Retrograde Lab

8/7/2019 Retrograde Lab

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Jonathan Dickinson

Astronomy Laboratory

Sept. 9, 2002http://www.courses.vcu.edu/PHYS-aab/PHYZ103/

You are here

Geocentric versus HeliocentricOr why the average 13 year-old is not really the center

of the universe, I am.


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Everyday ScienceOr, How many scientists does it take to change a light bulb?

Ok, so maybe this is not the most profound scientific endeavor, but it is an example of how we all engage in the scientific method to troubleshot our lives.

In my case the problem is the right light bulb flickering and then going out on my bathroom fixture. Hang in there with me it is a valid lesson.

We begin with a photo of the light fixture turned off. Notice that the flash fires as a result of the low light conditions.Now the light has been turned on. In this case the flash of the camera did not fire because the left light bulb provided enough light that its sensor felt the

flash was not needed.Observation: Right light bulb does not light up.

Based on previous experience, my first reaction to a light bulb not coming on is to suspect a break in the brittle tungsten filament of the light bulb. (akathat the bulb has burned out)

Hypothesis: Bulb has burned out.Now usually I would have just shrugged and just lived with a single functioning bulb, but normally a bulb burns out with a bright flash of light. (Ask me

why, I dare you. It is actually a simple explanation.) Since this light flickered before going out, I am a little leery that something else might be wrong.Experiment: Replace the bulb.

To test my hypothesis, and to hopefully come to a quick resolution to this momentous problem in my life, I replaced the light bulb with what I believed tobe a good bulb. To demonstrate the identity of the two bulbs I used a grow light bulb which is cast slightly blue. (Of course at first I used a normal bulb,

but for your illumination I repeated my experiment in a manner more conducive to clear discernment of the bulbs, but not the diction.)


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Everyday ScienceOr, How many scientists does it take to change a light bulb?

Ok, so maybe this is not the most profound scientific endeavor, but it is an example of how we all engage in the scientific method to troubleshot our lives.

In my case the problem is the right light bulb flickering and then going out on my bathroom fixture. Hang in there with me it is a valid lesson.

Observation: Grow light bulb does not light up in right socket.Okay, the simple solution failed. Is my hypothesis about the first bulb wrong, or is the grow light bulb also burned out.

Hypothesis: Grow light bulb is also burned out.Experiment: Switch the two bulbs.

To test my new hypothesis I put the grow light bulb into the left socket. And just to provide experimental redundancy (which is a good thing in science) Ialso put the working bulb from the left socket into the right socket. And voila, the grow light works in the left socket and the bulb that we knew to be

functional does not light up in the right socket. Notice the grow light is not as bright so my f lash fired.Observation: Grow light bulb lights up in left socket.

So we are now led to the conclusion that it is the right socket that is not functioning. I even went so far as to put the bulb that started in the right socketand put it in the left socket. You guessed it, it worked.

Hypothesis: The right socket is not working.As I have exhausted the other obvious possibilities I now make this my working hypothesis and begin the experiment on how many phone calls to my

landlord it takes to get basic maintenance. (This experiment is still ongoing.)

Not exciting, but this common domestic phenomena does provide an opportunity to use the scientific method. Observe, Hypothesize, Experiment, andRepeat the process.

In addition, basic knowledge of circuits tells me that the problem is at the fixture and that the fixture uses a parallel circuit.

Okay, wake up the discussion is over.


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Motions Within MotionsOr, why you always feel like you are just going in circles.

Stars: Rise in the east, set in the west. On a yearly cycle which starsare visible at night changes.

Sun: Rises in the east, sets in the west. On a yearly cycle thefollowing occur: length of day changes, seasons, height of the sun

at noon, and which stars are visible at night. There are alsooccasional eclipses.

Moon: Rises in the east, sets in the west and this coincides with thetides. Goes through phases on a near monthly basis. Full moonseems to bring out werewolves and odd behavior. There are also

occasional eclipses.

Planets: Rise in the east, set in the west. Pass through constellationson their own schedule. Occasionally reverse direction for shortperiods. Change in brightness and exhibit phases.


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The Theories: Geocentric

Ptolemaic UniverseUniverse consists of concentric spheres

with earth at the center.

Moon, Sun, Mercury, Venus, Mars,

Jupiter, and Saturn each have their

own sphere. The stars are all one

sphere.

All heavenly motion (read

astronomical) is consists of perfect

uniform circular motion.

The acceptance of this theory was

influenced by Aristotles

acceptance ofit.

Later this theory was given the support

of the Roman Catholic Church.http://csep10.phys.utk.edu/astr161/lect/retrograde/aristotle.html


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The Theories: Heliocentric

Copernican Universe

Planets orbit around the Sun,

which is the center of the

universe.

The earth rotates.

The moon orbits around the

earth.

The stars have a fixed location.

Galileos legendary comment,

But it does move.


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The Observation: Retrograde

Motion of Planets

Planets are the Wanders of the Solar System.

If you observe a star at the same time each night, it will slowly move westward.

And to arrive back in the same location at the same time of night will take a

year.

If you observe a planet at the same time each night, the speed at which it

moves westward will slow until it briefly stops and then moves east ward fora little while before continuing its westward motion. It will return to the same

location at the same time of night at its own rate, not in a year.

This apparent backwards movement of the planets is called Retrograde Motion.

The geocentric and heliocentric models of the universe explain retrograde

motion in different ways.

This link is to an animation demonstrating the retrograde motion ofMars

from Oct 13, 1996 to June 26, 1997 it is a part of Ted Snows astronomy

webpage at the University of Colorado, Boulder.

http://cygnus.colorado.edu/Animations/mars.mov


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How the each model explains retrograde motion

In the interest of actually completing this lecture file I will refer you to the

various websites that explain these issues in detail.

http://alpha.lasalle.edu/~smithsc/Astronomy/retrograd.html

This webpage is brief and to the point. It borrows heavily from the other sites I

am listing, which are also linked at the bottom of this webpage.

http://csep10.phys.utk.edu/astr161/lect/retrograde/retrograde.html

This webpage is why I am not bothering to write this all out myself. The

information is thorough and clear. Just go through these pages until you

finish the parallax stuff and you will get everything you need.

http://physics.hallym.ac.kr/education/oregon/imamura/121/oct6/planet.html

This webpage addresses some of the finer detail and includes the standard

diagram that the other sites left off.

This is the one you

really want.


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What is not the question?

Who is on First.

Is the earth the center of the universe?

Science can answer this question using empirical evidence.

Religion and philosophy cannot refute physical evidence withoutrefuting physical reality.

What is the significance of the earth not being the center of the universe?

Religion and philosophy must analyze and try to answer this question.

Science cannot interpret metaphysical significance and meaning.

Science is not in opposition to religion and philosophy since it cannot

even address the same questions.

Science tries to answer what and how. Religion and philosophy try toanswer why.

Retrograde Lab

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