The world’s astronomers, under the auspices of the International Astronomical Union (IAU), have concluded two years of work defining the lower end of the planet scale - what defines the difference between “planets” and “solar system bodies”. If the definition is approved by the astronomers gathered 14-25 August 2006 at the IAU General Assembly in Prague, our Solar System will consist of 12 planets: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon and 2003 UB313. The three new proposed planets are Ceres, Charon (Pluto’s companion) and 2003 UB313. There is no change in the planetary status of Pluto.
Read more: http://www.iau2006.org/mirror/www.iau.org/NEWS.55.0.html
In this artist’s impression the planets are drawn to scale, but without correct relative distances.
Credit: The International Astronomical Union/Martin Kornmesser
Evidence continues to mount that the next solar cycle (Solar Cycle 24) is beginning. For the second time in a month, a backward sunspot has appeared. The first backward spot, sighted on July 31st, was tiny and fleeting. The latest, however, is big and sturdy, bipolar sunspot 905:
“Backward” means magnetically backward. Compared to how sunspots have been during the past 11-year solar cycle, the north and south magnetic poles of sunspot 905 are reversed. This is what happens when one solar cycle gives way to another–sunspots reverse polarity.
The onset of Solar Cycle 24 is big news, because the cycle is expected to be intense, but don’t expect any big storms right away. Solar cycles take years to ramp up to full power. The next Solar Max is expected in 2010.
Courtesy Space Weather.com
The IAU (International Astronomical Union) members gathered at the 2006 General Assembly agreed that a “planet” is defined as a 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.
This means that the Solar System consists of eight “planets” Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A new distinct class of objects called “dwarf planets” was also decided. It was agreed that “planets” and “dwarf planets” are two distinct classes of objects. The first members of the “dwarf planet” category are Ceres, Pluto and 2003 UB313 (temporary name). More “dwarf planets” are expected to be announced by the IAU in the coming months and years. Currently a dozen candidate “dwarf planets” are listed on IAU’s “dwarf planet” watchlist, which keeps changing as new objects are found and the physics of the existing candidates becomes better known.
The “dwarf planet” Pluto is recognised as an important proto-type of a new class of trans-Neptunian objects. The IAU will set up a process to name these objects.
From IAU Press Release, 24 August, 2006
Learn more: http://news.bbc.co.uk/go/em/fr/-/2/hi/science/nature/5282440.stm
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