The Motions of the Earth

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The Motions of the Earth

• Evidence of Movement and the Consequences

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How do we know that the Earth is Round?

• First, the sky is curved. This is a reflection of
  the Earths curvature.
• We can see the Earths shadow during a lunar
  eclipse.
• Different constellations are visible in Southern
  Hemisphere than here.
• Suns height changes with latitude.

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Lunar Eclipse Earths shadow on the Full Moon
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We see different constellations than South Africa
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The closer to the equator you are, the higher the
sun is in the sky. The Suns rays are most direct
on the equator, and most slanted in polar regions.
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Rays on Sun on Earth
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Paths of Sun Across the Sky
0 lat.
43 N lat
80 N lat
east south west
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What proof is there that the Earth rotates in 24
hours?

• The Sun, the Moon, the Planets, and the fixed
  stars all move from east to west.
• The stars leave trails across the sky that go
  around the celestial poles.
• Physical evidence comes from the Foucault
  pendulum.
• When its noon here, its midnight in Japan.

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Star Trails With Polaris Near the Center
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Similar Pattern in theSouthern Hemisphere
except in the opposite direction to the North!
South Celestial Pole
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Foucault Pendulum
All dominoes fall down in a 24 hour period.
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Different Time Zones one of the results of
Earths rotation
6 PM
North Pole
12 noon
12 Mid
6 AM
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43rd Parallel
Portsmouth Rochester Muskegon Madison
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The farther west you go, the later the sun rises
and sets. Solar noon is later too.
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Sundial - Tracking the Sun
What is wrong with this picture? (Its not the
watch!)
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Time Zone Maps
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The Earths Revolution!
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How do we know that the Earth revolves around the
Sun in 365 days?

• The Sun completes one trip through the zodiac
  in one year.
• The sky looks the same on Sept. 23, 2010 as it
  did on Sept. 23, 2009.
• The sun returns to the same place at the
  beginnings of each season, which can easily be
  marked.

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The Sun appears to move through the 12 signs of
the Zodiac in one year cycle.
Animation
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Orion dominates our southern sky every February.
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For centuries people have marked sun rise
positions for midsummer and midwinter.
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The Sun Dagger

• In Chaco Canyon, New Mexico, there is a rock
  painting aligned with the equinoxes and
  solstices.
• This gave the Anasazi people a way to check their
  calendar and make corrections as needed.
• Other cultures had similar monuments to help them
  keep track with the yearly cycle of the sun.

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The Effects of the Earths Tilt

• The Earth tilts 23.5 but it always points toward
  the North Star (Polaris).
• Because the two poles tilt in the opposite
  direction, seasons are reversed in Northern and
  Southern Hemispheres.
• The height of the Sun changes with the seasons.
• Length of daylight is long in summer and short in
  winter.

Seasons Animation
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The poles always point in the same direction,
which means the Earth either leans toward the sun
or away from it.
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Seasons are reversed in the two hemispheres
summer
winter
winter
summer
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The higher the suns path, the higher the
intensity
WINTER
SUMMER
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Here in Rochester, the Sun is high in the sky in
summer, and low in winter. (The top of the sky is
90)
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If you live in Arctic or Antarctic regions the
effect of the tilt is even greater
Alaska
Rochester
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In Alaska, days are very long in summer, and very
short in winter. The same is true for Antarctica.
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For locations in the Southern Hemisphere, the
seasons are reversed, so Dec. 21st is the longest
day, and June 21st is the shortest.
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The Earths Precession
The Earth slowly wobbles like a toponce every
26,000 years.
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By an incredible coincidence, Polaris is almost
directly over the North Pole. So it can be used
to help us navigate. This is a temporary
situation, however. Since the Earth is wobbling
like a top, the pole slowly moves. This is called
precession.
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The Precession Cycle
Now the North Celestial Pole is near Polaris (off
by about 1 degree). In the days of the Egyptian
pharaohs, it was near Thuban in Draco. In around
12,000 years the wandering pole will point toward
Vega, but there will be centuries when there is
no North Star.
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Quick Quiz

• How do we know the earth is round?
• What proof do we have that the Earth rotates once
  every 24 hours?
• If we lost all our calendars, how could we
  determine the length of a year?
• Why are seasons reversed in the southern
  hemisphere from the northern hemisphere?
• What is meant by precession? What does that have
  to do with Polaris?