Astronomy Exam 2
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- rate at which an object's velocity changes
- accerleration around a corner increases
anything that causes a change in momentum
- the overall force to which an object responds; the net force is equal tothe rate of change in the objects momentum
- Fnet=m X a
Weight and Mass
Mass is the amount of matter in a body or object. The difference between mass and weight is that mass does not change due to different gravity fields where as weight does. A good example is a person standing on a scale in an elevator. The weight of the person will fluctuate according to the scale but the mass of the person never changes.
"falling around" the Earth
- revolutionized science and math
- gravity operated in the heavens as well as earth
- he quantified the laws of motion and gravity
- he conducted experiments regarding light
- he built the first reflecting telescope
- he invented mathematics for calculus
Newton's Laws of Motion
- First law of motion states in the absence of a force, an object moves with constant velocity or remains still.
- Second law states how net force affects an object’s motion. This is represented with the equation F=momentum=mass X acceleration.
- Third law states that for any force, there is an equal and opposite reaction force.
Conservation of Momentum
in the absence of FN=, the total momentum of a system remains constant
- energy of motion
- KE= 1/2 mv2
energy stored for later conversion into KE
energy carried by light; the energy of a photon is Planck's constant(h) X frequency(f)
- collective KE, as measured by temp.,of the many individual particles moving within a substance
- EX) lake has more thermal energy than a 5 gallon of water at 210 degrees
Gravitational Potential Energy (GPE)
- energy that an object has by virtue of its position in a gravitational field
- an object has more GPE when it has an increased distance that it can fall
- the PE of mass
- EX) Bombs!
Newton's Universal Law of Gravitation
Newton’s Universal Law of Gravitation is the force of gravity between two objects. The equation F=G(M1M2/d2) means that every mass attracts every other mass. This explains Kepler’s laws of planetary motion, that described the simple and stable orbits of the planets. It also means that the strength of the force of gravity attracting any two objects is directly proportional. This equation follows the inverse square law which states that any quantity that decreases with the square of the distance between two objects.
How does Newton's Law of Gravity extend Kepler's Laws?
- Planets are not the only objects with elliptical orbits
- Ellipses are not the only possible orbital paths EX) parabolas, hyperbolas
- Objects orbit their common center of mass
- Orbital characteristics tell us the masses of distant objects
- the sum of an orbiting objects kinetic and GPE's - always stays the same - b/c of law of conservation of energy
- an orbiting planet has KE(orbital speed and distance from sun) and GPE
2 or more objects pass near enough so that each can feel the effect's of the other's gravity and they can therefore exchange energy
- a satellite orbitting low ->due to drag it falls -> lost orbital enery->thermal energy
- helps explain the moons of the outer planets
the speed necessary for an object to completely escape the gravity of a large body such as a planet
- gravity pulling on one side of an object is larger than that on the other side causing the object to stretch
- 2 high tides
- low tides 1/2 way btwn 2 tidal bulges
Occur at new moon and full moon
occurs at first and 3/4 moon
friction within an object that is caused by a tidal force
- Measured in joules
- Short wavelength = higher energy
- Long wavelength = lower energy
- Rate at which energy is carried away (used,flow)
- Measured in watts
Matter emits energy in the form of light
Matter absorbs radiative energy
Light passes through matter without being absorbed
- The process by which matter changes the direction of light
- How we see things in everyday life
- Scattering= a form of reflection
Properties of light
Light is a particle (gold foil) and a wave (pond ripple)
Are compression waves in air
How light travels
By electromagnetic fields- a synonym for light, which consists of waves of electric and magnetic fields
- Have properties of both particles and waves
- "particles of light"
- The process of obtaining spectra from astronomical objects
- Can find mass, temperature, and velocity
- Measure of the amount of energy coming from light of specific wavelength in the spectrum of an object
- Wavelength with a lot of light-> high intensity
- Wavelength with little light-> low intensity
- 1) continuous spectrum- rainbow spans a broad range of wavelength's without interruption
- 2) cloud of gas emits light at wavelengths depending on composition and temperature
- Emmision lines- light against a black background, called an emission line spectrum
- 3) cloud absorbs ligh of specific wavelength's, so the spectrum shows dark absorption lines on rainbow, called absorption line spectrum
- Absorption lines = dips
- Emission lines = spikes
How Does the emission line spectra work?
Collisions-> transfer of energy-> electron goes to a higher energy level-> the energy the electron loses = emitting a photon therefore a specific wavelength
Absoprtion line spectra
- After an electron absorbs a photon and rises to a higher energy level
- 1) electron moves to the original level, emmiting a photon of the same energy that it absorbed
- 2) we are left w/ an absorption line b/c photons of a specific wavelength have been removed from the spectrum of light coming towards us
- Both lines represent the same energy level transitions, but in opp. direction
- atoms, ions, and molecules have a unique fingerprint
- Ions- help figure out temp
- Molecules- can absorb or emit a photon when it changes rate of vibrating and rotating
the spectrum of radiation produced by an opague object that depends only on the objects temp.
Thermal radiation spectrum
- b/c of thermal radiation
- temp. given on Kelvin scale
Two laws of thermal radiation: Stefan-Boltzmann law
each square meter of a hotter object's surface emits more light at all wavelengths
Two laws of thermal radiation: Wien's Law
- hotter objects emit photon's witha higher average energy
- ex) poker in a fire
An actual spectrum
- reflected light: planet color
- absorbed light: temperature
The doppler effect
- effect that shifts the wavelengths of spectral features in objects that are moving toward or away from the observer
- Red shift: moving away
- Blue shift: coming towards
- can determine rotation rate of a distant object by measuring the width of its spectral lines
Appearance of the solar system
Where did asteroids come from?
- the rocky leftover plantestimals of the inner solar system
- asteroid belt btwn Mars and Jupiter
Where did comets come from?
- ice-rich leftover plantestimals of the outer solar system
- donut shaped region= kuiper belt
- Two 18th century scientists:
- Immanuel Kant- solar sys formed from the fravitational collapse of an interstellar cloud of gas
- Pierre-Simon Laplace- same idea independently
- ---> nebular hypothesis
Nebular theory (1950's)
- predicts existance of Oort cloud and the Kuiper belt
- observe other solar systems
Exceptions to the rule
- Earth's moon, tilt of Uranus
- Heavy Bombardment: the period in the first few million years after the solar system formed during which the tail end of planetary accretion created most of the craters found on ancient planetary surfaces
How do we explain the existance of our moon?
- giant impacts- a collision btwn a forming planet and a very large planetismal
- collision w/ Mars sized object->earth's outer layer blown into space->our moon
How did the terrestrial planets from?
- the solid seeds of metal and rock gradually grew into terrestrial planetsEarly in the accretion process, there are manu relatively large plantetismals on crisscrossing orbits
- As time passes, a few planetismals grow larger by accreting smaller ones, while mothers shatter in collision
- Ultimately, only the largest planetismals avoid shattering and grow into full-fledged planets
How did the jovian planets form?
- The young jovian planet swere surrounded by disks of gas, much like the disk of the entire solar nebula but smaller in size. According to the leading model, the planets grew as large, ice-rich planetismals captured hydrogen and helium gas from the solar nebula.
- ->huge planetismals gather hydrogen and helium to form jovian planets->while the disk forms large moons by condensation and accretion, and captures small moons
How were extra solar planets by transit?
in which the planet appears to move across the face of the star. We occasionally witness this effect in our solar system when Mercury or Venus crosses in frontof the sun.
How were extra solar planets by doppler wobble?
when a star wobbles it means that something is causing it
How many extra solar planets are there?
over 700 today
Orbit of extra solar planets
- big planets- large mass
- close to the star
- orbit is elliptical
What are the basic components of the eye?
- lens, pupil, and the retina that has cells called cones and rods
- an image goes through the lens and focuses in the retina
How do we record image?
- a lot like the eye
- can build up an image
- longer exposure time means that more photons reach the detector, allowing faint details to be visible
2 most important properties of a telescope
- Light collecting area(light grasp): the area of the primary mirror or lens that collects light in a telescope
- categorize size as diameter
- Angular resolution(resolving pwr): the smallest angular seperation that 2 point like objects can have and still be seen as distinct points of light
a telescope that uses lenses to focus light; needs 2 lenses
- a telescope that uses mirrors to focus light
- Cassegrain focus: (popular)out bottom, split mirror on bottom
- Newtonian focus: full mirror on bottom and eye piece at the top side
- Nasmyth/Coude focus: full mirror on bottom, 2 smaller mirrors on the inside and eye piece on bottom side
How do astronomers use telescopes?
- imaging: find light outside the visible spectrum
- Spectroscopy: seperate colors of light into spectra
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