Charles Hakes

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(No Transcript)
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Prologue

• Seasons/Theories

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Outline

• Outside Lab Notes
• SETI at home.
• RA/Dec
• Scientific Theories
• P.2 Earths Orbital Motion.
• Day to day changes
• Seasonal changes
• Long term changes
• Homework Due Wednesday

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Outside Lab

• Finish Noontime Sun
• Start Sunset, Part1 ASAP (whenever it is clear).
• Note new link to http//www.printfreegraphpaper.co
  m/
• Binocular Lab Monday, Thursday.
• Sign up.
• Dont forget your Starry Night printout to be
  handed in when you show up. (3 points!)

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Your Homework

• Answer PRS questions
• Turn in with your folder.
• Dont forget
• Write your name (including last name).
• Write your section.
• Staple!
• No spiral notebook fringes.
• Use a black or blue pen or pencil.
• Do not confuse Astronomy and Astrology.

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Your Folder

• Full name on the tab
• BIG name on the front
• Major on upper right
• Class on lower left
• A comment about yourself on the lower right
• Inside - your most recent 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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• SETI_at_home

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Chapter 18Is There Intelligent Life Elsewhere in
the Universe?
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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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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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Figure 18.7Drake Equation
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The Drake Equation

• 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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The Drake Equation

• Make your own estimate for the unknown values and
  calculate and answer for the Drake equation.

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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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The Drake Equation

• 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!

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The Drake Equation

• Go look for ET on your own!
• Run SETI_at_home on your computer, see
  http//faculty.fortlewis.edu/hakes_c/
• SETI_at_home is a scientific experiment that uses
  Internet-connected 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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Scale of the Universe
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Powers of Ten

• http//www.wordwizz.com/pwrsof10.htm

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Introduction

• The Celestial Sphere

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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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Figure P.4Right Ascension and Declination
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Declination

• Declination corresponds to latitude.
• Units are degrees (and minutes and seconds).
• Durangos latitude is 37.275 N. The
  declination line passing directly overhead is
  also 37.275 N.

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Oslo, Norway is 60N latitude. What declination
line passes through the zenith in Oslo?

• A) 0
• B) 30 N
• C) 60 N
• D) 90 N

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Oslo, Norway is 60N latitude. What declination
line passes through the zenith in Oslo?

• A) 0
• B) 30 N
• C) 60 N
• D) 90 N

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Oslo, Norway is 60N latitude. How high does the
star Polaris appear?

• A) 0
• B) 30 N
• C) 60 N
• D) 90 N

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Oslo, Norway is 60N latitude. How high does the
star Polaris appear?

• A) 0
• B) 30 N
• C) 60 N
• D) 90 N

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What is the southernmost declination line visible
from Oslo (at 60 N)?

• A) 60 N
• B) 30 N
• C) 0
• D) 30 S

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What is the southernmost declination line visible
from Oslo (at 60 N)?

• A) 60 N
• B) 30 N
• C) 0
• D) 30 S

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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.

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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.
• 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
  Earths tilt).

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Right Ascention

• 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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PRS question

• How long is the following exposure?

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Figure P.3The Northern Sky
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How long is the exposure? Enter the correct
number of hours.
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Introduction

• Scientific Theory

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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.
• Cant ever prove them right. They just get
  more widely accepted.
• Eventually, some theories can become law, (e.g.
  gravity) but they are still just theories.

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Scientific Theory

• Must be testable.
• Must continuously be tested.
• They should be simple.
• Occams 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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Discovery 1-1aThe Scientific Method
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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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Earths Orbital Motion

• Day to day changes
• Seasonal changes
• Long term changes

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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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Figure P.5Solar and Sidereal Days
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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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Figure P.6The Zodiac
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Seasonal changes

• One sentence - why we have seasons.

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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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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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Theory  the Earth is closer to the Sun in
summer

• A) This explains why it is hotter in the northern
  hemisphere during summer.
• B) This explains the longer days during summer.
• C) This explains why the sun looks larger during
  summer.
• D) None of the above.

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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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Seasonal changes
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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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Figure P.8Seasons
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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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Seasonal changes

• From the point of view of the Earth, the path of
  the Sun in the sky appears tilted compared to
  Earths 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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Figure P.7Ecliptic
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Long Term Changes

• The Earths tilt wobbles
• Precession takes 26,000 years.

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Figure P.9Precession
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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 todays
  topics?