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Chapter 2

AST 101 Chapter Notes - Chapter 2: Space Stars, Murchison Promontory, Tidal Locking

Course Code
AST 101
Walter Freeman

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Section 2.1
Patterns in the night sky
Constellations – a region of the sky with well-defined borders
oFamiliar patterns
The celestial sphere
Humans lack perception into space – stars lie close together, actually super far away
Earth is the center
oNorth celestial pole – over north pole
oSouth celestial pole – over south pole
oCelestial equator – projection of the equator into space
oEcliptic – the path the sun follows as it circles the celestial sphere
Local sky – sky as seen from where youre standing
Horizon – boundary between earth and sky
Zenith – point directly overhead
Angular size – the angle it appears to span in your field of view
Latitude- north/south
Longitude – east/west
Prime meridian – 0 degrees
Variation with time and year = the zodiac
12 constellations dependent on the sun’s location along ecliptic
Section 2.2 – The Reason for the Seasons
The tilt of earths axis causes sunlight to fall differently on Earth different times of the
oThe axis relative to the sun changes over the year
oTwo hemispheres – opposite seasons
oSteeper angle – higher path the sun follows = more daylight hours in summer
Solstices and equinoxes
oJune (summer) solstice – Nhemi is tipped most directly to the sun (June 21)
oDecember (winter) solstice – Nhemi receives the least direct sunlight
oMarch (spring) equinox – Nhemi goes from being tipped away from the Sun to
towards the sun
oSeptember (fall) equinox – Nhemi first starts to be tipped away from the Sun
Equinox = equal night
Section 2.3
The Moon
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