Presentation Information
[O12-P106]Estimation of Solar Differential Rotation via Digital Sunspot Position Determination Using Approximately One Month of Public Images
*Takahiro Yoshimoto1, *Koudai Yotsuya1, *Kento Adachi1 (1. Nagoya Senior High School)
Keywords:
Differential rotation,Latitude and longitude of sunspots,Digital Images
1. Introduction
The Nagoya Senior High School Earth Science Club studied sunspots using digital images (Nagoya Senior High School Earth Science Club and Nagoya Junior High School Natural Science Club,2026). We wanted to see how the sun’s rotation speed changes depending on the latitude (this is called "differential rotation"). It is important to have a good way to change sunspot positions on a digital image into latitude and longitude. This helps us understand solar movements better. In this study, we tested a new digital method using solar images from the National Astronomical Observatory of Japan (NAOJ).
2. How We Did It
The NAOJ solar images sometimes have a "10-degree grid" on them. This allows people to find the position of sunspots by hand (analog reading). To check if our new digital method was correct, we compared our results with data from Mr. Motohiko Okada. His data tracked sunspots for about one month.
We followed these rules to keep our data accurate:
Only track the biggest sunspot in a group.
If sunspots join together or split apart, use the data from before that happened.
Do not use sunspots that are blurry or hard to see.
We calculated the rotation period like this:
Preparation: We used an iPad to rotate the images so that the Sun’s North Pole was at the top.
Step 1: Using Windows "Paint," we found the coordinates (pixel values) of three points on the edge of the Sun.
Step 2: From those three points, we found the center and the radius of the Sun.
Step 3: We marked the center of a sunspot and found its pixel coordinates.
Step 4: We changed these pixel coordinates into latitude and longitude.
Step 5: We did the same thing for the same sunspot on a different day and checked how much time had passed.
Step 6: We calculated the rotation angle and the speed of the sunspot.
Step 7: Finally, we made a graph showing the relationship between latitude and the rotation period.
(We used Excel for the calculations.)
We used images from July and August 2023 from the NAOJ website.
3. Results
See plate. Both the digital method and the analog (hand-read) method showed similar curves on the graph. The longitude values were very close (the difference was usually less than 3 degrees). However, the latitude values had an average difference of about 4.3 degrees. Also, the rotation period had a difference of about 0.4 days.
4. Discussion
The difference in latitude might be because of the way we calculated the coordinates. Our definition of the "center of a sunspot" might not have worked perfectly with the way the image was stretched. For the 0.4-day difference in the rotation period, we think this might be an error from the analog reading side.
5. Conclusion
We successfully used digital images to find sunspot positions and calculate the rotation period. However, we still have some problems with the angle of the images and how we calculate latitude. We need to improve our calculation program.
6. Future Plans
We want to fix the errors in our calculation method. We also want to study more sunspots over a longer time to get better data.
Literature
Nagoya Senior High School Earth Science Club and Nagoya Junior High School Natural Science Club (2026). Investigation of Solar Differential Rotation. Proceedings of the 28th Junior Session, Astronomical Society of Japan.
The Nagoya Senior High School Earth Science Club studied sunspots using digital images (Nagoya Senior High School Earth Science Club and Nagoya Junior High School Natural Science Club,2026). We wanted to see how the sun’s rotation speed changes depending on the latitude (this is called "differential rotation"). It is important to have a good way to change sunspot positions on a digital image into latitude and longitude. This helps us understand solar movements better. In this study, we tested a new digital method using solar images from the National Astronomical Observatory of Japan (NAOJ).
2. How We Did It
The NAOJ solar images sometimes have a "10-degree grid" on them. This allows people to find the position of sunspots by hand (analog reading). To check if our new digital method was correct, we compared our results with data from Mr. Motohiko Okada. His data tracked sunspots for about one month.
We followed these rules to keep our data accurate:
Only track the biggest sunspot in a group.
If sunspots join together or split apart, use the data from before that happened.
Do not use sunspots that are blurry or hard to see.
We calculated the rotation period like this:
Preparation: We used an iPad to rotate the images so that the Sun’s North Pole was at the top.
Step 1: Using Windows "Paint," we found the coordinates (pixel values) of three points on the edge of the Sun.
Step 2: From those three points, we found the center and the radius of the Sun.
Step 3: We marked the center of a sunspot and found its pixel coordinates.
Step 4: We changed these pixel coordinates into latitude and longitude.
Step 5: We did the same thing for the same sunspot on a different day and checked how much time had passed.
Step 6: We calculated the rotation angle and the speed of the sunspot.
Step 7: Finally, we made a graph showing the relationship between latitude and the rotation period.
(We used Excel for the calculations.)
We used images from July and August 2023 from the NAOJ website.
3. Results
See plate. Both the digital method and the analog (hand-read) method showed similar curves on the graph. The longitude values were very close (the difference was usually less than 3 degrees). However, the latitude values had an average difference of about 4.3 degrees. Also, the rotation period had a difference of about 0.4 days.
4. Discussion
The difference in latitude might be because of the way we calculated the coordinates. Our definition of the "center of a sunspot" might not have worked perfectly with the way the image was stretched. For the 0.4-day difference in the rotation period, we think this might be an error from the analog reading side.
5. Conclusion
We successfully used digital images to find sunspot positions and calculate the rotation period. However, we still have some problems with the angle of the images and how we calculate latitude. We need to improve our calculation program.
6. Future Plans
We want to fix the errors in our calculation method. We also want to study more sunspots over a longer time to get better data.
Literature
Nagoya Senior High School Earth Science Club and Nagoya Junior High School Natural Science Club (2026). Investigation of Solar Differential Rotation. Proceedings of the 28th Junior Session, Astronomical Society of Japan.