Exam 1: ch 1, 2, and 4 Flashcards
astronomy
the study of all the objects beyond earth and the mechanisms governing them
scientific method
observations → hypothesis/model → experiments → refine/thrown out hyp./model
Sun → earth distance
150,000,000 km
how many inches in a meter
39.4 in
how many miles in 1 kilometer
0.6 mi
what derives the astronomical unit(AU)
average sun-earth distance
how many km are in 1 AU
1.5 x 10^8
lightyear
the distance light travels in 1 year
speed of light (c)
c = 3.5 x 10^5 km/s
celestial sphere
an imaginary sphere around the earth with stars, planets, etc. attached to it
zenith
directly above where you stand
how do the stars rotate
- E toW
- the opposite direction the earth spins, around the celestial poles, with the stars keeping their relative position
how can you find the altitude (angle above the horizon) of the celestial pole
equal to your latitude
circumpolar zone
at a given location, the portion of the sky that never sets relative to that location
how much does the sun’s position in the sky change relative to the stars
it moves about 1* per day and returns to its original position after 1 year
ecliptic
the line traced by the sun across the sky over a year
constellation
one of the 88 sections of the sky
If you are standing at the N pole, where is the celestial equator?
your horizon
If you are standing on the equator, where are the celestial poles and celestial equator?
- the celestial poles are at your horizons
- the celestial equator is at your zenith
If you are standing at 50°N latitude, where are the celestial poles?
- N celestial pole is 50* N
how many degrees across is the moon?
0.5* in diamater
how much later does the sun rise each day?
4 minutes relative to the stars
how many constellations intersect the ecliptic?
13, but only 12 are talked about
why does the ecliptic not lie on the celestial equator?
because the earth’s axis is tilted by about 23.5* from the plane of the ecliptic
what does the word planet mean in ancient greek?
wanderer
how wide is the ecliptic/zodiac
18*
asterisms
notable star patterns that do not correspond to the modern constellations
neutrinos
close to the speed of light
how many light minutes away is the sun
about 8 light minutes
star cluster
locations in which stars are grouped together, but not so close that they are in a single system
Local Group
both the Milky Way and the Andromeda galaxy are part of this small group of galaxies
Virgo Supercluster
what the Local Group is part of
parallax
Effect of one object moving relative to another due to motion
stellar parallax
is the apparent shift of position (parallax) of any nearby star (or other object) against the background of distant stars
Ptolemy
created the geocentric model of the solar system
how do the planets move in the sky
they usually move E, but sometimes they turn around and move W for a little while before moving E again
retrograde motion
- the orbital motion of an object in the direction opposite the rotation of a central object
- temporary westward motion of the planets
cosmology
the study of the structure and origin of the cosmos (or universe)
How does the distance to an object affect how much it shifts due to parallax?
The farther away the object is, the less it appears to shift
apparent magnitudes
how Hipparchus measured the brightness of the stars, from 1(bright)-6(dim)
precession
- refers to any of several slow changes in an astronomical body’s rotational or orbital parameters
- “wobble” of the earth’s axis
how long does it take earth’ xis to complete one precession cycle
26,000 years
epicycle
in Ptolemy’s model, each planet goes around a small circular orbit
deferent
in Ptolemy’s model, the center of the epicycle orbits the earth on a larger circular path
astrology
a system in which the positions of these objects relative to the zodiac could impart knowledge about the present or, more importantly, the future
horoscope
the chart that depicts the positions of the Sun, the Moon, and the planets in the sky when that person was born
Copernicus
- put forth the heliocentric model of the solar system
- orbits were still circular, not elliptical
Galileo
- 1st person to use a telescope
- discovered Jupiter’s moons
latitude
angle north or south or the equator
longitude
angle east or west of the prime meridian
what is the equivalent of latitude on the celestial sphere?
declination
declination
angle above or below the celestial equator
what is the equivalent of longitude on the celestial sphere
right ascension
right ascension
measured in time from the location of the vernal equinox
vernal equinox
location of the sun on the 1st day of spring
how is the celstial sphere vertically divided?
- 24 hours
- 15* per hour
how is declination divided?
split each degree into 60 arc minutes and each arcminute into 60 arcseconds
how is right ascension divided?
each hour is split into 60 arcminutes, and each minute is split into 60 arcseconds
how does the local coordinate system work
– the altitude is the angle above your horizon
– the azimuth is the compass direction relative to your location
Foucault pendulum
a pendulum swinging along a straight line will appear to rotate as time goes on; this only happens if it is the Earth that rotates (“the Earth rotates under the pendulum”)
when is a hemisphere experiencing summer
when that hemisphere is “leaning toward” the sun
why does the tilt create season
because the sunlight hits the hemisphere that is “leaning toward” the sun more directly, and for longer, so it heats up more
summer solstice
- June 21
- N tilted toward the sun (summer), S tilted away (winter)
autumnal equinox
- September 21
- Neither hemisphere is pointed toward the sun, so equal sunshine
- autumn/fall in N, spring in S
winter solstice
- December 21
- S is tilted toward the sun (summer), N is tiled away (winter)
Vernal equinox
- March 21
- Neither hemisphere pointed toward the sun
- Spring in the N, autumn in the S
N pole qualities
day for 6 months (3/21 - 9/21) then night for 6 months (9/21 - 3/21)
arctic circle qualities
- (lat. 66.5*N)
- anywhere above has 24 hrs of day on the summer solstice
Tropic of cancer qualities
- (lat. 23.5*N)
- Sun passes through zenith on the summer solstice
Tropic of Capricorn qualities
- (lat 23.5*S)
- sun passes through zenith on the winter solstice
Antarctic circle qualities
- (lat. 66.5*S)
- anywhere below has 24 hrs of day on the winter solstice
S pole qualities
day for 6 months (9/21 - 3/21) then night for 6 months (3/21 - 9/21)
how are seasons determined at the equator
by rainfall, not sunlight
how are seasons determined at the equator?
by rainfall, not sunlight
solar day
one rotation of the earth with respect to the sun
sidereal day
one rotation of the earth relative to the stars: 23 hr 56 min
apparent solar time
based on positions of the sun on your location
mean solar day
the average length of apparent solar day over a year
international date line
- lies roughly along longitude 180*; zig-zagging to avoid land
- It compensates for time changing 24hrs going around the earth
- When moving east, decrease the date
- If moving W, increase the date
why can we see some sunlight before sunrise and after sunset?
because the atmosphere refracts (bends) the sunlight around the horizon
day
rotation period of earth
solar month
time for moon to complete its cycle of phases; 29.5306 days
tropical year
orbital period of earth; 365.2422 days
Julian calendar
- year is 365.25 days
- 3 out of every 4 years is 365 days
- 1 out of every 4 years in 366 days
- Mainly a solar calendar, but the lengths of months are a relic of lunar timekeeping
Gregorian Calendar
- a year that is 365.2425 days long
- changes to leap years
leap year rules
- If the year is divisible by 4, it is a leap year
- Unless it is divisible by 100
- But if is divisible by 400, it is a leap year
phases
Over a month, the moon appears to change size because of which portion is lit
order of moon phases
New, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent
rule for waxing vs waning
- When lit portion of the moon is on right, it is waxing
- When on left, it is waning
sidereal month
the time it takes for the moon to go around the earth once, relative to the stars, 27.3217 days
synchronous rotation
The moon rotates on its axis at the same rate that it orbits earth
how much does the moon move in the sky each day
about 12*
what direction does the moon travel
- eastward
- travels its own diameter in about 50 minutes
what causes tides
moon’s gravity on earth
oblate spheroid
when earth distorts slightly due to moon’s gravity
tidal buldge
- This difference in gravitational pull causes water to “pile up” on the side of the earth facing the moon
- Same thing happens on the opposite side of earth, there are 2 bulges
- Over the course of the day, earth rotates once, so every location passes through both bulges each day
- The sun also rises tides on earth, but the effect is less than that of the moon
spring tides
When E, M, S are all lined up, we get particularly high high tides and low low tides
neap tides
when M and S are at right angles, their tidal effects partially cancel, and we get less extreme tides
how can eclipses occur
- because the S and M have the same apparent size in the sky
- because the diameter of the Sun is about 400x that of the Moon and the Sun is 400x farther away, so each object covers about 1/2°in the sky
solar eclipse
When M is directly between S and E, M casts a small shadow on part of E
lunar eclipse
- when M passes into E shadow, the entire night side of E sees an eclipse
- can last as long as 100 minutes
umbra
Darker middle part of the shadow
penumbra
- the lighter outer portion of the shadow
- extends out about 3,000 km on either side of the eclipse path
why don’t we get eclipses every month
because the orbit of M is 5* off from the orbit of the earth
annular eclipse
the Moon is slightly farther away, it cannot cover the entire Sun, so we get a ring of Sun around the Moon
total solar eclipse
- the Moon is slightly closer than usual and it covers the entire Sun
- in this case, the umbra of the Moon’s shadow actually reaches the surface of the Earth
duration of totality (total eclipse visible)
never longer than 7 minutes
penumbra
- the lighter portion
- extends out about 3,000 km on either side of the eclipse path
