Higher Luminaries.

The definition of a star is a burning ball of gas but that is incorrect
if the theory of Solar Luminescence is wrong. Incandescent perhaps.

So what is the definition of a planet?

Definition of Star from Dictionary.com:

1. A self-luminous celestial body consisting of a mass of gas held
together by its own gravity in which the energy generated by nuclear
reactions in the interior is balanced by the outflow of energy to the
surface, and the inward-directed gravitational forces are balanced by
the outward-directed gas and radiation pressures.

2. Any of the celestial bodies visible at night from Earth as
relatively stationary, usually twinkling points of light.

3. Something regarded as resembling such a celestial body.

Definition of Planet from Dictionary.com:

1. A nonluminous celestial body larger than an asteroid or comet,
illuminated by light from a star, such as the sun, around which it
revolves. In the solar system there are nine known planets: Mercury,
Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.

2. One of the seven celestial bodies, Mercury, Venus, the moon, the
sun, Mars, Jupiter, and Saturn, visible to the naked eye and thought by
ancient astronomers to revolve in the heavens about a fixed Earth and
among fixed stars.

Of course the definition of luminous might rule out Jupiter and maybe
several others from the list.

A sect has formed with the plan to disposses the solar system of a
planet. They insist that Pluto be demoted. (Something I personally
decided to do several years ago. Not that I am a member of the sect.)

There was a recent BBC Horizon programme about it. No draught on their
website yet but there is this:
http://news.bbc.co.uk/1/hi/sci/tech/5099292.stm

"Weatherlawyer" wrote in message
oups.com...

So what is the definition of a planet?
. . .
Definition of Planet from Dictionary.com:

1. A nonluminous celestial body larger than an asteroid or comet,
illuminated by light from a star, such as the sun, around . . .

2. One of the seven celestial bodies, Mercury, Venus, the moon, the
sun, Mars, Jupiter, and Saturn, visible to the naked eye and . . .

Of course the definition of luminous might rule out Jupiter and maybe
several others from the list.

You must read more carefully. You quote that planets are
nonluminous bodies i.e. give off only what light they reflect
from the sun.

--
Don Phillipson
Carlsbad Springs
(Ottawa, Canada)

Wasn't it Weatherlawyer who wrote:

So what is the definition of a planet?

At present there isn't any objective astronomical definition of a
planet, but the IAU have promised that they will produce one later this
year.

The problem is that there's a whole range of objects out there ranging
in size all the way from dust grains to 13 times the mass of Jupiter,
and ranging in composition between rock, ice and gas. We choose to stick
the labels like "dust grain", "meteoroid", "asteroid", "comet", "minor
planet", "moon" or "planet" on different objects. In many cases it's
clear which label to apply, but at the moment there are fuzzy boundaries
between all the labels.

There's a clear change of properties between "star", "brown dwarf" and
"planet", so the same problem doesn't really occur there. There's
hydrogen fusion in stars, deuterium fusion in brown dwarfs and no fusion
in planets.

Whatever the outcome of the IAU deliberations, there's bound to be a lot
of people who won't like the result. As shown in the Horizon program,
there's a lot of people who get quite emotional about any attempt to
exclude Pluto. I'd imagine that there'd be many people who wouldn't be
happy with a definition that added Sedna, Ceres, Pallas, Juno and Vesta
to the list of planets. Astronomers wouldn't be happy with a complex
definition that manages to wangle things so that the solar system ends
up with the nine planets we know and love, because that would be very
difficult to implement when we start to discover Pluto sized objects
orbiting other planets, which may well be possible in the next decade.

--
Mike Williams
Gentleman of Leisure

Mike Williams wrote in
news
Wasn't it Weatherlawyer who wrote:

So what is the definition of a planet?

At present there isn't any objective astronomical definition of a
planet, but the IAU have promised that they will produce one later
this year.

The problem is that there's a whole range of objects out there
ranging in size all the way from dust grains to 13 times the mass
of Jupiter, and ranging in composition between rock, ice and gas.
We choose to stick the labels like "dust grain", "meteoroid",
"asteroid", "comet", "minor planet", "moon" or "planet" on
different objects. In many cases it's clear which label to apply,
but at the moment there are fuzzy boundaries between all the
labels.

There's a clear change of properties between "star", "brown dwarf"
and "planet", so the same problem doesn't really occur there.
There's hydrogen fusion in stars, deuterium fusion in brown dwarfs
and no fusion in planets.

Whatever the outcome of the IAU deliberations, there's bound to be
a lot of people who won't like the result. As shown in the Horizon
program, there's a lot of people who get quite emotional about any
attempt to exclude Pluto. I'd imagine that there'd be many people
who wouldn't be happy with a definition that added Sedna, Ceres,
Pallas, Juno and Vesta to the list of planets. Astronomers
wouldn't be happy with a complex definition that manages to wangle
things so that the solar system ends up with the nine planets we
know and love, because that would be very difficult to implement
when we start to discover Pluto sized objects orbiting other
planets, which may well be possible in the next decade.


We have discovered new objects larger than Pluto circling our own
star. They are Kuyper Belt objects with orbits beyond that of Pluto,
and as I recall, there are already two of them known to be larger
than Pluto.

So far, I don't want to demote Pluto, and I don't want to accept the
new ones as planets.

Full disclosu I have absolutely no say in the matter :-)

--
Gene E. Bloch (Gino) ... letters617blochg3251
(replace the numbers by "at" and "dotcom")

"Don Phillipson" wrote in
:

"Weatherlawyer" wrote in message
oups.com...

So what is the definition of a planet?
. . .
Definition of Planet from Dictionary.com:

1. A nonluminous celestial body larger than an asteroid or comet,
illuminated by light from a star, such as the sun, around . . .

2. One of the seven celestial bodies, Mercury, Venus, the moon,
the sun, Mars, Jupiter, and Saturn, visible to the naked eye and
. . .

Of course the definition of luminous might rule out Jupiter and
maybe several others from the list.

You must read more carefully. You quote that planets are
nonluminous bodies i.e. give off only what light they reflect
from the sun.

Jupiter is known to radiate more light than it receives from the sun,
but it's mostly in the far infrared. It hasn't completely cooled down
from its birth pangs...

It's not considered a star, however.

--
Gene E. Bloch (Gino) ... letters617blochg3251
(replace the numbers by "at" and "dotcom")

Jupiter is known to radiate more light than it receives from the sun,
but it's mostly in the far infrared. It hasn't completely cooled down
from its birth pangs...

ANY planet that net radiates into its environment, thereby cooling
down, is "luminous". For example, Earth. It's just that the luminosity
may not be in the visible range of wavelengths.

"luminous" needs to be better defined.

I'm sure that every planet (and probably every moon) in out solar system
is "luminous" in that it radiates more mid-to-far IR than it receives,
and that it's still cooling down.


Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.livejournal.com/userinfo.bml?user=fleetie

Wasn't it Gene E. Bloch who wrote:

We have discovered new objects larger than Pluto circling our own
star. They are Kuyper Belt objects with orbits beyond that of Pluto,
and as I recall, there are already two of them known to be larger
than Pluto.

So far, I don't want to demote Pluto, and I don't want to accept the
new ones as planets.

I'd imagine most people would be happy with that if we could produce a
sensible objective definition of "planet" that gives that result and can
also be used when we start to observe Pluto sized objects in other solar
systems.

The problem is that any sensible criterion would be expected to either
include both Pluto and 2003-UB313 and some other large KBOs that are
only fractionally smaller, or exclude them all. The only thing that
Pluto has going for it, that 2003-UB313 doesn't, is history.

--
Mike Williams
Gentleman of Leisure

In message , Fleetie
writes
Jupiter is known to radiate more light than it receives from the sun,
but it's mostly in the far infrared. It hasn't completely cooled down
from its birth pangs...

ANY planet that net radiates into its environment, thereby cooling
down, is "luminous". For example, Earth. It's just that the luminosity
may not be in the visible range of wavelengths.

"luminous" needs to be better defined.

I'm sure that every planet (and probably every moon) in out solar system
is "luminous" in that it radiates more mid-to-far IR than it receives,
and that it's still cooling down.

Isn't the point that Jupiter (and Saturn, only more so) is radiating
more energy than it receives? They both have internal energy sources.
Uranus, OTOH, is not radiating an excess.
IIRC, the Earth is currently radiating slightly _less_ energy than it
receives.

"Weatherlawyer" wrote in message
oups.com...
The definition of a star is a burning ball of gas but that is incorrect
if the theory of Solar Luminescence is wrong. Incandescent perhaps.

I thought that a planet was anything that moved in the night sky. Planetes -
moving. Anything except stars, in fact.

"Weatherlawyer" wrote in
oups.com:

The definition of a star is a burning ball of gas but that is incorrect
if the theory of Solar Luminescence is wrong. Incandescent perhaps.


I would say that a better definition would be that a star is any body that
has at some stage during its' existence been able to initate the weak
nuclear reaction p + p = d + e+ + v. That rules out gas giants that could
only initiate deuterium burning.


So what is the definition of a planet?

How about whatever the IAU says it is? ;-).

Klazmon.


SNIP