hip-31978

Variable star

Its story

Also catalogued as S Monocerotis, 15 Monocerotis is the brightest star of the Christmas Tree Cluster —NGC 2264—, the cluster of young suns that traces the triangular outline of the famous asterism. Since 1943 it has served as the MK spectral standard for type O7 against which other massive stars are calibrated. It is also a binary with an orbital period near 112 years, and its blue light has crossed roughly seven centuries to reach us.

Constellation: Monoceros
Apparent magnitude: 4.66
Distance: 918.9 light years
Coordinates (J2000): RA 100.244° · Dec 9.896°
Catalogue: HIP 31978 · HD 47839

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Symbolic commemorative gift — no ownership, no IAU recognition.