August 2

Pluto Is Out — A Homeschool Science Lesson in Astronomy


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Pluto is out, and Zena and Ceres are in. Well, almost. Now all three are out.

Recently, Michael Brown, an astronomer from Caltech, discovered what he thought was a new planet, which he called Zena. He presented his findings and submitted his studies to the 26th General Assembly of the International Astronomical Union (IAU) who met last week, 20 – 26 August 2006 in Prague, Czechoslovakia to discuss this new discovery and to review the selection criteria for naming planets. Of the 2,700 delegates who attended the meeting only 720 were still in attendance at the end of the week. Only about 400 delegates were on hand the final day but only a handful of members were eligible to vote on a revised description of what constitutes a planet and Brown's studies were accepted. They added Zena to the roster of the Sun's planets (also knows as UB313, Zena is larger than Pluto). They also accepted a second nomination, Ceres.

Then suddenly, in a direct reversal of their previous decisions the IAU decided that the long-standing member planet, Pluto, no longer met the criteria to be a planet. Pluto was demoted to space dust. The two other small solar system bodies nominated, Zena and Ceres, were then summarily rejected.

The IAU also redefined the three criteria necessary to qualify an object as a planet.

1. A planet must be round in shape. What this means is that is planet must be large enough to have had its mass pulled into a round shape as the result of its own gravitational forces. It was also suggested, but not made part of the definition, that a planet must be at least 1000 kilometers in diameter.

2. Planets must have a defined, regular orbit around the Sun, and not be either stars themselves or satellites of other planets.

3. To be a planet a space object must dominate its own orbit and clear its own area of other smaller space objects.

A “dwarf planet” was defined as a celestial body that is in an orbit around the Sun, has sufficient mass for its own gravitational forces to assume a hydrostatic equilibrium or “nearly round” shape, has not cleared its orbital neighborhood of other space objects, and it is not a satellite.

The IAU also resolved that all other space objects, except satellites orbiting the Sun, shall be referred to collectively as “Small Solar-System Bodies”

The old mnemonic “My very energetic mother just served us nine pizzas”, by which millions of people learned to recite the planets, no longer applies. However, We do have a new one to help you remember the planets in the new line up.

“My very Energetic Mother Just Served Us Noodles.”

Here are some other, more original suggestions:

“My very exhausted mother just sent us nachos”

“Make Very Extraordinary Meals of Jell-O, Strawberries, and Unsalted Nuts.”

Just in case you may have forgotten, the names of the planets they are, listed in order of their distance from the Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and the newly demoted “dwarf planet”, Pluto.

Try making up your own mnemonic and get the kids involved, too. This could very easily be made a part of one of your science lessons. But don't use Pluto, Zena, or Ceres in your new mnemonic. At least not for now, the IAU may change their minds at their next meeting in 2009.

Homeschool Science: Pluto, Zena, Ceres- Astronomy

Jack Finnigan is a part-time writer-publisher and Webmaster at providing important homeschooling advice, tips and focused information for homeschool resources that can really help parents improve their homeschoolers.


homeschool science, planets, science

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    1. Becky, one of the wonderful things about homeschooling is that you learn along with your children. Don’t fear!! It is a wonderful journey!

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