(Wikipedia)
The first astronomer to record the Butterfly Cluster's existence was
Giovanni Battista Hodierna in 1654. However,
Robert Burnham Jr. has proposed that the 2nd century astronomer
Ptolemy may have seen it with the naked eye while observing its neighbor the
Ptolemy Cluster (M7).
[7] 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.
[5]Estimates of the Butterfly Cluster's distance have varied over the years.
[8] Wu et al. (2009) found a distance estimate of 1,590
light-years,
[1] giving it a spatial dimension of some 12 light years.
[3] Modern measurements show its total visual brightness to be magnitude 4.2. The cluster is estimated to be 94.2
[1] million years old. Cluster members show a slightly higher abundance of elements heavier than helium compared to the Sun;
[9] what astronomers refer to as the
metallicity.
Comments