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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