Transcript The Celestial Sphere

Charles Hakes
Fort Lewis College
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Introduction
The Celestial Sphere
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Fort Lewis College
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Outline
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•
•
•
•
Review
Unit Conversions
Observing the Sun
RA/Dec
SETI
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Fort Lewis College
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Notes
• Homework 1 due on Wednesday.
• Remove “spiral fringe” from three minute
papers
• In MasteringAstronomy, make sure your
student ID is your FLC student ID!
• If you are still having login issues – drop by
my office after class or during office hours.
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Fort Lewis College
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Conversion Factors
• Conversion factors are equivalence
statements expressed in the form of
ratios
• Example: 1 in = 2.54 cm
• Conversion factors let you express a
quantity in terms of other units without
changing its physical value.
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Fort Lewis College
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Conversion Exercise
• Convert 0.61 m to inches.
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Fort Lewis College
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How many inches is 0.61m?
A) 0.24 inches
B) 1.56 inches
C) 24.0 inches
D) 156 inches
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Fort Lewis College
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How many inches is 0.61m?
A) 0.24 inches
B) 1.56 inches
C) 24.0 inches
D) 156 inches
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Fort Lewis College
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Significant Figures
• Example
• 4.56 has three significant figures.
• 4.56x106 also has three significant figures.
• .000456 also has three significant figures.
• A calculation output can not have more significant
figures than the input.
• If an equation has a whole number (for example 2) it is
considered to be 2.00000 etc.
• Calculation hint - it is often best to keep all available
figures until the last step, and then round your answer.
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Fort Lewis College
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Scientific Notation
• What does 1.0x106 mean?
• Positive exponents mean shift the decimal place to the
right (bigger numbers).
• Negative exponents mean shift the decimal place to the
left (smaller numbers).
• Usually only have one digit to the left of the decimal.
• Most calculators have a single key to add the (x10^)
term. (EXP, EE)
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Fort Lewis College
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Measurements
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Fort Lewis College
Multiple
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Prefix
giga-
106
103
10-2
10-3
10-6
10-9
megakilocentimillimicronano11
Algebra Hint
• The following relationship will be
useful to remember:
A
B
C
D
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Fort Lewis College
A*D
=
B*C
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Dimensional Analysis
• Dimensional Analysis is VERY helpful in problem
solving.
• Check your equations with specific units.
• Velocity example - how do distance (x), time (t),
and Velocity (V) relate?
V = x/t
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Fort Lewis College
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Dimensional Analysis Example Which equation is correct?
A) velocity = distance * time
B) time = velocity * distance
C) time = distance / velocity
D) time = velocity / distance
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Fort Lewis College
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Which equation is correct?
A) velocity = distance * time
B) time = velocity * distance
C) time = distance / velocity
D) time = velocity / distance
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Fort Lewis College
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Velocity Exercise
• The laser travels 9.6m across the
room. How many seconds does it
take?
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Fort Lewis College
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Light Travel Time Across the Room
(9.6 meters)
A) 2.9x106 sec
B) 2.9x10-6 sec
C) 3.2x10-5 sec
D) 3.2x10-8 sec
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Fort Lewis College
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Light Travel Time Across the Room
(9.6 meters)
A) 2.9x106 sec
B) 2.9x10-6 sec
C) 3.2x10-5 sec
D) 3.2x10-8 sec
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Fort Lewis College
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How many light years was that 9.6 m?
A) 9.1x1012 ly
B) 1.0x10-15 ly
C) 2.9x109 ly
D) 1.1x10-14 ly
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Fort Lewis College
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How many light years was that 9.6 m?
A) 9.1x1012 ly
B) 1.0x10-15 ly
C) 2.9x109 ly
D) 1.1x10-14 ly
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Fort Lewis College
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Observing the Sun
• http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/safety2.html
• http://www.mreclipse.com/Special/filters.html
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Fort Lewis College
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Measuring Angles
•
•
•
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A fist at arms length is about 10°
Fingers spread wide are about 15°
Three fingers together are about 5°
One pinky width is about 1°
The full moon is almost exactly 0.5°
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Fort Lewis College
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How High is the Sun at noon?
A) 90°
B) >75°
C) <75°
D) cannot determine
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Fort Lewis College
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Introduction
The Celestial Sphere
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Fort Lewis College
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Oslo, Norway is 60°N latitude. What
declination line passes through the zenith in
Oslo?
A)
B)
C)
D)
0°
30° N
60° N
90° N
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Fort Lewis College
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Oslo, Norway is 60°N latitude. What
declination line passes through the zenith in
Oslo?
A)
B)
C)
D)
0°
30° N
60° N
90° N
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Fort Lewis College
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Astronomy Picture of the Day
http://antwrp.gsfc.nasa.gov/apod/ap080922.html
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Fort Lewis College
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The Celestial Sphere
• Locations to note
• North celestial pole
• Celestial equator
• Declination corresponds to latitude.
• Right ascension corresponds to
longitude.
• RA and Dec are “fixed” onto the
celestial sphere.
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Fort Lewis College
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Figure P.4
Right Ascension and Declination
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Fort Lewis College
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Declination
• Declination corresponds to latitude.
• Units are degrees (and minutes and
seconds).
• Durango’s latitude is +37.275° N.
The declination line passing directly
overhead is also +37.275° N.
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Fort Lewis College
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Oslo, Norway is 60°N latitude. How high does
the star Polaris appear?
A)
B)
C)
D)
0°
30° N
60° N
90° N
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Fort Lewis College
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Oslo, Norway is 60°N latitude. How high does
the star Polaris appear?
A)
B)
C)
D)
0°
30° N
60° N
90° N
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Fort Lewis College
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What is the southernmost declination line
visible from Oslo (at 60° N)?
A)
B)
C)
D)
60° N
30° N
0°
30° S
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Fort Lewis College
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What is the southernmost declination line
visible from Oslo (at 60° N)?
A)
B)
C)
D)
60° N
30° N
0°
30° S
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Fort Lewis College
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Standing on the equator, you can see…
A) the celestial equator directly overhead
B) entire celestial sphere during a 24 hour day
C) both celestial poles on your horizon
D) all of the above
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Fort Lewis College
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Standing on the equator, you can see…
A) the celestial equator directly overhead
B) entire celestial sphere during a 24 hour day
C) both celestial poles on your horizon
D) all of the above
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Fort Lewis College
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Durango’s latitude is 37.275° N. What
is the southernmost declination line
visible?
A) 0°
B) 37.275° S
C) 52.725° S
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Fort Lewis College
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Durango’s latitude is 37.275° N. What
is the southernmost declination line
visible?
A) 0°
B) 37.275° S
C) 52.725° S
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Fort Lewis College
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Right Ascension
• Right Ascension corresponds to longitude.
• Units are Hours (and minutes and
seconds).
• The trick (as with longitude) is to decide on
the zero point.
• Longitude zero is at the observatory in
Greenwich England.
• RA zero is where the sun crosses the
celestial equator going north.
• RA is always moving w.r.t. longitude.
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Fort Lewis College
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PRS question
• How long is the following exposure?
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Fort Lewis College
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Figure P.3
The Northern Sky
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Fort Lewis College
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How long is the exposure? Enter the
correct number of hours.
A) 4
B) 5
C) 6
D) 7
E) 8
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Fort Lewis College
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Three Minute Paper
• Write 1-3 sentences.
• What was the most important thing
you learned today?
• What questions do you still have
about today’s topics?
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Fort Lewis College
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