Lecture 5 Flashcards
what did tycho Brahe do
combined copernican and geocentric model with sun orbiting earth, planets orbit sun
showed supernovae appeared beyond moon
most accurate star and planetary table ever made
what did Kepler do
realised you could throw away the assumption of circular motion, found simpler models that explained observations accurately
what are Keplers laws
planets orbit in an ellipse with the sun at one focus
sun-planet line sweeps out area at a constant rate
square of a planets orbital period is proportional to the cube of the length of the semi-major axis of its orbit
what was newtons explanation for Keplers laws
same law of gravity applies on stars
when this is combined with newtons 3 laws, it predicts Keplers laws
speculated stars were like the sun and had their own planets
impact of newtons explanations
unified terrestrial and celestial mechanics
accurate enough for terrestrial purposes like navigation
what are the 1760s transits of Venus
venus passes infront of the sun rarely due to orbit angle, happens in pairs 8 years apart
in 1761&69, time of transit from different locations was measured and distance calculated within 1% accuracy
what happened in 1780’s-1900s to do with the models of the universe
nature and matter of stars was established, confirmed stars were sun like, established basic distances to nearby stars
what is the base for all modern cosmology
Einsteins special relativity and general relativity
what is special relativity
laws of physics, particularly electricity and magnetism, are the same in any non-accelerating situation, regardless of speed
what is general relativity
cannot distinguish free-falling under gravity from being weightless a long way from any gravity
matter tells space how to curve, space tells matter how to move
as a metric, GR describes structure of space time within GR, tells you the length of a journey along any path through space and time
what is the FLRW metric
metric for matter density constant throughout space
defined by an overall curvature, K, of space and a scalling of time as it passes
current model for the universe on large scales
what is the great debate
were spiral nebulae (galaxies)
clouds within Milky Way (Shapley)
or
distant galaxies about the same size as the MW (Curtis)
great debate main arguments for Curtis
- why would there be as many novae in one tiny cloud as in the rest of the Milky Way
- dark lanes in the nebulae look like dust in the MW
great debate main arguments for Shapley
pinwheel galaxy had been observed to rotate over the course of years if it was as big of the Milky Way, would have rotated faster
Andromeda would have to be very far away to be the size of the Milky Way
one nova in Andromeda outshone the rest of it, how could one star be brighter than billions of others
how are distances measured beyond the Milky Way
standard candles
what are cepheids
young bright star type found to pulsate
brightness and radius changes over days to months
relationship between brightness and period found by leavitt
what did Hubble observe and measure
individual stars in Andromeda and other galaxies
found cepheids
measured period, absolute luminosity thus distance
