Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
76 Cards in this Set
- Front
- Back
|
What contribution did the Greeks (pythagorus) make to astronomy?
|
The Earth is a sphere.
o During an eclipse the shadow is curved or circular so it must be a sphere. ~Boat sailing into the horizon does not get smaller and smaller and stay the same. You see the top of the boat and then the bottom. ~Made measurements of shadows on Earth |
|
|
What question did Aristotle answer about Astronomy? What did he think about it?
|
"How do the planets move?"
Earth is at the center of the universe and everything is spinning around the Earth. |
|
|
Which early Astronomers all worked together?
|
Brahe, Galileo, and Kepler.
|
|
|
What major contribution did Copernicus make to Astronomy?
|
He said that maybe the Earth moves around the sun. It's a simpler model. ~Planets move in circular orbits~
They thought that God would only make the orbits perfectly circular. |
|
|
What major contribution did Brahe make to Astronomy?
|
o Greatest observational astronomer who ever lived. Never used a telescope. Yet took years and years of accurate data.
o He firmly believed that Earth was the center of the Universe |
|
|
What major contribution did Kepler make to Astronomy?
|
Worked with Brahe.
o Believed in the sun-centered universe. o Discovered that planets orbit in ellipses, NOT perfect circles. |
|
|
What do Kepler's 3 empirical laws describe?
|
How the planets move.
|
|
|
What is Kepler's first law?
|
Planets move in ellipses (squashed circle) with the sun at one focus. You need two focuses to create an ellipse.
|
|
|
Talk about eccentricity.
|
-A perfect circle has an eccentricity of zero
-Eccentricity is never greater than one -Pluto (0.248) is a really eccentric orbit. The earth has a small eccentricity (0.017) and so does Venus (0.007). |
|
|
A comet’s orbit carries it beyond the orbit of Pluto and also inside the orbit of Mercury. What does this mean about the shape of a comet’s orbit?
|
The comet's orbit is about one.
|
|
|
What is Kepler's Second Law?
|
a planet in orbit around the sun is going to sweep out equal areas in equal time intervals.
|
|
|
What does Kepler's second law tell us about the speed of a planet?
|
Kepler’s second law says in effect that a planet moves fastest when it is in the portion of its orbit nearest the sun.
|
|
|
What is Kepler's third law?
|
P2=A3 ( P squared= A cubed).
|
|
|
What do "P" and "A" stand for in Kepler's 3rd law?
|
A is the semi-major axis of the ellipse. Basically the average radius of the orbit. A of the Earth is one A.U. 93 million miles (astronomical unit-created so that the earth to the sun is one).
P=period of an orbit—how long does it take a planet to complete one orbit? Period of the earth is 365 ¼ or one year. |
|
|
Consider two planets, A and B, orbiting a distant star. Planet B orbits twice and far from the star as planet A does. How does planet B’s orbital period compare to Planet A’s?
|
As you increase A, P increases and vice versa.
|
|
|
What kind of relationship to P and A (of Kepler's 3rd law) have?
|
P and A are a non-linear relationship. If you double one it does not double the other.
Yet if you increase one the other increase (or decrease), just not equally |
|
|
Planet Y takes 3 years to go around the sun. how many times further away from the Earth is it?
|
Not the same, not closer, not 3times as far. Acubed=Psquared. Acubed=3squared=9. Take the cube root—between 2-3 and closer to 2.
A is always going to be less than P |
|
|
What do Newton's laws describe?
|
How OBJECTS move.
|
|
|
What were some of the contributions that Newton made to Astronomy?
|
• The telescope was developed by the Dutch and not Galileo
• Pointed scope at the sky… o Saw moons around Jupiter. o Sunspots o Dark skies to the naked eye are not empty o Saturn’s rings • 3 laws of motion of all objects. Not just in space • Invented calculus |
|
|
What is Newton's first law?
|
The law of Inertia.
• An object at rest (or in motion) tends to stay at rest ( or in motion) until acted upon by an outside force. • There is no difference between being at rest and moving in a straight line at a constant speed. |
|
|
What is a good reference frame for Newton's first law?
|
• “reference frame” think of a coffee cup in your car. It behaves as if it were at rest even though that car can go 50 mph. Elevators.
o Mass: is constant. Measured in kg. Amount of material ( how many atoms do you have) in an object. o Weight: Depends on gravity. o Inertia: How much an object resists a change in motion. |
|
|
What is your mass in space compared to your mass on Earth?
|
your mass out in the space between the stars would be unchanged. Because you have that same amount of atoms.
|
|
|
What is the difference between speed and velocity?
|
o Speed: how fast an object is moving.
o Velocity: How fast an object is moving and in what direction. An object is moving at 60 mph southbound. |
|
|
• Imagine that you are a planet in a PERFECTLY CIRCULAR orbit around the sun.
Is your speed changing? Why or why not? |
No because of the perfect circle and equal areas and equal time. It does change in a non-perfect circle.
|
|
|
• Imagine that you are a planet in a PERFECTLY CIRCULAR orbit around the sun. Is your velocity changing? Why or Why not?
|
Yes. You are changing direction.
|
|
|
What is Newton's second law?
|
F=ma
|
|
|
What do the variables mean in Newton's second law?
|
• If a net outside force (F) acts on an object of mass (m), the object will experience an acceleration (a).
|
|
|
How does velocity affect acceleration?
|
• Any time you change the velocity of an object is speeds up.
o Acceleration is a change in velocity-either speed or direction. o How many accelerators are there in your car? At least three-steering wheel: changes direction. Gas pedal: changes speed. Brakes: changes speed. |
|
|
What does NOT describe an acceleration?
|
A car traveling with a constant speed along a straight highway.
|
|
|
What does describe an acceleration?
|
-car at constant speed along bend, planet in orbit, electron around the nucleus of an atom.
|
|
|
What is Newton's 3rd Law?
|
For every force there is an equal and opposite force.
• Forces are paired, if you have one, then you have two. |
|
|
What do you get when you put together Newton's and Kepler's law?
|
The reason why planets and objects move…Gravity!
|
|
|
Who discovered the theory of gravity and how?
|
Looking for the theory of gravity—Galileo discovers an apple and feather falling under gravity in a vacuum.
IT does NOT depend on mass! •Falling objects on Earth accelerate at 9.8 meters per second squared ALWAYS, and is constant. |
|
|
What happens when the objects are not in a vacuum?
|
wind resistance that changes the speed of falling.
|
|
|
Newton thinks…What is the force that accelerates the object toward the Earth?
|
• F(grav) is proportional to mass of object.
• Because for every force there is an equal and opposite force…there must be a force that that object is exerting on the Earth. Therefore the force of gravity takes into account the mass of the apple and the mass of the Earth. So the force of gravity is the product of both masses |
|
|
• Newton thinking about Kepler’s second law—Earth exerts a force on a planet and the force is stronger when the planet is closer to the sun why?
|
o The force of gravity is inversely proportional to distance. If the distance is farther then the force decreases, if the distance in closer the then force goes up.
• The force of gravity is proportional to one over the distance squared. Probably an inverse square law and depends on the distance. |
|
|
How are gravity and distance proportionally related?
|
The force of gravity is proportional to the mass of apple X mass of Earth OVER Distance between apple and the earth squared (use the radius). Fgrav~m1*m2/r2.
• Force of gravity=G*m1*m2/r2. G is the gravitational constant. |
|
|
How are Newton and Kepler's laws related?
|
• Newton’s laws of gravity predicts Kepler’s laws. Force of gravity =weight!
-• Mass of the moon is smaller therefore the force of gravity is smaller |
|
|
• Imageine you discover a new planet that has a radius equal to the Earth;s, but a mass that is twice as great as that of the Earth. What happens to your weight?
|
It increases by a factor of two.
o If the radius is twice as much. F=GMm/(2R) squared—GMm/4R2=1/4. So it went down. |
|
|
What kind of force is gravity?
|
ALWAYS and attractive force.
|
|
|
• If you are in a spacecraft orbiting the Earth you are floating around “weightless” is the Earth gravity pulling on you?
|
YES!!
|
|
|
What kind of thought experiments were done by Astronomers with the shooting of a cannon?
|
• When you fire a cannon over level ground, it is being forced forward but still being pulled on by gravity.
o If you fire a cannon faster it will go farther but will still go down. o If it is fired down a hill it goes further but still falls o If you fire a cannon ball so fast that it falls toward the Earth but the Earth curves underneath it so it never actually hits the ground.— |
|
|
What do the experiments with the cannon explain?
|
This is what an orbit is!
• Orbit: an object in freefall toward the Earth, but the Earth curves out from underneath it before it can hit the Earth. |
|
|
So, what does it mean to be weightless?
|
“zero gravity” is a misnomer. It means that the person is constantly in freefall.
o Sometimes orbits do decay. |
|
|
What is the main thing that Astronomers study?
|
LIGHT!
|
|
|
What is light?
|
• Light is how we see, but we can’t see light.
o We can only see things if light bounces off of it—reflects. o Sound is different from light completely |
|
|
What does light do?
|
o Transports energy
o Transports information |
|
|
What kind of information does light transport?
|
temperature, composition and motion
|
|
|
What is "light" as seen by humans?
|
o Visible light—light our eyes have evolved to see
o Newton named the ROY G BIV o Our eyes have evolved similarly to telescopes |
|
|
What are some other kinds of light?
|
o X-rays
o Infrared light (heat) o Radio (electro-magnetic) o Microwaves (electro-magnetic radiation) |
|
|
What is the range of light called?
|
The electromagnetic spectrum.
|
|
|
What kind of law governs light?
|
An inverse square law as related to distance-as you move away it gets weaker
|
|
|
Who pioneered the physics of light?
|
• James Clerk Maxwell
|
|
|
What do Maxwell's equations do?
|
o Describe electricity and magnetism
o He discovered that electricity and magnetism are like to side of a coin—basically the same. o Light is and electromagnetic wave |
|
|
What is the speed of light?
|
• C. 300*10to the 8th meters per second
• Nothing moves faster than this—every observer, regardless of reference frame, regardless of velocity, ALWAYS. • Constant in a vacuum. but ALWAYS. |
|
|
So what exactly is light?
|
An electromagnetic wave.
|
|
|
What is wavelength and what is it measured by?
|
Wavelength is the distance between to peaks in a wave. Measured in microns.
|
|
|
What is the period and what is it measured in?
|
Period (P)—the amount of time between peaks. Measured in seconds.
|
|
|
What is the frequency and what is it measured in?
|
Frequency (f)—inverse of the period. How many peaks per second go past a point. Measured in 1/seconds (hertz).
|
|
|
What is the equation for speed?
|
Speed(c)=distance(wavelength)/time(period).
|
|
|
What are the characteristics of red and blue light related to frequency and wavelength?
|
Red has long wavelength and low frequency
Blue light has short wavelength and high frequency |
|
|
So, how are wavelength and frequency related?
|
They are inversely proportional! As one increases the other decreases.
|
|
|
What waves have the smallest wavelength according to the electromagnetic spectrum?
|
Gamma rays--size of atom
|
|
|
What waves have the second smallest wavelength?
|
X-ray:molecule size
|
|
|
What waves have the 3rd largest wavelength?
|
UV--size of virus or protein.
|
|
|
What kind of light is from the sun?
|
Infrared, which is heat and the first after visible light or the 5th largest. However the sun emits the entire electromagnetic spectrum of light!
|
|
|
What is the second largest light wavelength?
|
Microwave--ovens and radar. The size of a period on a typed page.
|
|
|
What is the largest light wavelength?
|
radio waves--• Longest wavelength, shortest frequency
• TV, AM/FM radio, wireless internet, satellites. • Thousands or millions passing through us all the time. • Football sized to football stadium sized. |
|
|
Which type of electromagnetic radiation travels the fastest?
|
They all travel at the same speed (IT IS CONSTANT)
|
|
|
Light is not only a wave, what else is it?
|
A particle!
|
|
|
What charge to protons, neutrons and electrons have?
|
proton: +
Neutron: 0 found in the nucleus electron: - orbitals |
|
|
What does the atomic number tell us?
|
The number of protons
|
|
|
What happens when you add energy to an electron?
|
it is absorbed and jumps up a level
|
|
|
What happens when the electron wants to move to its natural state?
|
It emits energy and moves down levels.
|
|
|
What does the electron emit when it loses energy?
|
a Photon!
|
|
|
What kind of particle is light?
|
A photon!
|
