Astronomy a Go Go!

Thu, 24 August 2006

Direct from the IAU webpage...

"The IAU 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.

Below are the planet definition Resolutions that were passed:

RESOLUTIONS
Resolution 5A is the principal definition for the IAU usage of "planet" and related terms.

Resolution 6A creates for IAU usage a new class of objects, for which Pluto is the prototype. The IAU will set up a process to name these objects.

IAU Resolution: Definition of a Planet in the Solar System
Contemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation 'planets'. The word 'planet' originally described 'wanderers' that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.

RESOLUTION 5A
The IAU therefore resolves that "planets" and other bodies in our Solar System 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.

IAU Resolution: Pluto

RESOLUTION 6A
The IAU further resolves:

Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.1

Category: Planets -- posted at: 2:22 PM

Comments[2]

Thu, 17 August 2006

Show #27: The morning planets, Mars (again) and the IAU

Anyone for betting on the outcome of the IAU meeting?

Direct download: AAGG_show27.mp3
Category: Planets -- posted at: 7:27 PM

Comments[0]

Thu, 17 August 2006

AAGG Show #27: Show Notes

Carpe Noctem - Seize the Night!

Image credit: Stellarium Software

Escape at Bedtime

The lights from the parlour and kitchen shone out
Through the blinds and the windows and bars;
And high overhead and all moving about,
There were thousands of millions of stars.
There ne'er were such thousands of leaves on a tree
Nor of people in church or the Park,
As the crowds of the stars that looked down upon me,
And that glittered and winked in the dark.

The Dog, and the Plough, and the Hunter, and all,
And the star of the sailor, and Mars,
These shone in the sky, and the pail by the wall
Would be half full of water and stars.
They saw me at last, and they chased me with cries,
And they soon had me packed into bed;
But the glory kept shining and bright in my eyes,
And the stars going round in my head.

by Robert Louis Stevenson

AAGG Recall and general confusion

Last week we relayed the information about comet 177P/Barnard being a binocular object. I went out looking for it and I would be very surprised if it was really 8.3 as stated. Kevin also emailed to let me know he went hunting at turned up nada. So if you can't find comet Barnard, it probably isn't you!

News from the IAU General Meeting in Prague

(read the proposed draft definitions...)

"The part of "IAU Resolution 5 for GA-XXVI" that describes the planet definition, states "A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet."

"According to the new draft definition, two conditions must be satisfied for an object to be called a "planet." First, the object must be in orbit around a star, while not being itself a star. Second, the object must be large enough (or more technically correct, massive enough) for its own gravity to pull it into a nearly spherical shape."

"A secondary object satisfying these conditions is also designated a planet if the system barycentre resides outside the primary. Secondary objects not satisfying these criteria are "satellites"."

"The IAU draft Resolution also defines a new category of planet for official use: "pluton". Plutons are distinguished from classical planets in that they reside in orbits around the Sun that take longer than 200 years to complete (i.e. they orbit beyond Neptune). Plutons typically have orbits that are highly tilted with respect to the classical planets (technically referred to as a large orbital inclination). Plutons also typically have orbits that are far from being perfectly circular (technically referred to as having a large orbital eccentricity). All of these distinguishing characteristics for plutons are scientifically interesting in that they suggest a different origin from the classical planets."

For a little Pluton entertainment check out Slacker Astronomy at slackerastronomy.org

Planets

Photo credit: Stellarium Software

Evening Planets

Mars - Mag +1.8 is between the back legs of Leo the Lion. You will have to look hard in the haze of the horizon and it will help to be closer to the equator.

Jupiter - Mag -1.8 in Libra. Clearly visible high in the sky just after sunset. Any telescope can reveal its two widest cloud bands and four Galilean satellites.
Listener Kevin recommended a piece of free software that I now have on all my computers Jupiter 2 (Thanks Kevin!).

Uranus - Mag +5.9 in Aquarius Uranus is best seen in a dark moonless sky away from artificial lighting. It may be seen looking like a very faint star to the dark-adapted naked eye that shimmers in and out of visibility a thumbwidth east of Lambda Aquarii. Find the tipped over letter Y of Aquarius, go 4 thumbwidths southeast to find Lambda, and then look one thumbwidth east using binoculars..

Neptune - Mag +7.9 in Capricorn 1 degree north of the +4.3 magnitude star Iota Capricorni

Pluto Mag +13.9 in Serpens Cauda

Morning Planets

Venus - Mag -3.62 The brightest morning planet visible. To the ESE the bright star Sirius is rising with Venus in the morning.

Mercury - Mag -1.1 between the Sun and Venus (3.5 degrees East of Venus)

Saturn - Mag +0.4 In Cancer and on the eastern horizon just after sunset and favored for those of you close to the equator.

More "Scale of the Solar System"

From the Sunshine Movie site. Scroll across the bottom...you have to be patent and have a sharp eye!
Also from the same site a walking scale of the solar system 'kit' to put together
My all-time favorite comes from The Exploritorium, I love the ability to customise the scale and include Alpha Centarus and the center of the galaxy in the same scale formula.
And right up there with the Exploritorium is the good old "Thousand Yard Model" or "The Earth is a Peppercorn". This one is good because it is really easy for the audience to remeber the scale sizes Jupiter is a chestnut and the Earth a peppercorn.

Viewing

Found a great site for NGC images go to the Digitized Sky Survey Site (DSS) and check out the images. I like the fact that you can see a page worth of thumbprints and then open the one you are looking for.

Naked eye and Binoculars The real show is for naked eyes in the morning (okay maybe a little bino help). Check out the Moon, Venus, Mercury and Saturn.
Something for evening viewing? Check out variable star Chi Cygni. It is a long period variabel star along the long neck of Cygnus the Swan and is right now at mag 4.0 (range 5.0-13.4)

Photo in the infrared by Maurice Gavin

Telescope NGC 6864 or M75 globular cluster at 8.6 mag
NGC 7099 or M30 globular cluster at 6.9 mag a very bright
NGC 7089 or M2 globular cluster at 6.6 mag
NGC 6994 or M73 open cluster at 8.3 mag small 4 star cluster
NGC 6981 or M72 globular cluster at 9.2 mag

Challenge Object NGC 7293 the Helix Nebula a planetary nebula at 7.3 mag
NGC 7009 or the Saturn Nebula planetary nebula at 8.0

The Moon

Maps created with Lunar Phase Pro

Lunar photo is courtesy of Frank Barrett at celestialwonders.com I recommend visiting his site and checking out his lunar phase photos. You can zoom in for more detail.

This weekend waning gibbous
New Moon - Aug 23rd 1st Quarter - Sept 1st

Object	Latitude	Longitude	Comments
Crater Billy	-66.5	-69.1	Jean Sylvain; French astronomer and mathematician (1736-1793) The interior floor of Billy crater has been flooded by basaltic lava, leaving a dark surface.
Crater Mersenius	-21.5	-49.2	The interior has been flooded by basaltic-lava, which bludges upward forming a convex domed shape. Mersenne, Marin; French mathematician, physicist (1588-1648)
Crater Gassendi	-17.6	-40.1	Pierre; French astronomer, mathematician (1592-1655). The formation flooded by lava during the formation of Mare Humorum, so only the rim and the multiple central peaks remain above the surface.

Comets for August

Go the the Skyhound site for your daily dose of comet information but remember that your viewing may vary.

News

Mars Attacks! Phil Plait's Bad Astronomy blog says it best....

Grand Rapids Amateaur Astronomical Association (GRAAA) host public nights at the James C. Veen Observatory on the second and last Saturdays of the month (April through October), if the skies are clear. Please call the Starwatch number -- 897-7065 -- for updates and the status of a particular night if the weather conditions are questionable.
Admission for visitors' nights are $3 for Adults, $2 for 17 years and younger, and free for children under 5 years of age.

Music

Fools Gold - Josh Woodward

Woodland Hills Camera and Telescope is offering FREE web hosting on our servers for you or your organization's website. In order to promote the hobbies of Astronomy, Astrophotography, Photography, Birding or generally any topic that is of interest to our customer base, Woodland Hills Camera and Telescope is offering Hosting Grants.

Category: Planets -- posted at: 7:11 PM

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Thu, 10 August 2006

AAGG Show #26: Show Notes