21088 Chelyabinsk, provisional designation 1992 BL2, is a stony asteroid, classified as near-Earth object of the Amor group, approximately 4.2 kilometers in diameter. It was discovered on 30 January 1992, by Belgian astronomer Eric Elst at ESO's La Silla Observatory in northern Chile. Two rotational light-curves for this asteroid were obtained by Czech astronomer Petr Pravec at Ondřejov Observatory in December 2002 and September 2004, respectively. They gave a rotation period of 22.490 and 22.426 hours, each with a brightness variation of 0.13 magnitude (U=n.a./3-).