56
The Caracol at Chichen Itza
• Built around 1000AD.• The Mayans developed a very accurate calendar.• They also placed special significance on Venus.• Human Sacrifices were routinely performed to worship Venus
Orion the Hunter
North Pole
South Pole
Equator
South Pole
Equator
North Pole
Meridian
North Pole
South Pole
Equator
South Pole
Equator
North Pole
Meridian
South Celestial Pole
North Celestial Pole
Celestial Sphere
CelestialEquator
SCP
NCP
CelestialMeridian
CEq
Declination
N
W
E
S
Horizon
Zenith Local Sky
SCP
NCP
CEq
Below theHorizon
N
S
EW
Z
Visible Halfof the Sky
Horizon
MeasuringLatitude
N
W
E
S
NCPCEq
Zenith
Latitude
NS
W
E
Z
NCP
Equator
Z NCP
NS
W
E
40º N Latitude
Z
NCP
North Pole
Evidence of Earth’s Rotation
• Apparent Rotation of the Celestial Sphere– Star Trails – Cycle of Night and Day
• Inertial Effects of Stuff on Earth– Coriolis Effect– Focault Pendulum
• Precession of the Equinox
Zenith
W
E
S N
NCP
CEq
Never Sets
Above Horizon for 12h
Above Horizon for > 12h
Above Horizonfor < 12h
Never Rises
Binghamton, NY42º N: 1200 km/h
Arctic Circle66.5º N: 666 km/h
Equator1670 km/h
Differential Rotational Speeds
Draco
Ursa Minor
Cepheus
Thuban
Polaris
2000 AD
2700 BC
North Ecliptic Pole North Celestial Pole
2000 AD
Rotate EastwardPrecess Westward
North Ecliptic PoleNorth Celestial Pole
15000 AD
Precession of the Equinoxes
Precession of the Equinoxes
Evidence of Earth’s Revolution
• Sidereal Day vs. Solar Day
• Seasons– Due to Earth’s tilt in combination with its
Revolution about the Sun
• Constellations and the Zodiak– As Earth revolves, different stars are visible at
night
NoonT=0h
T=23h 56m 04s
(Sidereal Day)One Earth rotation
T=24h
(Solar day)Sun overhead
Noon
Not to Scale
Solar & Sidereal Days
December
March
June
September
SCP
NCP
CEqEcliptic
4th
1st
2nd
3rd
4 Seasons
WinterSolstice
SummerSolstice
VernalEquinox
AutumnalEquinox
SCP
NCP
CEq
Ecliptic
~23.5º
Obliquity of the Ecliptic
SCP
NCP
CEq
WinterSolstice
SummerSolstice
Ecliptic
SCP
NCP
CEq
WinterSolstice
SummerSolstice
VernalEquinox
AutumnalEquinox
Ecliptic
W
E
S N
NCPSummer Solstice
Vernal & AutumnalEquinoxes
Winter Solstice
Z
CEq
W
E
S N
NCP
CEq
Summer Solstice
Vernal & AutumnalEquinoxes
Winter Solstice
Z
1 KW/m2 1 KW/m2
1 m2 2 m2
Equinoxes: March 20 & Sept. 22
Spring and Fall
December 21: Winter Solstice
Northern Winter
Southern Summer
June 21: Summer Solstice
Northern Summer
Southern Winter
2000 Dec 21: Winter Solstice
2001 June 21: Summer Solstice
2001 Mar 20: Vernal Equinox
2001 Sept 22: Autumnal Equinox
Winter
Summer
Summer
Winter
Spring
Autumn
Autumn
Spring
Constellations provide evidence that Earth Revolves around the Sun
Cancer
Gemini
Taurus AriesPisces
Aquarius
Capricorn
Sagittarius
Scorpius
LibraVirgo
Leo
March 1999: Sun in Pisces
Cancer
Gemini
Taurus Aries Pisces Aquarius
Capricorn
Sagittarius
Scorpius
LibraVirgo
Leo
September 1999: Sun in Virgo
Cancer
Gemini
Taurus Aries Pisces Aquarius
Capricorn
Sagittarius
Scorpius
LibraVirgo
Leo
December 1999: Sun in Sagittarius
Cancer
Gemini
Taurus AriesPisces
Aquarius
Capricorn
Sagittarius
Scorpius
LibraVirgo
Leo
June 1999: Sun in Gemini
