origins of modern astronomy

retrograde motion

the apparent westward drift of the planets with respect to the stars

sidereal day

the time interval it takes for earth to make one complete rotation with respect to a star other than the sun and is 23 hours, 56 minutes and 4 seconds

heliocentric

-aristarchus
-sun centered universe

sidereal month

-the true period of the moons revolution around earth
-27 1/3 days

geocentric

belief that earth was a sphere that stayed motionless at its center

rotation

turning or spinning of a body on its axis

astronomical unit

unit that is the average distance from earth to the sun, about 150 kilometers

solar eclipse

when the moon moves in a line directly between earth and the sun, it casts a dark shadow on earth

declination

the angular distance north or south of the celestial equator denoting the position of a stellar body

perturbation

any variance in the orbit of a body from its predicted path

perihelion

the pint in the orbit of a planet where it is closest to the sun

ecliptic

the apparent annual path of the sun against the backdrop the celestial sphere

celestial sphere

imaginary, transparent, hollow sphere on which the ancients believed the stars traveled daily around earth

constellation

an apparent group of stars originally named in honor of mythological character or great hero

plane of the ecliptic

the imaginary plane that connects earths orbit with the celestial sphere

ptolemaic system

earth centered model of the universe proposed in a.d. 141 that uses epicycles and deferents to describe a planets motion

revolution

the motion of a body, such as a planet or moon, along a path around some point in space

phases of the moon

refers to the progression of changes in the moons appearance during the month

right ascension

the angular distance of a stellar object measured eastward along the celestial equator from the position of the vernal equinox

synodic month

the cycle of the moon through its phases requires 29 1/2 days

lunar eclipse

-during the full moon phase
-when the moon moves within the shadow of earth

equatorial system

a method used to locate stellar objects that is very similar to the latitude-longitude system used on earths surface

aphelion

the point in orbit of a planet where it is farthest from the sun

precession

the very slight movement of earths axis over a period of 26,000 years

mean solar day

-the time interval from one noon to the next
-about 24 hours