THE SOUTHWORTH PLANETARIUM
207-780-4249       www.usm.maine.edu/planet
70 Falmouth Street  Portland, Maine 04103
43.6667° N                   70.2667° W
Founded January 1970
              "Keeping a watchful eye on a complex sky"



*THE DAILY ASTRONOMER*

*Thursday, July 21, 2016*
*Poor Pluto*


As the DA lapses into its annual dormancy throughout most of August, we
wanted to take this opportunity to commemorate a particular anniversary
that occurs next month.   In August 2016, we will be celebrating
(lamenting) the 10th anniversary of Pluto's demotion from the status of
planet to non-planet.   Although some skywatchers considered this status
down shift to be the debacle of the decade, others thought it long
overdue.   While we'll refrain from taking a position, apart from saying
that PLUTO IS A PLANET,  we'll discuss why Pluto lost its planet privileges
in the heartbreaking month of August 2006.

In 2006, the International Astronomical Union (IAU) convened it triennial
meeting in Prague, capital of the Czech Republic.   At the end of this
meeting, the remaining delegates -all 450 of them- voted to implement a new
"planet definition," that imposed three conditions on any body aspiring to
planethood.

These conditions were set forth by a 19 person committee the IAU formed in
2005 following Sedna's discovery.   After many revisions and internal
debates, the following resolution was introduced on August 24, 2006

*"The IAU...resolves that planets be defined into three distinct categories
in the following way: *

*(1) A planet [1] is a celestial body that (a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces
so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c)
has cleared the neighbourhood around its orbit.*

Pluto and thousands of other bodies including asteroids and comets, have
established  stable orbits around the Sun.   Also, Pluto is a spheroid.  It
is sufficiently big and massive enough to have developed a spherical
shape.   However, Pluto is close to the inner Kuiper Belt, a region of
short period cometary nuclei.  Therefore, Pluto has not cleared its
neighborhood of other bodies and fails to fulfill the third condition of
the new IAU definition.  Consequently, Pluto was relegated to the status of
'dwarf planet.'

This demotion attracted a great deal attention from the world's media
sources.  Generally, IAU gatherings don't garner a lot of press coverage.
Astronomers who attended the 2006 meeting, however,  found themselves
uncomfortably in the nucleus of a swirling media frenzy.    Protests were
staged around the world.   (Fortunately, none of them obstructed traffic in
the Old Port to the delight of 100,000 inert motorists.) Pluto admirers
launched a petition drive to reinstate the disgraced Pluto back its
previous position.   Though theirs were earnest efforts, they were to no
avail.   Ten years on, Pluto remains a dwarf planet.  Or, more accurately,
a "Plutoid," an icy body beyond Neptune's orbit.

Will Pluto ever be a planet again?
We can't say.
All we know is that the issue won't go away anytime soon.











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FROM THE CATACOMBS OF INFINITE KNOWLEDGE
Contrary to popular belief, Alpha Centauri, the closest star system to the
Sun,
is not only visible in the southern hemisphere.  Any observer south of
30 degrees North can observe Alpha Centauri.
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