Astronomy First-Second Test Flashcards
tropical year
365.2422 mean solar days
calendar year
365 days
how to reconcile tropical and calendar years
one leap year every four years, add .25 days/yr, common years= centuries not divisible by 400 have no leap year, -.0075 days/year. result in avg year of 365.2425, good for 3 days in 10k years.
apparent motion of things in sky.
everything transits once per day, stars transit 4 mins earlier each day (resets every year). Moon and planets not so simple.
transit
crossing of celestial meridian (due N to due S) at top sky
earth’s rotational axis and orbital plane
not parallel- this is reason for season. earth’s axis tilted 23.5° compared to orbital plane.
terminator
day/night line on earth, perpendicular to sun’s rays. perpendicular to equator on equinox, 23.5° off on solstices.
zenith
highest point of sky
tropics of cancer and capricorn
highest latitude where sun reaches zenith. Cancer in N hemisphere, capricorn in south
limb
outside of ring of celestial body seen from space, ie circle
reasons for season
during winter same sunlight is spread over wider area: think square held up at different angles.
also: length of day, terminator moves as earth moves around sun, longer and shorter days means more and less sun’s heat on earth.
MAYBE JUST: During winter, that part of earth is tilted away from the sun and is less exposed to sunlight than in summer.
NOT reason for seasons
closeness to sun during earth’s elliptical orbit. sun’s apparent size only varies by 2%, not a factor
sun movement relative to stars
west, covers different stars every day.
celestial sphere
projection of earth’s coordinates out into space, infinite radius (pretend stars are infinitely far away). same rotation and poles and equator and axis as us. earth’s equator and poles become celestial equator and celestial poles
cut off polar 30° of earth and then cut vertically at jun 21
plot positions of sun seen from equator… it forms a SINE WAVE
equinox
when the sun crosses celestial equator. time and a place
stellar coordinates
declination and right ascension
declination
dec-lower case delta. measured in degrees. degrees north or south of celestial equator, like latitude
right ascension
RA- lower case alpha. measured in hours/minutes/seconds, NOT degrees. hours east of vernal equinox.
sun above arctic circle
jun 21, 23.5°, sun angle above horizon. sept 21 (equinox) halfway up, dec 21 twilight all day (goes 23.5° down)
seeing celestial poles from Earth
standing on a tall mountain on equator, looking up or down curvature of earth: long exposures can see the dot in the middle of the celestial poles
zenith diagram
angle from equator to where observing is standing on 2d circle representing earth is latitude. latitude that keeps going out into space is zenith, highest point in sky. Horizon is tangent to “limb” of earth. Point has its own celestial equator, jun 21 sunlight angle is 23.5° up, dec 21 is down.
precession of earth
rotates on axis in addition to N|S rotation. Period of ~26,000 years. NOT cause of seasons: that tilt stays basically the same throughout a year, what changes is how tilt is facing the sun. this tilt means that in 13k years earth’s tilt will be 44°.
star epochs
precession of earth means that star charts need to be constantly corrected. 2010.0 means chart is correct for jan of 2010. 2013.7 for now, probably, is done by tenths. have to precess coordinates.
reason for precession of earth
gravity of sun and moon combined. nutation is the difference between the sun’s part and the moon’s part. nutation 9arcsecs, 19yrs
cause of phases of moon
NOT earth blocking it: what side of moon is sun hitting, what side is earth looking at? It’s all about the angles.
phases of the moon
new, crescent, quarter, gibbous, full. waxing first then wanes backwards
moon’s orbit
e=.55. has apogee and perigee, distance changes during orbit. not actually bigger on horizon than in sky-optical illusion caused by small ground objects
synodic lunar month
from one phase to repeat of phase, usually quarter is best (terminator straightness can be seen)
sidereal lunar month
time between the moon occulting a certain star. synodic longer by two days because earth’s position around the sun changes by one month of orbiting, so moon has to go a bit further.
rotational speed of moon
same as orbital period, so that one side is always seen facing the earth/
reason for tidal locking.
moon’s original rotational speed slowed down because of “mascon” under the surface, earth’s gravity pulled it more towards it then pulled it back, slowing it down to current rate.
synchronous rotation
orbital period and rotational period the same, aka moon. Subset of spin-orbit coupling
spin-orbit coupling
some relationship between orbital period and rotational period.
lunar eclipses
when the earth shadows the moon. Restrictions: simple angles means it has to be on a full moon, 5° variation in moon’s orbit means not every full moon is an eclipse.
reddish color of moon during eclipse
though sun is blocked by earth, sunlight goes through atmosphere and scatters at moon. most blue light scatters down, red goes through the best.
umbra
total shadow of celestial body on another, i.e. > shape going from earth to moon. total shadow, white car would be black
penumbra
partial shadow of celestial body to another, ie < shape coming from earth and hitting opp sides of moon from origin. white car would be gray.
kinds of lunar eclipse
umbral (total), partial (half and half umbra/pen), penumbral (no one cares, light variation has to be meaured.
rate of eclipses
2-5 Pens/yr, 1.5 avg totals/yr.
rayleigh scattering
particles in atmosphere scatter light. efficiency is proportional to 1 over the wavelength^4. short wl blue light is scattered easily, long red light less so. causes red moon+sunsets/sunrise
solar eclipse
same idea as lunar, moon blocks sun. has umbra and penumbra, no such thing as penumbral solar eclipse though. leaves paths on earth for when it was blocked, paths W->E, for any point avg 1 eclipse every 360 yrs
annular eclipse
when the moon is near apogee and doesn’t block all of the sun, looks like concentric circles.
tides
as earth revolves, pull of gravity of the moon and antipolar side of earth trying to get away from moon cause force vectors along surface to bulges. always low tide at poles. amplitude depends on ocean floor
mare/maria
basaltic lava fields on moon. appear as dark flat areas on moon’s surface. 500k years younger than cratered regions. impact lava oozed in from side.
MOONFACTS
Diameter -1/4 earth Mass - 1/64 of earth (same density) 238,000 miles away from earth. Albedo - .07 Atmosphere- almost none Max/Min surface temp -240F, in -300F Age- 4.6 billion years Gravity- 1/6 of earth
moon’s albedo
reflected/incident light.
lower than you’d think- .07. Only bright against dark sky.
temperature on moon
240° in day, -300 in night. thermometer won’t work cause no air molecules, have to stick it in ground.
why moon has no atmosphere
atmosphere determined by heat vs escape velocity. moon has high heat and low escape velocity, so nothing sticks around
escape velocity
speed something has to be to escape. same as minimal impact velocity. thus, impacting bodies are the speed they already have plus MV. moon’s EV: 5k mph
moon day length+ earthrise
earth always in same position from moon due to tidal locking. day length is synodic month, daylight for two weeks.
Moon geological features
UP TO mountains 4k km high, crators 80km across.
Rille
geological feature on moon. thought originally to be dry riverbeds, now thought to be ancient lava flow tubes. apollo 15 photographed one up close.
Apollo LEM
Looked like a pod on spider legs. Slowed down for landing with retrorockets. Two astronauts in each. Rover was in bay on pod, wheels lowered first than rover layed onto it. They got to the surface after being launched from a lunar orbiter with an additional crewmember above it. There were X successful landings.
other moon info
Chemistry of moon very similar to earth. astronauts had to use film chest cameras which made for awkard posititioning. l
moon’s surface
2-4” of dust. dust was kicked up by a rover so astronauts duct taped extra part from lander to wheel as dust guard.
mare orientale
3-rimmed crater on far side of moon. 200 miles across.
gravity anomalies on moon
gravity strongest in mare- mascons below them, more mascons on close side.
if atoms are mostly empty space, why can’t you put your hand through stuff
electrostatic forces- the molecules in the stuff and your hand create solidity. these things are somewhat bonded in liquid and not bonded in gas.
of protons, neutrons, electrons
atomic number/element, isotope of element, ionization of element
when a charged particle moves through space
it radiated light
atomic absorption and emission of light
when an electron jumps from one orbit to another it either absorbs or emits light with energy equal to that of the difference in energy levels between teh two orbits.
specifics of absorbtion
when a wavelength of light that matches difference needed approaches an atom, if its within impact parameter the atom absorbs it and one of its electrons is bumped up.
specifics of emission
when electron drops down, it either jumps or cascades down energy levels, emitting light equal to each jump down.
equation for energy of light
E = hc/wavelength
electron orbit properties
at certain quantized energy level/radius. discrete, single-valued.
bigger jump
more energy/shorter wavelength. thus, blue light=higher energy.
two ways to knock electrons out of orbit
- hit it with a specific frequency of light
2. heat it up so it will collide more often, more faster random motions
fire
hi temps in air knock electrons out of orbit, they emit light
how spectroscopy works
if we know what wavelengths of light are emitted by certain electron jumps, we can see what elements are present by looking for absorption or emission of those specific frequencies.
star spectroscopy
stars basically emit all wavelengths because there’s so much crazy shit goin on in there. emits white light (all freqs), then star’s atmosphere absorbs some of it (hydrogen and helium)
absorption spectroscopy
white light - certain wavelengths, seen as black lines. looking at those lines we can tell what elements thing is made of
how prisms work
white light goes into a refracting medium (usually glass, in triangle shape) and passes out the other side. different wavelength lights refracted at different angles, with high wavelengths refracted least. this splits the beam so that black lines can be seen.
normal/better way of spectroscopy
use grating instead of prism, which uses diffraction instead.
why use slit with a spectroscope
primary image in spectroscope comes in very fuzzy and blurry, thus most seperated light overlaps in blobs making white light. use a slit so only a small portion of the light gets thru.
absorbtion spectroscopy besides stars
sunlight reflected from a planets surface (thru its atmosphere) also does this
different kind of stars look like
O-m2 stars, hot to cold. O stars have more blue light (higher E)
notable emission lines
H alpha, sodium double D
how spectra really looks as used by astronomers
in black and white, negative image
doppler effect
wavlength of thing moving towards us gets smaller, thing moving away from us gets bigger.
radial velocity
motion of object either towards or away from us, + means towards, - means away, 0 means no movement towards us
star doppler effect equation
delta wavelength / normal wavelength = radial velocity/c
use of star doppler effect equation
if delta wavelength and normal wavelength is known, radial velocity can be calculated
how to do spectroscopy if wavelengths change
all wavelengths shifted the same-look for patterns up or down spectrum that match known ones.
