# The Solar Benchmark: Rotational Modulation of the Sun Reconstructed from Archival Sunspot Records

## TL;DR

This study reconstructs the Sun's rotational modulation from archival sunspot data, estimating its rotation and activity cycle periods, and investigates differential rotation with results consistent with previous null findings.

## Contribution

It demonstrates a method to analyze solar rotation using archival sunspot records and assesses differential rotation signals over the activity cycle.

## Key findings

- Solar rotation period estimated at 26.3 days
- Activity cycle period estimated at 10.7 years
- No clear evidence of differential rotation detected

## Abstract

We use archival daily spot coverage measurements from Howard et al. (1984) to study the rotational modulation of the Sun as though it were a distant star. A quasi-periodic Gaussian process measures the solar rotation period $P_\mathrm{rot} = 26.3 \pm 0.1$ days, and activity cycle period $P_\mathrm{cyc} = 10.7 \pm 0.3$ years. We attempt to search for evidence of differential rotation in variations of the apparent rotation period throughout the activity cycle and do not detect a clear signal of differential rotation, consistent with the null results of the hare-and-hounds exercise of Aigrain et al. (2015). The full reconstructed solar light curve is available online.