The Source of Solar Energy, ca. 1840-1910: From Meteoric Hypothesis to Radioactive Speculations

TL;DR

This paper reviews historical theories of solar energy from 1840 to 1910, highlighting the evolution from meteoric and gravitational hypotheses to radioactive speculations before nuclear models emerged.

Contribution

It provides a comprehensive analysis of pre-nuclear ideas about solar energy, emphasizing the scientific context and shifts in understanding during the Victorian era.

Findings

Helmholtz-Thomson contraction theory was dominant for over 40 years.

Early theories included meteoric impacts and radioactive decay as potential energy sources.

The paper contextualizes the transition to nuclear-based explanations.

Abstract

Why does the Sun shine? Today we know the answer to the question and we also know that earlier answers were quite wrong. The problem of the source of solar energy became an important part of physics and astronomy only with the emergence of the law of energy conservation in the 1840s. The first theory of solar heat based on the new law, due to J. R. Mayer, assumed the heat to be the result of meteors or asteroids falling into the Sun. A different and more successful version of gravitation-to-heat energy conversion was proposed by H. Helmholtz in 1854 and further developed by W. Thomson. For more than forty years the once so celebrated Helmholtz-Thomson contraction theory was accepted as the standard theory of solar heat despite its prediction of an age of the Sun of only 20 million years. In between the gradual demise of this theory and the radically different one based on nuclear processes there was a period in which radioactivity was considered a possible alternative to gravitational contraction. The essay discusses various pre-nuclear ideas of solar energy production, including the broader relevance of the question as it was conceived in the Victorian era.