C/1956 F1 (Wirtanen)

Lore & Background

C/1956 F1 (Wirtanen) was observed from 1956 to 1960. In 1963, Elizabeth Roemer wrote that the comet's nucleus fragmented into two distinct components around 1 January 1957, about five months before van Biesbroeck first noticed the split nucleus, with the components moving apart at 1.5 m/sec. Zdenek Sekanina calculated that the original nucleus had an effective radius of about 14.0 km (8.7 mi) based on Roemer's findings. The split nucleus was used in formulating a new calculation for determining the relative motion of split comets in 1977.

In 2023, upon revisiting the studies, Sekanina remarked that Roemer's original astrometric data remained unpublished and the timing of the split may have been miscalculated. He later concluded that the nucleus may have split around September 1954, moving apart at 0.26 m/sec. This indicated that Wirtanen may have likely discovered the larger fragment rather than its original nucleus, with the smaller one not being observed until it was spotted by van Biesbroeck over a year later.

Reader's Guide

The significance of C/1956 F1 (Wirtanen) lies in its split nucleus, which provided data for a 1977 calculation method for determining the relative motion of split comets. The comet's fragmentation was initially described by Elizabeth Roemer in 1963, who placed the split around 1 January 1957, with van Biesbroeck noticing it about five months later. Zdenek Sekanina used Roemer's findings to estimate the original nucleus radius at 14.0 km. However, in 2023, Sekanina revisited the studies and noted that Roemer's original astrometric data remained unpublished, leading to a possible miscalculation of the split timing. He revised the split to around September 1954, with a slower separation rate of 0.26 m/sec. This revision suggested that Wirtanen may have discovered the larger fragment, not the original nucleus, and the smaller fragment went unobserved until van Biesbroeck spotted it over a year later. The legacy of this comet is thus marked by uncertainty and the importance of unpublished data in cometary science.

Did You Know?

• C/1956 F1 is the last of five comets discovered by American astronomer Carl A. Wirtanen.
• Elizabeth Roemer wrote in 1963 that the nucleus split around 1 January 1957, but the split was first noticed by van Biesbroeck about five months later.
• In 2023, Zdenek Sekanina revised the split timing to around September 1954, with a separation rate of 0.26 m/sec.
• The split nucleus was used in 1977 to formulate a new calculation for determining the relative motion of split comets.