NGC 2129

Lore & Background

NGC 2129 was discovered by William Herschel on November 16, 1784. The cluster is dominated by two close B-type stars, HD 250289 (B2III) and HD 250290 (B3I). These two stars share the same proper motion and radial velocity, making it likely that they constitute a binary system. On 21 December 2010, the cluster was occulted by the Moon during a total lunar eclipse over Japan, the North Pacific and North America. Similar occultations are predicted to occur during the December 2029 lunar eclipse over South America, the Atlantic Ocean and Africa, and again on 21 December 2094 over New Guinea, Northern Australia and the Pacific Ocean.

Reader's Guide

NGC 2129 is notable as a very young open cluster, with an age of only 10 million years, providing insight into early stellar evolution. Its location inside the Local spiral arm at a distance of about 7,200 light years places it within a region of active star formation. The likely binary system of two B-type stars at its core offers a rare opportunity to study massive star interactions in a young cluster. The cluster's angular diameter of 2.5 arcminutes corresponds to a physical diameter of about 10.4 light years, typical for a compact open cluster. Its discovery by William Herschel in 1784 adds historical significance. The rare lunar occultations during total lunar eclipses—observed in 2010 and predicted for 2029 and 2094—make NGC 2129 an object of interest for both professional and amateur astronomers, as such events allow precise positional measurements and studies of the cluster's structure.

Did You Know?

• NGC 2129 is approximately 7,200 light years from Earth.
• The cluster is dominated by two B-type stars that likely form a binary system.
• NGC 2129 was occulted by the Moon during the December 2010 total lunar eclipse.