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A comet has an orbit with a semi-major axis of 15 AU. What can you conclude? a)The comet’s orbit is circular b)The comet is always closer to the Sun than the Earth is c)The comet’s orbital period is longer than 1 Earth year d)The comet will be moving slowest at perihelion e)The comet will crash into Earth

Exploding Star in M82!

Lecture 6: Copernican Revolution Completed Astronomy Spring 2014

Key Ideas: Demonstrations of the Earth's Rotation: The Coriolis Effect The Foucault Pendulum Demonstration of the Earth's Revolution: Stellar Parallaxes Aberration of Starlight Measuring the Scale of the Solar System Distance from Earth to Sun first accurately measured using Transits of Venus Full scale of the Solar System revealed

Copernican Revolution completed The work of Galileo and Kepler had overthrown the geocentric view of the Universe However, none of the observations of theoretical work actually proved that the Earth moved Geocentric models could be made to work, though not attractively See for example Tycho’s hybrid system from the reading.

Does the Earth move? A rotating & revolving Earth seems to disagree with the senses Constituted the main scientific objection to the Heliocentric System Geocentric versions can be made that agree with positions and phases How do you prove that the Earth really rotates about its axis and revolves? (orbits) around the Sun?

As you go north or south of the Equator: East-West parallels gets smaller Takes 24 h to go around Speed of Rotation: Fastest at the Equator (1670 km/h) Gets slower with latitude: Columbus (40ºN): 1280 km/h Arctic Circle (66.5ºN): 666 km/h Riding a Rotating Sphere

Coriolis Force Gustave Coriolis (1835) Deflection due to Earth's Rotation: Fire a cannonball North from the Equator The cannon is moving east with the Earth's rotation at 1670 km/hr As it flies North, the Earth’s rotation is slower beneath its flight. Result: a slight eastward deflection from its original northward trajectory.

A little to the right (or left)… The result of the Coriolis force is: Projectiles swerve right at northern latitudes Projectiles swerve left at southern latitudes. Long-range artillery and guided missiles are designed to correct for the Coriolis force. Also affects weather systems: Hurricanes rotate counter-clockwise in the Northern Hemisphere. Cyclones rotate clockwise in the Southern Hemisphere.

Typhoon Nagi (North) Tropical Cyclone Edzani (South)

Flushing an Urban Legend The Coriolis force does not determine the direction water swirls down drains (or toilets) Size of a sink, tub, toilet, etc. is too small Coriolis effect is much smaller than other motions, (water jets, swirling with hands) Toilets do not flush clockwise in Australia (or any other place south of the Equator).

Foucault Pendulum Built by Léon Foucault in Hung a 67-meter pendulum inside the dome of the Paris Pantheon. Started it swinging North-South A few hours later, it was swinging NE-SW Later it was swinging East-West. The change in the direction of the swing is due to the rotation of the Earth.

The Pole and the Pendulum Build a pendulum at the North Pole and set it swinging towards the star Betelgeuse: An observer on Betelgeuse would see: Direction of the pendulum's swing is constant. Earth rotates eastward every 24 hours. Observer at the North Pole would see: Earth doesn't rotate relative to the observer. Pendulum's swing rotates clockwise every 24hrs What is rotating depends on your point of view.

Towards Betelgeuse

You Tube video of Foucault’s pendulum

Off of the Spinning Earth

Stellar Parallaxes As Earth orbits around the Sun, it moves 2 AU from one side to another in 6 months. A nearby star would appear to shift position with respect to more distant stars. The apparent shift is the "stellar parallax" It was not observed in Copernicus' time: Principal objection to the Copernican system The stars are too far to have large enough parallaxes to measure without telescopes

December Trigonometric Parallaxes June Distant Stars Foreground Star p = parallax angle

Parallaxes of Stars Stellar parallaxes are very small All are smaller than 1 arcsecond 1 arcsecond = the angle spanned by a dime at 2.5 miles Large distances to stars = not observed before telescopes and specialized instruments First parallax observed in 1837 (Bessell) for the star 61 Cygni. Copernicus’ explanation for why stellar parallaxes were not easily observed is correct

What’s the nearest star? ( Proxima Centauri, a not-too-bright star in the constellation Centaurus p = 0.77 arcseconds Nearest Star after the Sun

Where is the rain coming from?

Aberration of Starlight Stars also appear to shift their positions because of the aberration of starlight This effect happens because the motion of the Earth around the Sun + the finite speed of light makes stars appear to come from a slightly different direction Effect is similar to “horizontal rain” if traveling at highway or airplane speeds through a rain storm

First shifts detected 1680 – Jean Picard measured shifts in the positions of stars by using crosshairs in his telescope 40 arcseconds for Polaris ~20 arcseconds in general 1728 – James Bradley identifies the cause as the motion of the Earth 1675 – Ole Romer estimates the speed of light from the timing of Jupiter’s moons

The Cosmic Anticlimax Firm observational proofs of the rotation and revolution of the Earth did not come until more than 2 centuries after the death of Copernicus. By then, the use of the telescope and the revolution in thought started by Isaac Newton's laws of motion and gravitation had made the heliocentric version of the solar system the accepted version.

Measuring Distances: Parallax

Kepler’s Third Law

Transits of Venus If we know the distance between the Earth and Venus (in km, or miles, etc), we can determine the distance to the Sun using Kepler’s Third Law Currently, we bounce radar signals off of Venus to determine the distance to Venus. But the first measurements of the distance to Venus came from measuring transits of Venus.

1882 Transit of Venus Venus appears as a small black dot on the Sun Every ~ 100 years, there are two eclipses separated by 8 years Last ones were in 2004, 2012 Next one Dec 2117

Transit of Venus – June 6, 2012

Parallax of Venus Observations of Venus from North and South will appear at different places on the Sun A’B’A’B’ AB A’B’A’B’ Earth Sun Venus

Parallax of Venus Measuring the distance between AB and A’B’ is very difficult Measuring the time it takes to go from A to B vs. A’ to B’ is simpler (but not simple!) Need widely spaced north-south observations of the transit of Venus Major expeditions were launched in 1761 and 1769 to time the transits of Venus.

In the Name of Science….. Guillaume Le Gentil 1761: couldn’t observe on a ship near India 1769: couldn’t observe due to clouds in India (but Phillipines clear!) Returned home to find that he had been declared dead, estate gone Jean Chappe 1769: died of fever in Baja California (Charles) Mason and (Jeremiah) Dixon successfully observed the 1761 transit together

The Size of the Solar System From Greek measurements 1 AU=7.5 million kilometers From 1761 and 1769 transits 1 AU=153 million kilometers From 1761, 1769, 1874, 1882 transits 1 AU= million kilometers From modern radar measurements 1 AU= million kilometers

In-Class Scale Models

A Scale Model of the Sun-Proxima Centauri

By the mid-1800s Confirmation that the Earth rotated on its axis and revolved around the Sun Correct scale for the Solar System known Can use this to find the Sun’s radius, mass, and luminosity Sun not 5x bigger than the Earth, but 110x bigger than the Earth! Astronomy was moving from looking at motions in the sky to understanding the physical nature of bodies Astronomy to Astrophysics – universal laws of nature