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Flanked by Orion and Canis Minor, with Gemini above and Canis Major below, the faint constellation Monoceros ("the Unicorn") is often overlooked.
The only Bayer star of interest is beta Monocerotis, which is a
splendid triple. See below for a detailed description of this system.
15 Monocerotis, also known as S Monocerotis, is another
multiple system consisting of six stars. However most of them are
very faint:
S Monocerotis is also irregular, the central star in NGC 2264.
This star is a bright 4.5 visual magnitude, dipping down at times to
about 5.0.
This nebula has been extensively studied, for it seems to be
extraordinarily massive (over 10,000 Suns). Dark matter is woven in and
out of the surrounding gases. It is surmised that eventually the gases
will coalesce, producing either a new star or perhaps even a whole new
system of sun and planets, similar to our own.
NGC 2264 is a large and bright cluster with associated nebula (The Cone Nebula, so called because of its shape). The brightest star here is the variable S Monocerotis, which is found near the top of the cluster.
To find M50 draw a line between Sirius and Procyon; you'll find the
cluster about a third of the way up from Sirius.
Another way to find M50 is to locate the roughly-shaped square formed by
alpha, delta, and beta Monocerotis, along with Sirius. Right in the
middle of that square lies M50.
This giant double star system is recognised as the most massive pair yet discovered.
In 1913 the federal government provided funding for the construction of a 183 cm (72 inch) reflecting telescope, to be built near Victoria, BC. The Dominion Astrophysical Observatory officially opened in 1918 and was, for a time, the largest telescope in the world. Plaskett served as DAO's first director from 1917 to 1935.
It was here that Plaskett set about studying binary stars and in 1922 this work resulted in his discovering the very massive binary star which now bears his name.
The system is comprised of two giant O-type stars, each of which orbits
a common centre of gravity every 14.4 days. While Plaskett arrived at a mass of 90 Suns for each star, it is now probable that the total mass of the two does not exceed 100 Suns. Even so, this pair still stands as the most massive double star sytem yet discovered.
Plaskett's Star is probably a member of the NGC 2244 cluster (see above).
This reflection nebula has a usual visual magnitude of about 10, but
this fluctuates sporadically. It was originally thought that as R
Monocerotis's visual magnitude changed, so did the visual magnitude of
the nebula. But this proved to be false; the nebula's variations do not
seem to be associated with the star's variablility.
However, Valerie Illingworth (Facts On File Dictionary of Astronomy)
states that the variability of the nebula comes from what is called a bipolar
flow of emissions originating from R Monocerotis. This ejection of gas in two
opposite directions is typical in very young stars.
Other observers question the existence of R Monocerotis, considering
the area nothing more than an extremely dense gaseous area. Tirion's
SkyAtlas 2000.0 doesn't show the star, and major star catalogues
don't list the star. Burnham calls it "a bright nebulous condensation
with perceptible apparent size."
Observations at Kitt Peak and Mauna Kea have concluded that R Monocerotis
is a protoplanetary system. That is, that planets may presently be forming
in a highly condensed region: another "solar system" being born.
While the nebula is easily seen in small scopes, it is a little tricky
to find. Burnham's Celestial Handbook has a finder's guide (p.
1201). Or you may try this: once you locate epsilon Monocerotis star-hop
up to 13 Monocerotis. Farther up, to the northeast, is S Monocerotis.
Between these two, just about half way, the great nebulosity surrounding
S Monocerotis begins. At the extreme southern edge of this nebulosity is
the distinguishing form of Hubble's Variable Nebula: the comet-like
shape is unmistakeable.
For a more detailed appreciation of Monoceros, visit the Binocular Section.
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© Richard Dibon-Smith.