Observations of the Sky

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Observations of the Sky
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Observations of the Sky

• What patterns, motions, and events do we notice
  in the sky?
• What theories can we create to explain them?
• How can these theories be tested?

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How does the sky change over

• A day?
• A night?
• A month?
• A year?
• A lifetime?
• A millenium?

Why do we see these changes?
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How does the sky change over

• A day?
• The Sun rises in the East, sets in the West
• It rises and sets at an angle
• It takes about 24 hours from sunrise to sunrise

Good Science gt Careful observations?
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How does the sky change over

• A day?
• The Sun rises in the East, sets in the West

for most observers, but not all! not always
due East, nor due West
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How does the sky change over

• A day?
• The Sun rises and sets at an angle

but angle isnt the same everywhere!
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Alaska
Oakland
Canada
Sunrise 9 February in the North America
Venezuela
Rio
New Zealand
Sunrise 9 February in the Southern Hemisphere
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How does the sky change over

• A night?
• The Moon, planets, and most stars also rise in
  the East, set in the West, at an angle
• The sky seems to rotate around a fixed point
  Polaris.

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How does the sky change over

• A night?
• The sky rotates around Polaris (check out
  http//www.youtube.com/watch?v3V3rmDG5J8A )

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Did you know?

• The ANGLE of Polaris above the horizon indicates
  your latitude in the Northern Hemisphere

Altitude angle
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How does the sky change over

• A night?
• In the Southern Hemisphere, the sky seems to
  rotate the other way! (check out
  http//www.youtube.com/watch?vXfRFCdYCcZA

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How does the sky change over

• A night?
• Some constellations always visible (circumpolar)

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How does the sky change over

• A moonth?
• The Moon goes through phases
• We see slow change in which constellations are
  visible at night
• The Suns slowly shifts in front of different
  zodiac constellations

Good Science gt Careful observations?
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How does the sky change over

• A moonth?
• The Moon goes through phases

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How does the sky change over

• A moonth?
• We see slow change in which constellations are
  visible at night

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How does the sky change over

• A moonth?
• The Suns slowly shifts in front of different
  zodiac constellations

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How does the sky change over

• A year?
• Suns rising/setting points, and noon-time height
  return to the same points.
• Constellations return to the same pattern
• But planets wander in front of the zodiac at
  different rates, and even dance!

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Sunrise Planting Calendars Southwestern US
Peoples
Walpi (Hopi) horizon calendar. McCloskey, after
Stephen. Observations from Bear Clan House.
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Sunrise Planting Calendars Southwestern US
Peoples
From Zeilik (1985) Hopi planting calendar.
Village of Shungopavi.
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How does the sky change over

• A year?
• The Suns height changes slowly

Photo of the sun, taken _at_ same time every day,
over a year
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How does the sky change over a year?
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How does the sky change over a year?

• Suns speed across the sky varies

Upper loop Summer, Earth moves slower in its
orbit
lower loop Winter, Earth moves faster in its
orbit
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The analemma

• Bergamo, Italy

Photos by John Nystuen, University of Michigan
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How does the sky change over

• A year?
• Summer
• Sun higher in the sky, shining more DIRECTLY
• Sun up longer, more hours in the day
• Winter
• Sun lower in the sky, less direct light
• Sun not up as long

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How does the sky change over

• A year?
• Constellations return to the same pattern
• But planets wander in front of the zodiac at
  different rates, and even dance!

Tunc Tezel, apod031216
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How does the sky change over

• A lifetime?
• Annual patterns repeat Moon Phases, Seasons,
  constellations
• Longer patterns apparent Planetary motions,
  solar eclipses

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How does the sky change over

• A millenium?
• Slow change in location of North star

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How does the sky change over

• A millenium?
• Slow change in location of North star
• Slower, even smaller change in direct positions
  of stars themselves