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Enceladus and the Rings of Saturn

On March 9, 2006, the Cassini Space probe took an astounding photograph that confirmed the theory that the moon Enceladus was contributing to the ring system of Saturn.  The photo here was taken by NASA after engineers used Saturn itself to obscure the Sun but illuminate the rings and satellite, here clearly shown with a cryovolcano erupting water and gas into the E-ring.  

Three years later, the Cassini space probe was positioned again to use the light from the sun to illuminate the rings and surface of the giant planet, with a shadow thrown across the ring system.  Mathematical models of the ring system show that they are unstable beyond 10,000 years, meaning that they are constantly replenished from a source such as Enceladus.  

Launched on October 15, 1997, the Cassini-Huygens spacecraft left Earth for flybys of Earth, Venus and Jupiter, before arriving at Saturn on Christmas Day, 2004 and separating the Huygens probe which reached Titan a few weeks later.  Cassini-Huygens was named for Italo-French Astronomer Giovanni Domenico Cassini (later known as Jean Dominque Cassini), known  for his discovery of four moons of Saturn, and Dutch astronomer Christiaan Huygens, who discovered Saturn’s moon Titan.  The Cassini spacecraft is still in service today, currently located at the south Pole of Saturn, taking images of the famous hexagon.  The spacecraft is scheduled to remain in service until September 2017.

Images courtesy NASA/ESA, in the public domain.

Sunday, February 23, 2014
Today is the anniversary of the discovery of the first modern supernova, currently named SN1987A, located in the Tarantala Nebula in the Large Magellanic Cloud.  It was independently discovered by both  Ian Shelton and Oscar Duhalde of the Las Campanas Observatory in Chile on the night of February 23/24, 1987, and within the same 24 hours independently by Albert Jones in New Zealand. Two weeks later, between March 4–12, 1987 it was observed from space by Astron, a large ultraviolet space telescope. The supernova has yet to receive an official name.  
While plenty of modern scientific words can be dated accurately, the older a word is (in general) the harder it is to pin down a date.  The word supernova however, defies this logic.  Late October 1604 (and some sources give the date 6 November 1604) a new and bright object appeared in the sky.  German astronomer and mathematician Johannes Kepler (born 27 December 1571-15 November 1630) noticed the ‘new' object and unsure what exactly it was, simply named it stella nova, from the Latin words for new star.  It wasn’t until the 1930s that astronomers Walter Baade and Fritz Zwicky started using the term super-nova and by 1938 the hyphen was dropped and the word became supernova.  The first reliably recorded supernova was noted by Pliny in AD 185.  Notable supernovae (note the plural maintains the Latin form and does not take the -s that English mostly uses) occurred in 1054, noted mainly by Chinese and Arabic astronomers, and the supernova of 1572 noted extensively by Tycho Brahe.
Time-lapse animation of SN1987A from 1994 to 2009, video compilation courtesy Mark Macdonald, via Larsson, J. et al. (2011). “X-ray illumination of the ejecta of supernova 1987A”. Nature 474 (7352): 484–486., used with permission under a Creative Commons 3.0 license.  

Today is the anniversary of the discovery of the first modern supernova, currently named SN1987A, located in the Tarantala Nebula in the Large Magellanic Cloud.  It was independently discovered by both  Ian Shelton and Oscar Duhalde of the Las Campanas Observatory in Chile on the night of February 23/24, 1987, and within the same 24 hours independently by Albert Jones in New Zealand. Two weeks later, between March 4–12, 1987 it was observed from space by Astron, a large ultraviolet space telescope. The supernova has yet to receive an official name.  

While plenty of modern scientific words can be dated accurately, the older a word is (in general) the harder it is to pin down a date.  The word supernova however, defies this logic.  Late October 1604 (and some sources give the date 6 November 1604) a new and bright object appeared in the sky.  German astronomer and mathematician Johannes Kepler (born 27 December 1571-15 November 1630) noticed the ‘new' object and unsure what exactly it was, simply named it stella nova, from the Latin words for new star.  It wasn’t until the 1930s that astronomers Walter Baade and Fritz Zwicky started using the term super-nova and by 1938 the hyphen was dropped and the word became supernova.  The first reliably recorded supernova was noted by Pliny in AD 185.  Notable supernovae (note the plural maintains the Latin form and does not take the -s that English mostly uses) occurred in 1054, noted mainly by Chinese and Arabic astronomers, and the supernova of 1572 noted extensively by Tycho Brahe.

Time-lapse animation of SN1987A from 1994 to 2009, video compilation courtesy Mark Macdonald, via Larsson, J. et al. (2011). “X-ray illumination of the ejecta of supernova 1987A”. Nature 474 (7352): 484–486., used with permission under a Creative Commons 3.0 license.  

Saturday, February 15, 2014
Happy Birthday, Galileo Galilei, born February 15, 1564.  

On the nights of January 7/8, 1610, Galileo Galilei noted in his notebooks the discovery of the first 4 Jovian moons, which he named after the powerful Medici family, naming them Medicean I, II and III.  The name Europa (second from right) comes from Greek mythology-Europa was abducted by Zeus (the Greek name for Jupiter) in the form of a bull and bore him many children.  Io (the yellow moon on the left) is also named for a child of Zeus (Jupiter) the daughter of Inachus, who was raped by Jupiter. Jupiter, in an effort to hide his crime from his wife, Juno, transformed Io into a heifer.  Calllisto (on the far right) was named for another seduction of Jupiter.  Callisto was the daughter of Lycaon, who was a follower of Artemis, famous as goddess of the hunt and for her chastity.  To punish Callisto for lying with Jupiter, Artemis banished her.  Without protection, Jupiter was forced to change Callisto and her son into bears to hide them from his wife Hera’s fury.  Eventually, Jupiter placed them both in the sky as the Ursa Major and Minor, the Big and Little Bears (known today as the Big and Little Dippers).  Ganymede (largest moon pictured here, third from right) was the fourth moon discovered by Galileo, named for the shepherd boy known for his incredible beauty and kidnapped by Jupiter.  These names would not become common for several hundred years.  Today, Jupiter has fifty named moons:
1. Io  2. Europa 
3. Ganymede 4. Callisto 5. Amalthea 6. Himalia 7. Elara 8. Pasiphae 9. Sinope 10. Lysithea 11. Carme 12. Ananke 13. Leda 14. Thebe 15. Adrastea 16. Metis 17. Callirrhoe 18. Themisto 19. Megaclite 20. Taygete 21. Chaldene 22. Harpalyke 23. Kalyke 24. Iocaste 25. Erinome 26. Isonoe 27. Praxidike 28. Autonoe 29. Thyone 30. Hermippe 31. Aitne 32. Eurydome 33. Euanthe 34. Euporie 35. Orthosie 36. Sponde 37. Kale 38. Pasithee 39. Hegemone 40. Mneme 41. Aoede 42. Thelxinoe 43. Arche 44. Kallichore 45. Helike 46. Carpo 47. Eukelade 48. Cyllene 49. Kore 50. Herse 
and an additional 16 provisional moons:
1. S/2003 J2 2. S/2003 J3 3. S/2003 J4 4. S/2003 J5 5. S/2003 J9 6. S/2003 J10 7. S/2003 J12 8. S/2003 J15 9. S/2003 J16 10. S/2003 J18 11. S/2003 J19 12. S/2003 J23 13. S/2010 J 1 14. S/2010 J 2 15. S/2011 J1 16. S/2011 J2 



All images courtesy NASA.  Thanks also to NASA for additional historical background

Happy Birthday, Galileo Galilei, born February 15, 1564.  

On the nights of January 7/8, 1610, Galileo Galilei noted in his notebooks the discovery of the first 4 Jovian moons, which he named after the powerful Medici family, naming them Medicean I, II and III.  The name Europa (second from right) comes from Greek mythology-Europa was abducted by Zeus (the Greek name for Jupiter) in the form of a bull and bore him many children.  Io (the yellow moon on the left) is also named for a child of Zeus (Jupiter) the daughter of Inachus, who was raped by Jupiter. Jupiter, in an effort to hide his crime from his wife, Juno, transformed Io into a heifer.  Calllisto (on the far right) was named for another seduction of Jupiter.  Callisto was the daughter of Lycaon, who was a follower of Artemis, famous as goddess of the hunt and for her chastity.  To punish Callisto for lying with Jupiter, Artemis banished her.  Without protection, Jupiter was forced to change Callisto and her son into bears to hide them from his wife Hera’s fury.  Eventually, Jupiter placed them both in the sky as the Ursa Major and Minor, the Big and Little Bears (known today as the Big and Little Dippers).  Ganymede (largest moon pictured here, third from right) was the fourth moon discovered by Galileo, named for the shepherd boy known for his incredible beauty and kidnapped by Jupiter.  These names would not become common for several hundred years.  Today, Jupiter has fifty named moons:

1. Io  2. Europa 

and an additional 16 provisional moons:
All images courtesy NASA.  Thanks also to NASA for additional historical background

Galileo and the heliocentric model

Although scientists as early as Aristarchus of Samos knew the relationship between the sun and earth around 270 BCE, it wasn’t until 1543 that Nicholas Copernicus published his masterwork De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres), published the same year that he died that the heliocentric model received wide distribution. Perhaps his death and inability to defend his thesis led to the very slow spread and adoption of his idea, so that by the year 1616 a group of cardinals and bishops under the direction of the Vatican met to denounce Galileo Galilei, who was using the results of his observations made with the new technology of the telescope to re-introduce the heliocentric model of the solar system.

A decade and half passed before Galileo was dangerous enough to draw a trial, which commenced in 1633. Galileo was furious with the philosophers, theologians and scientists who denounced his idea, complaining to his friend and fellow astronomer Johannes Kepler,

My dear Kepler, I wish that we might laugh at the remarkable stupidity of the common herd. What do you have to say about the principal philosophers of this academy who are filled with the stubbornness of an asp and do not want to look at either the planets, the moon or the telescope, even though I have freely and deliberately offered them the opportunity a thousand times? Truly, just as the asp stops its ears, so do these philosophers shut their eyes to the light of truth.

He lost the trial and spent his last eight years under house arrest, working on his theories from his home in Pisa.

The word heliocentric comes from Ancient Greek, a combination of the words ἥλιος (helios) meaning sun and κέντρον (kentron) meaning center. It would take another three centuries for scientists to understand that not only is the Earth not the center of the Universe, neither is the Sun.

Happy Birthday Galileo Galilei, born February 15, 1564.

Painting of Galileo Facing the Roman Inquisition by Cristiano Banti, 1857, in the public domain.

Image from Copernicus in the public domain.

Sunday, January 5, 2014

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.

Tuesday, December 24, 2013

Apollo 8, the Moon, and the first ‘Earthrise’

All the romance and credit go to Apollo XI and Armstrong, Aldrin and Collins, but please don’t forget Apollo 8 and the amazing contribution made by these Astronauts: Commander Frank Borman, Command Module Pilot James Lovell, and Lunar Module Pilot William Anders, who circled the Moon ten times exactly 45 years ago today on Christmas Eve 1968.

Do not underestimate the technical achievement or ambition of Apollo 8:  the mission had originally been scheduled as an Earth orbit only mission for early 1969 but was bumped up in the schedule and re-designed to travel to the moon months earlier as the Lunar Module was not ready for flight.  Apollo 8 took three days to travel to the Moon, then spent 20 hours making 10 orbits, taking the famous ‘Earthrise’ photo  on its fourth orbit, after Borman turned the craft to face the lunar surface.  Apollo 8 would return safely to Earth for splash down on December 27, 1968.  Lovell would later fly the near disastrous Apollo 13 mission, while Borman and Anders were on their last flight.  Go out tonight and pause to remember these three men, travelling over half a million miles to take a photo-a photo that re-defined the way we look at the Earth. 

The Earth’s moon holds a special place in the human heart:  it exists not only as our nearest celestial neighbor, it is also one of the richest sources of metaphor and poetry.  Despite Shakespeare’s denigration that “the moon's an arrant thief, And her pale fire she snatches from the sun,” the moonhas a long history in literature, poetry and song.  The word itself comes from Old English mona, from Proto Germanic *mænon- (cf. Old Saxon, Old High German mano, Old Frisian mona, Old Norse mani, Dutch maan, German Mond, Gothic mena all meaning moon), from Proto Indo European *me(n)ses- meaning moon, month (cf. Sanskrit. masah meaning moon, month; Avestan ma, Persian. mah, Armenian mis month; Ancient Greek. mene moonmen month; L. mensis “month;” O.C.S. meseci, Lith. menesis meaning  moon, month; Old Irish mi, Welsh mis, Breton miz  month), probably from base *me- meaning to measure, in reference to the moon's phases as the measure of time. In Greek, Italic, Celtic, Armenian the cognate words now mean only month.  First used to describe the satellites of other planet’s 1665.

Shakespeare quote from Timon of Athens.

All Images courtesy NASA in the public domain.  Earthrise photo by William Anders.

Saturday, December 21, 2013

Happy Winter Solstice!

image

The first day of winter and the shortest day of the year begin later today, the day of the winter solstice.  At 5:11 pm Greenwich Mean time, the Solstice will arrive.  The word solstice is relatively old in English, dating back to the 13th century.  Solstice derives from the Latin word solstitium meaning very literally the point at which the sun stands still, a combination of the words sol meaning sun and the past participial stem of sistere meaning to come to a stop, make stand still.  Celebrated thoughout history as either a secular or religious day, the solsticemarks the point on the ecliptic when the Northern Hemisphere is pointed most away from the sun and therefore has the shortest day. 

Monday, December 9, 2013

The Dumbbell Nebula

The first planetary nebula discovered was the Dumbbell Nebula or Apple Core nebula and was discovered by Charles Messier in 1764.  Approximately 1400 light years from earth, the Dumbbell Nebula has several distinguishing features: the white dwarf at the center is considered the largest known white dwarf at the center of a nebula at a radius of 0.055 ± 0.02 R.  

When Messier found the nebula in the constellation Vulpecula, the constellation was only a century old, named by Polish astronomer Hevelius in 1687  Of the name Vulpecula, Hevelius said this:  

I wished to place a fox and a goose in the space of the sky well fitted to it; because such an animal is very cunning, voracious and fierce. Aquila and Vultur are of the same nature, rapacious and greedy.

Messier composed his famous catalog while comet hunting-he created a list of asterisms that were neither comets nor stars to keep track of them as he searched for comets.  The term planetary nebula came from German Astronomer William Herschel in the 1780s who though he was seeing planets forming, though they are formed of ionized gas expanding out from old red giants late in their lives.

When the word nebula entered English in the early 15th century, it had nothing to do with astronomy.  Arriving as nebule meaning a cloud or mist from the Latin word nebula meaning mist, which in turn came from the Proto Indo-European root word *nebh-meaning cloud, vapor, fog, moist, sky.  Ancient Greek had the related word nephele, nephos which also meant cloud. When the word nebula reappeared in English it had a medical meaning for cataracts or cloudy defects in the eye.  The astronomical meaning of a cloud-like patch in the night sky was first recorded around 1730. It wasn’t until the early 20th century with the advent of modern and powerful telescopes that nebula were fully understood as massive clouds of gas and dust.  

Friday, November 15, 2013

Yes, that gorgeous ringed planet with the satellites out of Shakespeare is Uranus and not Saturn.  Today is the birthday of William Herschel (15 November 1738 – 25 August 1822) a German born British astronomer known today as the discoverer of the planet Uranus in March of 1781.  He also discovered two of Uranus's moons, Titania and Oberon and two moons of Saturn.  

He is also credited with the discovery of Infrared radiation, and to honor that the image above of Uranus is a 1998 false-colour near-infrared image of the planet showing cloud bands, rings, and moons obtained by the Hubble Space Telescope’s NICMOS camera.

Herschel named his discovery George, oddly enough, to commemorate his new patron, King George III.  At the time he said this:  

In the fabulous ages of ancient times the appellations of Mercury, Venus, Mars, Jupiter and Saturn were given to the Planets, as being the names of their principal heroes and divinities. In the present more philosophical era it would hardly be allowable to have recourse to the same method and call it Juno, Pallas, Apollo or Minerva, for a name to our new heavenly body. The first consideration of any particular event, or remarkable incident, seems to be its chronology: if in any future age it should be asked, when this last-found Planet was discovered? It would be a very satisfactory answer to say, ‘In the reign of King George the Third’.

Few astronomers outside of England liked the name, however, and astronomers began proposing alternatives almost immediately.  German astronomer Johann Elert Bode called it Uranus  (Ancient Greek: Οὐρανός) after the Ancient Greek god of the sky, the logic being that as Saturn was the father of Jupiter, the new planet should be the father of Saturn.  It wasn’t until the middle of the next century that atlases dropped Herschel’s name and adopted Uranus. Learn all about William Herschel here:

All images in the public domain

 
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