Astronomy 101 Planetarium Lab

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Astronomy 101 Planetarium Lab

• Instructor Brian Pohl
• ConOps Craig Zdanowicz
• www.physics.unc.edu/bpohl/
• PLEASE SIT IN SAME SEAT AS LAST TIME!!

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Morehead Observatory Guest Night

• Each Friday night that UNC classes are in
  session.
• Reservations, email
• Sallie Anderson
• sallie_at_physics.unc.edu

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Celestial Navigation
Where in the World Are We??

• Is the Earth round or flat?
• How can we measure the size of the Earth
• How can we determine where on the Earth we are?

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STARS!!

• The Celestial Sphere
• The position of stars is constant
• The CS is stationary relative to the Earth
• We need to measure angles
• Need a method more precise than hand
  measurements.
• But first we measure the Sun!

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Earths Circumference and Diameter
7.2 5000stadia ?? ?????? 360
circumference
Eratosthenes ( 225 B.C.E.)
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Measuring angles with the sextant (1759)
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Lines of Latitude are parallel, and resemble the
coordinate of Declination on the Celestial Sphere.
Lines of Longitude converge at both
poles, Meaning they are NOT parallel. This
coordinate Is analogous to the coordinate of
Right Ascension.
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Measure Radius of Earth

• We observe Arcturus (arc-to-Arcturus) from Chapel
  Hill and from Key West
• Measure the angle from Arcturus to zenith at each
  location
• Remember to use the calibration ratio
• Note the mileage (BOOK IS WRONG)
• New starting mileage 11,666!
• Angular difference is arc of Earth
• We know angle (convert to radians)
• We know miles between two
• Calculate radius of Earth
• As always, calculate error for all measurements!

LST 14h13m
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Measure Latitude

• Move to South side of Planetarium
• The Planetarium is least like the sky at horizon
  so we wish to minimize the distortion by moving
  South
• DO NOT USE CALIBRATION RATIO!!
• Polaris is stationary in sky, no clocks required
• Latitude is the angle bet. Polaris and Horizon
• Measure Latitude for Chapel Hill
• As always, compute percent error

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Measure Longitude

• This is our version of a good clock
• We will perform the same measurement at different
  longitudes (Chapel Hill, Memphis) at the SAME
  TIME!!
• Measure Spica to Meridian
• Spike to Spica
• Calculate the angular difference
• SIGN IS VERY, VERY IMPORTANT!!!

LST 13h25m
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Memphis Longitude

• DO NOT CALCULATE DISTANCE TO MEMPHIS!!
• We want to know the longitude of Memphis
• This is different from the book!
• Note direction of angle ( or -)
• Chapel Hill Longitude (-79degrees)
• Memphis Longitude CHlong Ang. diff.
• Does your answer make sense?
• Is Memphis East or West of Chapel Hill?
• What does the - mean in the CH Longitude?
• Calculate percent error, of course!!

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The Lab Report

• Rewrite ALL the data
• Include sample calculations
• Staple the original data sheet to end of lab
• Three measurements, three percent errors!
• Radius of Earth
• Chapel Hill Latitude
• Memphis Longitude
• Two sources of error

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All Power Points are on my websitehttp//www.phy
sics.unc.edu/bpohl Visit office hours or email
me if you have questions! bpohl_at_physics.unc.edu

• NEW OFFICE HOURS
• Morehead room 403
• Mondays, Tuesdays (week-after-lab) 300pm-500pm