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When is a planet not a planet?

When is a planet not a planet?  This question has troubled scientists and students for decades, and the recent demotion of Pluto from planet to plutoid marked a significant change in how scientists classify planets. In 2006 the International Astromical Union identified three key criteria to classify a body as a planet:  

  1. The body is in orbit around the Sun,
  2. The body has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
  3. The body has “cleared the neighbourhood” around its orbit.

By this definition Pluto was excluded, but the discovery of a transneptunian object on January 5, 2005 added very briefly a planet to the solar system.  

Many teams were racing to map the outer solar system, specifically the belt of asteroids and debris in the scattered disc known as transneptunian objects, and the discovery of Eris and Dysnomia took several years of searching, two years of analysis with both computers and good old fashioned legwork.  The team of Mike Brown, Chad Trujillo, and David Rabinowitz had programmed their computers to rule out objects moving too slowly to count and missed seeing Eris when it was first photographed.  Manually pouring over the photos almost a year and a half later, they found the largest (to date) plutoid or dwarf planet.

 Wanting to name more sky objects after women, internally the team referred to the dwarf planet as Xena, after the popular television series.  After a period of several years (and much consensus building) the name Eris was settled on.  Eris was the goddess of strife in Greek mythology, the meddling troublemaker who doomed the marriage of Peleus and Thetis, the parents of Achilles, which led to the disastrous war that destroyed both Troy and much of the invading Greek armies.  Eris’s own son was named Dysnomia, meaning lawlessness, and when the Hubble Space Telescope discovered that Eris had a moon, well, the name was inevitable.  Since the discovery of Eris and Dysnomia, several more plutoids have been discovered, but none yet as large.  Eris was considered a planet for less than a year, before both Eris and Pluto were reclassified as plutoids.  

Images of Eris and Dysnomia courtesy NASA/Hubble.

Monday, December 30, 2013

On December 30, 1995 the Hubble Space Telescope completed the series of 342 images that were rendered in to the Hubble Deep Field View, perhaps the most astonishing and humbling scientific achievement made by humans in the field of space science. The area for the Deep Field View was chosen as one of the ‘darkest’ spots in the sky:  imagine holding a grain of sand at arms length or a viewing a tennis ball at 100 meters, and looking in the direction of the darkest, least populated portions of the night sky.  The total area is equivalent to  one twenty four millionth of the total night sky.  There were many skeptics when the Deep Field View was first proposed-many assumed that the this portion of ‘dark sky’ would show that in fact there are portions of ‘dark sky’ from our vantage point.  Most of the three thousand or so images in the Deep Field View are in fact entire galaxies and form some of the oldest and farthest structures ever seen, with only 20 or so nearer stars.  Few images hint at the immensity or complexity of our universe as much as this image.

In addition to its day to day duties, Hubble has returned to its deep field views several times, with the Deep Field View South a couple years later, the 2004 Hubble Ultra Deep Field, and the Hubble Extreme Deep Field of 2012.  Named for American astronomer Edwin Powell Hubble  (November 20, 1889 – September 28, 1953), the Hubble Space Telescope continues to work in Edwin Hubble’s field of deep cosmological inquiry and extra-galactic astronomy.  Despite early problems including a dramatic in-space repair mission, the Hubble has been sending back pictures and data of every corner of the universe, making it one of the most important scientific tools every created.  

The Hubble Deep Field, the Hubble Space Telescope as seen from Atlantis Space Shuttle, and the rendering of the Hubble making the DFV, all courtesy NASA/Hubble.

Thursday, April 25, 2013

On April 25, 1990 the Hubble Space Telescope was placed into orbit 381 miles above the earth, making it the first optical telescope in space.  Named for American astronomer Edwin Powell Hubble  (November 20, 1889 – September 28, 1953), the Hubble Space Telescope continues to work in Edwin Hubble’s field of deep cosmological inquiry and extra-galactic astronomy.  Despite early problems including a dramatic in-space repair mission, the Hubble has been sending back pictures and data of every corner of the universe, making it one of the most important scientific tools every created.  The Deep Field View pictured above, was a series of 342 photos taken in December 1995 and composed and rendered into a single image.  The area for the Deep Field View was chosen as one of the ‘darkest’ spots in the sky:  imagine holding a grain of sand at arms length or a viewing a tennis ball at 100 meters, and looking in the direction of the darkest, least populated portions of the night sky.  In addition to its day to day duties, Hubble has returned to its Deep Field views several times, with the Deep Field View South a couple years later, the 2004 Hubble Ultra Deep Field, and the Hubble Extreme Deep Field of 2012.

The Hubble Deep Field, the Hubble Space Telescope as seen from Atlantis Space Shuttle, and the Cat’s Eye Nebula as photographed by Hubble, all images courtesy NASA/Hubble.

Tuesday, November 20, 2012

Today is the birthday of Edwin Hubble (20 November 1889-23 September 1953), American astronomer known for expanding the limit of the universe.  When Hubble began his studies it was thought that there was no universe beyond the Milky Way galaxy.  Hubble was fortunate to land at the Hooker Observatory just as the it became the world’s largest telescope-with it he discovered and identified a type of star now known as Cepheid variables which he determined were to far away to be a part of the Milky Way.  His paper describing his findings changed the way astronomers looked at the night sky.    

Tuesday, May 1, 2012

First predicted in the 1840s by the French astronomer Urbain le Verrier, the planet Pluto wasn’t located and identified for almost a hundred years. American astronomer Percival Lowell took it upon himself and his observatory to find the planet that was predicted using Newtonian mechanics and the perturbations of the planet Neptune. Lowell threw resources at the problem for over a decade, actually imaging the planet in 1915 but not recognizing it. His death slowed the project for a decade until 23 year old Kansas native Clyde Tomsbaugh began searching again in earnest, finally identifying it February 1930. It was a huge international scientific sensation, and a search for a name began. 11 year old Venetia Burney from Oxford England suggested the name Pluto through her grandfather (a librarian at the Bodleian Library) who passed it along to colleagues at the Observatory. Pluto, the ruler of the Greek Underworld, was a shadowy and nearly invisible figure-much like the planet. Although they received over 1,000 suggestions, only three made the final vote: Pluto, Minerva and Cronus. Minerva was already the name of an asteroid and Pluto received all the votes. Pluto was named May 1, 1930.

Pluto has four moons, Chiron, discovered in 1978 by astronomer James Christy; Nix and Hydra, both discovered by the Hubble team in 2005, and P4, an unnamed moon discovered in 2011 and not yet named.

In 2006 the International Astronomical Union created a controversy by developing a system of criteria for planets that mean Pluto was inelible for the distinction and was relegated to ‘dwarf planet’ status. There were world wide objections, both in the scientific community and in the culture at large, culminating in a meeting at Johns Hopkins University that led to the designation of plutoids.

Venetia died April 30, 2009 after a long career as an educator.

Image of Pluto and its moons courtesy NASA/Hubble. Image of Venetia Burney courtesy of the BBC, now in the public domain.

Tuesday, February 14, 2012

The word galaxy has a long and complicated history to get to English. Arriving around the time of Geoffrey Chaucer in the late 14th century from Old French which in turn came from Late Latin to denote the Milky Way. The Latin form of galaxias was a direct transliteration of the Ancient Greek galaxias (adj.) from galaxias kyklos, literally a milky circle. The adjective galaxias came from the word for milk, gala (gen. galaktos). Our galaxy, which we call in English the Milky Way is a translation of Latin via lactea. From Chaucer’s House of Fame:

See yonder, lo, the Galaxyë Which men clepeth the Milky Wey, For hit is whyt. 

It wasn’t until the early twentieth century that astronomers began to understand how vast the Universe is and how many galaxies are in it, and it wasn’t until the last ten years that astronomers really began to fathom the depth and size of the universe, with the Hubble Ultra Deep Field Survey.  At the end of 2003, astronomers using the Hubble Space Telescope began pointing it at a very small and very dark patch of sky.  With a total collection of just under a million seconds taken over 400 orbits, what the survey found was astonishing:  another 10,000 galaxies from the very beginning of the universe.  This from a very small and very very dark patch of sky.  These deep field images date back to the beginning of the universe, some 400 million to 800 years after the Big Bang and are the farthest and oldest objects yet seen.

Video of the Milky Way Galaxy over the ALMA (Atacama Large Millimeter/submillimeter Array) at Chajnantor plateau, 5000 meters altitude in northern Chile by Jose Francisco Salgado, copyright and all rights reserved by Salgado.  Click the link to learn about the largest astronomical project on Earth!

Tuesday, October 11, 2011
The word Astronomy is used to denote the study of stars, planets and space. The word astrology is derided as the corrupted and non-scientific study of the effect that stars and planets have on human activities. The etymologies and histories show an interesting link. Both use the Ancient Greek word aster (plural: astron) meaning star. Astronomy adds the suffix nomos meaning law, custom or arrangement. Astrology adds the suffix more typically used to indicate the study of a subject: logos meaning word or thought.
How did one come to indicate science and one get relegated to the comics pages of newspapers? Astronomy is both the older word and the word that early on had its modern meaning. Largely synonymous during the Dark Ages, astronomy was the study of stars and space while astrology adopted the definition of the effect of the stars on human activity. From the 14th through the 17th centuries the words slowly diverged until by the mid-17th century astronomy stood alone as the study of stars and space.
Image of the Pillars of Creation courtesy NASA Hubble Program.

The word Astronomy is used to denote the study of stars, planets and space. The word astrology is derided as the corrupted and non-scientific study of the effect that stars and planets have on human activities. The etymologies and histories show an interesting link. Both use the Ancient Greek word aster (plural: astron) meaning star. Astronomy adds the suffix nomos meaning law, custom or arrangement. Astrology adds the suffix more typically used to indicate the study of a subject: logos meaning word or thought.

How did one come to indicate science and one get relegated to the comics pages of newspapers? Astronomy is both the older word and the word that early on had its modern meaning. Largely synonymous during the Dark Ages, astronomy was the study of stars and space while astrology adopted the definition of the effect of the stars on human activity. From the 14th through the 17th centuries the words slowly diverged until by the mid-17th century astronomy stood alone as the study of stars and space.

Image of the Pillars of Creation courtesy NASA Hubble Program.