Geological Chronicle
Located near the Moon's eastern limb along the southern edge of Mare Marginis, Neper spans 144.32 kilometers in diameter. Due to this position near the limb, the crater appears heavily foreshortened from Earth and requires a favorable libration to observe clearly. On the lunar geologic timescale, Neper ranks among the largest craters formed during the Nectarian age.
The crater's inner walls show worn terraces, bounded by lower rim sections at the northern and southern extremes. Its dark, flat floor contains several small impact scars along the western margin, with the most notable situated near the north-northwestern edge. At the center rises a peak where infrared observations have detected pure crystalline plagioclase.
Neper lies directly east of the crater Jansky and southeast of Goddard across Mare Marginis. The formation is named for John Napier, the Scottish mathematician and astronomer. Two former satellite craters, Neper G and Neper K, were subsequently renamed Virchow and Tacchini by the International Astronomical Union.