09-SolarRotation - Name________________________

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Unformatted text preview: Name________________________ Section______________________ Date_________________________ PRELAB CLEA : 9. Period of Rotation of the Sun Objective: Determine the nature and rate of the sun’s rotation by observing the movement of sunspots across the field of view of a CCD image. • This lab uses heliographic coordinates, which are illustrated below. • (4pt) *Question: Why is there greater uncertainty in the measurement of a sunspot towards the edge of the sun as opposed to the center? • A linear fit is characterized by the slope and the T ­zero. The slope is the angle of tilt and the T ­zero is the time or x value where the line crosses the zero point of the y axis. It is important to write down the entire T ­zero value. • Synodic Period: Value of Sun’s rotation as viewed from Earth. This is not the TRUE rotation rate of the sun since the Earth is also moving, orbiting the sun. • Sidereal Period: The true rotation rate of the sun. The time it takes for one point on the sun’s surface to rotate once with respect to the distant stars. • The Synodic period is slightly longer than the Sidereal period as the sun has to turn slightly further to catch up with the orbital motion of the Earth. In this lab, you will measure the synodic rotation rate. This value must be divided into 360 degrees to obtain the Synodic PERIOD. You will then calculate the Sidereal period. Psynodic • 360 = Slope We calculate the Sidereal period from the Synodic period as follows: Psidereal Psynodic ∗ (365.25) = Psynodic + 365.25 • (6pt) *Question: We measure a sunspot to measure a slope of 18 degrees/day. What is the Synodic period? What is the Sidereal period? Name________________________ Section______________________ Date_________________________ CLEA : 6. Period of Rotation of the Sun Objective: Determine the nature and rate of the sun’s rotation by observing the movement of sunspots across the field of view of a CCD image. Background: • For this lab you will need a calculator. • This lab uses heliographic coordinates, which are illustrated below. • A linear fit is characterized by the slope and the T ­zero. The slope is the angle of tilt and the T ­zero is the time or x value where the line crosses the zero point of the y axis. It is important to write down the entire T ­zero value. • Synodic Period: Value of Sun’s rotation as viewed from Earth. This is not the TRUE rotation rate of the sun since the Earth is also moving, orbiting the sun. • Sidereal Period: The true rotation rate of the sun. The time it takes for one point on the sun’s surface to rotate once with respect to the distant stars. • The Synodic period is slightly longer than the Sidereal period as the sun has to turn slightly further to catch up with the orbital motion of the Earth. In this lab, you will measure the synodic rotation rate. This value must be divided into 360 degrees to obtain the Synodic PERIOD. You will then calculate the Sidereal period. • We calculate the Sidereal period from the Synodic period as follows: Psidereal Psynodic ∗ (365.25) = Psynodic + 365.25 Procedure: • Open the CLEA lab titled “The Period of Rotation of the Sun” by double clicking on the Icon labeled SOLAR ROTATION. • Click on File  ­> Login. Enter the first names of each group member and click OK and then YES. • Click on File  ­> Run • Click File  ­> Image Database  ­> Image Directory  ­> Load. Choose the file alist.txt to load images of the solar disk from the GONG network of solar telescopes. Images will appear similar to the example below in Figure 1. • Click File  ­> Image Database  ­> Select all • Click File  ­> Image Database  ­> Load Selected Images • Make sure to click Images  ­> Sort image list. • Now that you have loaded all the images of the solar disk, we can see how the sunspots change over the time period of the selected images. • To see the images animated, click on Images  ­> Animation  ­> On. Once you are comfortable with the motion of the sun spots, turn this animation off. • Record the range of dates your images span on the provided sheet. Figure 1: A typical image of the Sun from GONG. Arrows have been added to indicate directions on the solar globe. • Now we want to identify several sun spots on the disk of the sun and monitor their position over the next set of images. You should begin with the image on 2002/1/13 and identify 3 spots on the left hemisphere of the image. Draw these spots on circle on the provided sheet. • Click on each sunspot and fill in the Spot ID box before clicking record. Use something like 1,2,3 or A,B,C to identify your spots. • Make sure that you are clear which spot is located where and use the SAME Spot ID in each image for each spot. • When done with image, click Finished. • Repeat this for each image in the list until all 3 spots are identified in each image. If a spot goes off the right side of the disk, DON’T WORRY! Continue labeling the remaining spots. You may add in more spots as they appear from the left if you wish. The minimum number of labeled spots is 3. • Now, we would like to analyze the motion of our sun spots. By doing this we can understand the ROTATION OF THE SUN. • • Click Analysis  ­> Plot/Fit Data In the new window, click File  ­> Dataset  ­> Load Longitudinal Values • Load one Spot ID at a time and use the adjustment of T ­zero (in Julian Days) and the Slope (in degrees per day) to fit the observations as well as possible. For our purposes, the slope of the line represents the number of degrees per day a sunspot moves on average. • As an example, your RMS value (the error measurement – how well your observations are fit by the line) should be below 1.00 RMS degrees. • Record the Spot ID, T Zero, Slope, and RMS on the sheet provided. • Continue loading the longitudinal values for each spot until you have fit and recorded each spot. • Print a plot of all sunspot longitudinal values and their best fits. • Click File  ­> Dataset  ­> Clear data • Now load the latitudinal values as we did for longitudinal values. • Record the Mean Latitude (in degrees) for each spot on the sheet provided. • Complete the Post Lab questions and calculations. Name________________________ Section______________________ Date_________________________ Record Sheet – The Period of Rotation of the Sun 1. 2. 3. Draw the Location and Spot ID of your sun spots. (3pt) Date range of Solar images: ___________________ to ______________________ (1pt) Which direction does the Sun rotate ( L to R or R to L)? ______________ (1pt) On average how many spots are on the disk of the sun? _________________ (1pt) (3pt) Spot ID T ­zero (JD) Slope (deg/day) RMS (deg) Mean Latitude (deg) What changes do you see in latitude of the sunspots through each image? 4. (1pt) 360 Psynodic ∗ (365.25) Psynodic = Psidereal = Slope Psynodic + 365.25 (5pt) Spot ID Synodic Period (days) Sidereal Period (days) XXXXXXXXXXXXX AVERAGE of SIDEREAL PERIOD 5. Why do the sunspots not move exactly horizontally across the disk of the sun? (2pt) 6. Why is there greater uncertainty in the measurement of a sunspot towards the edge of the sun as opposed to the center? Consider the implications of heliographic coordinates and projecting a 3D object onto a 2D image. (3pt) ...
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This note was uploaded on 02/01/2012 for the course PHYS 133 taught by Professor Staff during the Fall '08 term at University of Delaware.

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