24 August 2006

Observing Location	PSC
Observational Period	1200-1215 EDT
Atmospheric Conditions	Hot and humid with a moderate breeze; haze and fast moving cirrus. Transparency Fair Seeing Good It is not looking good for sighting the first crescent Moon tonight. CSC graphic NOAA graphic
Instruments	Canon 15x50 IS binocular w/Baader AstroSolar filter film - Charlie
Observing Party	Charlie Ridgway

Target Sunspots Constellation Leo Category Solar Time 20060824.1200 EDT Comments 905 The p-spot appears to be two spots in a common penumbra. The f-spot does not appear to have a penumbra. Both spots appear stretched parallel to the equator, but the appearance is more striking in the f-spot, which is also not as dark.   Groups Spots R North 0 0 0 South 1 3 13 Total 1 3 13 R = (Groups * 10) + Spots)

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I have seen news articles today that indicate that Pluto may still be a planet and others that say that it defiantly is not. None of the articles are citing an official IAU press release or any other source for that matter so I don't know who to believe.

It sounds like the scientists voting in Prague were given a choice of proposals to choose from. One of them appears to be the original IAU proposal without the top level categorization, Planet, and adding in that there can't be any other stuff in the planet's orbit.

I am still taking the position that nothing has been decided until there has been an official IAU press release (the IAU web site appears to be getting hammered with requests and I can'’t get in). In the immortal words of the San Antonio sportscaster Dan Cook:

The opera ain't over until the fat lady sings.

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Well, here is the skinny, direct from the IAU conference mirror Web site.

All of the resolutions the executive committee put forth were passed including the four listed below concerning the definition of the word “planet” and its implications for out solar system. The other resolutions concerned

• Resolution 1 for GA-XXVI : "Precession Theory and Definition of the Ecliptic"
• Resolution 2 for GA-XXVI: "Supplement to the IAU 2000 Resolutions on reference systems"
• Resolution 3 for GA-XXVI: "Re-definition of Barycentric Dynamical Time, TDB"
• Resolution 4 for GA-XXVI: "Endorsement of the Washington Charter for Communicating Astronomy with the Public"

I would like to read resolution 1 but haven't found a link to it.

The IAU members gathered at the 2006 General Assembly agreed that a "planet" is defined as 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.

This means that the Solar System consists of eight "planets" Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A new distinct class of objects called "dwarf planets" was also decided. It was agreed that "planets" and "dwarf planets" are two distinct classes of objects. The first members of the "dwarf planet" category are Ceres, Pluto and 2003 UB313 (temporary name). More "dwarf planets" are expected to be announced by the IAU in the coming months and years. Currently a dozen candidate "dwarf planets" are listed on IAU's "dwarf planet" watchlist, which keeps changing as new objects are found and the physics of the existing candidates becomes better known.

The "dwarf planet" Pluto is recognised as an important proto-type of a new class of trans-Neptunian objects. The IAU will set up a process to name these objects.

RESOLUTIONS
Resolution 5A is the principal definition for the IAU usage of "planet" and related terms. Resolution 5B adds the word "classical" to the collective name of the eight planets Mercury through Neptune.

Resolution 6A creates for IAU usage a new class of objects, for which Pluto is the prototype. Resolution 6B introduces the name "plutonian objects" for this class. The Merriam-Webster dictionary defines "plutonian" as:
Main Entry: plu to ni an
Pronunciation: plu-'tO-nE-an
Function: adjective Usage: often capitalized
: of, relating to, or characteristic of Pluto or the lower world

After having received inputs from many sides -- especially the geological community -- the term "Pluton" is no longer being considered.

IAU Resolution: Definition of a Planet in the Solar System
Contemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation 'planets'. The word 'planet' originally described 'wanderers' that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.

RESOLUTION 5A
The IAU therefore resolves that planets and other bodies in our Solar System be defined into three distinct categories in the following way:

(1) A planet¹ 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.

(2) A dwarf planet 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) shape², (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects³ orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

¹The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
²An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
³These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

RESOLUTION 5B
Insert the word "classical" before the word "planet" in Resolution 5A, Section (1), and footnote 1. Thus reading:

(1) A classical planet¹ is a celestial body . . .

and

¹The eight classical planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

IAU Resolution: Pluto

RESOLUTION 6A
The IAU further resolves:

Pluto is a dwarf planet by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.

RESOLUTION 6B
The following sentence is added to Resolution 6A:

This category is to be called "plutonian objects."

Condensing the four resolutions into one statement I come up with the following:
Planets and other bodies in our Solar System be defined into three distinct categories in the following way:

(1) A classical planet¹ 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.

(2) A dwarf planet 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) shape², (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects³ orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

Pluto is a dwarf planet by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects. This category is to be called "plutonian objects."

¹The eight classical planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
²An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
³These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

So here is how it all shakes out:

Classical Planet	Dwarf Planet		Small Solar System Body
		Plutonian Objects
Mercury
Venus
Earth
Mars
	(1) Ceres
Jupiter
Saturn
Uranus
Neptune
		Pluto
		2003 UB313 (Xena)
			everything else comets asteroids Trans-Neutonian Objects (NTOs) other small bodies

The history of Pluto from National Public Radio

The NPR article points out that Pluto can't be a planet because it's orbit overlaps that of Neptune so it hasn't cleared its orbit of all other objects. But can't we look at this from the other side as well? Neptune's orbit overlaps that of Pluto so it hasn't cleared its orbit of all other objects so it can't be a planet. Saturn has rings that are not part of the planet. Jupiter has what, 63 moons that are in its orbit. And what about that rocky body orbiting the Earth? Isn't it in Earth's orbit? So is the Earth a planet or is it just another dwarf planet? Mercury and Venus, being the only planets without other known objects sharing their orbit are the only two classical planets by the IAU definition. Earth through 2004 UB313 are dwarf planets.

And if a dwarf planet is not a planet why does it have the word planet it its name. That either defines it as a planet or creates a linguistic ambiguity for both classical planets and dwarf planets.