Astronomy 101 Planetarium Lab

1. Astronomy 101 Planetarium Lab Instructor: Brian Pohl ConOps: Craig Zdanowicz www.physics.unc.edu/~bpohl/ PLEASE SIT IN SAME SEAT AS LAST TIME!!

2. Morehead Observatory Guest Night Each Friday night that UNC classes are in session. Reservations, email Sallie Anderson sallie@physics.unc.edu

3. Celestial Navigation • 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? Where in the World Are We??

4. 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!

5. Earth’s Circumference and Diameter 7.2° 5000stadia ―― = ―――――― 360° circumference Eratosthenes (~ 225 B.C.E.)

6. Measuring angles with the sextant (1759)

7. 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.

9. 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

10. 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

11. 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

12. 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!!

13. 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

14. All Power Points are on my website:http://www.physics.unc.edu/~bpohl Visit office hours or email me if you have questions! bpohl@physics.unc.edu NEW OFFICE HOURS Morehead room 403 Mondays, Tuesdays (week-after-lab) 3:00pm-5:00pm