THE SOUTHWORTH PLANETARIUM
207-780-4249       www.usm.maine.edu/planet
70 Falmouth Street  Portland, Mai \
 ne 04103
43.6667° N                   70.2667° W
Founded January 1970
             "Did you think we forgot?"


THE DAILY ASTRONOMER
Tuesday, July 26, 2016
Goodbye, Beehive


For now, that is.

Unless something catastrophic occurs, we don't actually offer a final
farewell to any celestial object.   Like actors, they merely exit stage
west for awhile before returning to the pre-dawn eastern sky.     The
Praesepe Star Cluster (a.k.a.  The Beehive) is already backstage, as it
appears too close to the Sun to be observed.
Praesepe is a galactic, or open, star cluster marking Cancer the Crab's
center.   Naked-eye observers see it as a nebulous oval, but without a
sharply defined circumference.   Its diffuse glow derives from its hundreds
of imbedded stars, most of which are only resolvable telescopically.   When
so viewed, Praesepe is revealed as a beautiful agglomeration of stars,
though not as tightly bound as the equally beguiling Pleiades Star
Cluster.*

Mythologically, Praesepe is literally inanimate: a manger off of which two
nearby donkeys (the star Asellus Borealis and Asellus Australis) are
feeding.  The actual name "Praesepe," means "manger," signifying its
practical,  if not glamorous, mythological role.    At a distance of
approximately 570 light years, Praesepe is one of the closest star clusters
and has lent itself to thorough examination.    Like many other such
clusters, Praesepe's structure is "segregated."  A process called
"dynamical mass segregration" has drawn the heaviest stars toward the core,
while the lighter stars have migrated toward the outer regions.      Since
the most massive stars in this clusters are also the most luminous,
Praseepe exhibits a bright interior enclosed in a comparatively dim shell.


*Beehive Star Cluster.    Image by Mike Sherrick*
​
Such segregation is not limited to clusters.  Any system containing objects
or material of various densities or masses will, in time, experience such
differentiation.   Our planet, for instance, consists of a heavy, metallic
core surrounding by "lighter" material.


Praesepe is also called the "February comfort cluster" as it almost
precisely marks the Sun's August 1st position.  (The Sun occupies the same
point in the sky as Praesepe on August 1st.)  So, in the deep winter night,
when one observes the Beehive, one can see the eventual location the Sun
will occupy during the year's warmest period.   Thus, one can watch
Praesepe drawing gradually closer to the western horizon throughout the
winter: evidence of summer's inevitable return.

Even though we can't see the Beehive presently, it will return to the
pre-dawn eastern sky by early autumn.  Or, at least, it has done so for
thousands of years and we're naively assuming it will again.