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