Astronomy First-Second Test

Question 1

tropical year

Answer 1

365.2422 mean solar days

Question 2

calendar year

Answer 2

365 days

Question 3

how to reconcile tropical and calendar years

Answer 3

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.

Question 4

apparent motion of things in sky.

Answer 4

everything transits once per day, stars transit 4 mins earlier each day (resets every year). Moon and planets not so simple.

Question 5

transit

Answer 5

crossing of celestial meridian (due N to due S) at top sky

Question 6

earth’s rotational axis and orbital plane

Answer 6

not parallel- this is reason for season. earth’s axis tilted 23.5° compared to orbital plane.

Question 7

terminator

Answer 7

day/night line on earth, perpendicular to sun’s rays. perpendicular to equator on equinox, 23.5° off on solstices.

Question 8

zenith

Answer 8

highest point of sky

Question 9

tropics of cancer and capricorn

Answer 9

highest latitude where sun reaches zenith. Cancer in N hemisphere, capricorn in south

Question 10

limb

Answer 10

outside of ring of celestial body seen from space, ie circle

Question 11

reasons for season

Answer 11

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.

Question 12

NOT reason for seasons

Answer 12

closeness to sun during earth’s elliptical orbit. sun’s apparent size only varies by 2%, not a factor

Question 13

sun movement relative to stars

Answer 13

west, covers different stars every day.

Question 14

celestial sphere

Answer 14

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

Question 15

cut off polar 30° of earth and then cut vertically at jun 21

Answer 15

plot positions of sun seen from equator… it forms a SINE WAVE

Question 16

equinox

Answer 16

when the sun crosses celestial equator. time and a place

Question 17

stellar coordinates

Answer 17

declination and right ascension

Question 18

declination

Answer 18

dec-lower case delta. measured in degrees. degrees north or south of celestial equator, like latitude

Question 19

right ascension

Answer 19

RA- lower case alpha. measured in hours/minutes/seconds, NOT degrees. hours east of vernal equinox.

Question 20

sun above arctic circle

Answer 20

jun 21, 23.5°, sun angle above horizon. sept 21 (equinox) halfway up, dec 21 twilight all day (goes 23.5° down)

Question 21

seeing celestial poles from Earth

Answer 21

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

Question 22

zenith diagram

Answer 22

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.

Question 23

precession of earth

Answer 23

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°.

Question 24

star epochs

Answer 24

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.

Question 25

reason for precession of earth

Answer 25

gravity of sun and moon combined. nutation is the difference between the sun's part and the moon's part. nutation 9arcsecs, 19yrs

Question 26

cause of phases of moon

Answer 26

NOT earth blocking it: what side of moon is sun hitting, what side is earth looking at? It's all about the angles.

Question 27

phases of the moon

Answer 27

new, crescent, quarter, gibbous, full. waxing first then wanes backwards

Question 28

moon's orbit

Answer 28

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

Question 29

synodic lunar month

Answer 29

from one phase to repeat of phase, usually quarter is best (terminator straightness can be seen)

Question 30

sidereal lunar month

Answer 30

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.

Question 31

rotational speed of moon

Answer 31

same as orbital period, so that one side is always seen facing the earth/

Question 32

reason for tidal locking.

Answer 32

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.

Question 33

synchronous rotation

Answer 33

orbital period and rotational period the same, aka moon. Subset of spin-orbit coupling

Question 34

spin-orbit coupling

Answer 34

some relationship between orbital period and rotational period.

Question 35

lunar eclipses

Answer 35

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.

Question 36

reddish color of moon during eclipse

Answer 36

though sun is blocked by earth, sunlight goes through atmosphere and scatters at moon. most blue light scatters down, red goes through the best.

Question 37

umbra

Answer 37

total shadow of celestial body on another, i.e. > shape going from earth to moon. total shadow, white car would be black

Question 38

penumbra

Answer 38

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.

Question 39

kinds of lunar eclipse

Answer 39

umbral (total), partial (half and half umbra/pen), penumbral (no one cares, light variation has to be meaured.

Question 40

rate of eclipses

Answer 40

2-5 Pens/yr, 1.5 avg totals/yr.

Question 41

rayleigh scattering

Answer 41

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

Question 42

solar eclipse

Answer 42

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

Question 43

annular eclipse

Answer 43

when the moon is near apogee and doesn't block all of the sun, looks like concentric circles.

Question 44

tides

Answer 44

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

Question 45

mare/maria

Answer 45

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.

Question 46

MOONFACTS

Answer 46

``` 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 ```

Question 47

moon's albedo

Answer 47

reflected/incident light. | lower than you'd think- .07. Only bright against dark sky.

Question 48

temperature on moon

Answer 48

240° in day, -300 in night. thermometer won't work cause no air molecules, have to stick it in ground.

Question 49

why moon has no atmosphere

Answer 49

atmosphere determined by heat vs escape velocity. moon has high heat and low escape velocity, so nothing sticks around

Question 50

escape velocity

Answer 50

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

Question 51

moon day length+ earthrise

Answer 51

earth always in same position from moon due to tidal locking. day length is synodic month, daylight for two weeks.

Question 52

Moon geological features

Answer 52

UP TO mountains 4k km high, crators 80km across.

Question 53

Rille

Answer 53

geological feature on moon. thought originally to be dry riverbeds, now thought to be ancient lava flow tubes. apollo 15 photographed one up close.

Question 54

Apollo LEM

Answer 54

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.

Question 55

other moon info

Answer 55

Chemistry of moon very similar to earth. astronauts had to use film chest cameras which made for awkard posititioning. l

Question 56

moon's surface

Answer 56

2-4" of dust. dust was kicked up by a rover so astronauts duct taped extra part from lander to wheel as dust guard.

Question 57

mare orientale

Answer 57

3-rimmed crater on far side of moon. 200 miles across.

Question 58

gravity anomalies on moon

Answer 58

gravity strongest in mare- mascons below them, more mascons on close side.

Question 59

if atoms are mostly empty space, why can't you put your hand through stuff

Answer 59

electrostatic forces- the molecules in the stuff and your hand create solidity. these things are somewhat bonded in liquid and not bonded in gas.

Question 60

of protons, neutrons, electrons

Answer 60

atomic number/element, isotope of element, ionization of element

Question 61

when a charged particle moves through space

Answer 61

it radiated light

Question 62

atomic absorption and emission of light

Answer 62

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.

Question 63

specifics of absorbtion

Answer 63

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.

Question 64

specifics of emission

Answer 64

when electron drops down, it either jumps or cascades down energy levels, emitting light equal to each jump down.

Question 65

equation for energy of light

Answer 65

E = hc/wavelength

Question 66

electron orbit properties

Answer 66

at certain quantized energy level/radius. discrete, single-valued.

Question 67

bigger jump

Answer 67

more energy/shorter wavelength. thus, blue light=higher energy.

Question 68

two ways to knock electrons out of orbit

Answer 68

1. hit it with a specific frequency of light | 2. heat it up so it will collide more often, more faster random motions

Question 69

fire

Answer 69

hi temps in air knock electrons out of orbit, they emit light

Question 70

how spectroscopy works

Answer 70

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.

Question 71

star spectroscopy

Answer 71

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)

Question 72

absorption spectroscopy

Answer 72

white light - certain wavelengths, seen as black lines. looking at those lines we can tell what elements thing is made of

Question 73

how prisms work

Answer 73

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.

Question 74

normal/better way of spectroscopy

Answer 74

use grating instead of prism, which uses diffraction instead.

Question 75

why use slit with a spectroscope

Answer 75

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.

Question 76

absorbtion spectroscopy besides stars

Answer 76

sunlight reflected from a planets surface (thru its atmosphere) also does this

Question 77

different kind of stars look like

Answer 77

O-m2 stars, hot to cold. O stars have more blue light (higher E)

Question 78

notable emission lines

Answer 78

H alpha, sodium double D

Question 79

how spectra really looks as used by astronomers

Answer 79

in black and white, negative image

Question 80

doppler effect

Answer 80

wavlength of thing moving towards us gets smaller, thing moving away from us gets bigger.

Question 81

radial velocity

Answer 81

motion of object either towards or away from us, + means towards, - means away, 0 means no movement towards us

Question 82

star doppler effect equation

Answer 82

delta wavelength / normal wavelength = radial velocity/c

Question 83

use of star doppler effect equation

Answer 83

if delta wavelength and normal wavelength is known, radial velocity can be calculated

Question 84

how to do spectroscopy if wavelengths change

Answer 84

all wavelengths shifted the same-look for patterns up or down spectrum that match known ones.