faraday: showed electric fields produced around a static charge, when electricy moves, magnetic field produced
maxwell: explained rings of saturn were small particles. in 1860's discovered it should be possible to produce a wave that combines electrical & magnetic effects
concluded speed should be 300,000km /sec, speed of light- from that he conluded light was an electromagnetic wave – 9 years later radio waves were discovered
kelvin temperature scale: 0 at coldest possible temp, absolute 0, -273 degrees C - degrees same size as celsius degree – showed that changes in electric fields
produce changes in magnetic fields and visa versa. these changing fields cause a disturbance that propagates as a wave at speed of light – called it
electromagnetic wave came ot this based on faradays work.
light is different: varying electromagnetic radiation of energy, color, wavelength, frequency
inverse square law: as light propagates, it intensity drops 1/r squared – different colors of light bend & disperse differently
spectrum: order of colors produced when light is dispersed, by treveling through a prism – white light is made up of light of many different wavelengths
wave speed = wavelength x frequency higher frequency = shorter wavelength - wavelength of reddest of red light is about 7 x 10E-7 or .0000007
wavelength decreases across spectrum from red to violet, violet is about 4 x 10E-7 - our atmosphere is transparent to visble light & radio wavesnanometer = nm = 10 x E-9 - angstrom = 10 x 10E-10 m, there are 10 angstroms in a nanmeter –
white light strikes object, object absorbs some wavelengths what we see is the part of the spectrum not absorbed or reflected- this is the color we see
we experience infrared radiation as heat –
the peak of the intensity/wavelength curve for a light-emitting object always falls at a wavelength that depends on an objects temperaturein this rough order: white being the relative hottest, then yellow, orange, red (relative coolest) - blackbody object: object that absorbs all wavelengths completely
kirchhoff's laws: -a hot, dense glowing object (solid or dense gas) emits a continuous spectrum
-a hot low-density gas emits light of only certain wavelengths- a bright line spectrum
-when light having a continiuos spectrum passes through a cool gas, dark lines appear in the continious spectrum
dark lines that result when light passes through a cool gas (last example above), have same wavelength as bright lines that are emitted if the same gas is heatedbohr atom nucleas: central massive part, positive charge - electrons: orbit nucleas, negatively charged particle postulates:
-electrons in orbit around a nucleas can have only certain specific energies can only be in allowed orbits or distances from nucleas
ex: H has only 1 electron that can exist in many posible energy levels
-an electron can move from one energy level to another, changing the energy of the atomwhen energy is added, electron moves farther from nucleas- when an atom drops to a closer orbit to the nucleas, the atom loses energy and that lost energy comes
out in the form of electromagnetic radiation
-light is emitted when an electron falls to a lower orbit, outer orbit to inner orbit- not in a continuous wave, but in bursts of energy when electron moves to an
orbit closer to the nucleas. the energy is released as a photon of electromagntic radiation energy of photon depends on spacing between orbits
photon: smallest possible amount of electromagnetc energy of a particular wavelength
-the energy of a photon determines the frequency (or wavelength) of light that is associated with the photon.
the greater the energy of the photon, the greater the frequency of light - ground state: lowest energy state of an atom, normal state.
energized states are called excited states - example: if H in its normal low energy state is given energy (by electrical charge or by collisions with other atoms) the
electron might jump to a more distant orbit. the atom will not stay in this energized state for long. the electron falls down to lower orbit, emitting a photon as it
does. the energy of this photon is exactly equal to the energy difference between the two orbits. since the energy of of the photon determines the frequency of the
radiation, the radiation coming from this atom must be of corresponding frequency and color - 2 photons may be emitted if an electron drops two shells (orbits)
in two steps. the emitted 2 photons energy will be equal to the energy if one were emitted from a fall of two orbits – there are many paths an electron can take to
get back to its normal orbit and each emits a different energy of photon
-the spectrum form heated gas is not continuous, has only certain definite frequencies- emission spectrum, the bright line spectrum
no two elements have the same set of energy levels - as light passes through gases, certain element absorb certain energy and thats how we know what element it
is. by the parts of the spectrum missing.
dopler effect: redshift: change in wavelength towards longer wavelengths object moving away - blueshift: change in wavelength towards shorter wavelengths
object moving towards us - most objects dont move fast enough to see color changes- spectral lines are used, absorbtion lines are shifted
sound higher pitched when approaching -radial velocity: along line of sight, toward or away from observer- tangetial velocity: across, perpendicular to line of sight
reflection: light bouncing of object
light as wave cannot explain emission or absorbtion, but explains refection, refraction
light travels in a straight line as long as it remains in the same medium - when light passes through a wedge of glass, it is bentthe smaller the angle of the wedge, the less bending – light travels in a stright line before entering, inside and exiting the glassit is bent as it passes through each surface on the glass
refraction: bending of light as it cross the boundry between two materials in which it travels at different speeds - light is refracted by earth's atmosphere
light travels slightly slower in air vs a vacuum (3x10E8) slower still in glass (2x10E8)
the smaller the angle between the ray of light and the surface, the more the light bends upon passing through the surface
image: the visual counterpart of an object, formed by refraction or reflection of light from the object
focal point: point at which light from a very distant object converges after being refracted or reflected.
focal length: distance from the center of a lens or a mirror to its focal point - objective lens: main light gathering element, lens or mirror, of a telescope
(objective, primary lens) - eyepiece: magnifying lens used to view the image formed by the objective of a telescope
dispersion: the sepearation of light into its various wavelengths upon refraction – when light bends as it disperses
chromatic aberration: defect of optical systems that results in light of different colors being focused at different places
achromatic lens: optical element that has been corrected so that its free of chromatic abberation
angular size: angle between two lines drawn fromn the viewer to opposite sides of the object
magnifying power: ratio of the angular size of an object when it is seen through telescope vs when it is seen with the naked eye
focal length of objective
magnification power = ----------------------------focal length of eyepiece
this means greatest magnification is achieved with long focal lenght objectives and short focal length eyepieces
as magnication increases, field of view decreases
light gathering power: measure of the amount of light collected by an optical instrument use a larger objective to gather more lightarea of circle depends on square of its diameter
resolving power: the smallest angular seperation detectable with an instrument, its ability to see detail. the smallest angular seperation 2 stars can have and be
resolved by the instrument
diffraction: the spreading of light upon passing the edge of an object depends on the wavelength of the light and the size of the opening
the longer the wavelength, the more diffraction- the larger the opening, the less diffraction
inwardly curved mirror: concave outwardly: convex
why reflectors can be larger than refractors: -a refractor has two lenses, four surfaces. reflector has only one - imposible to correct lenses of chromatic
aberration (refracting) reflectors use mirrors and there is no aberration problems - reflectors mirror is front surfaced, light does not pass through glassdoesnt need to be perfect and its cheaper not to have so many perfect lenses made that a refractor uses
newtonian focus: eyepiece at side of telescopes body cassegrain: eyepiece at back of body, secondary mirror has outward curve
prime focus: point where the light from objective is focused - active optics: system that monitors changes in shape of a scopes objective to produce best image
ccd: charge-coupled device: semiconductor that serves as a light detector photometry: measurement of light intensity from a source
spectrometer: instrument that seperates electromagnetic radiation according to wavelength
diffraction grating: device that uses the wave properties of electromagnetic radiation to seperate the radiation into its various wavelengths
radio telescopes problems: intensity of radio waves from a star is much less than lightwaves - since wavelengths are a million times greater than visible light,
corresponding decrease in resoulution these problems are resolved by making radio telescopes very large - resolution depends on diameter of telescope
(bigger=higher) and wavelength (bigger=lower) interferometry: procedure that allows a number of scopes to be used as 1 by taking account the time at which
individual waves from an object strike each scope the farther apart, the better the resolution - signals created by the scopes from radiation must be sync'ed time
wise together- waves arrive at a scope that is higher in altitude sooner must be delayed when processed with lower scopes -vlba:very long baseline array: 10
scopes in hawaii, new hampshire, washington, virgin islands- control centeris in sorroco new mexico. resoloutions to fractions of milliarcseconds- 10, 000 times
better than earth bound optical scopes. a milliarcsecond in less than the angular diameter of a dime at 1000 miles
SUN has an average angular diameter of 31'59", just less than 32 minuts of arc - average distance from earth 1.5 x 10E8km - diameter 1.39 x 10E6km
about 110 times that of earth - mass 1.99 x 10E30kg, 300,000 times earth - average density 1.41 gm/cm cubed - differential rotation: 25.4 days at equator
40 days near poles - luminosity: 3.9 x 10E26 watts - tilt of equator to ecliptic: 7.25 degrees - surface temp: 6000 degrees
sunspots: region of the photosphere that is temporarily cool and dark compared to surronding regions – usually appear in pairs are 1500 degrees cooler –
have strong localized magnetic fields (3000x normal) move in a butterfly like pattern towards equator – never at poles 35-40 latitudes 11 year cycle
luminosity: rate at which electromagnetic energy is being emitted, total power output - solar energy strikes upper atmosphere at the rate of 1380 w per sq metertotal energy output by sun is calulated by imagining a sphere the size of the distance of sun to earth, calculating the square footage of that sphere, and multiplying
by above number area of sphere = 4(pi=3.14)(r squared) r = radius total solar power = watts per square meter x (area of sphere)
nucleas of atom = 99.98% of the mass of the atom and contains 2 types of particles: protons: massive positive charge, number determine what element atom is
neutron: massive nuclear particle with no charge - fusion reaction: two nuclei combine to form a larger nucleas, they fuse
the primary source of energy of the sun and in all stars is nuclear fusion reactions in which four hydrogen nuclei are fused to form on helium nucleas a small
portion of the mass is converted to energy - the temperature of a gas is determined by the speed of its particles
particle density: the number of seperate atomic and or nuclear particles per unit of volume
pressure of a gas determined by the speed of the molecules of gas and their density - heated gas, molecules move faster, collisions are more violent, exerting
more pressure faster molecules means more collisions pressure and temp are related in a gas
hydrostatic equilibrium: star or planet, the balance between pressure caused by the weight of material above and upward pressure exerted by the material below
three methods of heat transfer from core of sun to surface: conduction (of heat): the transfer of heat in a solid by collisions between atoms and/or molecules
convection: the transfer of heat in a gas or liquid by means of the motion of the material (the warmer fluid moves) radiation: the transfer of energy by
electromagnetic waves principal means of heat transport in a star - heated air is less dense than cooler air
standard solar model: today's generally accepted theory of solar energy production - limb: the apparent edge of an object as seen in the sky
the solar pectrum peaks near the center of the visible regionphotosphere: deepest we can see into sun - temp from 8000C to 4000C near outer edge - the light we receive is representative of an object 5800C - mass is 78%
H, 20% He, 2% is some 60 elements - 94% of atoms in sun are H - granulation: division of the sun's surface into small convection cells granules are ares where
hot material (seen as light ares) is rising from below and then descending (into dark areas)
chromosphere: region between photosphere and corona - spicule: narrow jet of gas that is part of the chromosphere and extends upward into the corona
6000-10,000km and can last from 10-20 minutes - prominence: eruption of solar material beyond the disk of the sun - solar wind: the flow of nuclear paricles
from the sun travels at about 400km/sec and is 2-10 particles per cubic cm – escapes from corona holes solar flares: explosion near or at the sun's surface, seen
as an increase in activity such as prominences. electromagnetic theory: unified electric & magnetic fields
chromosphere & corona produce emission lines not spectrum
sun is hotter farther from core cause of magnetic energy being converted into other forms of energy- when a planet has a liquid core, charged particles (ions) are
moving creating a magnetic field – magnetic lines are tangled, this stores up energy - core of sun is moving alot
i sq m on earth is hit by 1380-1400 watts of power from sun
spectral types of stars: O B A F G K M sun is G2