Archives for February 2009
Defining Planets (Part VIII)
Published on 24 Feb 2009 at 7:41 pm.
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All month long, I have been posting about the definition of the term planet, and I still have not come up with a definitive definition. That suggests that either I am really slow, or else I am trying to be thorough and that this is not an easy thing to define. I rather […]
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Defining Planets (Part VII)
Published on 23 Feb 2009 at 2:46 pm.
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In my previous installment of this series, I wrote about the role that structure may have in defining planet. It would seem that differentiated bodies would be different from non-differentiated bodies. However, differentiation is difficult to determine simply by looking at a potential planet. In fact, it has been proposed that even […]
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Defining Planets (Part VI)
Published on 19 Feb 2009 at 11:27 pm.
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The next installment of my series is to look at whether planets and non-planets can have a difference in structure that helps to distinguish them apart. So, that means that we need to know the structure of a planet. That is not as easy as it sounds.
It took a long time before geologists […]
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Defining Planets (Part V)
Published on 14 Feb 2009 at 4:43 pm.
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In my last posting, I talked about mass and size as possible discriminators for planets. The size issue was one of the first arguments put forth to remove the asteroids from the list of planets. But, as I point out, there are some problems with simply using mass and size. So, perhaps […]
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Defining Planets (Part IV)
Published on 9 Feb 2009 at 10:29 pm.
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The very first definition for planet was simply to designate a celestial body that appeared to move in the sky as a planet. But, that was ultimately deemed insufficient once telescopes discovered more bodies. The first satellites discovered of Jupiter and Saturn were called planets. But, astronomers eventually decided to restrict the […]
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Defining Planets (Part III)
Published on 7 Feb 2009 at 2:19 pm.
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Pluto was an oddity among the planets for much of the Twentieth Century. As I said in my last post, it just didn’t seem to fit with the other eight planets. There was debate for decades on whether or not Pluto should really have been on the list. In the end, most […]
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Defining Planets (Part II)
Published on 4 Feb 2009 at 11:43 am.
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In my last post, I gave a sort of history of how we got to having 9 planets in the Solar System, according to science textbooks for most of the Twentieth Century. But, Pluto was a problem from the very beginning.
Already, by the beginning of the Twentieth Century, astronomers knew that there was a […]
