On August 24, 2006, professional astronomers gathered for the meeting of the
International Astronomy Union (IAU) decided to make a formal declaration concerning
the Solar System. At the meeting it was agreed that 8 objects that orbit the
Sun would receive the designation of "planet" and Pluto
would be demoted to a new and lower status of "dwarf planet."
While the general public is disappointed in this demotion, the decision is final
and thus the textbooks and this course are undergoing revisions to reflect this.
At present (September, 20014) there are 5 objects defined as "dwarf planets:"
Ceres, which is within the main Asteroid Belt, Pluto and Charon, which are just
beyond the orbit of Neptune, and Eris, which is farther out yet, Makemake and Haumea. A dwarf planet,
according to the rules of the IAU must be:
1) round ... meaning that sufficient mass exists within the object for gravity
to collapse the entire object toward the center, creating a spherical object
2) independently orbiting the Sun, without the major influence of other objects
3) able to clear its orbital path of significant debris.
There is a good deal of contention regarding the demotion of Pluto, and as
of September, 2006 ... there is an effort underway to restore Pluto to its former
position. To seemore of this debate, click on Dwarf
Planet debate. While the debate, and perhaps even potential "boycotts"
of various professional and amateur astronomers may be underway even as I write,
this course will assume that Pluto is now in a new class of Solar System objects
and we will proceed that way until further developments force a change.
With this brief introduction, this section of the Planet unit is devoted to
a study of the Solar System objects now defined as dwarf planets. You are asked
to move through the pages of this section, beginning with the object closest
to the Sun and moving progressively outward.
News about new objects being discovered the outermost parts of the Solar System
This unit will feature four sections to work through, beginning in the innermost
parts of the Solar System to the outermost reaches. It will be the unit of this
course that experiences the most frequent changes as new objects are discovered
farther and farther out. I hope that you will enjoy a study of the least known
and perhaps mpst mysterious bodies orbiting the Sun.
Direct links outside of my course to Haumea and Makemake
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