Astronomy 101 Planetarium Lab

Instructor: Brian Pohl

ConOps: Craig Zdanowicz

www.physics.unc.edu/~bpohl/

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A before-thought

Ludwig Wittgenstein: “Tell me, why do people always say it was natural for man to assume that the Sun went round the Earth rather than that the Earth went round the Sun?”

Friend: “Well, obviously because it just looks as though the Sun is going round the Earth.”

W: “Well, what would it have looked like if it had looked as though the Earth was going round the Sun??”

What can we observe to make astronomical observations?

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Stonehenge, England (c.2500-2000 BCE)

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Mayan & Aztecs (500 – 1500 ACE)

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Mayan Dresden Codex

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Astrology

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Astrological “Ages”• “When the moon is in the Seventh House

And Jupiter aligns with MarsThen peace will guide the planetsAnd love will steer the stars

This is the dawning of the age of AquariusThe age of Aquarius” -Hair, the musical ©(Rado, Ragni, 1967)

• The precession of the Earth changes the “age” we live in– Great Year = 25,800 years– Great Month = 2,150 years

– Age of Aquarius → ~ 2150 C.E.

Planetarium Show

Loooooooook Up!!!!

How do the motions of the Sun and Moon give us days, months,

and years?

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14Sidereal vs. Synodic Months

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Lab Procedure: Measure the length of the

day, month, and year

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Calibrations

• At home, calibrated personal tools (pinkie, thumb, fist, extended hand) to a ruler, pg. 171

• Calibrate hand angles with seat arrangement– Each place in theater sees differently because closer to some

stars than others, Fig 2– Measure distance with hand, fist, thumb, pinkie from Spica to 5

different stars around it, column 1– Use formula, e.g. : 1h + 1f + 2t +1.5p– Compare this to real value you would get if you were outside (I’ll

tell you this), column 2– At home, calculate calibration ratio, column 3

• DO NOT TURN IN CALIBRATION EXERCISE

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Length of Day• Take measurement every 1/2 hour, [col. 1]• Measure distance from Spica to Meridian, [col. 3]

– Sign of angle is (-) if east of meridian, (+) if west

• Calculate the angle from hand-fist measurements• Multiply by calibration ratio, [col. 4]• Change from previous angle to current angle, [col. 5]

– Row (n), col. 5 = row (n) - row (n-1), col. 4– You are looking for the change in position over time

• Hourly rate, [col 6] = col 5 / col 2• Calculate average rate, then length of day

– Average rate over 360° is the length of time

• Percent error using number from book

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Length of Month

• Measure daily intervals• Sidereal month - how long it takes moon to

get back to same position relative to stars• Measure moons distance from Spica

– [col 3]– Watch sign!

• Fill out table same way as before• Calculate length of sidereal lunar month• Percent error compared to value in book

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Length of Year

• Measure weekly intervals, [col 1]• Sidereal Year – how long it takes Sun to get

back to same position relative to the stars• Distance from Sun to Spica, [col 3]

– Watch Sign as well!

• Fill out table same as length of day• Calculate length of sidereal year in terms of

weeks• Percent error compared to book

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Lab Write-Up• 4 tables, filled out

– 1 sample calculation for each type of column in a table

• Equations, work, and RESULTS:– length of day, month, and year

• Equation, work, and results for percent (%) errors• Summary and error sources (2)

– Food for thought regarding error:• What is the thing you are measuring?• What is your measuring device?• What is the single greatest aspect of the lab procedure that may

inhibit measuring the ‘correct’ value?

• Turn in original data sheet, re-write hand-calibration numbers on the inside cover of your lab book for safe-keeping– H-F-F values (fist = x deg, thumb = y deg, etc.)– Average Calibration Ratio (very important!!)– 5 numbers, essentially

Visit office hours or email me if you have

questions!bpohl@physics.unc.edu

www.physics.unc.edu/~bpohl/

Rm 403 Morehead

Wed, Thu (week-of-lab) 4:00 pm - 5:00 pm

Mon, Tue (week-after-lab) 4:00 pm - 5:00 pm