Chapter 1 Discovering the Night Sky

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Chapter 1Discovering the Night Sky
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What do you think?

• Are constellations just mythic figures in the
  sky?
• What causes the seasons?
• How many zodiac constellations are there?
• When, if ever, is the Moon visible during the
  daytime?
• Does the Moon have a dark side that we never see
  from Earth?

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THE SCALES OF THE UNIVERSE The range of objects
we study are from the extremely small subatomic
particles, to objects which are gigantic, such
as a galaxy or the size of the known universe
itself. Each division up the line indicates an
increase in size by 100,000.
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Constellations make locating stars easy
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Constellations and Asterisms

• Constellations are areas in the daytime and
  nighttime sky.
• They originated from myths, but today they help
  star gazers to organize and describe what they
  see
• Asterisms are the mythical figures in the sky.
• The asterism Orion is in the Constellation Orion

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Use the Big Dipper in the northern sky as a way
to find other groups of stars
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Use the winter triangle to find southern
constellations during winter evenings
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Use the Summer Triangle to find southern
constellations during summer evenings
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Angular distances between stars in the sky are
measured in degrees
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Angular distances between stars in the sky are
measured in degrees
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Night time Sky

• The sky in and around Lisle isnt very dark
• I seems a lot darker than Chicago, and it is, but
  it is still not very dark.
• This is a map that will help to compare the light
  pollution at different places in the U.S.
• Dark Sky finder

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Using Angular Size to Solve a Problem

• How does the Angular size of the Moon on the
  horizon compare to the angular size of the moon
  when it is high in the sky?

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Using Angular Size to Solve a Problem

• How does the Angular size of the Moon on the
  horizon compare to the angular size of the moon
  when it is high in the sky?
• How does the Angular size of the Sun on the
  horizon compare to the angular size of the Sun
  when it is high in the sky?
• How does the Angular size of the Sun compare to
  the angular size of the Moon?

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Solar Eclipse
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Solar Elclipse
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Hyperlink to Sidereal vs. synodic month
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Solar Eclipse
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An anular eclipse is when a small ring of the Sun
is visible
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Here is some cool information on Lunar Eclipses
http//www.mreclipse.com/Special/LEprimer.html
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Eclipses occur only when the Moon crosses the
ecliptic during the new or full phase
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Power of the Mayans
The serpent comes only on the days of the
equinoxes
Video of serpent
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• The Greek philosopher Aristotle (died 324 B.C.)
  proposed that the heavens were literally composed
  of 55 concentric, crystalline spheres to which
  the celestial objects were attached and which
  rotated at different velocities with the Earth at
  the center. The following figure illustrates the
  ordering of the spheres to which the Sun, Moon,
  and visible planets were attached.
• With the help of the Catholic Church, this view
  predominated until 1611 when Galileo was able to
  show otherwise.
• The church believed that the holy scripture had
  clearly indicated that the Earth is at the center
  of the Universe, anything else would be heresy

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An imaginary Celestial Sphere surrounding Earth
aids in navigating the sky
Ophiuchus
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A neat trick for when you become a Sailor

• Polaris is the North Star
• It is directly above the North Pole on the
  Celestial Sphere
• The North Star is always the same degrees of
  declination as you position in latitude

• This is one of the modes of maritime navigation
  before GPS (Beware of technology it can make you
  stupid/helpless if you are not careful!)

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What we see in the Sky

• Here is a simulation that will help to visualize
  our perspective on the celestial sphere

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Earths rotation causes the Sun and stars to
appear to move
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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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What about the Sun? It seems to move across the
celestial sphere on a path called the ecliptic.
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Signs of the zodiac

• Before the family guy, people used to spend much
  more time gazing at the night sky.
• Over periods of 1000s of years, human kind began
  to share stories about the night sky and spread
  mythologies about how the stars got into the
  sky
• Humans had seen figures in the sky and named
  them.
• The most important of those are the asterisms
  that make up the asterisms of the zodiac

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Astronomy and Astrology dont always agree
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The Sun rises at different points along the
horizon at different times of the year and also
peaks at different heights.
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Position of the noon-time Sun when photographed
every two weeks over a year
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The altitude of the Sun impacts how much energy
is received on Earth resulting in seasons.
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The seasons are caused by the tilt of the Earths
axis of rotation
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In other words ...

• The Earths rotation on its axis determines the
  length of the day
• The Earths orbit around the Sun (revolution)
  determines the length of the year
• The Earths tilt with respect to the ecliptic
  causes the seasons.

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One common misconception is that the Moon is only
visible at night. However, the time of day in
which the Moon is in our sky varies depending on
its phase. This picture clearly displays the
Moon, visible during the day.
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The changing phases of the Moon originally
inspired the concept of the month
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What did you think?

• Are constellations just mythic figures in the
  sky?
• A constellation is an entire region of the
  celestial sphere and all that stars in it.
• What causes the seasons?
• The tilt of Earths rotational axis causes the
  seasons.
• How many zodiac constellations are there?
• There are 13 zodiac constellations, the unknown
  one is Ophiuchus.
• When, if ever, is the Moon visible during the
  daytime?
• The Moon is visible during the day for half of
  the lunar cycle of phases.

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Self-Check

• 1. Describe the nature and value of
  constellations and asterysms.
• 2. Define the elements of the celestial sphere.
• 3. Describe how the appearance of the sky changes
  over time because of the motion on Earth.
• 3. Define two solstices and two equinoxes
  explain the orientation of the ecliptic on the
  celestial sphere and how it produces seasons on
  the Earth.

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Self-Check

• 5. Explain by drawing a diagram showing how lunar
  phases are controlled by the relative positions
  of the Sun and the Moon.
• 6. Explain when and why solar and lunar eclipses
  occur and why there are not such eclipses every
  month.
• 7. Be able to describe the parts of an eclipse.