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I. Constellation
A constellation is a recognizable pattern of stars that has
official borders and an officidesignation.
There are 88 officially recognized constellations.
listed by the International Astronomical Union(IAU). No one has
named or postulated a new constellation in centuries.
Astronomers simply add a newly discovered star to the
constellation that it isclosest to.
Dont forget that we often recognize star patterns but these are
asterisms and not
constellations.
To be a constellation it has to have official borders and an
official designation!
A. First Constellations
Ptolemy was an ancient astronomer. In his early work, the
Almagest, he listed 48 known constellations.
Almagest - a mathematical and astronomical treatise proposing
the complex motions of thestars and planetary paths.
The book itself was brilliant, covering the problems of daily
motion of celestial objecttime spans of daylight, determination of
latitude, the points at which the Sun is verticathe shadows of the
sundials gnomon at the equinoxes and solstices, and othobservations
that change with the spectators position.
The view of the night sky represented was quite a bit limited,
but many of those sameconstellations are still accepted and retain
their original names.
However, there was only one small problem with the Almagest and
its constellationThe charts that Ptolemy used came from Hipparchus
time and only included the starthat he could see from his
position.
It wasnt long until it was improved greatly by the Islamic
culture, whose astronomerdescribed observations of the stars, their
positions, magnitudes, brightness and color even adding drawings
for each constellation.
Consequently, even today some of our brightest cataloged stars
are still referred to btheir Arabic names!
Centaurus is the closest to Earth.
The closest star within that constellation is Proxima Centauri
at 4.2 light years. That is a
mere 39,735,067,984,839.36 kilometers away.
B. The Modern Constellations
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Formed in 1919, the International Astronomical Union (IAU) is a
collection of professionastronomers whose job it to act as the
internationally recognized authority for assignindesignations. In
1930 the IAU decided to choose the work of Belgian astronomer,
EugenJoseph Delporte for a worldwide standard. At this point, he
fixed the modern boundariebetween all of the constellations in the
sky, along lines of right ascension and declination fothe epoch
B1875.0 and the 88 officially recognized constellations went into
effect. Becaus
Delport chose such an early epoch for the work of Benjamin
Gould, these 80 year old work
are no longer perfectly vertical or horizontal thanks to the
precession of the equinox, and wone day have to be re-worked.
However, a standard was set and constellation names, patternand
borders finally recognized.
II. Galaxies
Our galaxy, the Milky Way, is typical:
It has hundreds of billions of stars, enough gas and dust to
make billions morstars, and at least ten times as much dark matter
as all the stars and gas pu
together. And its all held together by gravity.
Like more than two-thirds of the known galaxies, the Milky Way
has a spiral shape.
At the center of the spiral, a lot of energy and, occasionally,
vivid flares. are beingenerated.
Based on the immense gravity that would be required explain the
movement of starand the energy expelled, the astronomers conclude
that the center of the Milky Wais a supermassive black hole.
Other galaxies have elliptical shapes, and a few have unusual
shapes like toothpicks or ring
The Hubble Ultra Deep Field (HUDF) shows this diversity. Hubble
observed a tiny patch of sk(one-tenth the diameter of the moon) for
one million seconds (11.6 days) and founapproximately 10,000
galaxies, of all sizes, shapes, and colors. From the ground, we see
velittle in this spot, which is in the constellation Fornax.
Formation
After the Big Bang, the Universe was composed of radiation and
subatomic particles. Whahappened next is up for debate - did small
particles slowly team up and gradually form starsstar clusters, and
eventually galaxies? Or did the Universe first organize as immense
clumps matter that later subdivided into galaxies?
Collisions
The shapes of galaxies are influenced by their neighbors, and,
often, galaxies collide. ThMilky Way is itself on a collision
course with our nearest neighbor, the Andromeda galaxy. Eve
http://www.spitzer.caltech.edu/images/1925-ssc2008-10b-A-Roadmap-to-the-Milky-Way-Annotated-http://www.nasa.gov/centers/goddard/news/topstory/2008/blackhole_slumber.htmlhttp://www.nasa.gov/centers/goddard/news/topstory/2008/blackhole_slumber.htmlhttp://www.spitzer.caltech.edu/images/1925-ssc2008-10b-A-Roadmap-to-the-Milky-Way-Annotated-
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though it is the same age as the Milky Way, Hubble observations
reveal that the stars i
Andromeda's halo are much younger than those in the Milky Way.
From this and otheevidence, astronomers infer that Andromeda has
already smashed into at least one and maybseveral other
galaxies.
