Transcript Astronomy pp notes - Duplin County Schools

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
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:
1. The orbit of every planet is an ellipse (a special kind of
circle) with the Sun at one of the foci.
2. An imaginary line joining a planet and the Sun sweeps
out equal areas during equal intervals of time.
3. 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?feature=player_embedded&v=lm9Ej-YMXto#at=17
•
http://www.youtube.com/watch?feature=player_embedded&v=UVdqxYyFRK