Robittybob1

Yes it is rather good reading. I read a bit about sputtering and loss of mass of a dust particle as it spiraled in from 2 AU to 1 AU. Home time.

How reliable is that information. Fracking depths would not be significant to the depths of earthquakes. www.forbes.com/sites/timworstall/.../ten-things-to-know-about-fracking/

That was a book; 242 pages of difficult maths!

Take your washing off the line first! May, June, July and August. Too cold to sit on the ground in those months around here. That is a good one!

Where is that?

Trying to get some basic understanding of these 4 things and came across this YT introduction to the Solar Wind "Solar Wind Introduction | Sun Series 1" It is only a couple of minutes long but it will make you think. Why does the Solar Wind contain all the known elements ( I could only imagine those comets being blasted back into space in the form of molecules. Sorry about that.) How come the Solar Wind is not affected by the gravitation of the Sun? I've asked this question before (another forum) and never got an answer.This section from Wikipedia covers it a bit but maybe it isn't known yet. http://en.wikipedia.org/wiki/Solar_wind#Emission The Solar wind particles seems to be able to be accelerated beyond the escape velocity of the Sun, (solar escape velocity of 618 km/s). Radiant Pressure: http://en.wikipedia.org/wiki/Radiation_pressure Either way! "Spiral into the Sun" is obviously a reference to the P-R effect. If the P-R effect was really significant there would be no clearing of the inner Solar system while there is still major dust further out! Well that's what I think at this stage but still researching. That looks like radiant pressure is the dominant effect over all.

It could be greater than the PR effect. This is such a detailed discussion and I need some time to look into it. I'm at work and I have other things to do but I'll research it later and get back to you. One thing I feel certain about is that the orbital motion of the dust is what overcomes the force of gravity, so then it is a matter of what additional effects upset this balance. 1. Slowing due to the PR effect 2. Promotion due to this other Blueshift effect 3. Radiant pressure 4. Solar wind

That was a helpful answer. I can see where you are coming from regarding the size of the particles. The direction of the emitting source on average might be "radially outward", but as the Sun rotates on it axis from the West to the East, as does the Earth, photons from the west (side going toward any dust particles) will have a slightly higher frequency than the ones coming from the Eastern side (side going away from dust particles). If this is correct the radiant pressure should promote dust in its orbital path. Radiant power must be the summation of the power in all the individual photons and their wavelengths.

We see the comet fall towards the Sun and then we see this plume of matter being ejected from the Sun. Both aspects are seen and I believe they are causaully related. Yes that's right, but do you agree the photons from the Sun will have different energy values depending on the direction of the emitting source?

OK if temperatures are involved the light energy must be absorbed rather than reflected. I disagree about your momentum statement. Momentum of a photon is proportional to its frequency. http://en.wikipedia.org/wiki/Photon Its velocity is always c but when emitted from a moving source the moving source will increase the photon's frequency.

I wonder if the solar radiation pressure will not always swamp out the PR effect. It has really got me baffled for I know about the aberration of light and how the apparent incident angle changes, so I don't have a problem with that, but what I couldn't understand was what was the interaction of the photon with the dust particle? Was it reflection or absorption? The Sun is rotating WRT to the Solar System (the equatorial regions take about a month (26 days?) to transit the circumference of the Sun), so the radiation coming off the Sun should be blueshifted for the photons that come off in the direction of rotation and redshifted for the opposite direction, so any interaction with dust particles will reflect this imbalanced momentum. Does the PR effect take that into account?

The speaker thought they could not be formed there, therefore moved there, but could it not have formed there prior to the star going thermonuclear?

Look at those video clips, there is a huge and rapid movement of mass away from the Sun associated with the comet impact. The Poynting Robertson effect (PR) (inward) only deals with a particular sized particle and all other sizes are driven the other way (outward). It has really upset me and I am determined to look into it again. Now seeing is scientific surely. Even on the outward leg of a comet's journey the tails are pointing (predominantly) away from the Sun. Now you give me a scientific reason why the dust particles will at some stage change direction and go toward the Sun. My "beg to differ" was a challenge to the poster's (pavelcherepan) opinion. He expressed an opinion and I begged to differ. (What was that negative score for?)

If they found granules embedded in the felled trees that would be pretty convincing evidence. But I beg to differ as to whether the same would occur on the Sun.

What we are trying to discover is the physics of this situation which has become visible through these very recent photos of comets crashing into the Sun. At first glance one might think the comet has crashed into the Sun but look at it again and again and the timing of the jet of matter being jettisoned from the Sun at the very time the comet impacts shows they generally disintegrate and are thrown back out into space by the radiation pressure and the solar wind. Radiation pressure and the solar wind acting on the comet is the same mechanism behind the production of the comet's tail as well. OK there is the issue of the magnetic field lines to get your head around as well. http://en.wikipedia.org/wiki/Tunguska_event The Tunguska event maybe similar to this where a comet is thought to have exploded in the atmosphere rather than hitting the ground. I am in full agreement with what you say here.

Not really, as they have been filmed to "fall into the Sun". The same mechanism that forces the dust tail so far from the body is the same reason that makes it very difficult for the mass of a comet to add to the mass of the Sun.

Acme - I think you need to be able to explain how the dust tail gets so far out from the comet body.

So is the comet tail tagging along with the comet and not just something streaming out behind it? Water molecules won't be orbit the Sun surely not so some part of the tail can't be following it in orbit. I don't believe orbital motion will explain how a comet tail moves. What do you reckon?

I have often wondered how they work? So could we say they are slowly being pushed further out into the SS? No it sounds like the chunks that come off a disintegrating comet orbit the Sun just like the comet did? That is hard to believe! Lyrids http://en.wikipedia.org/wiki/Lyrids I don't quite understand that as yet. If they fall into the Sun yes I agree but what I saw in most of those clips I think the comet disintegrates and burns up without falling into the Sun. I'm not sure how we can really tell for certain.

But then it could be argued that a distant planet doesn't know if the inner planets are part of the Sun or not too. Is that because the distant planet lacks the ability to separate out those gravitational effects, whereas we can see what is happening? We see the comet grazing past the Sun or we see the comet is evaporated and the plasma carried off by the solar wind so I'd say it never became part of the Sun. But we'd all agree there would be masses large enough to resist total evaporation and that residual bit would sink into the substance on the Sun. Compare this to when Shoemaker-Levy 9 comet crashed into Jupiter, even though that created an enormous series of explosions one presumes Jupiter gained mass from that. Found an article that may explain it: "Comets, Asteroids, Meteorites and Impacts" http://www.uni.edu/morgans/astro/course/Notes/section4/new22.html It is obvious that this "blown off" effect gets more intense as the comet gets closer to the Sun I didn't know this next bit: Well it is still a bit contradictory as to what happens to the heavier elements. Are these two tails of a comet also visible on the leg where the comet is going away from the sun? If it is then even the heavier elements are blown away from the Sun faster than the comet is moving.

It must be because everything is moving along with you at the same rate whereas on the bike you are moving (relatively) and everything else is not.

Are you meaning temporarily while the evaporated mass is further in than that other stuff that is gravitationally attracted to it? I agree with you, but that would just be for a short time until it travelled out far enough. Well when do you think the incoming comet adds to the gravitational effect? It must be before the impact and before the vaporization too then. Surely you're not going to argue that the comet has added to the mass of the Sun before the impact.

It would just move out to a higher orbit where the escape velocity is less.

They would be time lapse movie clips, wouldn't they. So yes the collision and vaporization would not happen as fast as it appears in those clips. This is what I was querying. I think if there was vaporisation before entering the substance of the Sun maybe it is just blown away and not added to the mass of the Sun. I tend to think you are wrong about saying the mass is added regardless where the vaporization occurs. (That would be a difference between the Sun and a planet.)

Looking at these clips over and over I would say a comet explodes as it nears the Sun and very little of the mass of the comet actually enters the Sun, if any, the majority is evaporated and drifts off with the radiation pressure. Very interesting.