For a few hours before the first quarter, the crater's rim contributes to the "Lunar X" visual phenomenon, in which an 'X' shape briefly appears on the Moon's terminator as sunlight glances on the tops of shadowed hills.

[1] Like many of the craters on the Moon's near side, it was named (in the Latin form, 'Purbachius') by Giovanni Riccioli, whose 1651 nomenclature system has become standardized.

[2] Earlier lunar cartographers had given the feature different names: Michael van Langren's 1645 map calls it "Christierni IV Reg.

Daniae", after King Christian IV of Denmark,[3] and Johannes Hevelius grouped it with Walther and Regiomontanus under the name "Mons Libanus", after Mount Lebanon.

[4] By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Purbach.