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Astronomy Ch 4-6

James Cooney UCF
STUDY
PLAY
Velocity
- rate of change of position
- the combination of speed & direction of motion
- how fast you go from one place to another
Speed
rate at which an object moves
Acceleration
rate of change of velocity
Force
anything that can cause change in momentum
Newton's Laws
1. remains at rest, or moves with constant velocity unless acted upon by an outside force
2. force equals mass times acceleration (F=ma)
3. for every applied force, a force of equal size but opposite direction arises.
Weight
- a force of gravity
- weight equals mass times acceleration of gravity (W=mg)
Universal Law of Gravitation
- Newton created
- F= m1m2/d^2
- m1 is pulling on m2 as m2 is pulling on m1. forces are the same. In exact opposite directions
- doubling the mass of one object doubles the force of gravity between the two objects
Inverse Square Law
any quantity that decreases with the square of the distance between two objects
Tidal Force
- caused when the gravity pulling on one side of an object is larger than that on the other side, causing it to stretch
- stretches the entire Earth to create two tidal bulges
- two high tides (or bulges) a day
- sun's tidal force not as strong (due to distance)
Spring Tide
- new and full moon
- high tide higher than normal
- they "spring up"
Neap Tide
- 1st & 3rd quarter moon
- small tides (high tide lower than normal)
Tidal Friction
- the moon's gravity tires to keep the tidal bulges on the earth-moon line, while earth's rotation tries to pull the bulge around with it
- earth's rotation slows down
- moon moves farther away
Synchronous Rotation
- moon rotates on its axis in exactly the same time period that it takes to orbit earth
- we always see the same side of the moon
Momentum
- equals mass times velocity (mv)
- angular momentum (r times mv)(r is radius)
- r decreases = faster/increases = slower
Kinetic Energy
"motion" the energy of movement
Potential Energy
- stored hidden energy (later converts into kinetic)
- gravitational is most important
- also chemical & nuclear
Radiative Energy
energy carried by light
Temperature
measures the average kinetic energy of particles
Kelvin Scale
starts at absolute zero (no negatives)
- equals -273C
Photon
- an individual particle of light, characterized by wavelength & frequency
- packets of energy
Electromagnetic Spectrum
-the complete spectrum of light
-includes: radio waves, infared, visable light, ultraviolet light, x rays, and gamma rays
Wavelength
λ the distance between adjacent peaks
Frequency
ƒ rate at which peaks of a wave pass by a point
- how many waves every second pass me
Proton
positive electrical charge
Neutron
no electrical charge
Electron
- negative electrical charge
- they give the atom its size
Nucleus
where protons and neutrons are found in the center of the atom
Ion
- if electrons missing or added
- atoms with positive or negative electrical charge
Isotope
versions of an element with same number of protons &different numbers of neutrons
Atomic Number
the number of protons in its nucleus
Atomic Mass Number
the combined number of protons and neutrons
Solid
atoms or molecules are held tightly in place
Liquid
atoms or molecules remain together but move relatively freely
Gas
atoms or molecules move unconstrained
Plasma
- is in the world the most
- free electrons move along positively charged ions
- atoms in plasma become increasingly ionized
Electron Energy Levels
- Only allowed to have specific levels.
- Starts off at ground state then gets excited
Ground State
- level one or energy of 9 eV
- lowest energy possible
Excited State
higher energy levels (more)
Emission Spectrum
- matter emits visible light
- each element emits its own pattern of colors
Absorption Spectrum
- matter absorbs radiative energy
- absorb those photons whose colors match their electron energy levels
- has all colors minus those that were absorbed.
Continuous Spectrum
- all the colors of the rainbow
- continuous but not equal in intensity at all wavelengths.
- spans a broad range of wavelengths without interruption
Doppler Effect
the effect that shifts the wavelengths of spectral features in objects that are moving toward or away from the observer
Redshift
Light emitted from an object moving away from you will have its wavelength lengthened.
Blueshift
Light emitted from an object moving towards you will have its wavelength shortened.
Refraction
- bending light by passing it from one medium to a second medium
- focuses light using lenses
Reflection
- bends light by mirroring it.
- focuses light using mirrors
- used more today
Spherical Aberration
- the shape of the mirrors and lens have to be exactly right (a parabola)
- A lack of focus because of shape if it's not built perfectly right.
Chromatic Aberration
Refractors Only
- different colors of light bend differently.
- focuses are all at different spots
- the bigger the lens the more serious problem.
Sagging
Refractors Only
- sagging of the telescope structure under its weight etc., and therefore result in a static stray light halo strewn with planet-like but spurious speckles.
Inhomogeneities
Refractors Only
- not the same everywhere (imperfection)
Angular Resolution
- smallest angle which can be seen
- the smallest angle at which you can distinguish two objects
- the ability to separate two objects
Twinkling
- Air turbulence in the atmosphere distorts light
- Angular resolution is degraded.
- biggest issue
Light Pollution
Man-made light is reflected by the atmosphere, thus making the night sky brighter.
Adaptive Optics
- Angular resolution improves
- eliminates the blurring caused by the atmosphere
Interferometry
- Two (or more) radio dishes observe the same object. (the angular resolution of a larger telescope)
Terrestrial Planet
- Mercury, Venus, Earth, Mars
- Rocky surfaces, metallic interiors.
- Few large moons
Jovian Planet
- Jupiter, Saturn, Uranus, Neptune
- Gas Giant Planets: Made up mostly of hydrogen, helium, and hydrogen compounds.
- Rings and many moons
Asteroid
- rocky bodies that orbit the sun much like planets, but are much smaller
- leftover rocky planetesimals which did not accrete onto a planet
Solar Nebula
the idea that our solar system was born from a cloud of gas that collapsed under its own gravity
Condensation
- elements & compounds began to condense (i.e. solidify) out of the nebula.... depending on temperature!
- solid particles form in a gas
Accretion
small grains stick to one another via electromagnetic force until they are massive enough to attract via gravity to form.
- the process where small "seeds" grew into planets
Planetesimal
"pieces of planets"
Make themselves into planets and the stuff left over are asteroids.
- combine near the Sun to form rocky planets
- combine beyond the frostline to form icy planetesimals which...
- capture H/He far from Sun to form gas planets
Nebular Theory of Solar System Formation
- start with cold cloud of gas & dust
- push - so part of the nebula becomes denser than another part of the cloud
- Everything starts to fall towards the denser part. (collapses)
- Conservation of Energy (hotter) & Conservation of Angular Momentum (spins faster)
Frost Line
the minimum distance at which it was cold enough for ice to condense
- lies between mars and jupiter
- only rocks & metals condensed on inside, Hydrogen compounds (ices) condensed beyond the frost line.
Protoplanetary Disk
a disk of material surrounding a young star (or protostar) that may eventually form planets
Radiometric Dating
the most reliable method for measuring the age of a rock
Half-Life
The time it takes half the amount of a radioactive isotope to decay
energy
what can make matter move
conservation laws
handful of quantities that you can calculate in nature
conservation of energy
energy can be neither created or destroyed, but can only change from one form to another
different forms of energy
Kinetic, Potential, & Radiative
nature of light
...
light like a wave
ƒλ = c or ƒλ = s
s=speed
c=speed of light which is a constant
light like a particle
-E = hƒ= hc/λ ["h" is called Planck's Constant]
-The energy carried by each photon depends on its frequency (color)
- blue=more energy
kinds of information we can glean from these spectra
Composition, Temperature, Velocity
How do telescopes help us in astronomy?
- Collects a lot of light.
- The bigger the telescope the more photons fall on it.

- It improves your angular resolution.
- Makes it sharper and have finer details