APOD: Surprising Comet ISON (2013 Nov 30)

[APOD Robot]

Surprising Comet ISON

Explanation: After failing to appear for Sun staring spacecraft at perihelion, its harrowing closest approach to the Sun, sungrazing Comet ISON was presumed lost. But ISON surprised observers yesterday as material still traveling along the comet's trajectory became visible and even developed an extensive fan-shaped dust tail. Edited and processed to HD format, this video (vimeo, youtube) is composed of frames from the SOHO spacecraft's coronographs. It follows the comet in view of the wide (blue tint) and narrow (red tint) field cameras in the hours both before and after perihelion passage. In both fields, overwhelming sunlight is blocked by a central occulting disk. A white circle indicates the Sun's positon and scale. With questions to be answered and the tantalizing possibility that a small cometary nucleus has survived in whole or part, surprising comet ISON will be rising before dawn in planet Earth's skies in the coming days.

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[owlice]

Yowza!!! Very cool!!!

[firstmagnitude]

I think the cat analogy works well with this comet - "Comets are like cats; they have tails, and they do precisely what they want." - David H. Levy. Plus the fact that this comet has 9 lives like a cat works well too.

[StarTrailer]

Awesome video! But what is the sound and from where is it coming? Will try to see Ison in the AM if the weather in western PA ever clears.

[BMAONE23]

Looks more and more like the Comet actually evaporated but only well after perihelion

[MargaritaMc]

http://earthsky.org/space/big-sun-divin ... ar-in-2013

There is an interesting video at this link, which seems to show the brightening clearly. The video has to be downloaded to view. (That is, on my Android tablet, I could only view it by downloading the file and playing it with MX Player.)
M

[Boomer12k]

It is interesting that the tail does not point directly away from the sun....as is sometimes depicted in drawings and things...


:---[===] *

[Boomer12k]

I don't really recommend "Sundiving".....Bad for your complexion....

:---[===] *

[neufer]

It is interesting that the tail does not point directly away from the sun....as is sometimes depicted in drawings and things...

:---[===] *

At perihelion the comet was moving faster than the solar wind.

[BMAONE23]

Latest SOHO image shows what appears to be only a debris field

Click to view full size image

No more apparent bright Coma
The latest GIF shows dispersal with a diffuse and darkening coma

[Chris Peterson]

It is interesting that the tail does not point directly away from the sun....as is sometimes depicted in drawings and things...

:---[===] *

At perihelion the comet was moving faster than the solar wind.

More or less. The perihelion speed was 370 km/s. The densest solar wind has a speed of about 400 km/s, with faster winds from coronal holes about twice that. Material from CMEs can move in excess of 1000 km/s.

Of course, the comet did not need to exceed the speed of the solar wind to show a substantial apparent deflection in the direction of its ion tail.

That said, I think we are seeing a dust tail in these images, and the dust tail isn't affected by the solar wind, but by radiation pressure. That doesn't provide much force, so near the Sun we see the dust trail virtually in the same orbit as the comet, and not pointing away from the Sun much at all.

[Myrkle]

I just reviewed the 3-day video of perihelion available at SpaceWeather.com, and, given how quickly it is fading, comet ISON should be renamed comet Icarus...

[BMAONE23]

There once was a Comet named ISON
Twas promised "The best you'll lay Eyes on"
although near the end
it did brighten again
it fizzled out into a Bye-Gone

[Zerosan]

Is the sound actual recording? Is this what space sounds like? Amazing Video!

[owlice]

If you will watch to the end of the video, you will see where the audio for this video comes from.

[Ann]

ISON is like Bison?

http://en.wikipedia.org/wiki/American_bison wrote:

The American bison (Bison bison), also commonly known as the American buffalo, is a North American species of bison that once roamed the grasslands of North America in massive herds, became nearly extinct by a combination of commercial hunting and slaughter in the 19th century and introduction of bovine diseases from domestic cattle, and has made a recent resurgence largely restricted to a few national parks and reserves.

Only smithereens are left.

Ann

[Beyond]

ISON is like Bison



REALLY

[neufer]

ISON is like Bison REALLY

It sure had us all buffaloed

[neufer]

It is interesting that the tail does not point directly away from the sun....as is sometimes depicted in drawings and things...

:---[===] *

At perihelion the comet was moving faster than the solar wind.

More or less. The perihelion speed was 370 km/s. The densest solar wind has a speed of about 400 km/s, with faster winds from coronal holes about twice that. Material from CMEs can move in excess of 1000 km/s. Of course, the comet did not need to exceed the speed of the solar wind to show a substantial apparent deflection in the direction of its ion tail. That said, I think we are seeing a dust tail in these images, and the dust tail isn't affected by the solar wind, but by radiation pressure. That doesn't provide much force, so near the Sun we see the dust trail virtually in the same orbit as the comet, and not pointing away from the Sun much at all.

There certainly was a recent CME in the vicinity

however, the super-sonic solar wind is rather difficult to define closer than 10 solar radii:

[b][color=#0000FF][size=115]Super-sonic solar wind Parker solution V as a function of radiu[/size]s[/color][/b] [img]http://www-solar.mcs.st-and.ac.uk/~alan/sun_course/Chapter6/img60.gif[/img]

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Parker's solar wind model

<<Parker (1958) suggested that the corona could not remain in static equilibrium but must be continually expanding since the interstellar pressure cannot contain a static corona. The continual expansion is called the solar wind. The existence of a solar wind had been known from comet observations but the properties predicted by Parker were confirmed by the satellites Lunik III and Venus I in 1959 and by Mariner II in the early 1960s. The main assumptions of Parker's model are that the outflow is steady, spherically symmetric and isothermal. It is straightforward to relax the isothermal assumption and consider an adiabatic or polytropic atmosphere.


where C is a constant.

Five distinct types of solutions for different values of C are indicated. Solution I is doubled valued and so is unphysical. It is not possible for the plasma to leave the solar surface with a velocity below the sound speed, reach a maximum radius below r_c and then turn round and return to the Sun with a super-sonic speed. Solution II is also double valued but it never even starts from the solar surface and it is also unphysical. Solution III starts with a velocity greater than the sound speed but such a fast steady outflow is not observed. Hence, this solution must also be neglected. The only two types of solution that are physically reasonable at this stage are IV and V. Solution V is the particular case where the plasma leaves the solar surface with a particular speed and passes through the critical point (also called the sonic point) at r = r_c and v = c_s. Solution IV always remains below the sound speed and is called the solar breeze solution. For solution V we choose the constant C so that r = r_c and v = c_s and this requires C = -3. Is it possible to decide between solutions IV and V?

Assuming a typical coronal temperature of 10⁶K the sound speed is





The real solar wind does not come from the whole of the solar surface but only from the coronal hole regions where the magnetic field is open. This is only about 20 percent of the whole surface. The strong magnetic field of the other 80 percent is closed and effectively holds in the hot corona.>>

[geckzilla]

ISON is like Bison REALLY

It sure had us all buffaloed

You had an opportunity to reference this and you didn't?

[Beyond]

The Indians avoid all that Buffalo Bull. They call Bison... Tatonka.

[neufer]

[b]geckzilla wrote: [color=#0000FF][i]You had an opportunity to reference this and you didn't?[/i] :D[/color][/b]

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ISON is like Bison REALLY

It sure had us all buffaloed

The Indians avoid all that Buffalo Bull.
They call Bison... Tatonka.

<<On September 18, 1946, Mound Metalcraft was created in Mound, Minnesota to produce metal tie-racks. But the building's former occupant, the Streater Company, had made and patented several toys and the men at Mound Metalcraft thought that toys might make a good side line business. So the company began selling metal toys under a new logo: the Dakota Sioux word "Tanka" or Tonka, which means "Great" or "Big".

[Chris Peterson]

The Indians avoid all that Buffalo Bull. They call Bison... Tatonka.

If you haven't had these, you don't know what you're missing.

[Beyond]

And don't forget the beer-->
I didn't realize there were soooo many variations of Tatonka.

[Wildbegonia]

Thank you for sharing this stunning images. I love the background electroacoustic music too. Who's credit is it?
More, more and more of the beauty and mystery above us.