Solar Tracking

A Python tool for tracking sunspots in solar images and analyzing the Sun's differential rotation. Developed as part of a Bachelor's thesis.

Overview

This project processes HMI (Helioseismic and Magnetic Imager) continuum images from the Solar Dynamics Observatory (SDO) to:

• Detect sunspots using adaptive thresholding and connected component analysis
• Track sunspot motion across image sequences using OpenCV's MIL tracker
• Convert coordinates from pixel space to heliographic coordinates (latitude/longitude)
• Calculate differential rotation rates and fit to the standard solar rotation model
• Visualize results with interactive displays and PDF output

Demo

Interactive sunspot tracking with real-time bounding box overlay

Scientific Background

The Sun does not rotate as a rigid body. Instead, it exhibits differential rotation - the equator rotates faster (~25 days) than the poles (~35 days). This rotation profile follows the empirical law:

$$\Omega(B) = A + B \cdot \sin^2(B)$$

where $\Omega$ is the angular velocity and $B$ is the heliographic latitude.

This tool measures differential rotation by tracking sunspot positions over time and fitting the observed velocities to this model.

Installation

Prerequisites

• Python 3.8 or higher
• OpenCV with GUI support

Install from source

git clone https://github.com/quooky/solar_tracking.git
cd solar_tracking
pip install -e .

Or install dependencies directly:

pip install -r requirements.txt

Usage

Command Line Interface

The package provides a solar-tracking CLI with three main commands:

1. Download Solar Data

solar-tracking downloader --start "2023-11-23 00:00:00" --end "2023-11-25 00:00:00" --sample 1

Options:

• --start: Start time (YYYY-MM-DD HH:MM:SS)
• --end: End time (YYYY-MM-DD HH:MM:SS)
• --instrument: Instrument name (default: hmi)
• --sample: Sampling interval in hours (default: 1)

2. Run Sunspot Tracking

solar-tracking run_tracking --trace 1

Options:

• --trace: Trace series number (corresponds to data/TR_0X folder)
• --no-interactive: Run without user interaction

Interactive Controls:

• Space: Pause/resume tracking
• S: Skip current spot
• Q: Save results and quit
• N: Next spot

3. View FITS Files

solar-tracking view_fits path/to/file.fits

Python API

from solar_tracking.downloader import download_fits
from solar_tracking.tracking import run_tracking
from solar_tracking.sunspot_detection import find_spots_and_bounding_boxes
from solar_tracking.fitting import perform_fitting

# Download data
files = download_fits("2023-11-23 00:00:00", "2023-11-25 00:00:00")

# Run tracking
run_tracking(trace=1, interactive=True)

# Or use individual components
spots, boxes = find_spots_and_bounding_boxes(image, sun_center, sun_radius)

Project Structure

solar_tracking/
├── solar_tracking/          # Main package
│   ├── cli.py              # Command line interface
│   ├── downloader.py       # FITS file downloading via SunPy
│   ├── tracking.py         # Main tracking algorithm
│   ├── sunspot_detection.py # Spot detection with OpenCV
│   ├── image_processing.py # FITS preprocessing
│   ├── rotation_analysis.py # Coordinate transformation
│   ├── fitting.py          # Differential rotation fitting
│   └── plotting.py         # Result visualization
├── tests/                  # Test suite
├── data/                   # Solar observation data (not in repo)
├── docs/                   # Documentation and thesis
└── setup.py

Data

The tracking requires HMI continuum intensity images (hmi_ic_45s). Data is automatically downloaded from the Virtual Solar Observatory using SunPy.

Sample data structure:

data/
├── TR_01/
│   ├── *.fits          # HMI FITS files
│   ├── names.txt       # File listing
│   └── data_points.csv # Tracking results

Results

The tool outputs:

• CSV files with tracked positions (pixel and heliographic coordinates)
• PDF plots showing the differential rotation curve with fitted parameters

See example rotation plots (PDF) for sample output.

Dependencies

• SunPy - Solar data analysis
• OpenCV - Computer vision and tracking
• Astropy - FITS handling and coordinates
• NumPy - Numerical computing
• Matplotlib - Visualization
• SciPy - Curve fitting

Testing

pytest tests/

Thesis

This project was developed as part of a Bachelor's thesis on solar differential rotation analysis.

📄 Read the full thesis (PDF)

License

This project is licensed under the MIT License - see the LICENSE file for details.

Author

Dominic Foerster

Acknowledgments

• Solar Dynamics Observatory (SDO) for providing HMI data
• SunPy community for the excellent solar physics library