General Astronomy

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General Astronomy

• Physics 103

Dr. Tyler E. Nordgren Dr. Julie A. Rathbun
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Topics The Night Sky
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from the Solar System
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to the Stars
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to the Milky Way
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and to the Universe Beyond.
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Our Goal

• Understand
• The sky above
• Whats that bright yellow star over head?
• How can I tell what time it is by where the Sun
  is?
• News reports
• Scientists discover giant black hole. Should I
  be afraid?
• Popular entertainment
• Armageddon, Enterprise, etc
• Learn how science works and how we know what we
  know.

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Organization

• Lecture two days a week (Tues. and Thurs.)
• 1 hour and 20 minutes
• Lab one day a week (Mon. or Wed.)
• 2 hours and 50 minutes in Hornby 2
• Evening observing (4 times) 730 pm 930 pm
• Check the syllabus and web site for exact dates!

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Grading

• Homework 20
• Quizzes 10
• Labs 20
• Exams 30 (15 each)
• 3 exams, lowest grade dropped
• Final 20

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Naked-Eye Astronomy

• The second oldest profession

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Goals

• How does astronomy affect your daily life?
• The Sun Time without clocks
• The Seasons Dates without calendars
• The ancients did it, so can you!

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The Sun

• The Sun is a star.
• We live by its warmth.
• We die by its extreme heat or frigid absence.
• It is the source of nearly all our energy.
• How?
• It is the source of all our food.
• How?

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The Day

• The Earth is a sphere that turns on its axis.
• How long does it take to turn once on its axis?
• Light from the sun lights only one half of Earth.
• As the Earth turns the sun rises and sets.
• So does the moon.
• So do the stars.

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The Year

• The Earth orbits the Sun.
• How long does it take to go once around the Sun?
• The orbit is nearly circular, but is actually an
  ellipse.

An exaggeration.
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Group Question

• Why are there seasons? Hint It has nothing to do
  with the distance from the Sun.

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The Seasons

• The Earth is tilted on its axis.
• During half the year, the northern hemisphere is
  tilted more towards the Sun.
• Summer in California.
• Winter in Australia
• During the other half of the year the southern
  hemisphere is tilted towards the Sun.
• Winter in California
• Summer in Australia

http//kids.msfc.nasa.gov/News/2000/News-VernalEqu
inox.asp
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Summer

• During summer
• Hemisphere is tilted towards Sun.
• Sun is high overhead.
• Sunlight is more direct.
• Daytime is longer. Why?

N
S
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Winter

• During winter
• Hemisphere is tilted away from Sun.
• Sun is low on horizon.
• Sunlight is less direct.
• Daytime is shorter. Why?

N
S
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Time

• Q So, how can we use the Sun to tell time?
• A Sundials

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Time

• Sun rises in the East.
• If the Sun is towards the East, it is before
  noon.
• Sun sets in the West.
• If the Sun is towards the West, it is after noon.

• At noon?
• For most of northern hemisphere Sun is due
  south.
• For most of northern hemisphere Sun is due
  north.
• Near equator, Sun is overhead.

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Date

• During northern summer, Sun high over head.
• When Sun casts the smallest shadow at noon ?
  Summer solstice.
• During northern winter, Sun low to the south.
• When Sun casts the longest shadow at noon ?
  Winter solstice.
• During northern spring and fall, Sun in between.
• Sun also rises due east, sets due west.
• When Sun casts shadow due west at sunrise ?
  spring or fall equinox.

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• In Summer, the sun is high.
• In winter, the sun is low.
• The height of the sun (at a given time) can tell
  you the date.

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The Constellations

• We may also use the stars to tell time.
• We see stars projected on the sphere of the sky.
• They make patterns constellations.
• No physical association
• We see those constellations opposite the Sun from
  Earth.

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Seasonal Constellations

• As the Earth orbits the Sun, different stars are
  up at night.
• There are summer and winter constellations!
• The Dog Days of Summer

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Ancient Astronomy

• Stonehenge (3000 BC)

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Ancient Astronomy

• Chaco Canyon (Anasazi 1200 AD)

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Fajada Butte