Week 11 - Using Sunspots to Study the Rotation of the Sun

Name: Key Using Sunspots to Study the Rotation of the Sun Galileo was one of the first to observe sunspots on the surface of the Sun. He noticed that sunspots were not staying in one place on the Sun but moving. Notice three of Galileo’s drawings of the Sun below. Using the motion of the sunspots we can measure how long it takes the sun to rotate! We will use real data from the SOHO telescope, which sends back a picture each day of the Sun and any sunspots that are visible. 1) Look at the pictures from SOHO included at the end of this lab – I have included the pictures for every other day. You should be able to see sunspots moving from one picture to the next. a) Are all sunspots moving in the same direction? If so, what general direction (right to left, top to bottom, etc.) are the sunspots moving? Yes – they are all moving from left to right. b) The grid on each picture shows the latitude and longitude of the Sun. In general, how does the longitude of a sunspot change from one picture to the next? In general, how does the latitude of a sunspot change from one picture to the next? The longitude increases and the latitude stays about the same. 2) We are going to trace the motion of 4 sunspots in the images and use this data to try to calculate the rotational period of the Sun. For each sunspot, I will give you the latitude and longitude for the first day and you will provide the latitude and longtitude for the remaining days the sunspot is visible. You should not see much of a change in the latitude from one picture to the next.

Sunspot #1 Circle the sunspot in each of the pictures where it is visible and label it #1. Record the latitude and longitude in the table and calculate the change in longitude from the previous observation. (Be careful when you are subtracting negative numbers!). Date Sept. 7 Sept. 9 Sept. 11 Sept. 13 Sept. 15 Sept. 17 Latitude +21 o +19 o +17 o +17 o +18 o +20 o Longitude -65 o -40 o -13 o +12 o +37 o +62 o Change in Longitude Since Previous Observation N/A +25 o +27 o +25 o +25 o +25 o Sunspot #2 Circle the sunspot in each of the pictures where it is visible and label it #2. Record the latitude and longitude in the table and calculate the change in longitude from the previous observation. (Be careful when you are subtracting negative numbers!). Date Sept. 27 Sept. 29 Oct. 1 Oct. 3 Oct. 5 Latitude +8 o +5 o +6 o +7 o +9 o Longitude -44 o -16 o +11 o +37 o +66 o Change in Longitude Since Previous Observation N/A +28 o +27 o +26 o +29 o Sunspot #3 Circle the sunspot in each of the pictures where it is visible and label it #3. Record the latitude and longitude in the table and calculate the change in longitude from the previous observation. (Be careful when you are subtracting negative numbers!). Date Oct. 5 Oct. 7 Oct. 9 Oct. 11 Latitude +20 o +18 o +17 o +18 o Longitude -62 o -38 o -13 o +14 o Change in Longitude Since Previous Observation N/A +24 o +25 o +27 o Sunspot #4

a) Imagine a sunspot was first observed at a longitude of -55 o . If the sun makes one complete rotation, what will the longitude of the sunspot be now? Explain. -55 o -> when the sun has made a complete rotation the sunspot will be Back to where it was before. b) If you were to add up the changes in longitude of the sunspot as the Sun made one complete rotation, how many degrees would the sunspot’s longitude have changed in total? Explain. 360 o -> one complete rotation is 360 o of longitude since there are 360 o in a circle. c) For each sunspot, calculate the total change in longitude from the first observation to the last observation. Also, calculate the total number of days from the 1 st observation to the last observation (ex: Sept. 5 to Sept. 11 = 6 days). Record your answers in the Table below. d) Calculate the rotational period: Rotational Period = Total Number of Days x 360 . Total Change in Longitude Sunspot Total Change in Longitude Total Number of Days Rotational Period of the Sun 1 +127 o 10 28.3 days 2 +110 o 8 26.2 days 3 +76 o 6 28.4 days 4 +88 o 6 24.5 days Differential Rotation

5) What is differential rotation? Differential rotation is when different parts of an object rotate in different amounts of time. 6) Which part of the Sun will rotate in the least amount of time – the equator or near the poles? The Equator 7) Based on the latitudes you measured for the four sunspots, which sunspot SHOULD have had the smallest rotational period (ie. rotate in the least amount of time)? Explain. Sunspot #2 has the latitude that is closest to the Equator, so it should have the smallest rotational period. 8) Based on the latitudes you measured for the four sunspots, which sunspot SHOULD have had the largest rotational period (ie. rotate in the longest amount of time)? Explain. Sunspot #4 has the latitude that is the farthest from the Equator, so it should have the largest rotational period. 9) Do your actual answers match what you expected from questions 7 and 8? If not, don’t worry – it is very difficult to actually measure differential rotation! No --- the shortest rotational period was Sunspot #4 and the longest was Sunspot #3. 10) 4 planets in our solar system also have differential rotation. Which 4 planets do you think these are? Explain your choice. The gas giants (Jupiter, Saturn, Uranus, and Neptune) all have differential rotation. This makes sense because the outer part of these planets is just gas. The terrestrial planets can’t have differential rotation because they have a solid crust.

September 13, 2011 September 15, 2011 September 17, 2011 September 19, 2011 1 1 1

September 21, 2011 September 23, 2011 September 25, 2011 September 27, 2011 2

October 7, 2011 October 9, 2011 October 11, 2011 October 13, 2011 3 3 3