The Cycles of the Sky

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Chapter 1 The Cycles of the Sky
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Constellations help astronomers know the
positions of celestial objects
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Zodiac signs
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These coordinates can be used to describe the
position of stars locally
zenith
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Altitude
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Azimuth
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Angular distances of stars are measured in degrees
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An imaginary Celestial Sphere surrounding Earth
aids in navigating the sky
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What is wrong with this cartoon?
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Rotation vs. Revolution

• Rotation represents the Earths spin on its axis.
  
• This defines the length of 1 day.
• 1 day 24hours

• Revolution represents the Earths orbit around
  the Sun.
• This defines the length of 1 year
• 1 year 365.25 days

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Earths counter- clockwise rotation causes the
Sun and stars to appear to move from East to West
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Motion of Stars at the North Pole
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Motion of Stars at the Equator
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Precession causes the position of the North
Celestial Pole to change over a period of 26,000
years.
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UNLEARN
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Common Misconception

• The seasons occur due to the changing distance of
  the Earth from the Sun. When we are in our part
  of the orbit that is closer to the Sun, it is
  Summer, and when we are farther away from the
  Sun, it is winter
• This statement is NOT correct!

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LEARN
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Some Facts

• When the Earth is physically closer to the Sun,
  it is winter time in the Northern Hemisphere, NOT
  summer
• When the Earth is physically farther from the
  Sun, it is summer time in the Northern
  hemisphere, NOT winter

• The Northern hemisphere and Southern hemisphere
  have opposite seasons from each other.
• Thus, Earths seasons are NOT caused by its
  changing distance from the Sun!!!

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Birds in the Northern Hemisphere fly south for
the Winter...

• That is when it is winter in the Northern
  Hemisphere, it is summer in the Southern
  Hemisphere!

...which means that the Earths revolution around
the Sun can not be the only explanation for
seasons!
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• The correct reason for the seasons
• the tilt of the Earths axis of rotation and
• 2) Earths revolution around the Sun

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Earth is tilted!
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The altitude of the Sun impacts how much energy
is received on Earth.
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Concept Question
What would be different if the Earth had no
tilt?
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UNLEARN
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Common Misconception The phases of the
Moon occurs because as the Moon orbits the
Earth, the Earth casts a shadow on the Moon
and blocks some or all of the sunlight from
reaching the the Moon causing the amount of
sunlight reflecting off the Moon to change.
This statement is NOT correct!
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LEARN
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The correct reason for the phases of the Moon
Although half of the Moon is always lit by the
Sun, we can only see the side of the Moon
that is facing the Earth and only on that side
does the amount of illumination change
as the Moon orbits the Earth.
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Concept Question
If the moon was between the Earth and the Sun,
what phase do you think it will be? A)
full B) new C) first quarter D) third
quarter
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In other words ...

• The Earths rotation on its axis determines the
  length of the day.
• The moons orbit around the Earth determines the
  length of a month.
• The Earths orbit around the Sun (revolution)
  determines the length of the year.

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Lunar eclipses occur only when the Moon crosses
the ecliptic during the full phase
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Lunar Eclipses
Darkest part of the shadow
Full
Intermediate part of the shadow
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Lunar Eclipses
The moon is not completely dark during a total
lunar eclipse
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Lunar Eclipses
The moon is not completely dark during a total
lunar eclipse since small amount of light is bent
around the edge of the Earths atmosphere!!!
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Solar eclipses occur only when the Moon crosses
the ecliptic during the new phase
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Solar Eclipses
Moon 400 X smaller than the Sun, but 400X closer
The moon has the same angular size as the Sun!
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Solar Eclipse from Space
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Solar Eclipse
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Solar Eclipses
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