Samenvatting anw science for Public Understanding (spu) Summary Ch. 15 &


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Samenvatting ANW Science for Public Understanding (SPU) - Summary Ch. 15 &

Understanding the solar system.

Maak van acht meter japanse stof uw nachtjapon.

Ancient Astronomy.

Greek called planets wanderers.

Can see 5 planets with naked eye: Mercury, Venus, Mars, Jupiter and Saturn.

500 BC: followers of Pythagoras.

Earth at centre of set of crystalline spheres which move around carrying stars, Sun, Moon &

planets with them.

370 BC: Euxodus came up with way to explain how some details, especially the retrograde motion of the planets happen. Aristotle developed this idea with 55 spheres, still didn't work.

Retrograde: de andere kant dan de baan op.

Euxodus model. Spheres rotate and turn independently.

230 BC: Apollonius of Perga.
Suggested each planet moves in circle on larger circle. Further developed by Claudius Ptolemy. Nothing better thought of for 1000 years. (Ptolemely's model).

The Copernican revolution.
1260 AD: Thomas Aquinas. Combined Aristotle and Christian teaching. Became accepted viewpoint from Church. God kept spheres moving.

Ptolemy didn't predict precisely.

Early 16th century: Nicolaus Copernicus suggested that movements were easier if Sun was in the centre with other planets circling it (heliocentric). Also spins on own ax, explains retrograde movement. Published book after death, improved model then, could have been worried about opposition from the church. Luthian clerc wrote that this were just calculations and not how it could really be. Not immediately banned by Church. But later events (such as Counter Reformation) led to the bannishment of Copernicus book.

Parallax: onder kijkpunt (letterlijk).

Convincing others.

Some still didn't believe the heliocentric model, because the arguments were weak (opponents were people from Church and scholars).

Important people for general acceptance:

Tycho Brahe: The great observer.
Night of 24 August 1563: conjunction (samenkomen waardoor het 1 vlek lijkt) of Jupiter and Saturn. Had been predicted, but several days out. Did not accept heliocentric model. Got instrument of Danish king (he was Danish). Measured precisely the positions of stars and planets. Didn't accept Ptolemy too. 2 reasons: First: 1572, saw supernova (bright new star that slowly dims). Second: 1577: observed comet, tried to estimate distance by making parallex measurement from two places on Earth's surface. Saw that comet went through several spheres, so no Ptolemy. New theory: Earth in centre, Sun & Moon circling it. Other planets circling Sun.

Johannes Kepler: A model that fits the data.
Seemed to have accepted heliocentric model from young age. Fled on 1-1-1600 from Austria to Prague and became Brahe's assistent. When Brahe died, Kepler inherited his data. Found tiny mistake in Brahe's model (6/60 degree) and knew model was wrong. Conclusion; orbits were not circles, but ellipses. Kepler had 3 laws of planetary motion:

The orbits of the planets are ellipses.

Each planet moves round its orbit so that the line joining it to the Sun sweeps out equal areas in equal times.

The time it takes for each planet to orbit the Sun (T) is related to its average distance from the Sun (R ) by a simple rule: the number R/TӲ is the same for each planet.

Galileo Galilei: Challenging the authority of tradition.
Pisa 1564. Also accepted heliocentric model from young age, sincere Catholic. In 1609 got first telescope, made one himself that magnified 30x. Between 1609 and 1615 observel mountains on Moon and sunspots (no perfect circles), moons of Jupiter (showing that something can orbit around a centre other than the Earth) and phases of Venus. Wrote letter to Duchess in which he said the heliocentric model is a fact. Church censored him. He wrote book with dialogues. 3 characters, opponent, Galilei and neutral person. All copies of book ceised and Galileo (almost 70) got tortured to admit his deeds. That book: the Dialogue Concerning the Two Chief World Systems, is probably one of most important books ever written.

An explanation for the planetary motions.
Isaac Newton (1642, year Galilei died) developed Laws of Motion. Thought that Moon falls to Earth. Gravitational force.

Coping with a challenge.
13 March 1781 amateur astronomer in Bath discovered Uranus → William Herschel. Had photographical memory and found out that Uranus was further away than Saturn. This doubled the known size of the solar system. Strayed of its predicted course. Suggestions: struck by comet, had invisible moon, Newton's laws didn't apply at such large distances.

1843: John Couch Adams thought that Uranus difference could be caused by another planet. He told this to the director of the Cambridge Observatory and calculated where it could be. If someone had believed him and looked they would have seen it, within 2 degrees that Adams had predicted!

When someone else tried they started searching for the unknown planet which they found after two months in one night by the genious idea of a student: Neptune.

An understanding that works!
To show how it looked the NASA started sending spacecrafts such as the Voyager 1 and 2. It took the Voyager 2 12 years to travel to Neptune.

Understanding the universe.
The universe began in a big bang around 15 billion years ago (15.000.000.000).

Nearest star to sun: 4 light years away (1000 x radius solar system)

Sun is towards outer edge of Milky Way Galaxy. Other galaxies are moving away from us at high speeds.

How far are the stars?
1640's & 1650's: Heliocentric model accepted: simplicity Kepler's model + accurate predictions.

Stellar paralles: parallex of the stars: scientist looked for this when Copernicus introduced heliocentric model. (found none, too far away).

Parallex observed.

All stars move, we only see movement of close stars and stars that move relatively faster.

1838: Friedrich Wilhelm Bessel: measured paralles 0,31 s. star.

Was 61 Cygni. Calculation: distance: 11,2 ly's.

Closest stars are over 4 ly's away. (750x radius solar system).

Light year (ly): distance light travels in 1 year = E. 9,500,000,000,000 km.

New techniques.

19th century: 2 developments: photography: observation could be recorded, easier to spot changes

spectroscopy: measure composition: 1 of sun: helium &hydrogen.

Beyond the closer stars

late 19th century: no way to calculate how far a star is away.

Harvard College Observatory: compile a catalogue of stars: collect reliable data.

Too routine for professional astronomers, so hired women.

1890-1924: built up huge catalogue: ong. 225.000 stars.

Annie Jump Cannon: made 7 categories by colour of stars, rose to 13 categories.

1914: Henry Norris Zussel: compared brightness and distance and spectral class. By this they could see the intrinsic (real) brightness and the distance could be calculated.

Cepheid variables.

Henrietta Swan Leavitt: studied stars in 1 Magellanic Cloud (2 clusters of stars on Southern Hemisphere). Were app. Same distance, so intrinsic brightness.

Measured periods: the brighter, the longer.

By measuring apparent brightness: distance calculated

snag: need distance of 1 Cepheid (stars with certain pattern of brightness).

The structure of the universe.

Nebulae: fizzy/cloudy object in night sky (E.G. Milky Way, Magellanic Clouds).

Immanuel Kant: thought nebulae were star clusters

Nebulae: some have spectra of gas others have a spectra like a star.

Harlow Shapley: clusters seemed to form a huge sphere, whose centre was far away in the direction of the constellation Sagittarius (boogschutter, SH). This meant that our solar system is not in the middle of our galaxy. Shapley thought the Milky Way was the whole universe and estimated it 3x bigger than it was.

Island universes.
October 1923:Edwin Hubble: studied Andromeda nebula. Found its intrinsic brightness and calculated its distance from our galaxy (900.000 ly's). This meant that the Andromeda nebula was not a nebula, but a galaxy. This was also evidence that our galaxy was not the only one.

An expanding universe.
1914: Meeting American Astronomical Society. Vesto Slipher reported unexpected: several spiral nebulae moving away at high speeds (max 60 miles/s.)

Came from spectra (=doppler effect).

Humble found using Cepheid variables, how farther away a galaxy, the faster it moves. The bigger red shift in spectrum, the faster it's receding and the further away it is.

Blue shift = approaching (andromeda)

Universe = expanding (Einstein) confirmed by Hubble, Friedman, Slipher.

Confirms Big Bang (universe is 15.000.000.000.000 years old)

The 'echo' of the the Big Bang.
1964: robert Wilson & Arno Penzias. Found echo Big Bang (3 d. Kelvin). 1978: Nobel Prize for Physics.

An expanding universe: What does it mean?

Like balloon every point is getting further away from the others.

Every direction looks back to start point of universe, reason background radiation (= echo big bang)

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