APOD: PanSTARRS Anti Tail Grows (2013 May 26)

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APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby APOD Robot » Sun May 26, 2013 4:07 am

Image PanSTARRS Anti Tail Grows

Explanation: As planet Earth approached the plane of the Comet PanSTARRS (C/2011 L4) orbit on May 23rd, comet watchers were treated to this view of its magnificent anti-tail. The long, narrow anti-tail stretches to the right across this frame for nearly 4 degrees or about 8 times the angular size of the full Moon. The tail trails along the comet's orbit as it leaves the inner solar system behind. An almost edge-on perspective from near the outbound comet's orbital plane enhances the view of the anti-tail and makes it seem to point in the sunward direction, only apparently contrary to the behavior of comet dust tails pushed outward by the pressure of sunlight. Sweeping far north in planet Earth's skies, the comet is up all night for most of the northern hemisphere, but now bright moonlight interferes with its visibility. PanSTARRS anti-tail is one of the longest since the appearance of Comet Arend-Roland in 1957.

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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby alter-ego » Sun May 26, 2013 5:03 am

Wow! That is really something!
I clicked through hoping to see whole tail :(
It's funny, not seeing the end of the anti-tail is like listening to a musical piece that doesn't end on it's tonic.
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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby Willy » Sun May 26, 2013 10:08 am

Today's image is beautiful and very special, that's a huge tail.

I find that this picture reveals the anti tail better:

Image
Comet C/2011 L4 Panstarrs Widefield False Color - May 23, 2013 by Joseph Brimacombe, in Flickr.

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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby Boomer12k » Sun May 26, 2013 11:02 am

Wow!!!!! Go, Comet, Go!!!!!!

That is awesome, as you would think the tail should shrink as it gets father away....but maybe it is the angle of the picture....

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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby orin stepanek » Sun May 26, 2013 11:12 am

PanSTARRS putting on quite a show! :D
Orin

Smile today; tomorrow's another day!

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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby markc » Sun May 26, 2013 2:03 pm

What are the two tracks on the right of the image?

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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby papamattic » Sun May 26, 2013 2:09 pm

can anyone identify the x feature in the upper right hand of the negative in todays image ?

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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby Chris Peterson » Sun May 26, 2013 2:16 pm

markc wrote:What are the two tracks on the right of the image?

papamattic wrote:can anyone identify the x feature in the upper right hand of the negative in todays image ?

Almost certainly they are satellite trails. Hard to avoid in a single long exposure with a wide field.
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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby R C » Sun May 26, 2013 4:50 pm

IMHO The Post Seems To Hold Some Confusion About The Dust Content Of An ION Tail.
I Was Taught An Ion Tail Is Comprised Mostly Of IONS Not Dust.
I Have Learned About The Ion Tail Also The Dust Tail. I Ever Heard Of any supposed 'anti tail'.

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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby kruppml » Sun May 26, 2013 8:00 pm

What is an "anti tail" and how is it produced? Why don't we see the main tail in this picture? Or is the tail shown called an "anti tail" because it seems to extend in the direction the comet is moving?

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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby JohnD » Sun May 26, 2013 8:44 pm

Thank you! That explanation makes the 'anti-tail' concept clear to me!
JOhn

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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby gowron007 » Sun May 26, 2013 11:23 pm

A comet has 3 types of tails:

- Dust tail: material blown off the comet by solar wind, proximity to the sun tends to move the tail in opposite direction to it and losing that proximity tends to move the tail towards the comet's trail

- Ion tail: similar to dust tail only composed of ionised gas which is affected allot stronger by the solar wind and has a trajectory opposite to the sun

- Anti tail: a tail pointing directly towards the sun, causes for it are largely unknown; as suggested in today's picture explanation it is merely an apparence caused by large particles orbiting the comet, visible when crossing the plane of the comet(explanation which i find lacking); another idea is that the comet is acting like an electrical component and that's why the anti tail forms(for more on the subject go to "Comet Lovejoy Wrap-up" on youtube)

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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby Chris Peterson » Mon May 27, 2013 1:32 am

gowron007 wrote: - Dust tail: material blown off the comet by solar wind, proximity to the sun tends to move the tail in opposite direction to it and losing that proximity tends to move the tail towards the comet's trail

The dust trail sweeps backward because solar radiation pushes the tiny dust particles into a larger orbit, which necessarily means the particles move more slowly than the nucleus.

- Ion tail: similar to dust tail only composed of ionised gas which is affected allot stronger by the solar wind and has a trajectory opposite to the sun

That is, pointing away from the Sun.

- Anti tail: a tail pointing directly towards the sun, causes for it are largely unknown; as suggested in today's picture explanation it is merely an apparence caused by large particles orbiting the comet, visible when crossing the plane of the comet(explanation which i find lacking); another idea is that the comet is acting like an electrical component and that's why the anti tail forms(for more on the subject go to "Comet Lovejoy Wrap-up" on youtube)

The cause of an antitail is not unknown at all. It is completely understood as a projection against the sky, pointing toward the Sun, of large particles ejected earlier (which is why we see antitails after perihelion, because otherwise there isn't enough time to allow for the necessary spreading). I believe the author of the video is misidentifying something on the video as an antitail, when it isn't.
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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby JohnD » Mon May 27, 2013 8:56 am

Thank you Chris for further detailed explanation.
I fear that gowron suffers from a wide spread misapprehension that comets can have three types of tail, so widespread that the Wiki article begins, "An Antitail is a term used in astronomy to describe one of the three tails, all pointing in different directions, which may appear to emanate from a comet."

As diagrams can help when many words do not, I refer the bewildered to another page on the Wiki, that shows how an ion tail can appear to point forward from the comet, while a dust tail appears to point back at the sun. http://commons.wikimedia.org/wiki/File:Anti_tail.gif

John

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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby Chris Peterson » Mon May 27, 2013 5:00 pm

JohnD wrote:I fear that gowron suffers from a wide spread misapprehension that comets can have three types of tail, so widespread that the Wiki article begins, "An Antitail is a term used in astronomy to describe one of the three tails, all pointing in different directions, which may appear to emanate from a comet."

Well, it is a little confusing. There are only two physical kinds of tails, the dust and ion. But there are at least three apparent types of tails. So whether you argue for two or three tail types really depends on the context of the discussion.
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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby DavidLeodis » Mon May 27, 2013 5:24 pm

In information with the image in the Flickr website (brought up through the "treated to this view" link) it states the image is a 30 minutes exposure taken May 23 2013 at "10h 07m UT (mid-point)". I've found that on that date New Mexico was under Daylight Saving Time which was 6 hours behind Universal Time (UT), so the mid-point under the local time would have been 4:07. As I thought that would be dawn at this time of year in New Mexico I am wondering if it was as dark then as the image implies, as I would have expected it not to be. Thanks for any clarification.

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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby Chris Peterson » Mon May 27, 2013 5:47 pm

DavidLeodis wrote:In information with the image in the Flickr website (brought up through the "treated to this view" link) it states the image is a 30 minutes exposure taken May 23 2013 at "10h 07m UT (mid-point)". I've found that on that date New Mexico was under Daylight Saving Time which was 6 hours behind Universal Time (UT), so the mid-point under the local time would have been 4:07. As I thought that would be dawn at this time of year in New Mexico I am wondering if it was as dark then as the image implies, as I would have expected it not to be. Thanks for any clarification.

On that day, astronomical twilight at NMS began at 04:18 local, so the entire image was made under dark skies. Sunrise was at 05:57.
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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby DavidLeodis » Mon May 27, 2013 6:18 pm

Thanks for that Chris, which is appreciated. :)

I did not think it would be so dark there then.

gowron007

Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby gowron007 » Mon May 27, 2013 10:04 pm

I hope you got to the part in the video where you see the comet has 3 tails and the one pointing towards the sun can in no way be the end of the dust tail lagging behind and appearing in front of the comet from the viewers perspective simply because if it were so, the so called anti tail should have appeared to the right of the comet, not in front of it pointing directly to the sun. Sure, your graph probably applied very well to other sightings, but this one is in complete contradiction to that idea and you shouldn't toss it aside just because it won't fit your theory.

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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby Chris Peterson » Mon May 27, 2013 10:21 pm

gowron007 wrote:I hope you got to the part in the video where you see the comet has 3 tails and the one pointing towards the sun can in no way be the end of the dust tail lagging behind and appearing in front of the comet from the viewers perspective simply because if it were so, the so called anti tail should have appeared to the right of the comet, not in front of it pointing directly to the sun.

We commonly see "tails" like that in SOHO videos, where the comets are very overexposed. Sometimes they are optical artifacts, sometimes they are short-lived jet structures. Sometimes they are true antitails.

There is no mystery at all to comet antitails. Indeed, one can apply known mathematical models which describe how different sized particles are ejected and respond to solar radiation pressure, and see exactly how the planar nature of the debris stream develops. It is that planar nature that is responsible for the illusion of the antitail.

BTW, the video seems focused on the position of the comet with respect to the Earth's orbital plane. That is irrelevant to the visibility of an antitail. The antitail becomes apparent when the viewer is on the comet's orbital plane. We are seeing the antitail of C/2011 L4 right now because Earth is on the comet's orbital plane. The comet itself is very far off of Earth's orbital plane. If we see an antitail in a STEREO or SOHO image, it's because the instrument is on the comet's orbital plane (which doesn't mean the Earth is).
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Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby gowron007 » Mon May 27, 2013 10:47 pm

Precisely why I specified "viewers perspective", there was no need for further explanation regarding earth's position since it has nothing to do with it (I know SOHO is in H1). Sorry for not clarifying my statement, I am in no way supporting the one in the video about that aspect. What i am "attacking" is the explanation given in the graph by JohnD. As can be seen in the vid when that thing appears in front of the comet, the dust tail is not directly behind the comet... yes it is rather, close but that small inclination would make the far end of the dust tail that supposedly forms the anti tail show up to the right of the comet, not in front of it.
Actually if i think about it, that graph would look the way it does only if the viewer is located between the comet and the sun, as we know SOHO is looking directly at the sun, so it is clearly not the case.

gowron007

Re: APOD: PanSTARRS Anti Tail Grows (2013 May 26)

Postby gowron007 » Sat Jun 01, 2013 12:26 pm

*L1


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