On October 16 through the years

About this tool

This page looks up the same calendar day in every year of the community archive: the daily mean Wolf number, the number of observations and observers, and the images published that day. Set side by side, the years tell the story of the solar cycle — roughly eleven years from one minimum to the next, with the number of spots rising, peaking and fading again.

Comparing the same date across years is a fair comparison: the Sun’s declination and the length of the day are nearly identical, so the observing conditions of the community are comparable and only the activity changes. A year without a line simply means nobody published an observation on that day.

Pick another day with the date field, or follow a rotation instead with the Carrington tool. The daily values are the same as in the activity heatmap and in the open data; each image and observation links to its detail page and its observer.