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Posted to the UseNet Newsgroup "alt.astronomy" We've already talked about size... and we've seen that the planet Selene's size relative to the Earth as compared with the satellites of our Solar System relative to their planets is very large. This 4th reason also concerns Selene's size, and this time, relative to all the "rocky" planets and Pluto. So here's a table (remember, when we refer to "Selene", we're talking about Earth's "sister planet", the Moon)... Planet Diam (miles) Diam (Earth=1) -------- ----------- -------------- Earth 7913 1.00 Venus 7520 0.95 Mars 4223 0.53 Mercury 3029 0.38 Selene 2160 0.27 Pluto 1423 0.18 (I included Pluto to show that, while it is quite a bit smaller than Selene, Pluto was still classified as a major planet in its own right since a time that was long before it was discovered in 1930! And astronomers knew Pluto was smaller than the Moon for a good, long time before Pluto was finally reclassified as a minor, or "dwarf", planet in 2006!) So we see that, even though the smaller Pluto is more of an icy body and possibly a potential short-term comet, and even though Pluto has been reclassified as a dwarf planet, which actually makes Selene, the Moon, the smallest major planet in the Solar System, Selene still appears to fit in fairly well with the rock planets. The Moon is nearly 3/4 the size of planet Mercury, and has a diameter that is 1.5 times that of Pluto! This reason doesn't stand alone, of course. It cannot be used by itself as the lone reason to see our Moon as a full-fledged major planet. This can be seen more clearly when you look at the next table... Body Diam (miles) Diam (Moon=1) -------- ----------- -------------- Ganymede 3240 1.50 Titan 3200 1.48 Callisto 3040 1.41 Io 2261 1.05 Selene 2160 1.00 Planet Saturn's big moon, Titan, and three Galilean moons of Jupiter--Ganymede, Callisto and Io--are all larger than our Moon. And we might also remember that Ganymede, Titan and Callisto are even larger than planet Mercury! (Again, Mercury's diameter is 3029 miles.) So even though this reason, Selene's size compared with other solid planets, will not stand alone to get acceptance that our Moon is a major planet, both Isaac Asimov and i believe that it still stands up well in backup support of the other reasons listed and described in this series. The next reason, the 5th, stands alone much better. And when it is put together with the other reasons, it really strengthens the whole idea that Selene, the Moon, is a full-fledged major planet in its own right. You'll remember that the flat plane made by Earth's orbit around the Sun has a name. It's called the "ecliptic". And all of the other planets in our Solar System also go around the Sun on this ecliptic plane (or very near it). If our Solar System were a whole lot smaller, it would be flat enough to fit inside a pizza box! Another distinction between a planet and a satellite would have to include the plane of the orbit. Does the object go around the equator of the planet? Or does the object go around on or near the ecliptic plane? The plane in which our beautiful and awesome sister planet, Selene, orbits around (uhm, well, almost around) the Earth, and for that matter around the Sun as well, will be the subject of my next article. happy days and... starry starry nights! -- Indelibly yours, Paine P.S. Thank YOU for reading! P.P.S. Some secret sites (shh)... http://painellsworth.net http://savethechildren.org http://eBook-eDen.secretsgolden.com |