Messier 6 — Open Cluster in Scorpius

M6, the Butterfly Cluster, is a bright open cluster in the constellation Scorpius, located about 1,600 light-years from Earth. It contains roughly 80 stars spread across about 12 light-years of space. The cluster's brightest stars form a pattern resembling a butterfly with open wings when viewed through binoculars or a small telescope. The brightest member is BM Scorpii, an orange giant variable star of spectral type K that contrasts beautifully with the blue-white colors of the other hot, young cluster stars. The cluster is estimated to be about 100 million years old.

Located about 5 degrees north of the Scorpion's stinger, near M7. At magnitude 4.2, it is easily visible to the naked eye as a hazy patch. Binoculars reveal the butterfly shape with about 20 stars resolved. A small telescope at 50-75x gives the best view, showing the full cluster with beautiful color contrasts — look for the orange star BM Scorpii among the blue-white members. Too much magnification makes the butterfly pattern harder to see. Best observed from June through August, but from northern latitudes it stays low.

Possibly known to Ptolemy around 130 AD, who recorded a nebulous object near the Scorpion's stinger — though this may refer to M7 instead. Giovanni Batista Hodierna observed it before 1654. Charles Messier cataloged it in 1764. The common name 'Butterfly Cluster' was popularized in the 20th century due to the arrangement of its stars.