Who said that old data cant be interesting?
http://www.spacedaily.com/news/lunar-05zzzc.html
Full Version: Moon Storms?
Strange indeed.
It is generaly accepted that dust cannot stay in the "air" on the Moon, it falls as quickly as a lead block, and cannot form curls like in Earth atmosphere.
But static electricity may indeed raise tiny particles of dust, and make them hover like in an atmosphere. After, the dust grains get discharger by solar UV and they fall. But why would they raise in the morning? Perhaps solar wind reverts charges on the surface. Perhaps solar wind creates these charges.
Strange electrostatic clouds.
It is generaly accepted that dust cannot stay in the "air" on the Moon, it falls as quickly as a lead block, and cannot form curls like in Earth atmosphere.
But static electricity may indeed raise tiny particles of dust, and make them hover like in an atmosphere. After, the dust grains get discharger by solar UV and they fall. But why would they raise in the morning? Perhaps solar wind reverts charges on the surface. Perhaps solar wind creates these charges.
Strange electrostatic clouds.
This is truly amazing!
QUOTE (dilo @ Dec 13 2005, 04:34 PM)
This is truly amazing!
Bit more detail here.
http://science.nasa.gov/headlines/y2005/30...onfountains.htm
This could have profound consequences for long term power generation from solar cells set up in islands of constant light as found near the poles and any missions that stays for more than a few days. A similar problem may be encoutered when trying to land on asteroids, possibly??? even Hayabusa in its recent landing attempt. It had problems before it attempted to land but this seemed to fall apart when its made those gentle touchdown.
I think we can posit the following scenario:
1) solar wind creates the charges
2) charged particules hover above the surface, lke a gaz
3) solar UVs discharge the particules which fall again on the ground, sticking everywhere.
It would be interesting to know what happens when there is the full moon.
At this time the Moon enters the Earth's magneto-tail, a region of highly turbulent solar wind, which may even contain bubbles of plasmas (plasmoids). So there may be regions of higher density of solar wind, producing high dust storms, and eventually fluorescence.
Is not this what was sometimes observed as "Unidentified Lunar Events" (ULE) or "Lunar Transcient Phenomena" such as
-regions becoming blurred for some minutes (Plato tiny craters become invisible)
-lighs (often red) appearing over certain regions (some points are prone to this, like Aristarcus or Alphonsus)
-Even UFO-like lights moving fast against the Moon background.
All this could be produced by higher density strands of plasma hitting the Moon surface, giving dust storms and... auroras. Especially at the full moon.
Note that, in order to be visible against the sunny full Moon soil, these auroras must be much more luminous than ours.
1) solar wind creates the charges
2) charged particules hover above the surface, lke a gaz
3) solar UVs discharge the particules which fall again on the ground, sticking everywhere.
It would be interesting to know what happens when there is the full moon.
At this time the Moon enters the Earth's magneto-tail, a region of highly turbulent solar wind, which may even contain bubbles of plasmas (plasmoids). So there may be regions of higher density of solar wind, producing high dust storms, and eventually fluorescence.
Is not this what was sometimes observed as "Unidentified Lunar Events" (ULE) or "Lunar Transcient Phenomena" such as
-regions becoming blurred for some minutes (Plato tiny craters become invisible)
-lighs (often red) appearing over certain regions (some points are prone to this, like Aristarcus or Alphonsus)
-Even UFO-like lights moving fast against the Moon background.
All this could be produced by higher density strands of plasma hitting the Moon surface, giving dust storms and... auroras. Especially at the full moon.
Note that, in order to be visible against the sunny full Moon soil, these auroras must be much more luminous than ours.
Note that the brightness of the post-sunset glow observed by Surveyors was low. I believe it required long exposures relative to daytime shots. The viewing is optimum for observing fine dust: near 180 degrees phase angle, where diffraction effects are strong (like cirrus clouds 5 or 10 degrees from the sun in the sky, or like Jupiter's normalloy nearly invisible dust rings in Voyager and later mission's images taken from the nightside looking up-sun) The total optical depth of the suspended dust is probably very small.
The existance of Lunar Transient Phenomena is still unresolved. Impact flashes have certainly been observed from Earth in recent years, especially during meteor showers like the Leonids. The transient phenomena have never clearly been observed except by visual observers. There was a program back in the ?mid 70's? to observe the moon with a digital imaging system on a telescope and use image processing techniques to look for short term variability, but I never heard any significant positive results from it.
You really need a small telescope in the Earth-Moon L-1 point or something as a stable platform to take high signal-to-noise observations with maybe 1/10 km resolution.
The existance of Lunar Transient Phenomena is still unresolved. Impact flashes have certainly been observed from Earth in recent years, especially during meteor showers like the Leonids. The transient phenomena have never clearly been observed except by visual observers. There was a program back in the ?mid 70's? to observe the moon with a digital imaging system on a telescope and use image processing techniques to look for short term variability, but I never heard any significant positive results from it.
You really need a small telescope in the Earth-Moon L-1 point or something as a stable platform to take high signal-to-noise observations with maybe 1/10 km resolution.
QUOTE (Richard Trigaux @ Dec 13 2005, 08:43 PM)
I think we can posit the following scenario:
1) solar wind creates the charges
2) charged particules hover above the surface, lke a gaz
3) solar UVs discharge the particules which fall again on the ground, sticking everywhere.
1) solar wind creates the charges
2) charged particules hover above the surface, lke a gaz
3) solar UVs discharge the particules which fall again on the ground, sticking everywhere.
To quote from already cited article
"On the daylit side of the Moon, solar ultraviolet and X-ray radiation is so energetic that it knocks electrons out of atoms and molecules in the lunar soil. Positive charges build up.................................. the natural question then becomes, what happens on the night side? The dust there, Stubbs believes, is negatively charged. This charge comes from electrons in the solar wind, which flows around the Moon onto the night side. Indeed, the fountain model suggests that the night side would charge up to higher voltages than the day side, possibly launching dust particles to higher velocities and altitudes."
There seem to be two distinct processes, the first (daylight side) due to the photoelectric effect from ultraviolet and X-ray radiation and the second due to solar wind electrons being lighter than protons and thus more easily deflected onto the night side of the moon.
These two processes would work the same on any asteroid. Eros showed this dust mobility in having all small craters smothered in dust. In fact many of the small bodies that we have had recent photos of show a similar trend.
QUOTE (abalone @ Dec 13 2005, 05:23 AM)
These two processes would work the same on any asteroid. Eros showed this dust mobility in having all small craters smothered in dust. In fact many of the small bodies that we have had recent photos of show a similar trend.
Right... and one would think that this effect would be much more noticeable on the smaller bodies because of their weaker gravity. If the Moon had experienced as much dust motion as Eros over the eons, the maria probably wouldn't be visible by now, because they'd be covered over with dust.
Of course, I'm probably missing about 20 important points here. This is pretty simplistic reasoning.
This lunar dust storm stuff is interesting, but it would be easy to misinterpret the media coverage of it. We're not talking about an effect that would be like a dust storm in Iraq or Manitoba... or even Mars. VERY small amounts of VERY tiny particles are on the move.
The fact that we can see albedo boundaries on the Moon shows very clearly that this effect is miniscule. I've just been looking at the Luna 24 landing site, where a bright patch south of Fahrenheit crater has an edge that is sharp to within a few tens of meters, probably only ten meters if my image was good enough. And it's probably been there for 3 billion years. So in all that time there isn't enough dust movement to obscure an albedo boundary with probably zero effective relief.
As for asteroids... Hmmm, not so sure. But the ponds on Eros and the plains on Itokawa, presumably the same things, don't suggest to me that dust is constantly on the move in large quantities. Fine debris is moving, certainly, but if it moves significantly every time the terminator sweeps by it would either show depositional characteristics or at least not be concentrated so much in low points. I mean... Itokawa... if dust is moving in such a low gravity environment will it really get concentrated in low areas like that? All small craters smothered in dust on Eros? I think they are smothered in ejecta, not the stuff this story is about.
Phil
The fact that we can see albedo boundaries on the Moon shows very clearly that this effect is miniscule. I've just been looking at the Luna 24 landing site, where a bright patch south of Fahrenheit crater has an edge that is sharp to within a few tens of meters, probably only ten meters if my image was good enough. And it's probably been there for 3 billion years. So in all that time there isn't enough dust movement to obscure an albedo boundary with probably zero effective relief.
As for asteroids... Hmmm, not so sure. But the ponds on Eros and the plains on Itokawa, presumably the same things, don't suggest to me that dust is constantly on the move in large quantities. Fine debris is moving, certainly, but if it moves significantly every time the terminator sweeps by it would either show depositional characteristics or at least not be concentrated so much in low points. I mean... Itokawa... if dust is moving in such a low gravity environment will it really get concentrated in low areas like that? All small craters smothered in dust on Eros? I think they are smothered in ejecta, not the stuff this story is about.
Phil
I clearly remember this phenomenon -- as detected by the LEAM instrument -- being mentioned in a document something like two decades ago (one of the documents listed in NASA's extensive "STAR" catalog, I believe). I also more dimly remember Tommy Gold crowing about it somewhere as partial vindication for his lunar-dust theories.
Interesting footnote on dust from the AGU meeting: abstract http://www.agu.org/cgi-bin/SFgate/SFgate?&...P11A-0099" refers to the color and albedo differences seen by NEAR in Eros' soil. But the poster itself -- which I saw at the meeting -- goes into more detail:
(1) Not only is there a distinct albedo difference between most of Eros' soil and the much lighter material exposed by landslides on slopes, but there's a color difference: the freshly exposed material is less reddish. Clearly evidence of some kind of space weathering process. But, as an added puzzle, the "ponds" on Eros are intermediate in their coloring: somewhat more bluish than the surrounding soil.
(2) The poster also raises the possibility that the relatively mild space weathering effects on asteroids (unlike the lunar surface) just might be due entirely to mechanical effects, rather than actual mineralogical changes. It turns out that when you grind up dark mafic rocks, they get more reddish -- until the particle size drops below 20 microns, at which point the powder starts turning bluer again. So, if you have a phenomenon that tends to plant smaller grains on surface soil -- such as micrometeoroid impacts, or seismic shaking that launches the smaller grains farther so that they land back on the surface later -- this by itself might produce the color effects seen on Eros, especially if the grains in the ponds are particularly fine (as in fact they seem to be).
(1) Not only is there a distinct albedo difference between most of Eros' soil and the much lighter material exposed by landslides on slopes, but there's a color difference: the freshly exposed material is less reddish. Clearly evidence of some kind of space weathering process. But, as an added puzzle, the "ponds" on Eros are intermediate in their coloring: somewhat more bluish than the surrounding soil.
(2) The poster also raises the possibility that the relatively mild space weathering effects on asteroids (unlike the lunar surface) just might be due entirely to mechanical effects, rather than actual mineralogical changes. It turns out that when you grind up dark mafic rocks, they get more reddish -- until the particle size drops below 20 microns, at which point the powder starts turning bluer again. So, if you have a phenomenon that tends to plant smaller grains on surface soil -- such as micrometeoroid impacts, or seismic shaking that launches the smaller grains farther so that they land back on the surface later -- this by itself might produce the color effects seen on Eros, especially if the grains in the ponds are particularly fine (as in fact they seem to be).
In the case of small bodies that are or closely resemble chondritic meteorites, there is another thing to consider. Up to some tens of percent of the total material isn't rock, it's nickel-iron and iron-sulfide. Mechanical, optical and I presume electrostatic properties of this component will be very different from the silicate rock component of the regolith. Various mechanical and electrostatic, perhaps electromagnetic processes may play roles in separating and transporting these very different materials compared with the rock compoinent. And seemingly insignificant processes may emerge as the big role players in mini-gravity, mili-gravity and micro-gravity conditions.
Maybe we'd better move this over to the Asteroids section, but...
http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1631.pdf :
"The findings of a chondritic composition for the GRS-derived Mg/Si and K values were in close agreement with compositions derived from the XRS
experiment. However, the GRS-derived Fe/O and Fe/Si values did not agree with most of the chondrite values; specifically the Fe abundance was low by about a factor of two. Three possible explanations for the apparent Fe depletion were considered in [5]. Among these, the most likely concerned physical processes within the asteroid regolith that might cause metal migration at the landing site and explain the discrepancy between the GRS and XRS results."
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2031.pdf :
"The NEAR GRS (gamma-ray spectrometer) derived Fe/Si ratio of 0.8 ± 0.3 is considerably lower than the XRS derived Fe/Si. The GRS samples to depths of tens of centimeters, whereas the X-rays only sample to hundreds of microns. This
suggests that the elevated Fe/Si is a surface phenomenon. At present it is unclear whether the observed Fe/Si may have been inflated by phase-angle effects or whether the Fe in the surface layer may in fact have been enhanced by size sorting
in the regolith (the “Brazil-nut” effect)."
Also see http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1868.pdf for speculations on such effects.
http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1631.pdf :
"The findings of a chondritic composition for the GRS-derived Mg/Si and K values were in close agreement with compositions derived from the XRS
experiment. However, the GRS-derived Fe/O and Fe/Si values did not agree with most of the chondrite values; specifically the Fe abundance was low by about a factor of two. Three possible explanations for the apparent Fe depletion were considered in [5]. Among these, the most likely concerned physical processes within the asteroid regolith that might cause metal migration at the landing site and explain the discrepancy between the GRS and XRS results."
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2031.pdf :
"The NEAR GRS (gamma-ray spectrometer) derived Fe/Si ratio of 0.8 ± 0.3 is considerably lower than the XRS derived Fe/Si. The GRS samples to depths of tens of centimeters, whereas the X-rays only sample to hundreds of microns. This
suggests that the elevated Fe/Si is a surface phenomenon. At present it is unclear whether the observed Fe/Si may have been inflated by phase-angle effects or whether the Fe in the surface layer may in fact have been enhanced by size sorting
in the regolith (the “Brazil-nut” effect)."
Also see http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1868.pdf for speculations on such effects.
QUOTE (BruceMoomaw @ Dec 14 2005, 05:40 AM)
I clearly remember this phenomenon -- as detected by the LEAM instrument -- being mentioned in a document something like two decades ago (one of the documents listed in NASA's extensive "STAR" catalog, I believe). I also more dimly remember Tommy Gold crowing about it somewhere as partial vindication for his lunar-dust theories.
Bruce:
It does, indeed, seem like a typical Gold/Hoyle 'edge-of-the-envelope' theory - interesting, stimulating, but, er, *wrong* in many cases...
Bob Shaw
Tommy Gold, like Fred Hoyle, was on of those tremendously gifted scientists who at times seemed constitutionally unable to a "Quantitative and Qualitative idea-matrix analysis" of the evidence for and against a theory or model. Rather, they seemed infinitely able to select and adjust the weighting on their evidence to optimally bias the interpretation of the evidence in favor of their highly, often over-quantitative conclusions.
But they were both so sharp, they were really hard to argue against. And Tommy Gold always (Fred not always, in later years) was worth listening to, no matter how cracked his idea might sound, cause there was always a sneaking suspicion he might well be right... AGAIN.
But they were both so sharp, they were really hard to argue against. And Tommy Gold always (Fred not always, in later years) was worth listening to, no matter how cracked his idea might sound, cause there was always a sneaking suspicion he might well be right... AGAIN.
The impression I got of Gold even when I was 15 -- based on his ever-changing Moon dust arguments -- was that he tended to regard scientific theory as Silly Putty. The low point of his career, however, surely came shortly before his death, when he announced that solar sails couldn't possibly work because any real physicist knew on thermodynamic grounds that photons couldn't exert pressure (and never mind that they'd been routinely used for spacecraft attitude control since 1964, and that the effect was the only thing that saved the Mariner 10 mission!)
The Mysterious Smell of Moondust
NASA Science News for January 30, 2006
Long after the last Apollo astronaut left the moon, a mystery lingers: Why does moondust smell like gunpowder? In this installment of Apollo Chronicles, astronauts describe the surprising smell and taste of moondust, which they experienced first-hand inside their lunar landers. The dust gave one astronaut a case of hay fever. What does it all mean? To find out, read the FULL STORY:
http://science.nasa.gov/headlines/y2006/30....htm?list161084
Find out about the Science@NASA Podcast feed at
http://science.nasa.gov/podcast.htm .
NASA Science News for January 30, 2006
Long after the last Apollo astronaut left the moon, a mystery lingers: Why does moondust smell like gunpowder? In this installment of Apollo Chronicles, astronauts describe the surprising smell and taste of moondust, which they experienced first-hand inside their lunar landers. The dust gave one astronaut a case of hay fever. What does it all mean? To find out, read the FULL STORY:
http://science.nasa.gov/headlines/y2006/30....htm?list161084
Find out about the Science@NASA Podcast feed at
http://science.nasa.gov/podcast.htm .
QUOTE (ljk4-1 @ Feb 3 2006, 03:31 AM)
The Mysterious Smell of Moondust
NASA Science News for January 30, 2006
Long after the last Apollo astronaut left the moon, a mystery lingers: Why does moondust smell like gunpowder?.
NASA Science News for January 30, 2006
Long after the last Apollo astronaut left the moon, a mystery lingers: Why does moondust smell like gunpowder?.
Aw that's easy, they never actually went to the moon and gunpwder was the cheapest black dust they could find to fill the movie studio.
No smoking on the set please!!
Science/Astronomy:
* Solving Settlement Problems: Dealing with Moon Dust
http://www.space.com/adastra/adastra_moondust_060223.html
As scientists and engineers figure out how to return astronauts to the Moon, set
up habitats, and mine lunar soil to produce anything from building materials to
rocket fuels, they are scratching their heads over what to do about Moon dust.
* Solving Settlement Problems: Dealing with Moon Dust
http://www.space.com/adastra/adastra_moondust_060223.html
As scientists and engineers figure out how to return astronauts to the Moon, set
up habitats, and mine lunar soil to produce anything from building materials to
rocket fuels, they are scratching their heads over what to do about Moon dust.
QUOTE (BruceMoomaw @ Dec 17 2005, 02:23 AM)
The impression I got of Gold even when I was 15 -- based on his ever-changing Moon dust arguments -- was that he tended to regard scientific theory as Silly Putty. The low point of his career, however, surely came shortly before his death, when he announced that solar sails couldn't possibly work because any real physicist knew on thermodynamic grounds that photons couldn't exert pressure (and never mind that they'd been routinely used for spacecraft attitude control since 1964, and that the effect was the only thing that saved the Mariner 10 mission!)
- I've chased you around this maypole before, elsewhere, and I won't start now. Here. I will say that I hope that after you've passed that you get more credit for your legacy than you give Tommy for his.
QUOTE (BruceMoomaw @ Dec 17 2005, 09:23 AM)
The impression I got of Gold even when I was 15 -- based on his ever-changing Moon dust arguments -- was that he tended to regard scientific theory as Silly Putty. The low point of his career, however, surely came shortly before his death, when he announced that solar sails couldn't possibly work because any real physicist knew on thermodynamic grounds that photons couldn't exert pressure (and never mind that they'd been routinely used for spacecraft attitude control since 1964, and that the effect was the only thing that saved the Mariner 10 mission!)
How photon pressure happens?
It seems impossible that the light could exert any kind of mechanical effect.
But when a photon hits an atom on the surface of something, it is absorbed (it stops existing as a particule) but its energy is still there, and it is changed into mechanical energy. In some cases this mechanical energy is added to an electron's energy (the electron gets on an upper orbit, and is said "excited", it can even be expelled) but in most case it is transferred to the whole atom, which gets some impulse, into the direction the photon was going to.
And an atom moving inward a surface soon hits the other atoms. The gross result is that the movement is transfered from atom to atom as a wave, usually called a phonon (elementary quantum of sound) and many phonons moving into a body make heat, quite simply. But a part of the movement is transferred as an impulse to the whole set of atoms: a force which moves it. So the whole something recoils, pushed by the light.
QUOTE (Richard Trigaux @ Feb 26 2006, 07:10 PM)
But when a photon hits an atom on the surface of something, it is absorbed (it stops existing as a particule) but its energy is still there, and it is changed into mechanical energy. In some cases this mechanical energy is added to an electron's energy (the electron gets on an upper orbit, and is said "excited", it can even be expelled) but in most case it is transferred to the whole atom, which gets some impulse, into the direction the photon was going to.
Sound like a good story but how does one use this analogy to explain that a surface that emits a photon experiences a reactive pressure in the opposite direction, and a surface that reflects a photon experiences a pressure 2X that of a surface that absorbs it.
It is best to to regard a photon as having momentum which has to be consereved both during absorption, reflection and emission.
QUOTE (Richard Trigaux @ Feb 26 2006, 07:10 PM)
But when a photon hits an atom on the surface of something, it is absorbed (it stops existing as a particule) but its energy is still there, and it is changed into mechanical energy. The energy of the photon is much greater than this.
The photons energy is totally different to if moment. A photon does not exert pressure because it energy is changed into kinetic or mechanical energy
The fact that photons have momentum is an inevitable consequence of E= MC squared. It is true that photons have no REST mass (which is one respect in which they differ from all particles of matter)-- but that's simply because, by their very nature, they are never at rest. They do possess MOVING mass -- or, as it's officially called, "relativistic mass" -- equal to the energy they contain. (In fact, ALL moving material objects also possess additional mass equal to the energy of their movement, which is why relativity predicts that the mass of a moving object actually increases as it moves at closer and closer to lightspeed.) There are some nice Google discussions of this at
http://www.physlink.com/Education/AskExperts/ae180.cfm
http://hyperphysics.phy-astr.gsu.edu/hbase...tiv/relmom.html
http://math.ucr.edu/home/baez/physics/Part...hoton_mass.html
http://www.physlink.com/Education/AskExperts/ae180.cfm
http://hyperphysics.phy-astr.gsu.edu/hbase...tiv/relmom.html
http://math.ucr.edu/home/baez/physics/Part...hoton_mass.html
QUOTE (abalone @ Feb 26 2006, 10:51 AM)
Sound like a good story but how does one use this analogy to explain that a surface that emits a photon experiences a reactive pressure in the opposite direction, and a surface that reflects a photon experiences a pressure 2X that of a surface that absorbs it.
It is best to to regard a photon as having momentum which has to be consereved both during absorption, reflection and emission.
The photons energy is totally different to if moment. A photon does not exert pressure because it energy is changed into kinetic or mechanical energy
It is best to to regard a photon as having momentum which has to be consereved both during absorption, reflection and emission.
The photons energy is totally different to if moment. A photon does not exert pressure because it energy is changed into kinetic or mechanical energy
This is not a theory, but what I learned at school, about how photons are absorbed. But I don't know all the possible processes.
In the case of an emission, I guess that there is some reverse process of that of the absorption (for instance in a heated surface, a phonon is absorbed, thus removing a momentum from the surface) but I am not sure of this.
In the case of a reflection, it is a very different process, as the photon is not absorbed. But, as an electromagnetic wave, it induces a current into the reflective surface. This current in turn results in another wave, the reflected wave, that the photon follows. But in order to give an impulse to the surface, the photon must lose energy, and thus lower its wavelength, a thing which is preciselly not observed into a reflection. Are you sure of what you say about a 2X force? If it is true, I don't know exactly what happens. Perhaps simply a Lorentz force between the incoming wave and the current induced into the surface.
What I am sure on the other hand is that a photon don't have a momentum, and you are both false, abalone and Bruce. Momentum is the product of mass per speed square (Ec=1/2 mv2), and it is an energy. Mass of a photon is null, and speed is the speed of light, equivalent of an infinite speed in classical mechanics. The current notions of mechanics don't apply into these conditions, and especially zero multiplied by infinite can give either zero, a discrete value, or an infinite value. It happens that the actual energy of a photon has no relation with its speed. You can no more take the energy of a photon, and put its speed in the formula to calculate its mass.
So radiation pressure result of subtle interactions of light with matter, not of a mechanical reflection of grains of light. If it were so, a beam of sun light (1kw/m2) would slam our faces, and sun light would project the planets into space.
Richard, you are right when you say "The current notions of mechanics don't apply into these conditions, and [..] the actual energy of a photon has no relation with its speed". In fact, energy of a photon is related to it's wavelenght. If you can accept that a zero-mass photon can transport energy, why shouldn't transport momentum too?
In fact, pressure of light is equal to it's energy density; this, considering the huge velocity of light, brings to a very diluited pressure... in fact, the light which impact the earth from sun transport 1370 W/m2 but, in a second, this light covers a distance c; this give a energy density of (1.37E3 J/s/m2)/(2.998E8 m/s)=4.57E-6 J/m3.
In other words, sunlight pressure is only 4.57E-6N/m2, about 22 billion times smaller than atmospheric pressure! (on the Earth surface, is 30% smaller due to atmosphere loss).
Not only this amount is impossible to feel, it is comparable or smaller than other effect perturbing planetary orbits (eg solar wind pressure or other planets attraction) so cannot really disturb orbits.
However, it push cometary tails and, perhaps, one day will help to make interstellar trips
In fact, pressure of light is equal to it's energy density; this, considering the huge velocity of light, brings to a very diluited pressure... in fact, the light which impact the earth from sun transport 1370 W/m2 but, in a second, this light covers a distance c; this give a energy density of (1.37E3 J/s/m2)/(2.998E8 m/s)=4.57E-6 J/m3.
In other words, sunlight pressure is only 4.57E-6N/m2, about 22 billion times smaller than atmospheric pressure! (on the Earth surface, is 30% smaller due to atmosphere loss).
Not only this amount is impossible to feel, it is comparable or smaller than other effect perturbing planetary orbits (eg solar wind pressure or other planets attraction) so cannot really disturb orbits.
However, it push cometary tails and, perhaps, one day will help to make interstellar trips
QUOTE (dilo @ Feb 27 2006, 01:04 AM)
Richard, you are right when you say "The current notions of mechanics don't apply into these conditions, and [..] the actual energy of a photon has no relation with its speed". In fact, energy of a photon is related to it's wavelenght. If you can accept that a zero-mass photon can transport energy, why shouldn't transport momentum too?
In fact, pressure of light is equal to it's energy density; this, considering the huge velocity of light, brings to a very diluited pressure... in fact, the light which impact the earth from sun transport 1370 W/m2 but, in a second, this light covers a distance c; this give a energy density of (1.37E3 J/s/m2)/(2.998E8 m/s)=4.57E-6 J/m3.
In other words, sunlight pressure is only 4.57E-6N/m2, about 22 billion times smaller than atmospheric pressure! (on the Earth surface, is 30% smaller due to atmosphere loss).
Not only this amount is impossible to feel, it is comparable or smaller than other effect perturbing planetary orbits (eg solar wind pressure or other planets attraction) so cannot really disturb orbits.
However, it push cometary tails and, perhaps, one day will help to make interstellar trips
In fact, pressure of light is equal to it's energy density; this, considering the huge velocity of light, brings to a very diluited pressure... in fact, the light which impact the earth from sun transport 1370 W/m2 but, in a second, this light covers a distance c; this give a energy density of (1.37E3 J/s/m2)/(2.998E8 m/s)=4.57E-6 J/m3.
In other words, sunlight pressure is only 4.57E-6N/m2, about 22 billion times smaller than atmospheric pressure! (on the Earth surface, is 30% smaller due to atmosphere loss).
Not only this amount is impossible to feel, it is comparable or smaller than other effect perturbing planetary orbits (eg solar wind pressure or other planets attraction) so cannot really disturb orbits.
However, it push cometary tails and, perhaps, one day will help to make interstellar trips
Errr... I don't want to be too affirmative, but a 1m2 sail receives 1300 watts of light energy. If only a small part of it was transferred into mechanical energy, this sail would be slammed away. We cannot reason as if photons were little bullets, with a mass and a finite speed. If it was so, of course, when bouncing off a reflective surface, they would transfer a part of their energy to the surface, from the collision. And with a very minute mass compared to the sail, they would have a very minute effect, what is observed. But photons have no mass, and they go at the velocity of light, so this reasoning cannot be made in this way. But the effects exist, no doubt. Perhaps the solution is a relativistic version of the mechanical analogy above. But I don't know it.
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