WHERE: AT EXPLORIT at Mace Ranch, 3141 5th Street, Davis. (530) 756-0191

Hosts: Vinita & Calvin Domier
(530) 756-7443 vcdomier@yahoo.com

Pluto Demoted!

Join us Saturday, Oct. 7 th , at 7:30 p.m., when we will discuss the very recent reclassification of Pluto from the ninth planet to the second largest (so far) dwarf planet of our Solar System (SS). We will also look at the planets, stars, and deep sky objects in the night sky, weather permitting.

Pluto, named for the god of the underworld, was discovered in 1930 by Clyde Tom-baugh. Its discovery expanded the family of planets in our Solar System to 9 . The other 8 planets ( Mercury , Venus , Earth , Mars , Jupiter , Saturn , Uranus and Neptune ) were all discovered before the 20 th century.

Pluto is very different from the other planets. It is very small in size, even smaller than our Moon . Its orbit is highly inclined (17°) above the plane of the ecliptic , the narrow band in the sky where all the other planets are found. Its orbit is also highly elliptical (non-circular), resulting in Pluto's orbit crossing Neptune's orbit. So, for part of its long journey around the Sun, Pluto is closer to the Sun than Neptune. Also, Pluto is a rocky and icy body, unlike its gas giant neighbors. To verify Pluto's composition (estimated at 2:1 rock to ice), NASA launched its first spacecraft to Pluto, New Horizons on 1/19/06 . It is scheduled to flyby Pluto and its moon, Charon , in July 2015 .

The spacecraft will then continue on to the Kuiper Belt (KB) , a disk-shaped region in space extending beyond Neptune's orbit, containing thousands of icy planetoids. The Scattered Disk (SD), a region thinly populated by icy planetoids, surrounds the KB. The Oort Cloud , a vast spherical outermost region of the SS containing thousands of primordial icy bodies known as comets, envelops the SD. Celestial bodies in these 3 regions are collectively known as Trans-Neptunian objects ( TNOs ). 2003UB 313 , discovered in 2003 by Mike Brown, is the largest TNO known so far.

2003UB 313 's discovery rekindled the debate about Pluto's designation as a planet , as it is 25% bigger in size than Pluto . If Pluto is a planet, then it too should be considered a planet along with Ceres (an asteroid) and another TNO, as they are comparable in size to Pluto. This would expand the number of SS planets to 12 now and to 50+ in the near future with the discoveries of more Pluto-size TNOs. If Pluto is not a planet, then there will only be 8 SS planets forever.

The International Astronomical Union ( IAU ) finally resolved the Pluto debate at its 26 th General Assembly of professional astronomers in Aug. 2006 . The IAU "serves as the internationally recognized authority for assigning designations to celestial bodies and any surface features on them."

On 8/24/06 , IAU decided that all bodies in the Solar System, except satellites, be defined into 3 distinct categories. They defined a planet as a non-moon "celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit." A dwarf planet is defined as satisfying (a) and (b), but not (c) condition of IAU's new planet definition. All other non-moon SS objects are defined as small Solar-System bodies .

As Pluto crosses Neptune's orbit without assimilating it, it does not satisfy the new planet definition. The IAU now classifies Pluto , Ceres, 2003UB 313 , and other nearly round TNOs as dwarf planets . Pluto is also recognized as an important prototype of a new Pluto-size class of TNOs .

On 9/13/06, the IAU also formally named 2003UB 313 Eris , and its moon Dysnomia .

Sky Info for October 2006

Planets : Jupiter (mag. -1.6 in Libra ) is a very bright planet low in the southwestern evening sky, setting ~ 9pm. Saturn (mag. +0.5 in Leo ) is a bright planet in the eastern sky before sunrise, rising ~ 3am. Venus and Mars are not visible in the night sky in Oct.

Moon phases : First Qrt.: 9/30 & 10/29, Full : 10/6, Last Qrt. : 10/13, and New : 10/21.

Autumnal Equinox was on Sept. 22 , 2006 .

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The Astronomy Club is for everyone - adults, children, knowledgeable or ignorant. Come to listen, look and learn, or to share your expertise or experience.