Comet West and Comet d'Arrest

Comet West and Comet d’Arrest

For those unfortunates – and they must be few in number – who missed comet West in March and April 1976, the close passage by comet d’Arrest of Earth in August 1976 will provide another chance at comet observation. The comet will be making its most favorable appearance in our skies since its 1851 discovery.

This does not mean, however, that comet d’Arrest will put on anywhere near as spectacular a show as West provided; at best, d’Arrest will be about sixth magnitude, visible in richest field telescopes, small telescopes, or (if you’re lucky) binoculars. Its nearest approach to Earth will take it to within about 14 million miles (about half the closest Earth-Venus distance). The comet will reach perihelion on August 12, 1976.

Comet West. These photos of comet West, taken one day apart, demonstrate the changes in the comet’s position and in tail structure that took place in a short space of time. At left, one bright streamer extends back from the nucleus in a photo taken on March 27, 1976. The next day (night), the streamer has shifted slightly toward the right as the comet itself has moved against the background of stars. In both pictures, the comet is located in the constellation Delphinus. A home built six inch reflector at f/6 was used for each of these 20 minute exposures on GAF 200 film. Photographs by Brad Wallis.

Comet d’Arrest is a periodic comet: its orbit has been accurately calculated and it returns to the vicinity of the sun on a regular schedule – every 6.2 years. Watch for it as it moves southeast through the constellations Delphinus, Aquarius and Sculptor. By early September, it will be fading and close to the horizon for United States observers. The comet’s predicted positions are given in the accompanying table.

Predicted Positions for Comet D’Arrest. Predicted magnitudes are approximate (table from Astronomy magazine, August, 1976).

Table, Comet D'Arrest, predicted positions