Solar Observations

Summary Questions


Clearly show ALL work.


Gathering Data:

1.  Go to and click on “Lastest Images” (the link is located on the left hand side under “Data”).

2.  In the center column, under “Images By Date” and “SOHO summary data”, click on “Earlier dates”.

3.  From this page, you can find images of the Sun on any date (we will focus on dates during the latter half of October, 2003).  Type in the date Oct. 18, 2003 using the format shown (YYMMDD, or in our case, 031018).

4.  You will find a list of various images of the Sun.  You want to click on one of the “Intensitygram, full disk” links.  (Hint:  It would be best if you consistently choose close to the same time of day for each image.  Not all dates have a variety of times).

5.  Notice the positions of various sunspots.  Save the image to a file (to be printed out later).

6.  Go back to the list of images for a given day.  From here, you can forward to the next day by simply clicking on the “next day” link at the top of the page.

7.  Continue viewing sunspots on the Sun until the end of the month (Oct. 31, 2003).


Analyzing Data:

1.  Once you have viewed the sunspot pattern over the two week period, locate two specific sunspots which you can clearly track across the surface of the Sun over time (Hint:  Due to the rotation of the Sun, sunspots appear to move from left to right).

2.  In the center of each image is a square.  Determine the date and time at which each of your two sunspots first appear on the left edge of the square, and the amount of time it takes for them to reach the opposite edge.  This is the amount of time it takes the sunspot to travel roughly 10% of the way around the Sun.  Based on this, what is the rotation period of each sunspot?  (Note, unless your images were taken at EXACTLY the same time, you need to take into account the fraction of a day between observations as well.)

3.  Based on the motion of the sunspots across the surface of the Sun, determine the location of the Sun’s equator.  The Sun’s equator has a rotation period of 26 days.  This should be different from the number you calculated above.  Give at least two reasons why your answer might be different.

4.  Pick any one sunspot (preferably a large one) and determine its size.  To do this, you need to know that the diameter of the Sun is 1.39 x 106 km.  (Hint:  Think of the image as a scale model of the actual Sun).  Compare this to the size of the Earth (which has a diameter of 1.28 x 104 km).  Clearly show all work.


Submission for Grade:

1.  A print-out of four images of the Sun over the two week period.  These should consist of the images during which each of your sunspots first crosses the left edge of the square and the day it crosses the right edge.  Clearly label on each image each sunspot (number them 1 & 2).

2.  On each of these images, clearly draw a line indicating the equator of the Sun.

3.  On a separate piece of paper, submit calculations showing the size of the sunspot and its comparative size to Earth.

4.  On a separate piece of paper, submit calculations showing the rate of rotation of both sunspots.

5.  In one paragraph, describe (IN YOUR OWN WORDS) what SOHO is, and what its mission is.