APOD: Atlas, Daphnis, and Pan (2017 Jul 06)

[APOD Robot]

Atlas, Daphnis, and Pan

Explanation: Atlas, Daphnis, and Pan are small, inner, ring moons of Saturn, shown at the same scale in this montage of images from the still Saturn-orbiting Cassini spacecraft. In fact, Daphnis was discovered in Cassini images from 2005. Atlas and Pan were first sighted in images from the Voyager 1 and 2 spacecraft. Flying saucer-shaped Atlas orbits near the outer edge of Saturn's bright A Ring while Daphnis orbits inside the A Ring's narrow Keeler Gap and Pan within the A Ring's larger Encke Gap. The curious equatorial ridges of the small ring moons could be built up by the accumulation of ring material over time. Even diminutive Daphnis makes waves in the ring material as it glides along the edge of the Keeler Gap.

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[Ann]

APOD Robot wrote:
Flying saucer-shaped Atlas

Click to view full size image

Pan is pretty flying saucer-shaped, too.

Dr David Clarke wrote:

Click to view full size image

What's out there?
(Actually, it's the eruption of Mount Saint Helen.)
Source: http://imgur.com/gallery/hG7jG/comment/648432194

Formerly secret RAF files opened at The National Archives include a detailed account of an incident on 19 October 1982 when a USAF RC-135 plane, monitoring Soviet military activity, was buzzed by ‘a big object’ over the Eastern Mediterranean.
...
The UFO – – described as covered in ‘a multitude of flashing lights 20 at a time’ – was picked up on the spylane’s radar as it approached from the south.

It then circled around the plane, call-sign Beano 73 – and closed in as the navigator appealed for help from the ground.

Two US Navy F-14 fighters were scrambled from an aircraft carrier and a RAF Phantom was diverted from a night flying exercise to intercept the UFO, south of the island of Cyprus.

As the three interceptors approached the USAF crew saw the UFO depart towards the African coast. Nothing was seen by the fighter pilots.
...
(A) tentative explanation is offered by a senior RAF official, who wrote: ‘We have a strong suspicion that the “UFO” was a mirage effect from lights on the coast of Israel or Lebanon’.

Wikipedia wrote:

Click to view full size image

Pan. Illustration by sinmadison on deviantART

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In Greek religion and mythology, Pan (/ˈpæn/;[1] Ancient Greek: Πάν, Pan) is the god of the wild, shepherds and flocks, nature of mountain wilds and rustic music, and companion of the nymphs.
...
Disturbed in his secluded afternoon naps, Pan's angry shout inspired panic (panikon deima) in lonely places.

Ann

[ta152h0]

too bad the camera's going to be turned off at entry, like Shoemaker-Levy at EROS

[GCSunsfan11]

These are not moons, they are rocks. If Pluto is not a planet (really?!?), then these are not moons. Call them something else too.

[JohnD]

Some time ago, we commented with surprise on the ring on Pan, and compared it with that on Iapetus.
Now Atlas has a most prominent ring, and Daphnis looks to be a miniature version.
Are we discovering a life cycle of Saturnian moons?
Do they rotate? As they grow, will they reach a centrifugal limit and burst? Cycling the ice of the rings in this way is an exciting idea, that on Iapetus has built a ring on rock, so it doesn't fall apart.

GCSunsfan11,
They are not 'rocks' either, but made of ice. Call them ices, not moons? "The Ices of Saturn"? Messrs Ben & Jerry, your moment has come!

John

[ta152h0]

Dwarf moons ? Compact Moons ? Toddlers ?

[neufer]

Do they rotate? As they grow, will they reach a centrifugal limit and burst? Cycling the ice of the rings in this way is an exciting idea, that on Iapetus has built a ring on rock, so it doesn't fall apart.

<<Atlas has a synchronous rotational/orbital period of 14.44 hours (slightly longer than Saturn's own rotation period of 10.55 hours). The size of [Atlas's] equatorial ridge is comparable with the expected Roche lobe of the moon. This would mean that for any additional particles impacting the equator, the centrifugal force will nearly overcome Atlas's tiny gravity, and they will likely be lost.>>

[ta152h0]

Charon is called a " moon ", right ? And there was an asteroid discovered with a " moon "

[neufer]

These are not moons, they are rocks.

Traditionally:

• 1) Titan should be called a moon or luna (Christiaan Huygens).
  2) All smaller Saturn satellites should be called stars or sidera (Giovanni Cassini).

<<Titan was discovered on March 25, 1655 by the Dutch astronomer Christiaan Huygens. Huygens was inspired by Galileo's discovery of Jupiter's four largest moons in 1610 and his improvements in telescope technology. Christiaan, with the help of his brother Constantijn Huygens, Jr., began building telescopes around 1650 and discovered the first observed moon orbiting Saturn with one of the telescopes they built. It was the sixth moon to be discovered. [Christiaan Huygens] named [Titan] Saturni Luna (or Luna Saturni, Latin for "Saturn's moon"), publishing in the 1655 tract De Saturni Luna Observatio Nova (A New Observation of Saturn's Moon). Other early epithets for Titan include "Saturn's ordinary satellite".>>

<<Sidera Lodoicea is the name given by the astronomer Giovanni Domenico Cassini to the four moons of Saturn discovered by him in the years 1671, 1672, and 1684 and published in his Découverte de deux nouvelles planètes autour de Saturne in 1673 and in the Journal des sçavans in 1686. These satellites are today known by the following names, given in 1847:

• Iapetus or Saturn VIII, discovered October 25, 1671
  Rhea or Saturn V, discovered December 23, 1672
  Tethys or Saturn III, discovered March 21, 1684
  Dione or Saturn IV, discovered March 21, 1684

The name Sidera Lodoicea means "Louisian Stars", from Latin sidus "star" and Lodoiceus, a nonce adjective coined from Lodoicus, one of several Latin forms of the French name Louis (reflecting an older form, Lodhuwig). Cassini intended the name to honor King Louis XIV of France, who reigned from 1643 to 1715, and who was Cassini's benefactor as patron of the Paris Observatory, of which Cassini was the director. The name was modelled on Sidera Medicea, "Medicean stars", the Latin name used by Galileo to name the four Galilean satellites of Jupiter, in honor of the Florentine house of Medici.

The following contemporary (1686) notice records Cassini's choice of name, and explains his rationale for the same:

In the Conclusion, the Discoverer considers that the Antient Astronomers, having translated the Names of their Heroes among the Starrs, those Names have continued down to us unchanged, notwithstanding the endeavour of following Ages to alter them; and that Galileo, after their Example, had honoured the House of the Medici with the discovery of the Satellites of Jupiter, made by him under the Protection of Cosmus II; which Starrs will be always known by the Name of Sidera Medicea. Wherefore he concludes that the Satellites of Saturn, being much more exalted and more difficult to discover, are not unworthy to bear the Name of Louis le Grand, under whose Reign and in whose Observatory the same have been detected, which therefore he calls Sidera Lodoicea, not doubting but to have perpetuated the Name of that King, by a Monument much more lasting than those of Brass and Marble, which shall be erected to his Memory.>>

moon (n.) Old English mona, from Proto-Germanic *menon- (source also of Old Saxon and Old High German mano, Old Frisian mona, Old Norse mani, Danish maane, Dutch maan, German Mond, Gothic mena "moon");" Greek mene "moon," men "month;" Latin mensis "month;" Old Church Slavonic meseci, Lithuanian menesis "moon, month;"
Extended 1655 to satellites of other planets

satellite (n.) 1540s, "follower or attendant of a superior person," from Middle French satellite (14c.), from Latin satellitem (nominative satelles) "attendant, companion, courtier, accomplice, assistant." Meaning "planet that revolves about a larger one" first attested 1660s, in reference to the moons of Jupiter, from Latin satellites, which was used in this sense 1610s by German astronomer Johannes Kepler (1571-1630). Galileo, who had discovered them, called them Sidera Medicæa in honor of the Medici family.Meaning "man-made machinery orbiting the Earth" first recorded 1936 as theory, 1957 as fact.>>

[orin stepanek]

Charon is called a " moon ", right ? And there was an asteroid discovered with a " moon "

I believe that Charon is a companion to Pluto; and also shares the planet status! Oh; its probably just me; But I don't like the terminology 'Dwarf'!

[neufer]

Charon is called a " moon ", right ? And there was an asteroid discovered with a " moon "

I believe that Charon is a companion to Pluto; and also shares the planet status!

---

<<The center of mass (barycenter) of the Pluto–Charon system lies outside either body. Because neither object truly orbits the other, and Charon has 12.2% the mass of Pluto, it has been argued that Charon should be considered to be part of a binary system with Pluto. The International Astronomical Union (IAU) states that Charon is considered to be just a satellite of Pluto, but the idea that Charon might be classified a dwarf planet in its own right may be considered at a later date. In a draft proposal for the 2006 redefinition of the term, the IAU proposed that a planet be defined as a body that orbits the Sun that is large enough for gravitational forces to render the object (nearly) spherical. Under this proposal, Charon would have been classified as a planet, because the draft explicitly defined a planetary satellite as one in which the barycenter lies within the major body. In the final definition, Pluto was reclassified as a dwarf planet, but the formal definition of a planetary satellite was not decided upon. Charon is not in the list of dwarf planets currently recognized by the IAU.[39] Had the draft proposal been accepted, even the Moon would be classified as a planet in billions of years when the tidal acceleration that is gradually moving the Moon away from Earth takes it far enough away that the center of mass of the system no longer lies within Earth. The other moons of Pluto, Nix, Hydra, Kerberos and Styx, orbit the same barycenter, but they are not large enough to be spherical, and they are simply considered to be satellites of Pluto (or of Pluto–Charon).>>

Oh; its probably just me; But I don't like the terminology 'Dwarf'!

<<The appropriate term for describing a person of particularly short stature (or with the genetic condition achondroplasia) has historically been ambiguous, and has developed euphemistically over the past few centuries. The terms "dwarf", "little person", "LP", and "person of short stature" are now generally considered acceptable by most people affected by these disorders. However, the plural "dwarfs" as opposed to "dwarves" is generally preferred in the medical context, possibly because the plural "dwarves" was popularized by author J.R.R. Tolkien, describing a race of characters in his The Lord of the Rings books resembling Norse dwarves.

The noun dwarf stems from Old English dweorg, originally referring to a being from Germanic mythology—a dwarf—that dwells in mountains and in the earth, and is associated with wisdom, smithing, mining, and crafting. The etymology of the word dwarf is contested, and scholars have proposed varying theories about the origins of the being, including that dwarfs may have originated as nature spirits or as beings associated with death, or as a mixture of concepts. The being may not have gained associations with small stature until a later period.

"Midget", whose etymology indicates a "tiny biting insect", came into prominence in the mid-19th century after Harriet Beecher Stowe used it in her novels Sunny Memories of Foreign Lands and Old Town Folks where she described children and an extremely short man, respectively. Later some people of short stature considered the word to be offensive because it was the descriptive term applied to P. T. Barnum's dwarfs used for public amusement during the freak show era. It is also not considered accurate as it is not a medical term or diagnosis, though it is sometimes used as a slang term to describe those who are particularly short, whether or not they have dwarfism.>>

[rstevenson]

... Oh; its probably just me; But I don't like the terminology 'Dwarf'!

Perhaps we should just toss that word on the dustbin of history.

Rob

[Ann]

Charon is called a " moon ", right ? And there was an asteroid discovered with a " moon "

Click to view full size image

Asteroid 243 Ida with moon Dactyl.
Photo: NASA/Galileo.

Ann