Astronomy Exam #2
What is the atmosphere block?
The atmosphere blocks out most of the UV part of the spectrum only UVA and UVB passed through the atmosphere -much of the IR spectrum is blocked by the atmosphere -The atmosphere does not transmit all light
Center of Mass
The balance point between two or more objects —physics allows us to treat the mass of a body as if all the masks were concentrated at the center of mass
Blackbody curves
The curve obtained when the intensity of radiation from a blackbody at a particular temperature is plotted against wavelength. —visible light it's at its peak
Transverse wave
The electric and magnetic fields are perpendicular to the direction of travel —Creates ripples
Unbound orbit
These are orbits where the object has escaped the gravitational pull of the second object Speed is greater than escape speed Can be parabolic or hyperbolic in shape
Which part of the visible spectrum has the highest frequency?
Violets or blue
Which regions of the electromagnetic spectrum pass through the earths atmosphere without being absorbed?
Visible (optical) and radio
Spectrographs or spectrometers
break up incoming light into different wavelengths Allows astronomers to analyze those different wavelengths
Doppler effect
-The motion of a light source towards an observer causes a blueshift in the wavelengths of the light to be observed -Motion of a light source away from(receding) and observer causes a red shift in the wavelengths of the light to be observed -Motion perpendicular to an observer causes no Doppler shift to be observed -If the object is moving away from us (preceding) it is red-shifted -If the object is moving towards us it is blue-shifted
Weight
1. A measure of how much gravity pulls on an object 2. the force of gravity on an object 3. depends on the mass of the object 4. depends on the acceleration due to gravity of the object F = m x a
Bound orbit
1. Circular orbit- constant speed, but acceleration is changing because the direction of the orbiting object is changing — The force that is creating the acceleration has a direction toward the center of gravity/mass —Speed = circular velocity: v(circ) = sgrt(GM/r) 2. Elliptical orbit —orbital speed is fastest at closest approach —orbital speed is slowest the farthest approach —speed is greater than circular velocity but less than escape speed
Blackbody
A black body is an object that absorbs all the light that falls on it —the blackbody than re-emits the light but not as the same intensity as the various parts of the electromagnetic that fell on it —instead the blackbody emits a characteristic blackbody spectrum of light that has the highest intensity at a maximum (peak) wavelength that corresponds to the temperature of the surface of the blackbody
Density
A measure of how tightly mass is packed into an object Density= mass/volume Density= d or p(rho)
Temperature
A measure of the average speed of the motions of atoms
Light
A wave that consists of self propagating magnetic and electric fields -Light is a wave but can behave as a particle -A light wave has zero mass
Blackbody spectra
All dense objects (solids, liquids and cores of stars) emit light in a blackbody spectrum — dense objects emit a continuum spectrum that is a blackbody(or planck) spectrum. This looks like a solid rainbow with all the colors of light present. —— Blackbodies emit light at all wavelengths ——Example: coal, incandescent light bulb, core of sun
All parts of the electromagnetic spectrum...
All light travels at the speed of light in a vacuum this is the fastest speed there any object can travel
At sea level
All objects on earth fall with the same acceleration(g) G = 9.8m/s^2 F(weight) = m x g
Gravity
An attractive force between two or more objects Depends on the objects masses and on the distance between them — The greater the mass, the greater the attraction- the greater the force between the two masses
Ellipse properties
An ellipse has a size described by the semi major access the longest length it's twice the length of the semi major access
Newtons first law
An object in motion remains in motion (modified from Galileo's conservation of momentum) A moving object will stay in constant motion meaning at a constant speed and in a constant direction An object at rest stays at rest For example: the voyager spacecraft will continue in a straight line as they travel away from our solar system
Consequences Of Wien's Law
An object that is hotter is blue An object that is cooler is rather this is opposite of what we are used to from using hot and cold water or temperature controls in cars
Newtons second law
An unbalanced force causes acceleration (change in motion) —->(F=ma) For example: when you push on the door the door accelerates and opens
Types of orbits
Bound & Unbound
Electromagnetic wave
Changing electric(E)and magnetic(B)fields create a self-sustaining electromagnetic wave
What did Copernicus propose
Copernicus propose circular orbit's for planets around the sun The Copernican model fails to accurately predict positions of planets the failure of circular orbits to provide a working model is one of the reasons the ancient Greeks such as Aristotle rejected this model when other ancient Greeks proposed it
Wien's Law
Describes the relationship between the surface temperature of an object and the peak wavelength at which the blackbody spectrum emits at the highest intensity λpeak = 0.0029mK/ T
Force of gravity
Directly dependent on mass If you increase the mass of one object the force of gravity increases —if one mass increases by a factor of 4 the gravitational force increases by a factor of 4 —if one mass decreases by a factor of 3 the gravitational force decreases by a factor of 3 Inversely dependent on the square of the distance If you increase the distance between two objects the force of gravity between two objects decreases by the square of the distance — if the distance between two objects increases by a factor of 3 the gravitational force decreases by a factor of 1/9 — if the distance between two objects decreases by a factor of 3 the gravitational force increases by a factor of 9
Brightness
Distance affects the brightness of an object, so the brightness that we see is proportional to the inverse square of the distance Brightness- infinity(1/d^2)
Consequences of Kepler's third law
Distant planets take longer to orbit the sun Distant planets travel at slower speeds
Various names for light
Electromagnetic waves, electromagnetic radiation, EM waves, EM radiation, radiation, waves, photons, light, light waves
For two objects of the same size, the hotter one well...
Emit more total light at all wavelengths Emit more total energy every second Emit that light at shorter wavelengths on average—->bluer
Stefan's law
F= σT^4 F= flux the energy per area per second emitted by an object T= the surface temperature σ= the Stefan-Boltzmann constant σ= 5.67 x 10^-8 W/(m^2)(K^2) An object that is hotter emits much more energy(has a higher intensity) at every wavelength than a cooler object
Mars orbits around the sun faster than the earth orbits
False
Radio waves are sound waves
False
Force due to gravity between two objects- Newton's 3rd law(inverse square law)
Fg = G (m1 x m2) / r2 Fg - is the force due to gravity G - is the universal gravitational constant m1 - is the mass of the first object m2 - is the mass of the second object r - is the distance between the centres of the two objects
Nicolai Copernicus
First modern astronomer to propose a heliocentric, sun centered model, we now call this the start of the Copernican revolution which eventually resulted in the acceptance of the helliocentric model of the solar system
Newtons third law
For every action there's an equal and opposite reaction For example: a rocket. The combusting fuel pushes on the rocket causing the rocket to lift into the atmosphere. At the same time the rocket is pushing on the combusted fuel which causes the rocket fuel to be pushed in the opposite direction as exhaust
Newtons universal gravitational constant
G
Which regions of electromagnetic spectrum are completely blocked by the atmosphere?
Gamma Ray and x-ray
Which part of the electromagnetic spectrum has the highest energy?
Gamma Rays
Which part of the electromagnetic spectrum has the highest frequency?
Gamma Rays
Which part of the electromagnetic spectrum has the shortest wavelength?
Gamma Rays
For planets in real world orbits
Gravity changes both the direction and the speed of the planet -will not be circular -results in Kepler second law
Amplitude
Height of a wave
Frequency versus energy
Higher frequency = higher energy
An object that has a higher surface temperature emits
Higher intensity of light at all colors
Speed
How fast an object travels
Velocity
How fast and the direction an object travels
Newtons laws describe
How the gravitational force behaves and also leads us to the concepts of circular velocity, escape velocity, and weight
Wien's law in different formats
In microns(μm)(human) λpeak= 2900μmK/ Τ In nanometers(nm) λpeak= 2.90 x 10^6 nmK/ T
The earth is closest to the sun in January and furthest from the sun in July when is the earth moving the fastest in its orbit?
January
Johannes Kepler
Kepler proposed the first accurate heliocentric model and he discovered his three laws empirically by looking at decades worth of planetary positions that had been cataloged by Tycho Brahe
Summary of Kepler's laws
Kepler's laws describe planetary orbits Planetary orbits are ellipses Planets sweep out equal areas in their orbits in equal times The larger the orbit of the planets the longer the orbital period at the planet
Luminosity of a star
L(star)= 4πR^2 σT^4
Luminosity
L= flux x Surface Area = F x S.A.
Kepler's second law
Law of equal areas in equal time
Wavelength
Length between crests of the electric or magnetic field Wavelength= Speed/Frequency or λ=c/f
Duality of light
Light behaves as both a particle and a wave —the wave nature of light manifests in diffraction, refraction, and constructive and destructive interference
Spectrum
Light sorted by frequency
Mars is the fourth planet from the sun using Kepler's third law how long does it take Mars to orbit the sun compared to the earth?
Longer period
Visible spectrum in order of wavelength
Longest to shortest wavelength Red, Orange, yellow, Green, blue, indigo, Violet
Inertia
Mass resists changes in motion
Common unit of length for a visible light is
Nanometer(nm) 1nm = 1 x 10^-9m
Which photon travels faster in a vacuum, an x-ray photon or a radio photon?
Neither they travel at the same speed— the speed of light
Newton's laws facts
Newton derives Kepler's rules from his law of gravity —physical laws the law of gravity explains Kepler's empirical results Newtons laws were tested by other astronomers based on their observation of planets —their exact agreement show that newtons law of gravitation was correct Edmond Halley use newtons law of gravity to correctly predict the year the Halley's comment would return
Sir Isaac Newton
Newton explains why planets orbit the sun—-> gravity!
Frequency
Number of wave peaks that pass by each second
Orbits
One body following around another - the less massive object is a satellite of the more massive object —a cannonball fired at just the right speed we keep falling around the earth never hitting the ground
Tycho Brahe
One of the best naked eye astronomers in history proponent of geocentric model of solar system he employed Kepler as a research assistant and tasked him to compare both the geocentric and Copernicus heliocentric model of the solar system Kepler found that both models had many errors in predicting the positions of the planets this inspired Kepler to come up with a new model, which he did
The two regions with 100% transparency
Optical and radio windows
Kepler's third law
P^2 = A^3 P= period measured in years A= semi-major axis(or size of the orbit) measured in A.U. — this equation can be used for any object orbiting the sun -semi major axis has other names if the orbit is circular or near circular (slightly elliptical): —— size of the orbit, average distance from the sun, if the ellipse has an eccentricity of 0 (a circle) then the semi major access is just the radius
Photon
Particle of light — A photon has no mass — A photon travels at the speed of light,c, in a vacuum ——light moves at 300,000 km/s or 3.o0 x 10^8 m/s in a vacuum ——First measured by Rømer when observing Jupiter's moons ——Speed of light is slightly slower in other materials e.g. glass and air
Kepler's first law
Planets orbit on elliptical paths not circular( revolutionary idea) the planets orbit a long elliptical pass with the sun at one focus the second focus is empty ellipse is defined by the semi-major access and the eccentricity A = the semi-major access E= eccentricity (how elongated or flattened the ellipse is) C= The distance from the center of the ellipse to one of the foci Equation to find eccentricity- E= c/A Eccentricity, e, varies from 0-1 Circle: e=0 A very flat ellipse(long): e=1
Galileo Galilei
Proposed heliocentric heliocentric model with circular Orbitz model failed to predict positions of planets he was one of the first scientist to use a telescope to observe the sky Galileo made four major discoveries with a telescope that challenged the thinking of the time scientifically and philosophically these include mountains on the moon, spots on the sun, moons of Jupiter, and phases of Venus. the gibbous phases of Venus observed by Galileo cannot be explained in a geocentric model this is the evidence approved the geocentric model is wrong
Which part of the electromagnetic spectrum has the longest wavelength?
Radio
Which part of the electromagnetic spectrum has the lowest energy
Radio Waves
Which part of the electromagnetic spectrum has the lowest frequency?
Radio Waves
Which part of the visible spectrum has the longest wavelength?
Red
Which part of the visible spectrum has the lowest energy?
Red
Which part of the visible spectrum has the lowest frequency?
Red
Surface of a sphere
S.A. = 4πR^2
The semi major access of earths orbit is one AU the semi major access of the Saturns orbit is 9.5 AU which planet has a longer orbital period?
Saturn
An object that has a higher temperature has its peak wavelength occur at
Shorter wavelengths
Electromagnetic spectrum
Shortest to longest Gamma(γ) ray, X-ray, Ultraviolet(UV), Visible(Optical) , Infrared(IR), Microwave, Radio
Doppler equations
The following equations describe the observed wavelength and the recessional velocity of a moving object that emits light λobs = (1 + v/c)λrest — λrest is the wavelength emitted by the object when it is not moving (at rest) also called λlab —λobs is the wavelength of a moving object emitting light as measured by the observer νrecession = ((λobserved-λrest)/λrest)c —if λobs is greater than λrest the object is redshifted —if λobs is lesser than λrest the object is blueshifted —if νrecession is positive then the object is moving away from us and is redshifted —if νrecession is negative then the object is moving towards us and is blueshifted
Momentum
The product of velocity (speed and direction of motion) and mass of the object
Acceleration
The rate at which speed changes and/or the direction of travel changes Measures how quickly a change in motion takes place Also happens when the direction changes even if the speed is constant An unbalanced force causes acceleration —greater forces mean greater accelerations —mass resist changes in motion —more mass = less acceleration
Astronimical Unit (AU)
The semi major access of earths orbit is one astronomical unit
Escape speed
The speed needed to escape from the gravitational influence of an object
What is λpeak?
The wavelength that which the blackbody (or Planck) spectrum emits the highest intensity of light —this peak wavelength determines the color of the object —this peak wavelength also determines the max wavelength
Period
Time to complete one cycle P= 1/frequency
Which part of the visible spectrum has the highest energy?
Violet or blue
Which part of the visible spectrum has the shortest wavelength?
Violet or blue
Kelvin scale
Water freezes/boils at 273K/ 373K
Photon/light wave properties
Wavelength, frequency, energy, amplitude — wavelength and frequency are inversely proportional to each other: λf=c (c=speed of light) — even though photons have no mass each photon at a particular wavelength/frequency has a different energy —The energy of a photon is given by: E(photon) = hf, where h=Planck's constant, and f= frequency
Does Kepler's first law allow for a circular planetary orbit?
Yes
Conic sections
four shapes, parabolas, circles, ellipses, and hyperbolas that are formed by the intersection of a plane and a double cone
Consequences of Keplers second law
orbital speed is fastest at closest to the sun; perihelion orbital speed is slowest at farthest to the sun; aphelion
Circular orbits
—The speed of an object in a circular orbit is constant —The circular speed is the minimum speed needed to maintain an orbit —An object in a circular orbit is constantly being pulled into a circle by the central mass that the object is orbiting —We can say that a planet orbiting the sun is "falling" around the sun