Vainu Bappu Memorial Lecture: What is a sunspot?

TL;DR

Sunspots are dark, magnetically concentrated regions on the Sun's surface with an approximately 11-year cycle, affecting space operations and climate, but their formation and decay mechanisms remain not fully understood.

Contribution

The paper reviews current understanding of sunspots, highlighting unresolved questions about their origin, structure, and lifecycle, and discusses ongoing efforts to deepen scientific knowledge.

Findings

Sunspots follow an approximately 11-year cycle.

Magnetic concentrations cause heat flow disruption.

Associated phenomena influence space weather and climate.

Abstract

Sunspots have been known in the West since Galileo Galilei and Thomas Harriot first used telescopes to observe the Sun nearly four centuries ago; they have been known to the Chinese for more than two thousand years. They appear as relatively dark patches on the surface of the Sun, and are caused by concentrations of magnetism which impede the flow of heat from deep inside the Sun up to its othewise brilliant surface. The spots are not permanent: the total number of spots on the Sun varies cyclically in time, with a period of about eleven years, associated with which there appear to be variations in our climate. When there are many spots, it is more dangerous for spacecraft to operate. The cause of the spots is not well understood; nor is it known for sure how they die. Their structure beneath the surface of the Sun is in some dispute, although much is known about their properties at the surface, including an outward material flow which was discovered by John Evershed observing the Sun from Kodaikanal a hundred years ago. I shall give you a glimpse of how we are striving to deepen our understanding of these fascinating features, and of some of the phenomena that appear to be associated with them.