The Celestial Swarm

The Celestial Swarm – March 2016

Hello everyone, I’m Darrell Heath with the UALR College of Arts, Letters, and Sciences;
welcome to The Night Sky.
Stars are usually born in groups inside dense, vast, and cold clouds of molecular
hydrogen and dust. After they become full­fledged stars they will disperse from their
parent clouds over a period of several million years.
Looking up at a star­filled sky you can see groups of stars in various stages of this
dispersal process. At around 9PM during the month of March face towards the southwest
and locate the constellation of Orion the Hunter. Then locate the three bright stars that
form his belt and the fainter group of stars that hang off the side towards the east. These
fainter stars form the Hunter’s sword. Here you can see with your unaided eye a misty-
looking star. Take a good look at it with binoculars or a telescope and you are personally
witnessing one of nature’s Holy of Holies: stars in the process of creation, for this is the
Orion Nebula, one of the finest of our deep sky objects. Inside the nebula are hundreds
of stars in the process of being born; with a pair of binoculars you can see two of them
emerging from out of the gas and dust, with a telescope you can make out four of these
infant stars forming a grouping known as the “Trapezium”.
The process of star birth is happening right this moment within the Orion Nebula but
shifting our gaze immediately west of Orion we find the constellation of Taurus the Bull
and within it are two star clusters of different ages and different stages of dispersal.
The Pleiades star cluster (also known as Messier 45) is an open star cluster that, at first
glance, seems to be made up of about six or seven faint stars. But binoculars reveal
many more and we know that there are actually as many as 400 stars all loosely bound to
one another by gravity. Over the next few million years the speed of any given star within
this cluster is sufficient enough to allow the star to escape the combined gravity of its
siblings and will eventually strike out on its own across the universe as a fully adult star.
Looking at the face of Taurus the Bull we see a V­shaped pattern made up of about 20 or
so faint stars, this is the Hyades cluster. And, just as with the Pleiades, there are actually
several hundred stars forming the cluster. While the Pleiades is estimated to be a
youthful 100 million years old, the Hyades cluster is thought to be close to 700 million
years old. That’s certainly old by human standards but just stop to think that our own Sun
is a middle­-aged star at about 4.5 billion years of age.
One of the first things you’ll notice about the Hyades is how much further along the cluster
is in regards to their dispersal compared to the younger Pleiades. While the Hyades and
Pleiades share a close proximity together upon the sky they are not related to each other
but some astronomers believe that the Hyades do share a physical relationship with
another beautiful open star cluster, which is prominent in our late winter and spring skies.
To find it we must locate the constellation of Cancer, the Crab. Being one of the zodiacal
constellations you might think that Cancer is going to be a very bright and conspicuous
star pattern, it isn’t. However, with the aid of a few other bright stars you should be able
to locate it fairly easily. My suggestion is to use a star chart or a stargazing app and step
outside at around 9 PM on a moonless night, in an area with only minimal light pollution,
and face the east. Look for the backward question mark pattern of stars forming the
mane of Leo the Lion. The bottom of the question mark is the Heart of the Lion, the bright
star Regulus. Throughout March you can use the planet Jupiter as a bright and handy
signpost to direct you towards Regulus. Now, using your star map or stargazing app
locate the nearby twin stars Pollux and Castor in the constellation of Gemini the twins. If
you draw an imaginary line from Regulus towards these twin stars, then about half way in
between them you should be in the Heart of the Crab and it is here that you will find the
wonderful star cluster known as The Beehive, or Messier 44.
The Beehive is one of those deep sky objects that’s best appreciated with binoculars
rather than a telescope. Why? Well, because it occupies an area upon the sky some one
and a half degrees across, or, roughly, the width of the three full moons placed side by
side. Viewing through binoculars will provide you with a much wider field of view with
which to encompass this impressive star cluster. A telescope will only provide you with a
very small field of view and you will miss out on all of M44’s grandeur.
But don’t think that the Beehive is bright and showy, it isn’t and you’ll need a moderately
dark sky in order to see it naked eye. With the binoculars though you will be able to see a
swarm of about 30 bright and glittery stars but bear in mind that the cluster has over a
thousand all told.
Because the Beehive is about the same age as the Hyades (say, some 500 to 700 million
years) and because the stars in each cluster are chemically very similar, it is thought that
the two share a common origin but broke off into separate groups millions of years ago.
Another line of evidence that supports this theory is that the stars from both clusters all
appear to be traveling in the same general direction.
Aside being known as the Beehive or Messier 44 this cluster has had a variety of
interesting names across time and different cultures. To the ancient Greeks it was often
referred to simply as “the small cloud”. While to others it was known by the Latin name of
“Praesepe”, the manger. The story goes that the manger housed the two donkeys
belonging to the gods Dionysus and Silenus. In fact, the names of the two stars found on
either side of Praesepe are: Assellus Borealis (the Northern Donkey) and Assellus
Australis (the southern donkey). To the ancient Chinese the cluster was known by the
rather gruesome name of “Exhalation of Piled­up Corpses.”
But I will leave you with one other little tidbit about this cluster that has come down to us
from history. According to Pliny, the Greek naturalist and philosopher: “If Praesaepe is
not visible in a clear sky it is a presage of a violent storm.” There may in fact be
something to this bit of ancient weather lore. While a sky may look clear to our eyes
there can sometimes be high, thin cirrus clouds containing lots of ice crystals in our
atmosphere. These may be invisible to you and me but there are just enough of them to
make a normally dim patch of stars disappear from view in an otherwise clear sky. We
know today that the presence of such clouds are a good indicator that unsettled weather
is indeed close at hand.
Be sure to visit our web site for news and announcements as well as a list of various
astronomy resources available to you.
Until next time, I encourage you to get outside and look up in both awe and wonder.

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