Charles Hakes Fort Lewis College1. Charles Hakes Fort Lewis College2 Prologue Seasons/Theories.

Charles HakesFort Lewis College 1


Prologue

Seasons/Theories


Outline

• Outside Lab Notes• 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


Lab Notes

• Resources Part 2 in class this week. • Noontime Sun for Friday

• Box outside Berndt 671.

• Sunset, Part1 for next Monday• Note link to

http://www.printfreegraphpaper.com/• Box outside Berndt 671.

• Binocular Lab Thursday, Monday(?).• Sign up…

http://www.printfreegraphpaper.com/


Homework Notes

• In Mastering Astronomy - make sure your ID is the same as your FLC ID.


Your Folder• Cut open “closed” folders.• 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, or current, math class

(subject, course number, and year taken.)• Include your daily three minute papers! You can

reuse pages, just add the date.


Three Minute Papers• 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


Introduction

The Celestial Sphere


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

A) 0°

B) 30° N

C) 60° N

D) 90° N


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

A) 60° N

B) 30° N

C) 0°

D) 30° S


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

A) 60° N

B) 30° N

C) 0°

D) 30° S


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

http://wps.aw.com/aw_chaisson_bg_6_mx/120/30970/7928552.cw/index.html






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.


Figure P.3The Northern Sky


How long is the exposure? Enter the correct number of hours.

A) 4

B) 5

C) 6

D) 7

E) 8


Earth’s Orbital Motion

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


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.


Figure P.5Solar and Sidereal Days


Solar vs. Sidereal day

• Edmund Scientific Star and Planet Finder• The view of the night sky changes during the year.


Figure P.6The Zodiac


Seasonal changes

• One sentence - why we have seasons.


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.


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.


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.


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.


Seasonal changes


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.

•


Figure P.8Seasons


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.


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)


Figure P.7Ecliptic


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).







Long Term Changes

• The Earth’s tilt wobbles• Precession takes ~26,000 years.


Figure P.9Precession


Introduction

Scientific Theory


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.”


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.


Discovery 1-1aThe Scientific Method


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


SETI@home


Chapter 18Is There Intelligent Life Elsewhere in the Universe?


Are we alone in the Milky Way?

A) definitely

B) probably

C) maybe

D) probably not

E) no way


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


Figure 18.7Drake Equation


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?)


The Drake Equation

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


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.


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!


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 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.

http://faculty.fortlewis.edu/hakes_c/





Scale of the Universe


Powers of Ten

• http://www.wordwizz.com/pwrsof10.htm

http://www.wordwizz.com/pwrsof10.htm





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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Charles Hakes Fort Lewis College1. Charles Hakes Fort Lewis College2 Prologue Seasons/Theories.

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