Celestial calendar - Dwarf Planets

Only 8 planets now. Credit: IAU
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Celestial calendar

DWARF PLANETS

We had 9 planets in 2005. Now we've only got 8. On August 24, 2006, astronomers at the 26^th General Assembly of the International Astronomical Union in Prague declare that Pluto is no longer a planet. Now Pluto, Charon, Ceres, and the newly discovered 2003 UB₃₁₃ (aka Xena) will merely be known as "dwarf planets". Under the new definition, planets must orbit a star, be spherical in shape, and clear out their neighbourhood of orbital debris. Pluto has failed to fulfill the third requirement, so it's out of the planet club.

See more at http://www.plutopetition.com/unplanet.php.

The 26^th IAU General Assembly:

RESOLUTION 5A: "Definition of 'planet'"

The IAU resolves that "planets" and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way:

(1) A "planet"¹ is 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.

(2) A "dwarf planet" is 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) shape², (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects³ except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".

¹The eight "planets" are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

²An IAU process will be established to assign borderline objects into either dwarf planet and other categories.

³These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

RESOLUTION 6A: "Definition of Pluto-class objects"

Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of Trans-Neptunian Objects.

Dwarf planet Pluto in 2008:

Satellite of Pluto (Charon):
Orbital, physical and photometric data.

PLUTO is in constellation Sagittarius throughout the year. The dwarf planet do not visible for amators.

Date	Apparent Right Ascension	Apparent Declination	Magnitude
Jan. 1, 2008	17^h 56.4^m	-17^o 09'	+14.0^m
Apr. 6	18^h 04.8^m	-17^o 04'	+14.0^m
July 11	17^h 57.2^m	-17^o 05'	+14.0^m
Oct. 15	17^h 55.1^m	-17^o 31'	+14.0^m
Jan. 17, 2009	18^h 07.4^m	-17^o 45'	+14.0^m

Dwarf planet Ceres in 2008:

Opposition Date	Magnitude (max)	Diameter (km)	Mean Distance (AU)	Eccentricity	Daily Motion
Nov. 9, 2007 Feb. 25, 2009	7.6^m 6.9^m	957	2.77	0.08	0.21^o

November 9, 2007 at opposition

Date	Apparent Right Ascension	Apparent Declination	Magnitude	Distance
Date	Apparent Right Ascension	Apparent Declination	Magnitude	from Sun (AU)	from Earth (AU)
Nov. 9, 2007	3^h 08.0^m	+8^o 05'	+7.2^m	2.81	1.84
Nov. 24	2^h 54.1^m	+7^o 59'	+7.4^m	2.80	1.86
Dec. 9	2^h 42.9^m	+8^o 17'	+7.8^m	2.79	1.94
Dec. 26	2^h 36.7^m	+9^o 12'	+8.1^m	2.78	2.09
Jan. 10, 2008	2^h 37.2^m	+10^o 26'	+8.3^m	2.77	2.26
Jan. 25	2^h 42.7^m	+11^o 56'	+8.5^m	2.75	2.44
Feb. 14	2^h 57.6^m	+14^o 14'	+8.8^m	2.74	2.70

Glossary

Astronomical Unit (AU):

middle distance between Earth and Sun, equal 149.6 millions km.

Eccentricity:

a parameter that specifies the shape of a conic section; one of the standard elements used to describe an elliptic orbit.

Mean Distance:

the semimajor axis of an elliptic orbit.

Opposition:

a configuration of the Sun, Earth and a planet in which the apparent geocentric longitude of the planet differs by 180^o from the apparent geocentric longitude of the Sun.

Note: All time moments are given in Universal Time (UT) units.
For Kyiv Local_Time=UT+2^h (and Local_Time=UT+3^h for summer time).