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by: Ashlee Heaney


Ashlee Heaney
GPA 3.78


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Class Notes
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This 2 page Class Notes was uploaded by Ashlee Heaney on Wednesday September 30, 2015. The Class Notes belongs to ASTR 106 at Western Kentucky University taught by Staff in Fall. Since its upload, it has received 12 views. For similar materials see /class/216702/astr-106-western-kentucky-university in Astronomy at Western Kentucky University.


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Date Created: 09/30/15
Name ASTR 106 Using Sunpots to Measure Solar Rotation due 25 Feb This year is the 400 11 anniversary of the study of sunspots In 1609 Galileo built a telescope and used it to observe that the Sun was covered with dark spots Furthermore he noted that these spots moved across the surface of the sun indicating that the sun was rotating At the time these were truly startling ideas We now know that sunspots are regions of the sun s photosphere that are cooler than their surroundings and thus look dark The cooling is the result of the sun s magnetic eld lines popping through the surface of the sun at the point where we see the sunspots Since the spots are physically located on the sun s photosphere the sun s rotation carries them around the sun In this lab exercise you will use sunspots to determine the rotation period of the sun as seen from earth DATA COLLECTION PROCEDURE Nine optical images of the Sun will be obtained from the image archive at the National Solar Observatory s GONG website httpgongnsoeduDailinmages The number of sunspots in the current solar cycle recently reached its minimum so most days for the past two years have not had any sunspots visible However in 2008 there were a few sunspots visible from March 25Lh through the 2quotd of April You will use images from these days as data for your lab In the Big Bear section of the GONG image gallery click on Archives JPEG then click on the Archive Year 2008 link to view the menu of dates when data is available for last year with Dec 31 data at the top of the list and Jan 01 data at the bottom of the list Scroll down the page and click on the thumbnail image labeled bb 080325 to view thumbnail images acquired March 25 2008 Click on the Scroll down the page of images until you get to the image named bbiqa080102tl454jpg where bbiqa identi es it as a Big Bear Solar Observatory visible light image 08 is the year 03 the month 25 the day and tl454 represents the time of day when the image was acquired Click on the thumbnail to see the full size image Do not use magnetograrn images from the right hand column 8 points For each of the nine days from 080325 through 080402 select the image acquired at 1454 Print the image for each day so they show the Sun at the same size Be sure the date and time of the image is on each hardcopy when your browser prints the page DATA ANALYSIS PROCEDURE On each of the fulldisk white light solar images identify a sunspot that you can clearly identify on at each images Identify an individual sunspot to follow not a group 1 3 points On each of the nine images identify the two darkest sunspots noting how they progress across the Sun from day to day Be sure you follow an individual sunspot not a group On each of the images mark the two sunspots you have chosen using arrows above and below E 2 1 point On the GONG images north is at the top of each image and east is to the left Which direction do the sunspots move from one day to the next 3 2 point Use a ruler to draw a horizontal line through the sunspot in each successive picture Start the line at the left edge of the Sun s image and end the line at the right edge Avoid choosing spots near either edge of the Sun 4 3 points For each day a given sunspot is visible measure the distance in millimeters from the Sun s eastern edge to the center of that sunspot Record your values in the table below The difference between the rst distance entered in the table and the last distance entered in the table is the distance the spot has traveled For example if a sunspot on the image from the earliest date was 1115 mm from the left edge of the Sun and the same sunspot was 3470 mm from the left edge of the dates Image name for each from le Ogstfm solar image 1 2 3 4 5 6 7 8 9 5 2 points Distance your spots traveled lefthand sunspot mm righthand sunspot mm 6 1 point Look up the Sun s m diameter as measured in kilometers km On your images measure the diameter the greatest distance across the disk in millimeters 7 1 point Diameter of the Sun on your printed images mm The scale factor of the images is the diameter in kilometers divided by the diameter in millimeters 8 1 point Scale factor kmmm 9 2 points Convert your measurement of the Sun s diameter from millimeters to kilometers using this scale factor to calculate the actual distance the sunspot traveled The lefthand sunspot traveled km The righthand sunspot traveled km 10 1 point Calculate the average distance traveled by the two sunspots km 11 1 point The time it took the sunspots to travel that distance was days Determine how fast the sunspots are moving across the surface of the Sun The distance the spot traveled was calculated above We know how long it took the spot to move this far since we know the date of each photograph The time it takes for a given spot to go the calculated distance is the difference between the dates in the first and last photograph you used The speed is the distance calculated in 9 divided by the time it took the spots to go that distance 12 2 points The average speed of the Sun s rotation was measured to be kmday Each sunspot must travel a distance equal to the Sun s circumference in order to make a full rotation around the Sun As observed from Earth the synodic rotation period the time it takes a spot to go around the sun once is given by the Sun s circumference rotation speed 13 1 point Synodic rotation period 437 XlO6 km measured rotation speed days 14 1 point Calculate the percent difference between your value and the accepted value of 273 days for the synodic rotation period of midlatitude sunspots measured synodic rotation period 7 273 273 X 100


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