Astronomy Test #4

Front 1

Cartesian coordinate system

Back 1

a 2 dimensional rectangular coordinate system

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Great circle

Back 2

a circle on surface of Earth with its center located at the center of the Earth

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parallels

Back 3

circles on surface of earth parallel to equator

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meridians

Back 4

half circles that are portions of a great circle

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latitude

Back 5

angular measurement in degrees north and south of equator

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longitude

Back 6

angular measurement in degrees east to west of the prime meridian

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Greenwich or prime meridian

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the zero meridian which goes through Greenwich, England

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solar day

Back 8

elapsed time between two successive crossings of the same meridian by the sun, solar day is 4 minutes longer than sidereal day

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sidereal day

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elapsed time between two successive crossings of the same meridian by a star other than the sun

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Greenwich mean time (GMT)

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time in first time zone, also called "Zulu"

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coordinated universal time (UTC)

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time referenced to a grid of atomic clocks

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international date line (IDL)

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meridian line where the date changes, at longitude 180, when you cross it traveling west the date advances one day, when you cross it traveling east the date is subtracted one day

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altitude

Back 13

the angle of the sun above the horizon at noon

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zenith angle

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complementary angle of altitude, angle from zenith to the sun at noon

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sextant

Back 15

instrument use to determine latitude by measuring the altitude of the sun

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summer solstice

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designates the beginning of summer, occurs June 21 or 22, date of farthest north position of sun, day of year with longest amount of daylight for northern hemisphere

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winter solstice

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designates the beginning of winter, occurs December 22 or 23, date of farthest south position of sun, day of year with shortest amount of daylight in northern hemisphere

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autumnal equinox

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occurs September 22 or 23, day with equal amount of daylight and night, sun's position is directly over the equator, first day of fall season

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vernal equinox

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occurs March 20 or 21, day with equal amount of daylight and night, sun's position is directly over the equator, first day of spring season

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tropical year

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the year of season, time interval from one vernal equinox to next

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sidereal year

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the time of one revolution of the earth with respect to a star other than the sun

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Gregorian calendar

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our modern calendar decreed by pope Gregory XIII, has 365 days, one day added every 4 years expect yeas divisible by 400

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precession

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the slow rotation (wobble) of the earth's axis, takes 25,800 years to complete cycle, its result will change north star from Polaris to Vega in 12,000 years

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standard time zones

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24 zones of 15 longitude which divide the time of day on earth into 24 hours

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time

Back 25

the continuous forward flow of events

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accurate clock

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instrument used to determine longitude

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zenith

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point directly overhead of an observer

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zodiac

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the central circular section of celestial sphere that contains 12 prominent constellations

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Julian calendar

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early roman calendar with 365 days and 1 leap day added every 4 years

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tilt of earth's axis of rotation

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23.5 from vertical, responsible for the seasons

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tropic of cancer

Back 31

the farthest north position of sun during a year, latitude 23.5 N

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tropic of Capricorn

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the farthest south position of sun during a year, latitude 23.5 S

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great circle distance

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shortest surface distance between 2 points on the earth

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nautical mile

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one minute of arc of a great circle, equals 1.15 terrestrial miles

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post meridian (P.M.)

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the hours after noon

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ante meridian (A.M.)

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the hours before noon

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global positioning system (GPS)

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modern system for determining latitude and longitude position on the earth. GPS receiver uses radio waves from orbiting satellites to determine position by triangulation

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Astronomy

Back 38

the scientific study of the universe including all matter, energy, space and time

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solar system

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complex system of all masses held together by the gravitational force of our sun, includes the eight planets, 70 moons, asteroids, comets. our solar system is believed to be 4.5 billion years old

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geocentric model

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considers the earth to be stationary and at the center of the solar system

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heliocentric model

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considers the sun to be the center of the solar system

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law of elliptical orbits

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Kepler's 1st Law, states all planets move in elliptical orbits about the sun

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astronomical unit

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the average distance between the earth and sun

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law of equal areas

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Kepler's 2nd Law, a planet sweeps out equal areas in equal periods of time

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harmonic law

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Kepler's 3rd Law, T2=kR3, relates the period of a planets orbit to its semi major axis

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terrestrial planets

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the inner planets, includes Mercury, Venus, Earth, and Mars, composed of rock like material

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Jovian planets

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the outer planets, includes Jupiter, Saturn, Uranus, and Neptune, composed of hydropgen and helium gas / liquid, much larger than terrestrial planets

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sidereal period

Back 48

the time it takes a planet to complete a complete orbit around the sun

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conjunction

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when earth and superior planet line up on the same side of the sun

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opposition

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when earth and superior planet line up on the opposite side of the sun

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inferior conjunction

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when earth and inferior planet line up on the same side of the sun

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superior conjunction

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when earth and inferior planet line up on the opposite side of the sun

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albedo

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fraction of sunlight reflected by a celestial object, earth's albedo is 33%, the moon's albedo is 7%, Venus' albedo is 76%

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rotation

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spinning on internal axis

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revolution

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movement of one object around another object

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Foucault pendulum

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long and heavy pendulum used to prove earth rotates on its axis

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parallax

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apparent shift of positions of two objects when an observer changes positions

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solar nebula

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a flattened, rotating disk of gas and dust from which the planets formed

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condensation theory

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describes the origin of the solar system

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milky way galaxy

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the galaxy which contains our solar system

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perihelion

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the closet point in a planet's orbit to the sun, where planet's speed is fastest

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aphelion

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the farthest point in planet's orbit to the sun, where planet's speed is slowest

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inferior planets

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planets with orbits smaller than earth's orbit

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superior planets

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planets with orbits larger than earth's orbit

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earth

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third planet from the sun, unique due to its oxygen atmosphere, large amount of liquid

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Mercury

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the closet planet to the sun, has shortest period of revolution, named after the swift messenger of the Greek gods

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Venus

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the closest planet to earth, third brightest object in sky, named after roman goddess of beauty

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Mars

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planet with red color, named after roman god of war, has polar ice caps made of frozen water and CO2

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Jupiter

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largest planet in the solar system, named after roman god of heaven, contains a huge storm which has lasted for hundreds of years

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Saturn

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planet with distinctive system of rings composed of ice and ice-coated rocks

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Uranus

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planet discovered in recent time by William Herschel

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Neptune

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planet whose existence was predicted by astronomers from irregularities observed in Uranus' orbit

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Pluto

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originally called the 9th planet, but in 2006 removed from the list of planets because of its small size

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Aberration of starlight

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the apparent displacement in the direction of light coming from a star because of the orbital motion of the earth

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Prograde motion

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normal direction of motion for most objects in solar system

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retrograde motion

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the opposite motion to prograde motion

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dwarf planets

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new category for objects that orbit the sun includes Pluto, Ceres, Haumea, Makemake, and Eris

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Extrasolar planet

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planets that orbit stars other than the sun

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Eris

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dwarf planet located far beyond Pluto

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Ceres

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Dwarf planet located in asteroid belt between Mars and Jupiter

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Trans-Neptunian objects

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generic name for objects orbiting a slight wobble in the stars

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termination shock

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extreme outer boundary of the solar wind

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Voyager 1 & 2

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space probes launched in late 1970's and still currently exploring the extreme outer reaches of the solar system