Sky MotionsSky Motions

Diurnal Motion

Annual Motion

DIURNAL MOTIONDIURNAL MOTION

Daily East / West motion of the skyDaily East / West motion of the skyDue to the Earth’s rotation (15°/hour)

[360°/24 hours = 15°/hour]

[1° in 4 minutes] Stars fall into two groupsStars fall into two groups

Circumpolar - never rise or setCircumpolar - never rise or set

EquatorialEquatorial

Circumpolar Circumpolar StarsStars

Equatorial Equatorial StarsStars

View from the North PoleView from the North Pole

View from the EquatorView from the Equator

Coordinate SystemCoordinate System

Celestial MeridianCelestial Meridian

Circle going through north and south Circle going through north and south points on the horizon and the zenithpoints on the horizon and the zenith

Z

Celestial MeridianCelestial Meridian

Objects on the Meridian are at their Objects on the Meridian are at their highest point in the sky (transit)highest point in the sky (transit)

Astronomical noon is when Sun is Astronomical noon is when Sun is on the Meridian.on the Meridian. Does not mean the Sun is directly Does not mean the Sun is directly

overhead.overhead. Midnight is when the Sun is on the Midnight is when the Sun is on the

Meridian below the horizon.Meridian below the horizon.

Annual Motion

Horizon CalendarHorizon Calendar

S

N

W

E

Polaris

On the day of an equinox…

On the day of an winter solstice…

On the day of an summer

solstice…

The Sky DomeSunrises and Sunsets

S

N

W

E

Polaris

Vernal or Autumnal Equinox

SummerSolstice

WinterSolstice

Starting Points for the SunStarting Points for the Sun

Sunrise in AthensSunrise in Athens

StonehengeStonehenge

Earth’s Annual MotionEarth’s Annual Motion

Leo

Celestial Sphere

Celestial Equator

SCP

NCP

EclipticVernal

Equinox

Autumnal Equinox

23.5°

Sun’s Motion Tool

Inclined Pole causes SeasonsInclined Pole causes Seasons

23.5°

Northern Hemisphere

Summer

Northern Hemisphere

Winter

N

S

Sun’s motion along the Sun’s motion along the EclipticEcliptic

Sun’s Motion

ANNUAL MOTIONANNUAL MOTION

Constellations move Constellations move westwardwestward during the year.during the year. Due to Earth’s orbital motion around Due to Earth’s orbital motion around

the Sunthe Sun Sun appears to moves Sun appears to moves eastwardeastward 1°/day 1°/day

Path of the Sun called the ECLIPTICPath of the Sun called the ECLIPTIC Ecliptic inclined 23.5° to EquatorEcliptic inclined 23.5° to Equator

Horizon calendarHorizon calendar

Annual Motion Affects the Annual Motion Affects the Nighttime SkyNighttime Sky

Day 1

9:00 PM

Annual Motion Affects the Annual Motion Affects the Nighttime SkyNighttime Sky

Day 2

8:56 PM

Annual Motion Affects the Annual Motion Affects the Nighttime SkyNighttime Sky

Day 3

8:52 PM

Annual Motion Affects the Annual Motion Affects the Nighttime SkyNighttime Sky

One Year Later

9:00 PM

““Stars”Stars” Fixed StarsFixed Stars

Modern concept of starsModern concept of stars Form the ConstellationsForm the Constellations

Planets - traveling or wandering Planets - traveling or wandering starsstars Sun, Moon, Mercury, Venus, Mars, Sun, Moon, Mercury, Venus, Mars,

Jupiter, and SaturnJupiter, and Saturn Meteors - “shooting stars”Meteors - “shooting stars” Comets - “long-haired stars”Comets - “long-haired stars”

Babylonian AstronomyBabylonian Astronomy

Babylonian AstronomyBabylonian Astronomy

Star Charts

Babylonian AstronomyBabylonian Astronomy

Fatalistic Pre-determinismEverything in nature pre-determined by the godsDoesn’t lend itself to model building

Infinite time line

End of SectionEnd of Section