Geological Chronicle
Hirayama is a lunar impact crater measuring 145.21 kilometers in diameter on the far side of the Moon, just beyond the eastern limb. Favorable libration occasionally brings this region into view from Earth, though it is best viewed from orbit. The crater lies along the southeastern edge of Mare Smythii, northeast of Brunner and southwest of Wyld, with the small, bright-rayed crater Bandfield resting on its western rim.
Worn and eroded, the crater is marked by multiple impacts overlapping both its outer rim and interior floor. Hirayama K has broken across the southeastern rim, Hirayama C crosses the northeastern rim, and Hirayama Q lies along the southwestern outer edge. Inside, Hirayama Y covers a significant part of the northern interior floor adjacent to the northern inner wall. The small Hirayama T sits along the western inner wall with Hirayama S attached to its eastern edge, while Hirayama N marks the southern interior, leaving the rest of the floor relatively level.
Named in honor of Japanese astronomers Kiyotsugu Hirayama and Shin Hirayama, the feature is surrounded by satellite craters identified on lunar maps by letters placed beside the crater midpoint nearest Hirayama. Previously, the names Tolstoy, Montesquieu, Longfellow, and Balzac were proposed for satellite craters Y, S, Q, and K, but were not approved by the IAU. The names Tolstoj and Balzac were instead used for craters on Mercury.