AST 111 Lecture Notes - Lecture 2: Dailymotion, Sept, Declination

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Published on 4 Sep 2015
AST 111- Lecture 2: Knowing the Heavens
Handout “Ch. 2 Terminology and Concepts
Naked Eye astronomy had an important place in civilizations of the past
The Greeks made it cohesive
-They were not alone in the study of the sky
-Stonehenge in England is astronomically significant
oThe living people who built it lived in a circle of (recently) living wood, while the
dead where memorialized in the stone
Eighty-Eight Constellations
-Constellations are the names of recognizable patterns in the sky as well as the sky
around the groupings
-Asterisms are less formal groups of stars
-The big dipper is NOT a constellation
The night sky changes during the night and from one night to the next
-Diurnal motion (daily motion) is caused by the rotation of the Earth around its 24 hour
-Annual (yearly) motion is caused by the revolution of the Earth around the Sun
It is convineint to imagine that the stars are in a sphere
-The celestial sphere is infinitely far away
-It is imaginary
-Appears to rotate from east to west because the Earth is rotating from East to west
-Important porints on the celestial sphere:
oNCP= North Celestial Pole
oSCP= South Celestial Pole
oCelestial Equator= the projection of the terrestrial equatior onto the celestial
sphere and lies halfway between the NCP and SCP
Terrestrial Celestial
East/West Component Longitude
(measured in degrees)
Right Ascension
(measured in hours)
North/South Component Lattitude
(measured in degrees)
(measured in degrees)
For northern hemisphere observers, there are several noteable regions.
-Stars in a region close to the NCP never set
-Stars in a region close to the SCP never rise
-Between the regions, the remaining stars rise and set once each day
The Seasons are caused by the tilt of the Earth’s Axis rotation
-Tilted approx.. 23.5 degrees,
-The spin axis points at celestial poles
-Because of the spin, the sun appears to trace one complete circle around the celestial
sphere- called ecliptic
-The ecliptic intersects the celestial equator at two special points: the Vernal Equinox
(when the sun moves from the South-North)(approx.. March 21) and, the mid point
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