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Astro things 1:.
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Astronomy
Undergraduate 1
05/28/2009

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Term
Astronomy
Definition
the study of the Universe in which humans live
Term
Planck time
Definition
smallest measurable unit of time
Term
Age of the Universe
Definition
12 billion years!
Term
Parsec
Definition
3.26 light years
Term
Radius of an atom
Definition
1 angstrom
Term
How many constellations today?
Definition
88; 40 new, 48 are from classical age by Babylonians, Egyptians, Mesopotamians, and Greeks.
Term
Constellation
Definition
what used to define a group of stars, now defines a section/area of sky with clear boundaries
Term
Asterism
Definition
Groupings of stars, smaller than a constellation. For example: The Big Dipper is an asterism of the constellation Ursa Major.
Term
Diurnal Motion
Definition
Daily motion of the sun, moon, planets and stars
Term
Circumpolar stars
Definition
means "around the pole"; stars that circle the pole and never set
Term
Precession
Definition
radius: 23.5deg; due to the fact that the earth is not a perfect sphere. It's top-like motion. Moves reference marks such as celestial poles.
Term
Magnitude Scale
Definition
first appeared in writings of Ptolemy; 1st mag. to 6th mag. 1 mag= 2.5 factor in brightness.
Term
luminosity of a star
Definition
inversely related to the square of its distance. If a star is twice as distance, 2^2 is 4...1/4 the luminosity of the first star.
Term
AU
Definition
Astronomical Unit; average distance between the earth and sun. (1.5 x 10^11 km
Term
Eratosthenes
Definition
first to calculate circum. of earth
Term
Aristarchus
Definition
Measured relative sizes of earth/moon/sun; was far off, but established that the sun was far away and larger than earth
Term
Aristotle
Definition
geocentric model; traced out the ecliptic
Term
Equinox
Definition
anytime the sun crosses the celestial equator, even amount of sunlight per day.
Term
Vernal Equinox
Definition
March 21st, our calendar's zero
Term
Autumnal Equinox
Definition
September 22/23
Term
Sulstice
Definition
Point where the sun is furthest north or south
Term
Aphelion
Definition
furthest from the sun (July 6th)
Term
Perihelion
Definition
closest to the sun (Jan 3rd)
Term
An effect of the tilt of the earth's axis
Definition
it causes sunlight to be more/less direct, which causes our seasons!
Term
Sidereal (star) Period
Definition
orbital period of the moon relative to the stars. 27.3 days
Term
Synodic period
Definition
orbital period relative to the sun; time between successive new moons, 29.5 days (has to catch up to the sun, who has moved a degree a day across the sky.
Term
Solar day
Definition
defined to be 24 hours. rotates 361 degrees to meet back to the sun after moving across its revolution.
Term
Sidereal Day
Definition
relative to the stars, 23 hr. 56min.
Term
Eclipse
Definition
only occurs when the line of nodes points toward the sun.
Term
Tilt between earth and lunar orbital plane:
Definition
5degrees
Term
Amount of eclipses in a year
Definition
min. 2 and max. 7 in one year
Term
Penumbra
Definition
observer sees partial covering of the sun; surrounds the umbra
Term
Umbra
Definition
observer sees the sun completely covered, darkest portion of shadow
Term
antiumbra
Definition
beyond the apex of the umbra, observer sees partial covering of the sun because the object covering is not large enough; only solar eclipses
Term
Lunar eclipse
Definition
occurs when the earth casts its shadow onto the moon; seen by everyone who can see the moon; separated by six months
Term
Length of Totality during Total Solar Eclipse
Definition
no more than about 7 minutes
Term
Length of partial coverage from a Solar Eclipse
Definition
Can last about two hours
Term
prominence
Definition
gas being projected off and back down to the Sun and above the Chromosphere
Term
Corona
Definition
The ring of white light emission during total solar eclipse
Term
Bailey's Beads
Definition
caused by mountains and valleys on Moon's surface; little rim of sun shining through on the edges
Term
Annular Eclipse
Definition
a partial eclipse where it can only be seen through the antiumbra, where there is an annulus, or ring.
Term
Saros Cycle
Definition
an eclipse cycle that has a period of about 18 years, 11 days, and 8 hours.
Term
Ptolemy
Definition
geocentric, used epicycles, was used for 1400 years, very accurate
Term
Copernicus
Definition
heliocentric, still used perfect circular motion, not as accurate as Ptolemy's model
Term
deferent
Definition
circle about which an epicycle travels
Term
equant
Definition
point about which the epicycle seems to make uniform circular motion about the deferent
Term
epicycle
Definition
circle about which planet travels, used to explain motions like retrograde motion
Term
Almagest
Definition
Ptolemy's model
Term
De Revolutionibus
Definition
Copernican's writing over heliocentricity
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