Astronomy Test 2

In the absence of external forces, things continue what they were doing

F=MA

action= - (reaction)

-goes in straight line
-more of an abstraction, not real
-useful for understanding reflection and refraction

-oscillation of electric, magnetic fields
-2 slit interference demonstration
-character of light (color, part of em spectrum) determined by wavelength

-in some experiments: photons
-energy related to the wavelength of the light:

E=hc/[wavelength]
where e is the energy of the photon in electron volts (eV), [wavelength] is in Ångstroms, and hc is a constant =12,400 eV - Å
-so as wavelength increases, E decreases

-relatively smooth variation of I with [wavelength]
-almost always produced by hot solid objects or hot ionized gas.
-known as blackbody radiation

-have sharp features (the lines) that are produced by the activities of free and undistrubed atoms and molecules

-bright lines in the spectra, or peaks on the graph.

-dark lines, or dips in the spectrum or graph

-emitted by hot stuff: composition doesn't matter as much
-smooth spectrum
-Intensity and peak wavelength depend on temperature

-nuclei surrounded by electrons
-electrons are in states with specific energies. classically referred to as electron orbits.

when an atom changes to a configuration with less energy in the electrons, the excess energy is released as a photon of light

since electron energies are quantized, only certain wavelengths can be emitted or absorbed

-lower state is n=1, light in the UV
-FOR HYDROGEN'S SPECTRAL LINES

-lower state is n=2, light in the visible
-For this reason particularly important in astronomy: hydrogen emission lines that occur in the visible part of the spectrum
-FOR HYDROGEN'S SPECTRAL LINES

-lower state is n=3, light in the IR
-FOR HYDROGEN'S SPECTRAL LINES

No because all balmer absorption lines come from transitions in which the lower state of the atom is n=2. At room temperature essentially all H atoms will be in the ground state, so these lines will not appear.

magnification=focal length of objective / focal length of eyepiece

use a lens to collect and focus light

use a mirror to collect and focus light

1. prime focus
2. newtonian
3. cassegrain
4. schmidt-cassegrain

reflecting telescope where you stick your head in. problem: your head gets in the way

reflecting telescope with a mirror at the prime focus so you don't have to stick your head in. you would have to stick your head into a prime focus telescope.

-reflecting telescope that reflects twice, then shoots the reflected light out a hole in the first reflecting mirror.
-long focal length, short tube length

like cassegrain, but with correcting plate that light passes through before hitting first reflecting surface.

-a large reflector is usually used to concentrate the very feeble radio signals. The design is frequently a lot like that of an optical reflecting telescope.
-resolution is proportional to wavelength, so since radio waves are long, it's often better to use an inferometer array.

-atmosphere blurs image from ground-based telescopes, so the higher up, the better
-?

1. cloud of gas and dust gets an initial nudge from something
2. gravity takes over, the cloud (solar nebula) compresses on its own
3. cloud shrinks, flattens, spins faster
4. inner part-->sun, rest-->planetesimals
5. planetesimals collide, stick-->planets
6. T Tauri wind
7. Gravitational interactions among early planets rearrange their positions, kick some out

probably, although mercury might not be stable enough to stay long

-too hot and small to hold atmosphere
-cratered: no way to erase craters formed long ago
-like moon, but with magnetic field

-planet got hit by stuff
-surface was solid enough to support craters
-impacting objects came in various sizes
-craters were, or were not, modified by atmospheric or geological processes
-the rate, or type, of cratering may have changed over time

-moves up/down/left/right: does not naturally follow stars

-just rotates around one axis: can follow stars. unlike altazimuth telescope

-(t tauri wind)
-but three real factors:
1. the more massive the planet, the stronger its gravity and more ability it has to hold all kinds of gases in its atmosphere
2. the hotter the planet, the faster the gas molecules move and the harder it is to hold onto them
3. at a given temperature light molecules are moving faster than heavier molecules and are therefore more difficult to hold in an atmosphere

-it's small and very hot, so unsurprising
-less gravity, faster moving particles

-thick atmosphere: mostly CO2, clouds of slufuric acid droplets
-some craters, but fewer than mercury
-temperature very high as a result of the greenhouse effect

-atmosphere: wet, reactive, moving
-few craters: floating crust results in volcanism
-magnetic field: probs has iron core. traps charged particles

-maria: smooth areas fomred by flowing (now solidified) lava
-mountains: from impacts, not plate tectonics or volcanoes
-craters: from meteor impacts
-probs result of asteroid collision with earth
-reason for earth's 2 tides per day

-thin atmosphere, mostly CO2
-craters, volcanoes, canyons, but *no canals
-polar caps: CO2 and ice
-LIFE? spacecrafts say probably not, probably too much UV radiation, although might be some underground water. but most likely no life

-1st planet outside asteroid belt, jovian
-rapid rotation causes complicated clouds
-Great Red Spot--been there for 300+ years
produces more heat in its interior than it receives from the sun
-strong magnetic field, radiation belts
-very thin ring

-has rings that are individual particles: we know because we can see through them
-rings rotate

-moon of saturn that might have life
-has atmosphere
-has icy surface
-has geysers

-1st "non-ancient" planet
-lots of moons
-can detect faint rings from occultations of stars

-gaseous
-existence predicted from perturbations of orbit of Uranus

-rocky/icy
-small: 1/5 of moon
-really a kuiper belt object

-no planets in asteroid belt because of gravitational competition between sun and jupiter
-cratered
-can determine size, shape from observations of occultations of stars

-small objects in elongated orbits around the sun
-move slowly in sky: don't streak like meteors
-frozen gases mixed with dust and other junk
-heat up and evaporate when they approach the sun, producing the coma and tail

-nucleus: small solid part that we don't see
-coma: the cloud of gas and dust surrounding the nucleus; up to 100km across (easiest to see)
-tail: extends away from the sun (not always back); two components: gas (or iron) tail and dust tail; can be up to 1AU long

-"shooting star," most the size of a grain of sand

a meteor before it enters the earth's atmosphere

object after it hits the ground

-stony (most)
-"irons" (some)

-produced when the earth passes through the trail of junk left along the orbit of a comet.
-can see more meteors in the hoursd before dawn because then you are on the "front" side of the earth as it orbits around the sun

-ball of gas heated by nuclear fusion
-no real surface, just a radius at which the gases become transparent
-mostly hydrogen, with some helium and small amounts of other elements ("metals")

-contintinuous spectrum formed by hot gases deeper down
-absorption lines formed in cooler gases nearer the "surface." The strength of these lines is strongly temperature-dependent

-based on spectra but closely related to SURFACE temperature
-OBAFGKM (hot/blue/"early"-->red/cool/"late")
-10 subdivisions per letter (A0, A1, etc.)
-in our galaxy, 90% K and M, 99% G, K, M.

-wave crests arrive more frequently if the source of the waves approaches us rather than remains stationary. if the source approaches us, we get waves that are shorter, higher pitched, and bluer.

-temperature
-composition, esp. for elements near surface of star
-motion: check red or blue shift (although only radial component of velocity)
-presence of companion: depending on redshift or blueshift in oscillatory manner, or if two sets of lines are visible
-rotation: unless axis of star pointed toward us, light from one part of the star will be redshifted, while the other will be blueshifted.
-density or pressure: cause random motions and blurring of the usually sharp energy levels. there is a way of telling them apart from rotational broadening
-magnetic field: energy levels of atoms are slightly split into multiple components. results in another, flat, type of broadening.