Demotion of Pluto as a planet

[franktaw at netscape.net]

Cino wrote:
 
>Take a look at encarta definition of planet. 
> 
>Planet, any major celestial body that orbits a star and does not emit 
visible light of its own but instead shines by reflected light. 
 
 From this definition, I would argue that there are only four planets in 
the solar system: Jupiter,
Saturn, Uranus, and Neptune.  "Major?  Those little balls of dirt?"

>What about volcanos, A-bombs, radiowaves, astroid impacts etc. Even if 
we can't see the light, 
>it is still emitted.

Well, if you interpret "visible light" to mean "light in the visible 
spectrum", this is correct.  On the
other hand, if you interpret it as "light you can see", you are 
contradicting yourself.

I think the intended interpretation is that the light from the body be 
predominately reflected.

>According to this, the earth is not a planet.
> 
>Planet, any major celestial body that orbits a star would have been 
sufficient. 

You need the second part of the definition, or something like it, to 
keep the smaller stars of
multiple star systems from being considered planets.
 
>Defining is a tough nut to crack. 
> 
>http://encarta.msn.com/encyclopedia_761577741/Planet.html 
> 
>I pose this incident because after all the good discussion and mention 
of specific sequences and 
>the opinions brought forth, I still do not know exactly what a "base" 
sequence is. 

Nobody else really does, either; that's the problem.

I think my proposed definition is fairly clear: sequences which at some 
point in the definition treat
numbers as numerals (strings).  But there is a problem if you interpret 
"definition" too narrowly.

Consider A006880: "Number of primes < 10^n".

As written, that would not be a base sequence.  But an alternative 
definition, in the comments,
"Number of primes with at most n digits", would make it a base 
sequence.  Yet these definitions
are strongly and obviously equivalent.

In this case, I am inclined to say that the number of primes with at 
most n digits is really the
underlying idea here.  If you doubt this, ask yourself why 10 was 
chosen instead of some other
number.

The case of A007053: "Number of primes <= 2^n" is less clear to me.

The bottom line is, there are always going to be ambiguous cases.  If 
we can find a definition
that covers 99% of the cases, the remainder doesn't matter that much.  
Currently, it's more
like 60%.
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