class 1 introduction, background class 2 solar systemclass 1 introduction, background class 2 solar...

Class 1 Introduction, Background Class 2 Solar System Class 3 Stars Class 4 Galaxies Class 5 Cosmology Class 6 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●Telescopes

1. History of Modern AstronomyAstronomy circa 1600, the Copernican Revolution

Copernicus 1514Tycho Brahe 1573 Galileo 1609Kepler 1605, 1609Newton 1684

Geocentric UniverseThe Problem: The Retrograde Motion of Mars

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

A Heliocentric Model of the Universesolves 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

Is there gravity in space?Is there gravity in 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 multiple-imaged 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

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

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

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.

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.