Download Slide - Fort Lewis College

Charles Hakes
Fort Lewis College
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Prologue
Seasons/Theories
Charles Hakes
Fort Lewis College
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Outline
• RA/Dec
• 0.2 Earth’s Orbital Motion.
• Day to day changes
• Seasonal changes
• Long term changes
• Scientific Theories
• SETI at home.
• Homework Due Wednesday
Charles Hakes
Fort Lewis College
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Homework Notes
• In Mastering Astronomy - make sure your
ID is the same as your FLC ID.
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Fort Lewis College
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Your Folder
• Cut open “closed” folders.
• Full name on the tab
• BIG name on the front
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Major on upper right
Class on lower left
A comment about yourself on the lower right
Inside - your most recent, or current, math class
(subject, course number, and year taken.)
• Include your daily three minute papers! You can
reuse pages, just add the date.
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Fort Lewis College
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Three Minute Papers
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Remove all spiral notebook fringe!
Re-use pages - save trees
Include date
Say something SPECIFIC. Don’t say “I learned
ABOUT…” unless you say what about it you
learned. Instead, say “I learned THAT…”
• Bad: I learned about the velocity equation
• Good: I learned that v = x/t
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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. 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
Charles Hakes
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
Charles Hakes
Fort Lewis College
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Scale on Meridian
• Declination at zenith (overhead) is your latitude
• The celestial equator (0° dec) is to the south of
your zenith by latitude amount.
• The celestial pole (90° dec) is your latitude
amount above the north horizon.
•
http://wps.aw.com/aw_chaisson_bg_6_mx/120/30970/7928552.cw/index.html
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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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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) 3
B) 5
C) 7
D) 9
E) 11
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Fort Lewis College
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Earth’s Orbital Motion
• Day to day changes
• Seasonal changes
• Long term changes
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Fort Lewis College
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Day to Day Changes
• Solar Day
• Time from one noon to the next
• 24hrs
• Sidereal Day
• Time that a star passes directly overhead until it
does so again.
• Less than 24 hrs.
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Fort Lewis College
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Figure P.5
Solar and Sidereal Days
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Fort Lewis College
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Solar vs. Sidereal day
• Edmund Scientific Star and Planet Finder
• The view of the night sky changes during the year.
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Fort Lewis College
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Figure P.6
The Zodiac
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Fort Lewis College
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Seasonal changes
• One sentence - why we have seasons.
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Fort Lewis College
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Seasonal changes
• What about seasonal changes in temperature?
• Let's propose a (wrong) theory: “the Earth is closer to the
Sun in summer”
• What testable predictions can we make? (E.g., what is life
like on the equator? Durango? Alaska? the North Pole? the
southern hemisphere?) Any successful theory will make
correct predictions regarding length of day and temperature,
which together define the seasons.
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Fort Lewis College
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Theory: “the Earth is closer to the
Sun in summer”
Where on Earth would it be warmer at
perihelion (closest approach to the Sun)?
A) Northern Hemisphere
B) Southern hemisphere
C) Everywhere at the same time.
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Fort Lewis College
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Seasonal changes
• Where on Earth would it be warmer at perihelion in
January? The answer is everywhere, unlike the
reality of our world's seasons which vary by
hemisphere.
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Fort Lewis College
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Seasonal changes
• Where on Earth would it be warmer at perihelion in
January? The answer is everywhere, unlike the
reality of our world's seasons which vary by
hemisphere.
• This is a huge piece of knowledge, which most
Americans get wrong! I absolutely insist that you
all do better.
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Fort Lewis College
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Seasonal changes
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Fort Lewis College
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Seasonal changes
• Let's look at a different view. The left frame shows
our initial theory, with no tilt. The right frame adds
a tilt to the Earth's rotation axis.
•
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Fort Lewis College
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Figure P.8
Seasons
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Fort Lewis College
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Seasonal changes
• When the sun is high, the light rays are more
concentrated - the sun feels hotter.
• When “your” hemisphere is pointed towards the
sun, it receives more daylight hours compared to
nighttime hours.
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Fort Lewis College
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Seasonal changes
• From the point of view of the Earth, the path of the
Sun in the sky appears tilted compared to Earth’s
equator.
• Ecliptic - The apparent path of the sun on the
celestial sphere during the year.
• Equinoxes - Two points where the ecliptic crosses
the celestial equator.
• Vernal equinox (first day of Spring ~Mar. 21)
• Autumnal equinox (first day of fall ~Sept 21)
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Fort Lewis College
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Figure P.7
Ecliptic
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Fort Lewis College
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Scale on Meridian
• Declination at zenith (overhead) is your latitude
• The celestial equator (0° dec) is to the south of
your zenith by latitude amount.
• The celestial pole (90° dec) is your latitude
amount above the north horizon.
•
http://wps.aw.com/aw_chaisson_bg_6_mx/120/30970/7928552.cw/index.html
• Lab note - at the equinoxes, the sun is ON the
celestial equator. At the solstices, the sun is north
(or south) of the equator by 23.5° (the Earth’s
tilt).
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Fort Lewis College
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Long Term Changes
• The Earth’s tilt wobbles
• Precession takes ~26,000 years.
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Fort Lewis College
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Figure P.9
Precession
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Fort Lewis College
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Introduction
Scientific Theory
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Fort Lewis College
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Scientific Theory
• Theory - the framework of ideas and
assumptions used to explain some set of
observations and make predictions about
the real world.
• Can prove them wrong by a single bad
prediction.
• Can’t ever prove them “right.” They just get
more widely accepted.
• Eventually, some theories might be called
“law,” (e.g. gravity) but they are still just
scientific “theories.”
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Fort Lewis College
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Scientific Theory
• Must be testable.
• Must continuously be tested.
• They should be simple.
• Occam’s Razor - if two competing theories
both explain the facts, then the simpler one is
better.
• KISS engineering - “Keep It Simple, Stupid.”
• They should be elegant.
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Fort Lewis College
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Discovery 1-1a
The Scientific Method
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Fort Lewis College
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Is it possible to prove or disprove a
scientific theory?
A) Yes prove, yes disprove
B) Yes prove, no disprove
C) No prove, yes disprove
D) No prove, no disprove
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Fort Lewis College
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SETI@home
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Fort Lewis College
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Chapter 18
Is There Intelligent Life Elsewhere in the Universe?
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Fort Lewis College
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Are we alone in the Milky Way?
A) definitely
B) probably
C) maybe
D) probably not
E) no way
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Fort Lewis College
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The Drake Equation
• In science, the complete lack of any useful data
does not always stop us. Instead, we proceed
anyway, with a specialized equation to
characterize our ignorance!
• The number of advanced civilizations in our
Galaxy with whom we can communicate is:
N = R fp np fl fi ft L
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Fort Lewis College
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Figure 18.7
Drake Equation
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Fort Lewis College
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The Drake Equation
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R is the average rate of star formation (~10 stars/year)
fp is the fraction of stars with planets (current evidence - nearly 1;
that is, ~100% of stars form with planets)
np is the habitable planets per star with planets (the Chaisson
textbook estimates 0.1)
fl is the fraction of those planets with life (?!?)
fi is the fraction of those life-bearing planets with at least one
intelligent species (?!?)
ft is the fraction of planets with an intelligent species in which that
species develops technology capable of interstellar radio
communication (?!?)
L is the average lifetime of a technological civilization (our society
has been capable of radio communication for only about 100 years;
how much longer will we remain so? Are we a good model for
other possible civilizations?)
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Fort Lewis College
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The Drake Equation
• Make your own estimate for the
unknown values and calculate and
answer for the Drake equation.
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Fort Lewis College
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How many technological civilizations are there
in the Milky Way?
(N = R fp np fl fi ft L)
A) 0
B) 1-9
C) 10-99
D) 102-104
E) more than 104.
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Fort Lewis College
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The Drake Equation
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Suppose all the f terms that aren't specified above are nearly 1 (or
100%). (optimistic!) If we do that, then the lifetime of a civilization
(in years) roughly equals the number of societies in our Galaxy. So
if a technological society lasts for 100 years say, there would be
100 of them in our Galaxy.
However, even if there are 100 other civilizations capable of radio
communication in our Galaxy, and even if they're interested in
talking to us, the average distance between civilized worlds is about
10,000 light years - so it would take 20,000 years to get a response
to any message we send.
Even if we suppose that there are 1 million civilizations out there,
they'd still be separated by about 300 light years!
Charles Hakes
Fort Lewis College
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The Drake Equation
• Go look for ET on your own!
• Run SETI@home on your computer, see:
http://faculty.fortlewis.edu/hakes_c/
• SETI@home is a scientific experiment that uses Internetconnected computers in the Search for Extraterrestrial
Intelligence (SETI). You can participate by running a free
program that downloads and analyzes radio telescope
data.
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Fort Lewis College
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Scale of the Universe
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Fort Lewis College
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Powers of Ten
• http://www.wordwizz.com/pwrsof10.htm
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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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