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Introducing Astronomy
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Why our subject is different
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Scale
Lack of true experiments
Fundamental origins
Fundamental units of distance
Intrasolar measurements
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Astronomical Units (AU)
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Average distance from the Earth to the Sun
1.496 x 108 km (93.7 million miles)
Fundamental units of distance
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Interstellar measurements
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Light – years (ly)
The distance a photon of light will travel
in one calendar year
 9.46 x 1012 km (6 trillion miles)
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Fundamental units of distance
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Parsec
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3.3 ly
Based on the angular measurement of
parallax to one arc-second
Lack of True Experiments
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Laboratory Simulations
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Due to the great scale of the universe,
astronomers must try to re-create
observed conditions in a laboratory
setting
Sometimes very difficult
Extreme temperatures
 Complete vacuum
 Intense radiation
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Fundamental Origins
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Stardust?
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As we and the Earth we live on are
accumulated stardust, studying
astronomy gives us insight on the
origins of the universe
All elements except Hydrogen are
created in the cores of stars, released
only upon the “death” and explosion of
that star
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Understanding origins allows us to
manipulate the four fundamental
forces of the universe
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The Unification Theory
Origins of life and complex
molecules
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Advances in medicine and healthcare
Do you ever just look at them, K?
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We see an essentially unchanging
sky at night
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Moon, Sun, Planets, “visitors” appear to
move against a background of
immobile stars
Objects seem suspended at an
unreachable distance
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Constellations are made from stars at
various distances
Slow processes are unobvious
Which is largest?
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Kilometer
Astronomical Unit
Light-year
Parsec
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Which unit best measures the distances
between stars?
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Light-seconds
Light-minutes
Light-hours
Light-months
Light-years
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The word “planet” means
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Forever
Wanderer
Stationary
Immobile
Indivisible
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Which condition is hard to re-create in
laboratory simulations?
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Extreme temperatures
Vacuum of space
Intense solar radiation
All of these
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Which is used within the solar system?
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Kilometer
Astronomical Unit
Light-year
Parsec
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The term “Stardust” refers to the fact that all
heavier elements were formed
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In the cores of other
stars
In black holes
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At the edge of the known
universe
At the moment of the Big
Bang
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Which unit is used primarily on the Earth?
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Kilometer
Astronomical Unit
Light-year
Parsec
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Participant Scores
700
Sid Cooper
700
Drew Griffin
700
Angelique Jackson
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Melissa James
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Elissa Keller
700
Jeremy King
700
Kenneth Lewis
700
Kristi Warner
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Thomas Armstrong
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Jessika Griffin
The Celestial Sphere
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Easy to picture the
Earth in the center
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Latitude, longitude
are “projected” onto
the Celestial Sphere
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The North Celestial
Pole is directly
above Earth’s
North Geographic
Pole
The South
Celestial Pole is
directly above
Earth’s South
Geographic Pole
The Celestial
Equator is directly
above Earth’s
Equator
The Ecliptic
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The apparent path of the Sun through
the background stars during a year
Tilted 23.5º to the CEq because the
Earth’s axis is tilted 23.5º from
vertical
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Vertical defined as perpendicular to the
Earth’s orbit
There is a season; turn, turn, turn
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The tilt of the Earth’s axis also
explains seasons
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The pole towards the Sun experiences
Summer
The pole away from the Sun
experiences Winter
Dates to remember
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March 21
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Vernal Equinox
Sun, on the ecliptic, moves from the
Southern Hemisphere to the Northern
Hemisphere
June 21
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Summer Solstice
Sun, on the ecliptic, reaches its highest point
in the Northern Hemisphere
23.5º N of the Equator (Tropic of Cancer)
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Cancer USED TO BE the northernmost Zodiacal
Constellation
Dates to remember
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September 22
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Autumnal Equinox
Sun, on the ecliptic, moves from the
Northern Hemisphere to the Southern
Hemisphere
December 22
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Winter Solstice
Sun, on the ecliptic, reaches its highest point
in the Southern Hemisphere
23.5º S of the Equator (Tropic of Capricorn)
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Capricorn USED TO BE the southernmost
Zodiacal Constellation
The Celestial Equator (CEq) is always
directly above
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The North Pole of the
Earth
The South Pole of the
Earth
The Earth’s equator
The Prime Meridian
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The North Celestial Pole (NCP) is always
directly above
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The magnetic North Pole
The geographic North
Pole
The magnetic South Pole
The geographic South
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Pole
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The path the Sun appears to travel through
the skies is tilted _____ to the CEq.
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104.7°
5.6°
98°
23.5°
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The Celestial Equator (CEq) is always
directly above
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The North Pole of the
Earth
The South Pole of the
Earth
The Earth’s equator
The Prime Meridian
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Seasons on Earth are caused by
The tilt of the Earth’s axis
Earth’s distance from the
Sun
Gravity between the
Earth and the Moon
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Gravity between the
Earth and the Sun
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Precession
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The Earth’s
rotation and the
forces acting on it
through the Sun
and Moon cause
the North Pole to
“wobble”
A “loop” of this
wobble takes
some 26,000
years or so
Precession
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The “North Star”
is actually
whichever star is
closest to the NCP
We live in a time
with a moderately
bright star close
to the NCP
Thuban, Vega,
etc.
Precession of the Equinoxes
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The slowly-rotating NCP causes the dates of
Equinoxes, etc. to change
Also, the dates of Earth’s aphelion (farthest
distance from sun) and perihelion (closest
approach to sun) change
“The Immovable Firmament”
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Star positions are calculated on the
Celestial Sphere
“Longitude” is measured as Right
Ascension, or the amount of time
taken from the Vernal Equinox
“Latitude” is measured as Declination,
a positive (above) or negative (below)
degree from the Celestial Equator
(CEq)
What name is given to the projection of
Earth’s latitude and longitude into the skies?
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The Chrysanthemum
Throne
The Celestial Sphere
The Sky Map
The Astronomical Chart
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What name is given to the point where the
Sun crosses the CEq northward?
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Vernal Equinox
Summer Solstice
Autumnal Equinox
Winter Solstice
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How much is Earth’s rotational axis tilted to
the Ecliptic?
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4º
360º
23.5º
5º
451º
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When is the Sun directly overhead if you are
in Montevideo, Uruguay (latitude 23.5º S)?
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June 21
September 22
December 22
March 21
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The Earth’s rotational axis is ALWAYS
pointed towards
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The Sun
The North Star
The North Celestial Pole
Away from the Sun
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A sample reading
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Summer Solstice
occurs on June 21
R.A.: 6 hours
Dec.: +23°22’ N
In the constellation
Gemini (moving into
Taurus, c. 2150 A.D.)
A sample reading
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Betelgeuse (α Orionis)
R.A.: 5 hours, 55’,
10.3“
Dec.: +07°24’25”N
In the constellation
Orion
“What is a day to Me?”
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A standard day
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24 hours
A sidereal day
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23h56m4s or so…
Time it takes for the Earth to face the
same star in space
Explains why the amount of daylight
changes per day at different latitudes
on the Earth
How old are you?
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A Mean Solar Year is 365.256 days
long
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One complete orbit around the Sun
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A Tropical Year is 365.242 days long
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The time from one Vernal Equinox to
the next
The difference (about 20min or so)
is the cause of the apparent
precession of the poles