juliensimon/silso-sunspot-number

---
license: cc-by-4.0
pretty_name: "SILSO Daily Sunspot Number"
language:
- en
description: "Daily total sunspot numbers from SILSO, the World Data Center for the Sunspot Index at the Royal Observatory of Belgium. The longest continuous scientific observation in history, since 1818."
task_categories:
- tabular-regression
- time-series-forecasting
tags:
- space
- sun
- sunspot
- solar-cycle
- space-weather
- silso
- open-data
size_categories:
- 100K<n<1M
---

# SILSO Daily Sunspot Number


Daily total sunspot numbers from the World Data Center SILSO at the Royal Observatory of Belgium.
This is **the longest continuous scientific observation in history**, with systematic daily records
since 1818 and international coordination since 1981. Currently **76,030** daily records.

## Dataset description

The International Sunspot Number is the primary index of solar activity, tracking the number of
sunspots visible on the solar disk each day. Sunspots are temporary phenomena on the Sun's
photosphere caused by magnetic flux concentrations. Their number follows an approximately 11-year
cycle (the Schwabe cycle) that profoundly affects space weather, satellite operations, radio
communications, and Earth's upper atmosphere.

SILSO (Sunspot Index and Long-term Solar Observations) at the Royal Observatory of Belgium
serves as the World Data Center for sunspot number computation, collecting observations from
a worldwide network of stations.

## Schema

| Column | Type | Description |
|--------|------|-------------|
| `date` | date | Observation date |
| `decimal_date` | float64 | Fractional year (e.g. 2024.5) |
| `sunspot_number` | Int64 | Daily total sunspot number (null if missing) |
| `std_dev` | float64 | Standard deviation from multiple stations |
| `n_observations` | Int64 | Number of observing stations |
| `is_provisional` | bool | True if value is provisional (not yet definitive) |

## Quick stats

- **76,030** daily records (1818-01-01 to 2026-02-28)
- All-time maximum: **528** on 1870-08-26
- **75,879** provisional values
- Solar Cycle 25 (current): peak so far **290**, mean **86.6**

## Usage

```python
from datasets import load_dataset

ds = load_dataset("juliensimon/silso-sunspot-number", split="train")
df = ds.to_pandas()

# Plot solar cycles
import matplotlib.pyplot as plt
df["date"] = pd.to_datetime(df["date"])
monthly = df.set_index("date").resample("MS")["sunspot_number"].mean()
monthly.plot(figsize=(14, 4), title="Solar Cycles - Monthly Mean Sunspot Number")
plt.ylabel("Sunspot Number")
plt.show()

# Current solar cycle 25
sc25 = df[df["date"] >= "2019-12-01"]
print(f"Cycle 25 max so far: {sc25['sunspot_number'].max()}")

# Compare cycle amplitudes
df["year"] = pd.to_datetime(df["date"]).dt.year
yearly = df.groupby("year")["sunspot_number"].mean()
```

## Data source

[SILSO, World Data Center for the Sunspot Index](https://www.sidc.be/SILSO/),
Royal Observatory of Belgium, Brussels.

## Update schedule

Monthly (1st at 09:00 UTC) via [GitHub Actions](https://github.com/juliensimon/space-datasets).

## Related datasets

- [solar-flare-index](https://huggingface.co/datasets/juliensimon/solar-flare-index) -- Solar flare observations
- [kp-index](https://huggingface.co/datasets/juliensimon/kp-index) -- Geomagnetic Kp index
- [dst-index](https://huggingface.co/datasets/juliensimon/dst-index) -- Geomagnetic Dst index

## Pipeline

Source code: [juliensimon/space-datasets](https://github.com/juliensimon/space-datasets)

## Citation

```bibtex
@dataset{silso_sunspot_number,
author = {Simon, Julien},
title = {SILSO Daily Sunspot Number},
year = {2026},
publisher = {Hugging Face},
url = {https://huggingface.co/datasets/juliensimon/silso-sunspot-number},
note = {Based on SILSO data, World Data Center for the Sunspot Index, Royal Observatory of Belgium}
}
```

## License

[CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/)