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Introduction, Background Solar System Stars Galaxies Cosmology Special Topics

Class 1

Introduction, Background

History of Modern Astronomy The Night Sky, Eclipses and the Seasons Kepler's Laws Newtonian Gravity General Relativity Matter and Light T lescopes e




1. History of Modern Astronomy Astronomy circa 1600, the Copernican Revolution
Copernicus 1514 Tycho Brahe 1573 Galileo 1609 Kepler 1605, 1609 Newton 1684


Geocentric Universe
The Problem: The Retrograde Motion of Mars


..add epicycles to the Geocentric Model, but still doesn't work


A Heliocentric Model of the Universe solves the problem


Galileo invents the telescope 400 years ago.


All of Galileo's observations can be explained by a heliocentric model.


Heliocentric Model and everyday observations: Phases of the Moon, Eclipses, Seasons


The constellations are patterns we perceive of stars in space. Those stars are generally not near each other.


Right ascension and Declination are the coordinates of the Celestial Sphere. They are analogous to longitude and latitude on Earth.


The moon's phases appear due to the relative positions of the Sun, the Earth, and the Moon.


What are eclipses and why don't they happen every month?


The origin of the seasons:



Kepler Laws of planetary motion


"The orbit of every planet is an ellipse with the sun at a focus."


Kepler's First Law Applet


"The line joining a planet and the sun sweeps out equal areas during equal intervals of time."


Kepler's Second Law Applet


"The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit."


Newton's Law of Gravitation


The forces are equal and opposite


IIs there gravity iin space? s there gravity n space?


Einstein's Law of Gravity


Space curves due to the presence of matter.


The path of light in curved space, near a black hole


Hubble Space Telescope: Gravitational lens G2237 + 0305, sometimes referred to as the "Einstein Cross". The photograph shows four images of a very distant quasar which has been multipleimaged by a relatively nearby galaxy acting as a gravitational lens. The quasar seen here is at a distance of approximately 8 billion light years, whereas the galaxy at a distance of 400 million light years is 20 times closer. The light from the quasar is bent in its path by the gravitational field of the galaxy. The bright central region of the galaxy is seen as the diffuse central object.


A view of the Milky Way with a black hole in front of it.


LISA : Laser Interferometer Space Antenna


Matter and Light


Light is an electromagnetic wave


The visible spectrum is a portion of the full electromagnetic spectrum



Blackbody Spec

1. A luminous solid or liquid, or a sufficiently dense gas, emits light of all wavelengths and so produces a continuous spectrum of radiation.

Kirchoff's Laws trum

Emission Line Spectrum

2. A low-density, hot gas emits light whose spectrum consists of a series of bright emission lines. These lines are characteristic of the chemical composition of the gas.

Absorption Spectrum

3. A cool, thin gas absorbs certain wavelengths from a continuous spectrum, leaving dark absorption lines in their place, superimposed on the continuous spectrum. Once again, these lines are characteristic of the composition of the intervening gas-they occur at precisely the same wavelengths as the emission lines produced by that gas at higher temperatures.


Blackbody Spectra



Emission Lines, Absorption Lines


Photon is another word for light
Like doesn't always just act like a wave. Sometimes it acts like a particle, like a billiard ball on a pool table. When light acts like a particle, it's generally referred to as a photon.

When an electron changes its position in an atom a photon is produced or absorbed.


Light dims as the inverse-square


Telescopes


A telescope captures and brings light to a focus


Modern telescopes are reflectors (mirrors) not refractors (lenses).


The light gathering power of a telescope varies by the square of its mirror's diameter.


Angular Resolution of a telescope


Seeing: the blurring of an image due to atmospheric turbulence


Different astronomies require different telescope designs


The Milky Way in each band of the electromagnetic spectrum.