APOD: The Medusa Nebula (2012 Oct 25)

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APOD: The Medusa Nebula (2012 Oct 25)

Post by APOD Robot » Thu Oct 25, 2012 4:06 am

Image The Medusa Nebula

Explanation: Braided, serpentine filaments of glowing gas suggest this nebula's popular name, The Medusa Nebula. Also known as Abell 21, this Medusa is an old planetary nebula some 1,500 light-years away in the constellation Gemini. Like its mythological namesake, the nebula is associated with a dramatic transformation. The planetary nebula phase represents a final stage in the evolution of low mass stars like the sun, as they transform themselves from red giants to hot white dwarf stars and in the process shrug off their outer layers. Ultraviolet radiation from the hot star powers the nebular glow. The Medusa's transforming star is near the center of the overall bright crescent shape. In this deep telescopic view, fainter filaments clearly extend below and to the left of the bright crescent region. The Medusa Nebula is estimated to be over 4 light-years across.

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Re: APOD: The Medusa Nebula (2012 Oct 25)

Post by Boomer12k » Thu Oct 25, 2012 6:37 am

"The Brain From 1500 light years"....

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Re: APOD: The Medusa Nebula (2012 Oct 25)

Post by Sinan İpek » Thu Oct 25, 2012 7:57 am

What is going to happen to the gas?

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Re: APOD: The Medusa Nebula (2012 Oct 25)

Post by Indigo_Sunrise » Thu Oct 25, 2012 10:35 am

Nice image.
'Crescent shape' seems to be a bit of a stretch, though. I don't see it. :|

But it is a beautiful image.

ETA: I searched on 'Abell 21, Medusa Nebula', and came up with a few images that somewhat resembled a crescent - if I squinted my eyes, tilted my head and stood back from the monitor some. :lol2:
[Just further confirmation that things can appear differently to differnet people, I guess.]

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Re: APOD: The Medusa Nebula (2012 Oct 25)

Post by starsurfer » Thu Oct 25, 2012 12:10 pm

Sinan İpek wrote:What is going to happen to the gas?
Over a period of a few thousand years, the gas will fade away and the whole planetary nebula will dissolve into the surrounding ISM. Planetary nebulae generally have a short (on cosmic terms) lifetime of about 10 000 years although recent surveys have discovered many ancient planetary nebulae that are tens of thousands of years in age.

I was really shocked to see this as APOD today considering the image was released nearly 2 years ago, definitely long overdue for APOD!! :D

Plus the crescent shape isn't as easily visible because the image is upside down!

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Re: APOD: The Medusa Nebula (2012 Oct 25)

Post by neufer » Thu Oct 25, 2012 1:27 pm

http://en.wikipedia.org/wiki/Gorgoneion wrote: <<The Gorgon (Greek: Γοργών or Γοργώ Gorgon/Gorgo) was a terrifying female creature. The name derives from the Greek word gorgós, which means "dreadful." The term commonly refers to any of three sisters who had hair of living, venomous snakes, and a horrifying visage that turned those who beheld her to stone. Traditionally, while two of the Gorgons were immortal, Stheno and Euryale, their sister Medusa (Greek: Μέδουσα, "guardian, protectress") was not, and she was slain by the mythical demigod and hero Perseus. Thereafter used her head as a weapon until he gave it to the goddess Athena to place on her shield. In classical antiquity the image of the head of Medusa appeared in the evil-averting device known as the Gorgoneion.

In Ancient Greece, the Gorgoneion (Greek: Γοργόνειον) was a special apotropaic amulet showing the Gorgon head, used most famously by the Olympian deities Athena and Zeus: both are said to have worn the gorgoneion as a protective pendant. It was assumed, among other godlike attributes, as a royal aegis to imply divine birth or protection, by rulers of the Hellenistic age, as shown, for instance, on the Alexander Mosaic and the Gonzaga Cameo.

According to Marija Gimbutas, gorgoneia represent certain aspects of the Mother Goddess cult associated with "dynamic life energy" and asserts that the images may be related to a cultural continuity persisting since Neolithic examples. She defined the gorgoneion as a quintessentially European image. Jane Ellen Harrison, on the other hand, claims that many primitive cultures use similar ritual masks in order to scare the owner from doing something wrong, or, as she terms it, to make an ugly face at the owner: "The ritual object comes first; then the monster is begotten to account for it; then the hero is supplied to account for the slaying of the monster".

Homer refers to the Gorgon on four occasions, each time alluding to the head alone, as if she had no body. Jane Ellen Harrison notes that "Medusa is a head and nothing more... a mask with a body later appended". Prior to the fifth century BC, she was depicted as particularly ugly, with a protruding tongue, boar tusks, puffy cheeks, her eyeballs staring fixedly on the viewer and the snakes twisting all around her.

Gorgoneia that decorate the shields of warriors on mid-fifth century Greek vases are considerably less grotesque and menacing. By that time, the Gorgon had lost her tusks and the snakes were rather stylized. The Hellenistic marble known as the Medusa Rondanini illustrates the Gorgon's eventual transformation into a beautiful woman.

Gorgoneia appear frequently in Greek art at the turn of the eighth century BC. One of the earliest representations is on an electrum stater discovered during excavations at Parium. Other early eighth-century examples were found at Tiryns. Going further back into history, there is a similar image from the Knossos palace, datable to the fifteenth century BC. Marija Gimbutas even argues that "the Gorgon extends back to at least 6000 BC, as a ceramic mask from the Sesklo culture illustrates", and in her book, Language of the Goddess, she also identifies the prototype of the Gorgoneion in Neolithic art motifs, especially in anthropomorphic vases and terracotta masks inlaid with gold.

In the sixth century, gorgoneia of a canonical "lion mask type" were ubiquitous on Greek temples, especially in and around Corinth. Pedimental gorgoneia were common in Sicily; probably the earliest occurrence being in the Temple of Apollo in Syracuse. Around 500 BC, they ceased to be used for the decoration of monumental buildings, but were still shown on antefixes of smaller structures throughout the next century.

Apart from temples, the Gorgon imagery is present on dress, dishes, weapons, and coins found across the Mediterranean region from Etruria to the Black Sea coast. The Gorgon coins were struck in 37 cities, making her image on coins second in numismatic ubiquity only to several principal Olympian gods. On mosaic floors, the gorgoneion usually was depicted next to the threshold, as if guarding it from hostile intruders. On Attic kilns, the gorgoneion over the kiln door protected from mishaps.>>
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Re: APOD: The Medusa Nebula (2012 Oct 25)

Post by orin stepanek » Thu Oct 25, 2012 4:13 pm

For me Medusa doesn't really fit this Nebula; I think it really looks mor like some type of helmit! :wink:

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Re: APOD: The Medusa Nebula (2012 Oct 25)

Post by quigley » Thu Oct 25, 2012 6:10 pm

Can someone explain the sort-of striated, layered, spiral gaseous structure to the lower left of the nebula?

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Re: APOD: The Medusa Nebula (2012 Oct 25)

Post by Ptui Spitter » Fri Oct 26, 2012 4:26 pm

quigley wrote:Can someone explain the sort-of striated, layered, spiral gaseous structure to the lower left of the nebula?
The star is spinning while it's out-gassing in spurts so those layers furthest from it were spewed into the interstellar medium much earlier than the layers closest to the star in an on-going though not perfectly even process.


Re: APOD: The Medusa Nebula (2012 Oct 25)

Post by quigley » Fri Oct 26, 2012 6:20 pm

So it is a structure formed in a somewhat similar fashion as the spiral nebula surrounding Star R Sculptoris that was highlighted on the October 16th APOD?

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Re: APOD: The Medusa Nebula (2012 Oct 25)

Post by starsurfer » Mon Oct 29, 2012 1:50 pm

quigley wrote:Can someone explain the sort-of striated, layered, spiral gaseous structure to the lower left of the nebula?
Although this structure hasn't been studied in detail, it is believed to be an example of an ISM halo by professionals. It might be formed from material stripped from the planetary nebula as it interacts with the ISM and ionized by radiation leaking from the nebula! The striated appearance might be due to ISM magnetic fields. Another example of a planetary nebula with an ISM halo is HDW 2, which also has a striated appearance across its main nebular shell. A great image by Don Goldman can be seen here: http://www.astrodonimaging.com/gallery/ ... ?imgID=250

Also to answer your second question, it is similar in the fact that both are the result of stellar mass ejection. The difference is that Abell 21 is a planetary nebula, the remains of a star that has puffed off its outer layers and evolved into a white dwarf. The nebula around R Sculptoris is composed of material ejected in a thermal pulse event, something that happens before the star dies and becomes a planetary nebula. Furthermore, the spiral pattern of R Sculptoris nebula is due to the presence of a companion star.