Astronomy Cosmology

Cosmology is the academic discipline that seeks to understand the origin, evolution, structure, and ultimate fate of the Universe, as well as the natural laws that keep it in order. Steady-State Theory Big Bang Theory

Steady-State Theory Proposes that the universe is the same as it has always been. New matter is created and added to the universe as it expands so overall density does not change

Big Bang Theory Theory that all matter and energy in the Universe was compressed into an extremely small volume that suddenly (~14 bya) began expanding in all directions. Not necessarily an explosion. It is an expansion. Evidence Red Shift – (need to understand the nature of light) Background radiation

Red Shift - Light Travels in waves Spectrum of colors – Roy G Biv

Wavelength - the distance from one crest of a wave to the next crest

Frequency- how often the wave cycles during a given period of time

Electromagnetic Spectrum

Doppler Effect The apparent shift in the wavelength of energy, emitted by a source moving away from or toward an observer, greater speed, greater shift Applet: Doppler Effect

Using a spectroscope, found that most galaxies are shifted toward the red end of the spectrum; most distant, greatest shift Conclusion: the universe is expanding

Background Radiation Law of conservation of mass and energy - Mass and energy can change from one form to another but cannot be created or destroyed. (energy – First law of thermodynamics) Found using radio telescopes in the 1960s Penzias and Wilson

http://www.youtube.com/watch?v=Y5KaeCZ_AaY

Formation of the Solar System Astronomy Formation of the Solar System

Origin of the Solar System Solar system – sun and bodies revolving around it French mathematician Marquis Pierre Simon de Laplace hypothesized in 1796 that the sun and planets formed at the same time from the same nebula (cloud of dust and gas) at about the same time. This is the nebular theory. Nebula that became our solar system is called solar nebula. Was larger than now.

Formation of the Sun 4 to 5 billion years ago, nebula began contract when heat from collisions and pressure from force of gravity became great enough, hydrogen fusion (discussed later) began; Sun formed in the center. ~99% of the matter in the nebula became part of the Sun.

Formation of the Planets Planets also forming Planetesimals – small bodies of matter in solar nebula; joined together and became larger protoplanets. Gravity acted like giant magnets pulling on other bodies and formed today’s planets and moons which are smaller and denser than protoplanets.

Planets Characteristics determined by proximity to Sun. Inner planets: Mercury, Venus, Earth, Mars (aka Terrestrial Planets) contain heavy elements like iron. Closeness to Sun (solar winds) may have stripped away lighter atmosphere. Outer planets: Jupiter, Saturn, Uranus, and Neptune (aka Gas Giants). Large, made of He and H and frozen gases like water, methane, and ammonia. Small solid core.

Astronomy Motions

Models Aristotle - Greek philosopher (384-322 BC) proposed geocentric (Earth-centered) model Nicolaus Copernicus – Polish astronomer (1500s) proposed heliocentric (Sun-centered) model and they move at different speeds Galileo Galilei – Italian scientist (1600s) confirmed heliocentric model using telescope

Kepler’s Laws of Planetary Motion Johannes Kepler (1571-1630) developed three laws that explain most planetary motion Law of Ellipses Law of Equal Areas Law of Periods

Law of Ellipses Kepler’s first law: each planet orbits the sun in a path called an ellipse; oval determined by two points called a focus; Sun is one focus. If you draw a line from any point on the ellipse to each of the two foci, the total length of the lines will always be the same.

Perihelion – point closest to sun (147 million km) Aphelion – point farthest from sun (152 million km) 1 astronomical unit (AU) ~150 million km

Law of Equal Areas Kepler’s second law: describes the speed at which planets travel at different points in their orbit. Earth moves fastest at perihelion Planets sweep through equal areas in equal periods of time

Law of Periods Kepler’s third law: describes the relationship between the average distance of a planet from the sun and its orbit period (time to revolve around sun) P2 = a3 where P is orbital period and a is semimajor axis of orbital ellipse

In other words: The orbit of every planet is an ellipse (a special kind of circle) with the Sun at one of the foci. An imaginary line joining a planet and the Sun sweeps out equal areas during equal intervals of time. The time it takes a planet to orbit the Sun is related to how far away from the Sun an object is. (This means that the larger the average distance from the Sun, the longer it takes for an object to orbit it.)

http://www. youtube. com/watch http://www.youtube.com/watch?feature=player_embedded&v=lm9Ej-YMXto#at=17 http://www.youtube.com/watch?feature=player_embedded&v=UVdqxYyFRK