Patterns in Celestial Motion

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Patterns in Celestial Motion

• By Dr. Harold Williams
• of Montgomery College Planetarium
• http//montgomerycollege.edu/Departments/planet/

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Time counting repeating patternsin the sky

• A second, 1/60 of a minute, 1/(246060)1/86,400
  of a day
• A minute, 1/60 of a hour, 1/(2460)1/1440 of a
  day
• A hour, 1/24 of a day
• DAY, originally from sun rise to sun rise or sun
  down to sun down, now a rotation of the earth
  about its axis
• A week, Jewish bundling of days, sacred calendars
• MONTH originally a lunation (same moon to
  identical moon)
• YEAR originally a revolution of the sun around
  the earth through the ecliptic, now a repeat of
  the earth around sun in its orbit.
• A decade, century, millennium different bundling
  of years
• PRECESSION CYCLE originally motion of the first
  day of a season around the ecliptic, now cycle of
  the rotation axis (day and night axis) about the
  year axis (this angle is around 23 ½ degrees now
  and takes around 26,000 years)
• GALACTIC YEAR revolution of solar system about
  the Galactic center in an orbit of around 250
  million years.

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Day and Night most basic, what you see every day,
without going into outer space!
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From outer space since 300BCE
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First of all earth is round

• It looks flat locally to me and you.
• Aristotle, shadow of the earth on the moon during
  a lunar eclipse is always round.
• Greek sailors observed that when ships left the
  harbor the top of the mast disappeared last and
  the bottom of the ship first. So the earth is
  definitely curved.
• But does the central fire, the sun, move around
  the earth or the earth rotate.

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History and Social Studies is very important in
Science (Aerospace)

• Evolution of models to explain things over time.
• You really cant understand day and night motion
  without folding in yearly motion particularly
  when you start observing the changes in the night
  sky through out the year. This started a long
  time ago.
• Language, reading and writing are essential.
• Mathematics, the self consistent abstraction of
  reality is very useful.

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Celestial Sphere
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Celestial sphere on Latitude Protractor
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Celestial Sphere Rectified forthe North Pole
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Celestial Sphere Rectified forthe Equator
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Celestial Sphere Rectified forthe some place
like here
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The Celestial Sphere
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• Zenith Point on the celestial sphere directly
  overhead
• Nadir Point on the c.s. directly underneath
  (not visible!)
• Celestial equator projection of Earths equator
  onto the c.s.
• North celestial pole projection of Earths
  north pole onto the c.s.

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The Celestial Sphere (II)
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• From geographic latitude l (northern hemisphere),
  you see the celestial north pole l degrees above
  the horizon
• From geographic latitude - l (southern
  hemisphere), you see the celestial south pole l
  degrees above the horizon.

90o - l
l

• Celestial equator culminates 90o l above the
  horizon.

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Night Time Star Motion
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Round Earth Rotating now
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Putting DAY and YEARtogether the modern way
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The Annual Motion of the sun
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Due to Earths revolution around the sun, the sun
appears to move through the zodiacal
constellations. The suns apparent path on the
sky is called the ecliptic. Equivalent The
ecliptic is the projection of Earths orbit onto
the celestial sphere.
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The Seasons (IV)
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Earths orbit (eccentricity greatly exaggerated)
Earth in January
Earth in July
sun
Earths distance from the sun has only a very
minor influence on seasonal temperature
variations.
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The Motion of the Planets (I)
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• The planets are orbiting the sun almost exactly
  in the plane of the ecliptic.

Jupiter
Venus
Mars
Earth
Mercury
The moon is orbiting Earth in almost the same
plane (ecliptic).
Saturn
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Precession
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