AST201 Midterm 1 Study Review.docx

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University of Toronto St. George
Astronomy & Astrophysics
Michael Reid

AST201 Midterm Review 1 Lecture 2/3 January 10 /15th -Milky way galaxy contains over 100 billion stars -Our solar system is located a little more than halfway from the galactic center of the edge of the galactic disk -Galaxy clusters- groups of galaxies with more than a few dozen members -Super clusters- the regions in which galaxies and galaxy clusters are most tightly packed -The big bang theory- 14 billion years ago- entire universe is expanding- continues to expand -A star is born when gravity compresses the material in a cloud to the point where the center becomes dense enough and hot enough to generate energy by nuclear fusion -Speed of light travels at 300,000 km a second -Light from the stars is measured in light years- one light year is the distance in which that light can travel in one year- about 10 trillion km, or 6 trillion miles- light years is a measure of distance, NOT time -Farther away we look in the distance, the farther back in time we look -Earth rotates once each day around its axis- yearly orbit around the sun -Earths average orbital distance is called an astronomical unit, or AU- which is equiv. to about 150 million km -Entire solar system is on a great journey within the Milky Way Galaxy -Dark matter is everywhere, as well as dark energy -For thousands of years astronomers insister on the Pythagorean ideal of circular motion- everything beyond earth should move in a perfect circle- found the circle the most perfect shape- assumption wrong, knew planets did not move in circles around earth -epicycle- moving in a circle, around a circle -Occam’s Razor -Nicholas Copernicus- applied Occam’s razor -Johannes Kepler- took Copernicus model over epicycle model- break assumptions that everything moved in circles- things move in ellipses - sun is at one focus of ellipse -Eccentricity- quantity that describes how much an ellipse is stretched out compared to perfect circle. Degree to what an ellipse is not a circle -Ellipse- Kepler’s discovery was that planetary orbits are not circles, but instead are special type of oval called an ellipse -Perihelion- near the sun -Aphelion- away from the sun Kepler’s First Law- applied to solar system, not useful if you move outside of solar system. **The orbit of each planet around the Sun is an ellipse with the Sun at one focus** A planets distance from the sun varies during its orbit Kepler’s Second Law- **As a planet moves around its orbit, it sweeps out equal areas in equal times** this means the planet moves at a greater distance when it is near perihelion than it does in the same amount of time near aphelion Kepler’s Third Law- **More distant planets orbit the sun at a slower average speeds, obeying a precise mathematical relationship** p2=a3  p= the planets orbital period in years, and a= the average distance from the sun in astronomical units Low eccentricity- 1 dot (e=0) High eccentricity- 2 dots (e=0.5) -Centre of mass closer to heavier item if wanting to balance evenly- Kepler did not know this -It is the center of mass, which is at one focus of every orbit -Objects at rest remain at rest= unless acted on by an external force -Gravity does not exist w/o an object- stars create gravity- anything with a mass or energy has gravity -Gravity is never negative, only positive, there is no ‘anti-gravity’ -Newton discovered the laws of motion, which could explain Kepler’s laws Newton’s First Law- **Objects at rest remain at rest and objects in motion remain in motion in a straight line, unless acted upon by an external force Newton’s Second Law- **F=ma (force= mass X acceleration) Lecture 4 January 17 th 5.1 -Light- Believed that light is a wave, or a stream of tiny particles, or a wave AND a particle -Light is a wave-particle- depending on how you observe it; it may act as a wave, or a particle -Wavelength- distance from one peak to the next -Light is not a wave IN something, but instead it is a wave OF something -Light is an electromagnetic wave-**makes atoms cling to each other- range is infinite, strength is 1/137 -Electromagnetic radiation=light -Wavelength is the distance between adjacent peaks of the electric (and magnetic) field -Frequency is the number of times each second that the electric (and magnetic) field vibrates up and down (or side to side) at any point -All light travels with speed c=5,300,000km/s -Spectrum- basic colours in a spectrum include red, orange, yellow, and green, blue, violet** we see white when the basic colours are mixed in roughly equal proportions -Light from the sun or a light bulb is often called white light because it contains all the colours of the rainbow -In science, the rate of energy flow is called power which is measured in unites of watts **1 watt= 1 joule/s -Emission- A light bulb emits visible light; the energy of the light comes from electrical potential energy supplied to the light bulb -Absorption- When you place your hand near an incandescent light bulb, your hand absorbs some of the light and this absorbed energy warms your hand -Transmission- Some forms of matter, such as glass or air, transmit light, which means allowing it to pass through -Reflection/Scattering- Light can bounce off matter, leading to what we call reflection (when the bouncing is all in the same general direction) or scattering (when the bouncing is more random) -Electromagnetic radiation=light -Speed of light=wavelength X frequency -Wavelength determines colour -When there is more of an increase in frequency and energy, it goes towards to blue (right) end of the spectrum -When there is less frequency and energy, it goes towards the red (left) end of the spectrum -When there is an increasing wavelength, it goes towards the red (left) end of the spectrum -When there is a decreasing wavelength, it goes towards the blue (right) end of the spectrum -Light can have ANY wavelength Gamma Rays Increasing Wavelength X Rays Ultra Violet Decreasing Frequency Visible Decreasing Energy Infrared light Microwaves “Redder” Radio Waves -True Colour- Visible light -False Colour- Infrared light -Different wavelengths show different physical conditions January 22 Lecture Light and Matter -The process of obtaining a spectrum and reading the information it contains is called a spectroscopy -Niels Bohr- Electrons can only orbit at certain fixed distances from the nucleus. Orbits are quantized -Light only comes in the colours in the increasing freq./increasing wavelength scale -White- get all the colours in equal amounts -Colour- human brain- not nature- brain makes the colours -Higher frequency carries more energy Quantum Physics- electrons in atoms are restricted to particular energy levels - Electrons have quantized energy levels in all atoms, not just in hydrogen - Allowed energy differs from element to element -Electrons in different orbitals have different energies -Atoms emit or absorb light only when electrons change orbitals -Emission- when atom moves inwards
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