This review of Messier 6, the Butterfly Cluster is to provide details about the observational history, details about how to find it in the sky, what the object could look like in your scope, and potential astrophotography options if available.

	Description
Visible From Pacific Northwest	Late April (early AM hours, like 3AM) to August (early evening)
Best Time To Observe	June and July
Minimum Size Of Viewing Device	7×50 or 10×50 Binoculars
Object Type	Open Cluster
Designations	Butterfly Cluster, Messier 6, M6, NGC 6405, Collinder 341, Lund 769, Melotte 178, OCL 1030, ESO 455-SC030, Lac. III.12
Right Ascension	17h 40.1m
Declination	-32°13′
Constellation	Scorpius
Absolute magnitude	13.4
Apparent magnitude	4.2
Apparent dimensions	25′
Object Radius	6 light years
Distance From Earth	1,600 light years

History

The first astronomer to record the Butterfly Cluster’s existence was Giovanni Battista Hodierna in 1654. However, Robert Burnham, Jr. has proposed that the 1st century astronomer Ptolemy may have seen it with the naked eye while observing its neighbor the Ptolemy Cluster (M7). Credit for the discovery is usually given to Jean-Philippe Loys de Chéseaux in 1746. Charles Messier observed the cluster on May 23, 1764 and added it to his Messier Catalog.

When recording this into his catalogue, Messier stated, ““A cluster of small stars between the bow of Sagittarius & the tail of Scorpius. To the naked eye, this cluster seems to form a nebula without stars; but even with the smallest instrument one employs for investigating one sees a cluster of small [faint] stars.”

Locating M6 In The Sky

Finding M6 can be a bit tough for some as there are no brilliant stars to help observers find the object. However, the M6 cluster lies in eastern Scorpius. constellation, and can be found 5 degrees north and 1.5 degrees east of the multiple star Shaula, or Lambda Scorpii. Finding Shaula might be a bit easier as it is the second brightest star in Scorpius, with a visual magnitude of 1.62, and it marks the scorpion’s tail. Shaula can be located by following the line of stars that curve from Antares in a southerly direction. Messier 6, Messier 7 and Shaula form a triangle that can be seen without binoculars to the right of the Teapot asterism in Sagittarius.

Viewing M6

Messier 6 is best seen in binoculars. Its apparent size is roughly the same as that of the full Moon. The cluster contains more than 300 stars. Binoculars reveal only a few dozen and a small telescope will show about 80 stars brighter than 11th magnitude.

Messier 6 is easy to see without binoculars under good viewing conditions. The butterfly shape appears in 7×50 or 10×50 binoculars, and more stars appear in small telescopes. When viewing with a telescope, it is recommended to observe using minimum magnification because this is a large open star cluster.

Photographing M6

It is possible to photography M6 with both 50mm normal and 300mm telephoto lenses two weeks, using a DSLR with an appropriate filter, as shown by this amazing photo. Because it will appear low in the Southern Sky, there might need to be several nights of capturing data to obtain the results one looks for.

Sources And Further Reading

Our reviews of Messier Objects can be found here for those looking for a full list.

Messier 6 – The Butterfly Cluster