Explanation: Sweeping slowly through the constellation Hercules, Comet Garradd (C2009/P1) passed with about 0.5 degrees of globular star cluster M92 on February 3. Captured here in its latest Messier moment, the steady performer remains just below naked-eye visibility with a central coma comparable in brightness to the dense, well-known star cluster. The rich telescopic view from New Mexico's, early morning skies, also features Garradd's broad fan shaped dust tail and a much narrower ion tail that extends up and beyond the right edge of the frame. Pushed out by the pressure of sunlight, the dust tail tends to trail the comet along its orbit while the ion tail, blown by the solar wind, streams away from the comet in the direction opposite the Sun. Of course, M92 is over 25,000 light-years away. Comet Garradd is 12.5 light-minutes from planet Earth, arcing above the ecliptic plane.
Well...OK....I am going to put the myth that there are no stupid questions to the test....
"Pressure from Sunlight", and "Solar Wind"....they appear to do the same thing...but evidently are NOT the same thing?
Because are not both going "OUTWARD" from the sun? So should not both tails be pointing at least more or less in the same direction?
Or does it have to do with the masses and density of the materials in each tail? The denser dust tends to follow the comet, while IONS, are affected outward from the sun...
Shouldn't they BOTH be affected outward?
:---[===] *
Re: APOD: Comet Garradd and M92 (2012 Feb 04)
Posted: Sat Feb 04, 2012 11:50 am
by Flase
Ions are electrically charged, so they are influenced by other charged particles in the solar wind, so these tails point away from the Sun.
The dust tail is just left behind by the comet, boiled off or something by the proximity to the Sun, so it's left in the comet's path and shows where it's been.
It all dissipates with time. Some little lumps of dust become meteors
Re: APOD: Comet Garradd and M92 (2012 Feb 04)
Posted: Sat Feb 04, 2012 3:22 pm
by Chris Peterson
Boomer12k wrote:Well...OK....I am going to put the myth that there are no stupid questions to the test....
"Pressure from Sunlight", and "Solar Wind"....they appear to do the same thing...but evidently are NOT the same thing? :?
Because are not both going "OUTWARD" from the sun? So should not both tails be pointing at least more or less in the same direction?
Or does it have to do with the masses and density of the materials in each tail? The denser dust tends to follow the comet, while IONS, are affected outward from the sun...
Shouldn't they BOTH be affected outward?
The solar wind consists of charged particles leaving the Sun at relatively low speed compared with the speed of light. Solar radiation is photons, which of course do travel at the speed of light. They are completely different things. Both the solar wind and solar radiation move outwards.
Dust ejected from the comet is massive, and in the absence of other forces would simply continue in orbit with the nucleus, spreading slowly forwards and back depending on the direction it was ejected. Radiation pressure, and to a lesser extent solar wind, do slow down the dust, which moves it outward and results in a tail substantially along (and behind) the orbit of the nucleus. Lighter dust is pushed more outwards, heavier dust stays closer to the original orbit. The dust tail never points directly away from the Sun, but lies on some angle between that and the comet's orbit. The situation with gas coming from the comet is different. Being very low mass, it is strongly affected by the solar wind (but not much by solar radiation), so it blows almost directly away from the Sun.
Re: APOD: Comet Garradd and M92 (2012 Feb 04)
Posted: Sat Feb 04, 2012 3:40 pm
by biddie67
Thanks Chris ~~ very helpful ~~ I was having trouble distinguishing between the 2 forces.
Re: APOD: Comet Garradd and M92 (2012 Feb 04)
Posted: Sat Feb 04, 2012 4:48 pm
by Batjac1
Good, I feel better now - thought tht's what a comet might look like if it was seen head on...
This lovely image of Comet Garradd (C/2009 PI) as it passes by the globular cluster M92 in the constellation Hercules, was taken remotely from the Tzek Maun Observatory in New Mexico by our friends Giovanni Sostero, Ernest Guido and Nick Howes. While the two objects look like they are right next to each other, M92 is over 25,000 light-years away while Comet Garradd is 12.5 light-minutes away from Earth! The comet looks almost like a bird or winged starship in flight with the dust tail and ion tail shooting off on either side. Comet Garradd is still on show in the northern hemisphere, although you’ll at least need binoculars to see it. The comet is around magnitude 7 now, and is heading north, so over the course of the next few weeks, it should become a little easier to see. For now, you need to get up early to see it, (around 5:30 to 6:30 am), but by the end of the month it should be visible all night long.
You can see another image of Garradd on today’s APOD (but personally I really like the one right here!)
Comet Garradd and M 92 are a interesting image.
Distance from Earth to M 92 25,000 light-years.
Distance from Earth to Comet Garradd 12.5 light-minutes ( 1.5 times the distance from Earth to the Sun).
I like the subtle colors here. The comet's coma is green, the dust tail is yellow-white and the straight narrow ion tail is blue.
Ann
Comment Gérard 'n Depardieu
Posted: Sun Feb 05, 2012 8:21 pm
by neufer
Click to play embedded YouTube video.
Re: APOD: Comet Garradd and M92 (2012 Feb 04)
Posted: Sun Feb 05, 2012 8:39 pm
by owlice
neufer, that's a great clip. Thank you for posting it!
Re: APOD: Comet Garradd and M92 (2012 Feb 04)
Posted: Tue Feb 07, 2012 9:20 pm
by bosonm
M92 is so damned beautiful it touches something deep inside me I can't adequately explain - it's almost a longing feeling, like I'm looking at my long, lost home, the place where I really belong. Actually, viewing most globular star clusters gives me that feeling. Weird.
I'm not an astronomer, not even an amateur one but I love APOD and have been visiting this sight nearly everyday since I first discovered it back in 1995. It has been a source of immense wonder and awe and learning. Which brings me to my question: Is there a powerful gravitational force inside the cluster that was instrumental in its formation, or was it the result of a super-dense dust cloud that collapsed into a group of original stars that began a chain reaction of star formation?
Re: APOD: Comet Garradd and M92 (2012 Feb 04)
Posted: Tue Feb 07, 2012 9:37 pm
by Chris Peterson
bosonm wrote:Which brings me to my question: Is there a powerful gravitational force inside the cluster that was instrumental in its formation, or was it the result of a super-dense dust cloud that collapsed into a group of original stars that began a chain reaction of star formation?
Nobody understands much about how globular clusters form. Although there are a handful of them which appear to contain massive black holes, most do not, and therefore probably do not form as the result of any unusual internal gravitational forces. Most likely their formation is tied to the presence of a rich interstellar medium, and interactions with galaxies- either during their formation or subsequent collisions with other galaxies. But beyond that very general idea, who knows?
Re: APOD: Comet Garradd and M92 (2012 Feb 04)
Posted: Tue Feb 28, 2012 3:04 pm
by fox17
I am curious, having only ever witnessed one comet in my life, I saw it with the naked eye, that was a super bright comet, passed in the late 1990's. So I am really curious to see another any idea where I could find it and at what time I would have to look for it. I live in Belize Central America, so the nights are fairly dark. So I am hoping I could get a genreal description when and where to look, for an amateur like me.
Re: APOD: Comet Garradd and M92 (2012 Feb 04)
Posted: Tue Feb 28, 2012 7:47 pm
by Chris Peterson
fox17 wrote:I am curious, having only ever witnessed one comet in my life, I saw it with the naked eye, that was a super bright comet, passed in the late 1990's. So I am really curious to see another any idea where I could find it and at what time I would have to look for it. I live in Belize Central America, so the nights are fairly dark. So I am hoping I could get a genreal description when and where to look, for an amateur like me.
There are many finder charts available on the Internet, such as this one, which is available here. The comet is a pretty easy binocular object right now. Look for it between midnight and dawn between Draco and the bowl of Ursa Minor.
You may or may not be able to make out a hint of tail structure; probably you should expect just to see the fuzzy spot of the coma. Certainly, this is nothing like Hyakutake or Hale-Bopp in the late 1990s, one of which is probably what you saw back then.
Comet Garradd and M92
