The Solar System Copernicus (1473) equant and doubling of Moon - disturbing revived Aristarchus'...
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Transcript of The Solar System Copernicus (1473) equant and doubling of Moon - disturbing revived Aristarchus'...
The Solar SystemCopernicus (1473)
• equant and doubling of Moon - disturbing
• revived Aristarchus' heliocentric model
De Revolutionibus Orbium Coelestium (1543)
• Sun at centre, all planets orbit Sun, Moon orbits Earth
• stars are on CS, at rest
• Earth rotates
• Mercury, Venus, Earth, Mars, Jupiter, Saturn
• same geometric tools as Ptolemy (no equant)
retrograde motion: result of relative motion of Earth and planets
• no savings in complexity• same predictions as Ptolemy • predicts periodic shift of stars - not observed • preface implied it was not to be taken seriously• banned 1616
Tycho Brahe (1546)
• repetition of measurements
• calibration
• Uraniborg (1576)
• Alfonsine and Prutenic tables disagreed • new star (nova) 1572, lack of motion meant it was on CS• more accurate predictions require better observations• prolific instrument maker
• 1577 – comet path crosses other planets' orbits - solid crystal spheres do not exist
• lack of parallax implies large distances to stars in heliocentric model
• preferred geocentric model
• hybrid model – Earth at centre, Moon and Sun orbit Earth, other planets orbit Sun • 1599, Prague – hires Kepler to analyse data
1 degree = 60 arcminutes
1 arcminute = 60 arcseconds
1 = 60 = 3600
• accuracy of 1 arcminute (1)
Celestial Coordinates• Declination (dec.) – latitude• angle above the celestial equator (degrees)
• Right Ascension (RA)– longitude• measured eastward from location of Sun at vernal equinox
• measured in hours, minutes, seconds (1 hr = 15 degrees, 1 minute RA = 15 arcminutes)
Johannes Kepler (1571)
• favoured Sun-centred solar system • analysed Brahe's data for Mars• best deferent/epicycle orbit disagreed with data • rejected deferents/epicycles
1st Law (1609): Planets revolve around the Sun in elliptical orbits with the Sun at one focus
Kepler’s Laws of Planetary Motion
Orbit specified by semi-major axis (size) and eccentricity (shape)
2nd Law (1609): As a planet orbits the Sun, a line joining the Sun and the planet sweeps out equal areas in equal times
Planets move faster in their orbits when closer to Sun (speed)
3rd Law (1619): The square of a planet's orbital period is proportional to the cube of its semi-major axis
The larger the orbit, the longer the period (time for one orbit)
Mercury 3 mo.
Venus 7.4 mo
Earth 1 year
Mars 1.9 year
Jupiter 12 years
Saturn 29 years
• absolute sizes of orbits unknown• tries to explain telative orbit sizes using geometric solids
• suggests that physical force is responsible for orbits • produces Rudolphine Tables
Galileo Galilei (1564)
• supports Copernicus' model
• 1609 – constructs telescope (3-20)
• 1610 – reports observations in Siderius Nuncius
many stars not visible to naked eye
Milky Way composed of many stars
some nebulae also made of stars
Moon has craters, mountains
planets appear as discs
Jupiter has satellites
Sun has sunspots
Later Observations
Saturn had structures attached
Venus showed all phases
• Jupiter's moons and Venus' phases evidence against geocentric
Geocentric Heliocentric
A Dialogue on the Two Great World Systems (1632)
• "debate" between geocentric and heliocentric ideas
• obviously favoured heliocentric
• Roman Inquisition forces Galileo to recant, placed under house arrest
• Dialogue banned until 1835
Mid - 1600's
• universe is heliocentric, infinite, stars scattered randomly
• Earth is one of the planets
• Earth rotates on axis
• orbits described by Kepler's Laws