SN 1999by was a peculiar Type Ia supernova event in the spiral galaxy NGC 2841, located in the northern constellation of Ursa Major.
[2] Located in the flocculent spiral galaxy NGC 2841, which had hosted three previous supernova events,[3] it was positioned 91″ North and 100″ West of the Galactic Center.
[5] SN 1999by was identified as a Type Ia supernova on May 2, but the peculiar spectrum suggested it was subluminous.
[6] It achieved maximum light on May 11, reaching an apparent visual magnitude of 13.10±0.05.
Geometrically, this indicated that the supernova had an axis of symmetry, which can be modeled by asphericity of about 20% seen along the equator.