: 1680 km/hour

No observational evidence of orbital motion:

• Stellar Parallaxes were not observed.

• Stars weren’t brighter at opposition.

Did not predict the positions of the planets better than the geocentric version

Simple in principle

Inferior and Superior Planets:• Mercury & Venus orbit closer to the Sun • Mars, Jupiter, & Saturn are in larger orbits.

Retrograde Motion:• Consequence of observing moving planets from a

moving Earth.• By contrast, Ptolemy required epicycles to get

retrograde motion.• Copernicus only needed them for non-uniform

speeds

EarthMars

Retrograde Motion

Venus Position at Sunset (Sun 7° below horizon)

Photo by Tunç Tezel (Ankara, Turkey)

Position of Mercury at Sunset(2004 March-April)

Mercury and Venus in Heliocentric Universe

Stay close to the Sun because they are closer to the

Sun than the Earth is

Mars, Jupiter, & Saturn in Heliocentric Universe

Can appear opposite in the sky to the Sun because

they are further away from the Sun than the Earth is

Out with the old….

The heliocentric model was not immediately adopted

• Had some of the same complexity as the Ptolemaic geocentric system

• Did not give more accurate predictions

• Scientific objections remained

However, over the next decades, observations would be made that challenged the views of Aristotle/Ptolemy.

Tycho Brahe (1546-1601)Danish nobleman, brilliant astronomer and instrument builder.

• Admired Copernicus as a mathematician.

• Did not like the idea of a moving Earth.

The greatest naked-eye astronomer of thepre-telescope age.

Uraniborg

He built “Uraniborg” (Heavenly Castle) on the island of Hven with royal support.

• Equipped with the best instruments.

• Achieved an unprecedented 12 arcminute measurement precision.

Became an important center for astronomical research in Europe.

Neither Ptolemaic nor Copernican systems could match his data.

Tools of Tycho Brahe

Sextant

Aristotle & the Heavens

One of the principles of Aristotle is that the heavens do not change. All change happens in atmosphere of Earth or below

The heavens are perfect, not like the Earth

Earth is the center of all motion

If these principles are wrong, could geocentrism also be wrong?

Tycho’s Observations

He observed the bright comet of 1577 and could not measure a parallax

Comet must be further away than the Moon

In 1572, he observed the appearance of a “new star”, what we now know is the explosion of a white dwarf, leaving behind a faint glowing remnant

This “Type Ia supernova” is another example that the heavens are changing.

SN 1572 -- ObservationsTycho published De nova stella in 1573Clearly showed that this was among the fixed starsCoined the term “nova” to describe the phenomenon.SN remnant identified in 1952 by Hanbury et al. as 3C10

SN 1572 -- Observations

This SN was recorded by the official astronomers in both China and Korea, no known Japanese records.

Big difference in European records compared to previous “nova”

• Tycho Brahe made extensive quantitative measurements of position and brightness

• Clearly a SN just from reading his records

• Sometimes known as Tycho’s SN

SN 1572-- Remnant

Look, ma, I exploded!

SN 1572 – Light Echoes

Galileo Galilei (1564-1642)Italian contemporary of Kepler:

• Gifted mathematician• Brilliant observer &

experimenter

Preferred experimentation and measurement to philosophical rhetoric.

• Staunch anti-Aristotelian• Often at odds with the

scholarly establishment

The TelescopeThe telescope was invented in 1608

by Hans Lipperhey, a Dutch spectaclemaker.

Word spread fast:• In April 1609, you could buy one in

eyeglass shops in Paris.• First one reached Italy in August of 1609

Close up of the originalprimary lens

Galileo’s Telescopes

“...a most beautiful & delightful sight ”

1610: published his observations as the Sidereus Nucius (The Starry Messenger)Later observations were published in letters

& in a longer work, The Assayer, in 1623.The most important to us here are:

• Craters & Mountains on the Moon• Sunspots & Solar Rotation• Moons of Jupiter• Phases of Venus

Sunspots

Moons of Jupiter (January 1610)

The Earth is not the only center of motion in the Universe.

Phases of Venus

3

3

4

4

2

2

1

1

5

5

6

6

Ptolemaic SystemCopernican System

6

6

5

5

4

4

3

3

2

2

1

1

The discovery of the phases of Venus was more evidence that the planets orbit the Sun and not the Earth.

Impact of Galileo’s ObservationsThe impact was immediate and forceful:

• Kepler was delighted, and soon acquired his own telescope, as did many others.

• Many scholars began to take the Copernican system seriously as a physical description.

• Hardcore skeptics claimed that the telescope (and Galileo) was lying and entrenched.

With the telescope, everyone could literally “see for themselves”.

Galileo’s villa in Arcetri, outside Florence

Eppur si muove (and still, it moves)

Galileo spent his final 4 years in blindness, and died under house arrest, on January 8, 1642.

On Christmas Day of that same year (O.S.), Isaac Newton was born in Woolsthorpe England.

In 1992, 350 years later, Pope John Paul II officially declared Galileo innocent.

Geocentric vs. Heliocentric

While the observations of Tycho and Galileo showed that not all ideas of the ancient Greeks were correct, they do not definitely show that the Earth moves.

Kepler and Newton were to seal the deal for the heliocentric version by their descriptions and explanations for the orbits of the planets.

Heliocentric theory was accepted before the first evidence that the Earth moves.