23.5 degrees
tilt of the earth/ecliptic plane
circumpolar stars
stars that never rise or set; just circle the poles
23 hours and 56 minutes
how long it takes for a star to travel from one person's meridian all the way around and back
24 hours
how long it takes for the sun to travel from one person's meridian all the way around and back
ecliptic
sun's apparent path on celestial sphere
tilt of the earth/tilt of ecliptic plane
how we can explain seasons
vernal equinox
March 21 - when the sun passes through the celestial equator when it is traveling from the southern hemisphere to the northern hemisphere
summer solstice
June 21 - the point on the ecliptic farthest north of the celestial equator
star
undergoing thermonuclear fusion
galaxy
a very large collection of stars all gravitationally bound together
universe
scientific term for everything
observable universe
billions of galaxies with billions of stars
equatorial coordinate system
earth: longitude/latitude; celestial sphere: declination/right ascension
latitude
north/south
longitude
east/west
declination
up/down (+/-)
right ascension
left/right - measured in hours (0-24) also called "hour lines
Azimuth
angle measured from intersection of celestial meridian and horizon (measured along horizon)
altitude
aka elevation; measured "up" from horizon toward zenith
celestial meridian
great circle passing through North and South points of horizon and observer's zenith
88
___ constellations arranged in patchwork that covers the entire sky
diurnal motion
daily movement of celestial objects (Sun, moon, stars); rise in the east, set in the west; caused by earth's rotation
autumnal equinox
September 22 - the day the Sun moves southward across the celestial equator, marking the beginning of fall
winter solstice
On December 21-December 22, the shortest day and longest night of the Northern hemisphere due to the fact that the Sun is directly over the Tropic of Capricorn
0 hours
right ascension of vernal equinox
0 degrees
declination of vernal equinox
6 hours
right ascension of summer solstice
+23.5 degrees
declination of summer solstice
12 hours
right ascension of autumnal equinox
0 degrees
declination of autumnal equinox
18 hours
right ascension of winter solstice
-23.5 degrees
declination of winter solstice
tropic of cancer
23.5 degrees north latitude (sun is at zenith on summer solstice)
tropic of capricorn
23.5 degrees south latitude (sun is at zenith on winter solstice)
autumnal equinox; vernal equinox
if you live exactly at the North Pole, the sun will be up for 6 months from the ___________ __________ to the ____________ ____________
earth's precession
the axis that the earth spins on also rotates because of the gravitational pull of the sun and moon
solar system
made up of the sun and all celestial bodies that orbit it - Earth, the other planets, all their various moons, and smaller bodies such as asteroids and comets
meteorites
the oldest objects found on Earth (all of which are 4.56 billion years old)
how the sun shines
thermonuclear reactions at the center convert hydrogen into helium - a violent process which releases a vast amount of energy
thermonuclear reactions
they consume the material of which all stars are made, therefore stars cannot last forever
4.56; 12.5
our sun is ______ billion years old and has a lifespan of ______ billion years
nebulae
huge clouds of interstellar gas
supernova
the spectacular detonation that blows stars apart at the end of their lifespan
pulsar
what some dead stars become - they spin rapidly at rates of tens or hundreds of rotations per second
black holes
what some stars become when they die - their gravity is so powerful that nothing (not even light) can escape
how the sun and its planets were formed
when stars die, the gas they are made of gets released back into space, enriching space with newly manufactured atoms and molecules
galaxies
huge assemblages of stars - our sun is part of the Milky Way __________
quasar
some of the most distant and luminous objects in the sky - thought to draw their energy from material falling into enormous black holes
angular measure
describes the size of an angle
angular distance
a measurement used to calculate the distance between two distant objects from a single point (measured in degrees)
angular size
a measurement used to describe the apparent size of a celestial object - how wide the object appears on the sky
1/2 degree
the angle covered by the diameter of the full moon
arcminutes
used to talk about smaller angles - degrees are divided into these (1 degree = 60 ______________)
arcseconds
60 _____________ = 1 arcminute
1'
60 arcseconds/60''
D= ?d/206265 D= Linear Size ?=angular size in arcsec, d=distance in km
small angle formula
astronomical unit
unit of length used when discussing distances across the solar system
light-year
distance that light travels in a year - the speed of light in empty space always has the same value
one light-year
63,240 AU (about 6 trillion miles)
1 parsec
the distance at which one AU subtends an angle of one arcsec
new moon
start of lunar cycle, face of moon is dark
waxing crescent
right crescent is illuminated
first quarter
right quarter of Moon's face is illuminated
waxing gibbous
moon is getting closer to being full - right three-quarters are illuminated
full moon
full face of moon is lit up
waning gibbous
right crescent of moon is dark
third quarter
left half of moon's face is illuminated
waning crescent
moon is growing smaller each night, left crescent is illuminated
positional astronomy
the study of the positions of objects in the sky and how these positions change
rotates
the earth ___________ once a day
revolves
the earth ___________ once a year
celestial sphere
apparent sphere of the sky
polaris
a star that is less than one degree away from the North Celestial Pole, therefore it is called the north star
zenith
the point in the sky directly overhead and observer anywhere on Earth
circumpolar
stars sufficiently near the north celestial pole which revolve around the pole, never rising or setting
East; West
for most observers on Earth, stars rise in the ________ and set in the _________
23.5 degrees
Earth's axis of rotation is inclined _________ away from the perpendicular to the plane of Earth's orbit
ecliptic plane
the plane of Earth's orbit around the sun
ecliptic
the circular path that the Sun appears to trace out against the background of stars
1 degree
the sun appears to move along the ecliptic at a rate of about _____ per day
ecliptic; celestial equator
the _____________ and the _________________ are inclined to each other by 23.5 degrees
equinox
the two points on the celestial sphere at which the ecliptic and celestial equator intersect
arctic circle
the circle around earth at 66.5 degrees north latitude
antarctic circle
the circle around earth at 66.5 degrees south latitude
4 weeks
the moon makes a complete trip around the celestial sphere in about ____________
1/2 degree
in one hour, the moon moves on the celestial sphere by about _________, or roughly its own angular size
zodiac
the band which the moon's path remains within - it extends about 8 degrees on either side of the ecliptic
epoch
the date used to define the coordinate system for objects on the sky
local noon
when the sun crosses the upper meridian (half of the meridian above the horizon)
local midnight
when the sun crosses the lower meridian (half the meridian below the horizon)
meridian transit
crossing of the meridian by any object in the sky
tropical year
the time needed fro the sun to return to the vernal equinox = 365d 5h 48m 46s
synchronous rotation
the moon rotates at the same rate it revolves around the earth, therefore we always see the same side of the moon
lunar eclipse
it must be a full moon and the moon must be on the ecliptic - the moon is in the earth's shadow and it appears reddish when it is completely in earth's shadow because the sunlight passes through our atmosphere and bounces off the moon back to earth
solar eclipse
must be a new moon and moon must be on ecliptic - happens when the moon is directly between earth and the sun
photosphere
the face of the sun
corona
the outer light of the sun - visible when the moon is in front of the sun
annular eclipse
when the sun is not completely covered by the moon because of our place in orbit and the moon appears smaller, therefore a ring of the sun's face still shows
lunar eclipses; solar eclipses
_______________ typically happen once a year; _______________ are much rarer
umbra
the central, completely dark portion of a shadow
penumbra
the portion of a shadow in which only part of the light source is covered by an opaque body
penumbral eclipse
a lunar eclipse in which the moon passes only through earth's penumbra
sidereal month
one orbit of the moon around earth measured with respect to the background stars (when moon is back in same constellation as before) = 27.32 days
synodic month
one orbit of the moon around earth measured with respect to the sun OR the amount of time from one new moon to the next = 29.53 days