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The past few years have been an exciting time for astronomy as improved telescopes, the use of computers to quickly compare parts of the sky at different times, and visits to various parts of the Solar System by robotic probes have all led to a mass of new discoveries. With what appears to have been an ever-increasing pace since the 1970's many new discoveries have been made, for instance:
On 24th August 2006 the International Astronomical Union (IAU) finally defined what a planet is (following much argument and debate).
The result of this has been that Pluto has been re-categorised, being moved from the
'planet' category to a new
category, 'dwarf planet', together with Ceres, the largest body in the Asteroid Belt
(which lies between the orbits of Mars and Jupiter), and a recently-discovered
(and very recently named) body, Eris (formerly called by its 'discovery' number 2003 UB313 or
sometimes referred to as 'Xena' - this last however was simply a temporary name that was used by its
discoverers Mike Brown, David Rabinowitz and Chad Trujillo).
Comment: Note that Pluto has not
been 'demoted', it's just had its category changed, the suggestion of 'demotion' is just media
hype. This is no different from when horticulturalists find new evidence and change the
categorisation of a plant species - which happens quite often. In this case the new evidence has
accumulated over the past several years that Pluto is one of many similar bodies, and also
that it is much smaller than originally thought.
Eris and Pluto are both also classified as Kuiper Belt Objects
(bodies that circle the Sun in and around a 'belt' beyond Neptune, roughly 40 to 50 times further
from the Sun than the Earth), along with thousands of other smaller objects - Pluto is a Plutino
(an object whose orbit is 'fixed' by the gravitational 'pull' of Neptune - Pluto orbits the Sun
twice for every three times Neptune orbits the Sun),
whilst Eris is part of the 'Scattered Disc'.
(Scattered Disc (or, Scattered Disk) Objects are objects beyond Neptune with
highly elliptical orbits
and/or orbits that are substantially inclined away from the plane in which the eight main planets
orbit the Sun - some astronomers believe they are in unusual orbits because they have been 'thrown'
there by Neptune's gravitational pull, and some astronomers also believe that Centaurs
- small bodies that orbit the Sun between Jupiter and Neptune - are also Scattered Disc Objects,
ones that have been 'thrown' inward rather than outward).
Other Kuiper Belt Objects are classified as 'Cubewanos' (Their orbits are not
highly inclined or highly elliptical, and not 'controlled' by Neptune).
A number of other bodies would appear to meet the definition of 'dwarf planet',
but information about them will be considered by the IAU before it confirms any
of them as 'dwarf planets'.
Likely candidate dwarf planets would be asteroid Vesta (and less likely, Hygeia and Pallas); Kuiper Belt Objects Ixion, Orcus,
Quaoar, Varuna, 2002 AW197, 2002 TC302, 2002 UX25, 2003 EL61 and 2005 FY9
(and less likely: 2002 MS4, 2002 TX300, 2003 AZ84, 2004 GV9 and 2005 RN43);
plus Sedna (and less likely, 2004 XR190) (which orbit the Sun wholly at a distance beyond the Kuiper Belt).
For the record , the EIGHT planets in the Solar System are:
(In order, nearest to the Sun first): Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
(In order, largest first): Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury
(In order, most massive first): Jupiter, Saturn, Neptune, Uranus, Earth, Venus, Mars, Mercury
I could go into detail about the planets and other objects in the Solar System
here on this site, but excellent resources for this already exist - the first six websites
listed in 'Links' below in particular - so I'll not try to 're-invent the wheel' here.
With such a large number of known moons in the Solar System (162 as at the end of 2006
just for the six planets with moons), it is possibly difficult to
know which ones to teach about. I'd suggest that teaching should concentrate on the 19
that are of planetary mass (Planemos) listed below, plus select some
others that are particularly interesting for various reasons -
the Trojan moons that accompany Saturn's moons Dione and Tethys,
and also Saturns moons Janus and Epimetheus, which are sometimes referred to as 'dancing moons'
because they occupy the same orbit and exchange places every four years.
Planemos (see definitions page) in the Solar System that are neither planets nor dwarf planets are the satellites of a number of the planets and currently confirmed dwarf planets, as follows:
Another nice site is 'Views of the Solar System'
Sol Station is an excellent site giving details of both Solar System objects and star systems within 100 light years of the Solar System (and they have a 3D 'near star' map).
Solar Space Station - great site about the Solar System by Chris Thomas
The Moons of the Solar System site. A great resource, with quite a lot of the moons and planets having links to rotating maps.
Astronomy Workshop - This site has great 'viewers' showing the movement of the planets round the sun and showing the movement of moons round the various planets.
Mike Brown, co-discoverer of Eris, explains the reason WHY a new definition of 'planet' was needed here
Comet and Kuiper Belt expert David Jewitt's Kuiper Belt page, Comet page, and Damocloids page,
Asteroids - An Overview, by J.Bakkelund.
Home pages for the co-discoverers of Eris, 2003 EL61, 2005 FY9, Orcus and Sedna (Brown and Trujillo also are the co-discoverers of Quaoar, 2002 MS4 and 2003 AZ84):
Mike Brown, David Rabinowitz, Chad Trujillo
Home page of brown dwarf expert Gibor Basri
Astronomer Scott Sheppard's page detailing all the known satellites of the giant planets (Jupiter, Saturn, Uranus and Neptune) - here
The home page of atronomer Paul Weigert has links to his pages about quasi-satellites, including his discovery of one of Earth's quasi-satellites, Cruithne, plus his work on how planets might behave in binary-star systems.
An article about Scott Sheppard and Chad Trujillo's discovery of new Trojans in Neptune's orbit here.
RECONS (Research Consortium on Nearby Stars) have a list of the 100 nearest stars
California & Carnegie Planet Search list known extrasolar planets of nearby stars.
Discovery Links
Detail about the discovery of Varuna by the Spacewatch Project (who also discovered 2002 UX25) can be found here.
Website for the Deep Ecliptic Survey, the discoverers of Ixion, here
A page about the discovery of 2004 XR190 is here
Hartmut 'Spider' Frommert runs a page with regularly updated information about past, current and future Mars exploration
NASA's Dawn Mission is intended to launch in 2007 and visit Vesta in 2011 and Ceres in 2015, whilst their New Horizons mission to Pluto and hopefully other parts of the Kuiper Belt is already en route and scheduled to reach Pluto in 2015.
NASA's Astronaut Biographies pages and Human Spaceflight pages are also of interest. (UK educators might like to note that current British-born NASA astronauts are Mike Foale, Piers Sellers and Nick Patrick. The first (and only other) Briton in space was Helen Sharman).
Heavens Above gives details of when and how to observe the International Space Station and other man-made objects cross the sky (on the best days, the International Space Station is quite bright and easy to spot).
In the meantime I will be adding information to the site as best I can and with what time I have available (not much) and adding links to information about the subject(s).