The Sun: A Garden-Variety Star (Astronomy)

Recall cards on the Sun, the ordinary star at the center of our solar system, and the activity that plays across its surface. Its structure and composition: a ball of mostly hydrogen and helium a million kilometers wide, from the 15-million-degree core out through the convective zone to the visible photosphere, the thin chromosphere, and the tenuous but million-degree corona that launches the solar wind. The solar cycle: sunspots and their umbra and penumbra, the roughly 11-year rhythm of sunspot maxima, differential rotation, the Zeeman effect that maps magnetic fields, and the 22-year magnetic cycle driven by the solar dynamo. Solar activity above the photosphere: plages, prominences, flares, coronal mass ejections, and the active regions where strong magnetic fields tie them together. And space weather, the way particles and radiation from the Sun disturb Earth's magnetosphere, from the Carrington Event of 1859 and the 1989 Quebec blackout to the Maunder Minimum.