Post on 22-Dec-2015
transcript
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General AstronomyGeneral Astronomy
Physics 103
Dr. Tyler E. NordgrenDr. 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 GoalOur Goal
• Understand:– The sky above
• “What’s 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): 7:30 pm – 9:30 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 AstronomyNaked-Eye Astronomy
The second oldest profession
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GoalsGoals
• 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 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.
The Year
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-VernalEquinox.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?
S
N
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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