A Dark Star Revealed

Abstract

In early 1843 a spectacular comet appeared in the sky. It grazed the surface of the sun on the last day of February, and in early March, as it raced back towards the outer regions of the solar system, it put on a brilliant display. For those in the northern hemisphere who witnessed the comet, it presented a glorious tail that stretched in an arc of 20 to 45 degrees across the southwestern sky after sunset. By all reports it was one of the brightest comets of the 19th century, clearly visible near the sun during daytime. It came to be known as the “Great March Comet” and was seen by large numbers of the public in North America where it provoked much comment and discussion. One tangible result of the Great March Comet was that some of the more prosperous citizens of Boston, Massachusetts were moved to contribute, by way of public subscription, the considerable sum of $25,000, towards the construction of a large refracting telescope, equal to any in Europe. The most critical component of the telescope was the 15-inch diameter objective lens contracted from the German firm of Merz & Mahler in Munich at a price of $12,000: there being no source of a lens of such size and quality in the United States of that day. The lens was the twin of one produced earlier for Friedrich Wilhelm Struve at the Pulkovo Observatory in Russia. The new observatory was completed in 1847 and located on Observatory Hill on the Harvard College campus. The director of the new observatory was William Cranch Bond (1789–1859), a Boston clock maker, who had been appointed in 1839, at no salary, by the Harvard Corporation as “Astronomical Observer to the University”.