Astrophysics/Questions Answered by Expert Philip A. Stahl
| Subject | Date Asked |
| Astonomy / Physics | 1/31/2012 |
| Q: 1. An asteroids closest approach to the Sun (perihelion) is 2AU and farthest distance from the sun ... A: Okay, let's make it more concrete using the problem below - with the accompanying diagram as a ... | |
| Astonomy / Physics | 1/31/2012 |
| Q: 1. An asteroids closest approach to the Sun (perihelion) is 2AU and farthest distance from the sun ... A: This sounds suspiciously like a homework problem which I don't do. However, I can provide some ... | |
| Time dilation and expansion of the universe | 1/27/2012 |
| Q: Why don´t the time dilation neutralize the effect of a universe which seems to expand in an ... A: You raise an intriguing question and one which, certainly at first glance, appears to have or ... | |
| Ric Ross questioin -infinite gravitational force | 1/12/2012 |
| Q: Having to do with infinite gravitational force. Black holes have infinite gravitational force. ... A: "Infinite gravitational force" is kind of a poor description of what's going on. Also, the new ... | |
| Auroral magnetic bottle problem | 1/4/2012 |
| Q: Your assistance in the previous self-study problem I had was so much appreciated, I wondered if you ... A: Okay, like the previous solution I provided for your self-study this is fairly straightforward. You ... | |
| Plasma orbit theory & magnetosphere | 1/2/2012 |
| Q: I am very interested in the aurora but want to get beyond the pretty pictures to the physics. I have ... A: It is nice to see someone doing self study in basic plasma physics, especially as it can help to ... | |
| Maxwell and the Speed of LIght | 11/4/2011 |
| Q: Did James Maxwell's calculation of the speed of light state that light's speed would vary inversely ... A: Bear in mind that the density of interstellar gas in a black hole’s vicinity is likely to be ... | |
| Maxwell and the Speed of LIght | 11/4/2011 |
| Q: Did James Maxwell's calculation of the speed of light state that light's speed would vary inversely ... A: Maxwell's key wave equations actually say nothing about light propagating with a velocity that will ... | |
| Expansion of the universe trough diffusion | 10/20/2011 |
| Q: After viewing an episode of "trough the wormhole" I was left pondering about dark matter and dark ... A: The problem with comparing the diffusion of ink spreading through water with the accelerating cosmic ... | |
| electromagnetic waves | 9/30/2011 |
| Q: sir pls tell why radio waves are non polarizing while light waves are A: I'm not sure where exactly you got the idea that radio waves are not polarized, but they are. For ... | |
| Ref: question | 9/11/2011 |
| Q: Good day How does spectroscopic analysis work and how do we know what we know about the light from ... A: This is simply too vast an area to casually address in a forum like this, so I post several links ... | |
| titans | 9/10/2011 |
| Q: Titan, one of Saturn's many moons, has an atmosphere, but our own Moon does not. What is the ... A: The bottom line is there's no easy explanation. ON the face of it, given Titan is about the same ... | |
| light | 6/21/2011 |
| Q: 1]Can the speed of light be increased? 2]Is it possible for light to move objects? ANSWER: ... A: This site is rich in information, more than I could ever give at one time, and also full of ... | |
| light | 6/20/2011 |
| Q: 1]Can the speed of light be increased? 2]Is it possible for light to move objects? ANSWER: ... A: No one knows 'why' light moves 'so fast', but that is also because in science we give more emphasis ... | |
| light | 6/20/2011 |
| Q: 1]Can the speed of light be increased? 2]Is it possible for light to move objects? A: Answers: 1) No, the speed of light can't be increased. But, an addendum and proviso. In a paper ... | |
| Dark energy | 6/13/2011 |
| Q: Can dark energy/dark matter be created? How can we detect dark matter/dark energy? Are there ... A: Whether dark energy can be created will depend on exactly what its nature is. So far this is an open ... | |
| universe | 5/27/2011 |
| Q: (could be a stupid question) scientist say they see an explosion 13 billion light years from earth, ... A: Okay first, true - in general when one looks out at objects in space, e.g. stars, star clusters, ... | |
| Two fluid theory | 5/18/2011 |
| Q: I'm not a student but just interested in plasma physics and have done lots of work on it, mostly ... A: Classification of differing fluid regimes is far beyond the scope of this answer, but you can find ... | |
| astrophysics | 4/9/2011 |
| Q: sir I went through following link ... A: The answer to your first question isn't very clear, and certainly not from the link! (where it ... | |
| aurora | 3/29/2011 |
| Q: What is an aurora? A: One can visualize the Earth as a giant spherical magnet, with magnetic field lines extending from ... | |
| tachyons & photons | 3/13/2011 |
| Q: Sorry for bombarding you with all those questions in one email. Here's two that I would appreciate ... A: In answer to your questions: 1) The prcise speed at which tachyons travel isn't known, only that ... | |
| How to solve complex problems | 2/20/2011 |
| Q: I was wondering if you could provide some advice on how to solve problems.When solving problems i ... A: You don't really specify what physics subject you are dealing with, whether General Physics, or ... | |
| is the solar system merely an atom in a much larger structure? | 2/6/2011 |
| Q: hope you can help me and that this is not a silly question. firstly, it has been prompted by an old ... A: The old "solar system" (Bohr model) of the atom basically fell through once the modern wave ... | |
| angular momentum of a black hole | 1/31/2011 |
| Q: Your Question was: why is the maximum angular momentum of a black hole limited to G * M^ 2 / c.? A: The key aspect to consider here is that a black hole assigned some mass M can’t have any arbitrary L ... | |
| Expanding Universe | 1/25/2011 |
| Q: After seeing Science programs on TV and reading articles, it seams that the Universe will just keep ... A: Your explanation (or interpretation) of why there won't be a "big Crunch" is one way to think of it. ... | |
| Gravity - Thought Experiement | 1/19/2011 |
| Q: This is a bit of a thought experiment question, hope it makes sense, If a void could be created at ... A: Okay- thanks for clarifying your question. Several problems here: first, the definition of "weight" ... | |
| Gravity - Thought Experiement | 1/18/2011 |
| Q: This is a bit of a thought experiment question, hope it makes sense, If a void could be created at ... A: I'd have to say that a 0 G experience would not be so produced, given that no matter how large your ... | |
| E cross B flow | 9/28/2010 |
| Q: In a frame moving with U_E = E cross B/B^2, the "E cross B" velocity, the motion of ions and ... A: Okay, first thanks for letting me know you are examining a situation in the *MHD* regime. This ... | |
| E cross B flow | 9/28/2010 |
| Q: In a frame moving with U_E = E cross B/B^2, the "E cross B" velocity, the motion of ions and ... A: The only place I can see where you might have gone wrong is in not properly accounting for an ... | |
| Dynamo Flare models | 9/22/2010 |
| Q: I'm interested in what you think of dynamo flare models which try to use aurora substorm processes ... A: The paper to which you’re referring is: “A Dynamo Theory of Solar Flares” by J.R. Kan, S.I. ... | |
| a living universe? | 8/27/2010 |
| Q: I've been thinking about the universe's expansion lately and I realized that growth is one of the ... A: Living things grow by a specific process that is based on multiplication of living cells - which ... | |
| Help with planet accelaration | 7/28/2010 |
| Q: I'm not asking you to solve it-I'm asking you to please show me how to set it up so I can find the ... A: NO...m is NOT 4.19 * 10 ^23 N, (Jupiter's mass). It is the putative FORCE (mg) - by which Jupiter is ... | |
| Help with planet accelaration | 7/25/2010 |
| Q: I'm not asking you to solve it-I'm asking you to please show me how to set it up so I can find the ... A: This problem is extremely straightforward. However, what you're calling 'g' is, in fact, NOT g (as ... | |
| Topology of the Universe | 7/24/2010 |
| Q: As I understand it, current evidence indicates the universe is essentially Euclidean and "flat", as ... A: which I not long ago received via e-mail from All Experts. As to this last question, unfortunately, ... | |
| Topology of the Universe | 7/20/2010 |
| Q: As I understand it, current evidence indicates the universe is essentially Euclidean and "flat", as ... A: Your question poses a number of problems because: 1) I'm not sure how much background you have in ... | |
| light speed | 7/10/2010 |
| Q: I love physics and the science that goes along with it especially when it comes to outer space. ... A: Your conjecture is interesting. So far as I can see the impact of such deviations in c as you ... | |
| My theory of | 7/1/2010 |
| Q: I dont know if this is the proper venue, but I wanted to post a theory I have about the big bang. I ... A: The problem is that your "model" is inapplicable because it's predicated on Newtonian gravitation ... | |
| My theory of "the big bang and the cycle of the universe" | 7/1/2010 |
| Q: I dont know if this is the proper venue, but I wanted to post a theory I have about the big bang. I ... A: (This is sent as a "revised answer" because the All experts "image sender" only allows one image to ... | |
| cosmic rays | 6/13/2010 |
| Q: can electricity be generated from cosmic rays and if so how? and what energy are they at ground ... A: The erroneous perception that cosmic rays might have an association with electricity probably ... | |
| Matter creation | 4/2/2010 |
| Q: I am reading Steven Weinberg's "Dreams of a Final Theory" (1992), and he mentions believing that ... A: So far as we know, major matter creation (by which I mean on the scale once proposed by Fred Hoyle ... | |
| Effect on Magnetosphere of Field Reversal | 3/22/2010 |
| Q: Does the magnetosphere's protective effect diminish during reversals of the earth's magnetic field? ... A: Yes, the protective effect of the Earth's magnetosphere will diminish during a field reversal, in ... | |
| E | 3/9/2010 |
| Q: OK, What is energy, and how does it manifest around us? - Tue A: First, let me preface this answer by saying that energy is a vast subject, not to mention the ... | |
| electron beam in space | 2/21/2010 |
| Q: I have another practice test problem I'm having difficulty working. It reads as follows: Given a ... A: Again, this one isn't terribly difficult but you need to be able to craft the problem in its correct ... | |
| Stromgren sphere problem | 2/18/2010 |
| Q: I have been trying to work out a practice test problem on the Stromgren sphere with no success. Can ... A: This is not too difficult a problem, but does require some attention to the units used. Let's look ... | |
| Time | 1/16/2010 |
| Q: My question is: do physicists view time as a real and independent entity or as a purely ... A: Time is surely a physical unit (since we use it such so regularly in physics-astrophysics), but that ... | |
| Using expansion to find the age of the universe | 1/11/2010 |
| Q: I've read that the age of the universe can be calculated from first determining the rate of the ... A: Actually, it isn't an issue of 'working back' with respect to anything (in terms of the actual ... | |
| Follow-up solution | 11/5/2009 |
| Q: Okay, I think I have worked this out, but can you tell me if it’s right? From the link you gave in ... A: Congrats! You have it correct! The key to the solution was in seeing that, after you obtain the ... | |
| Binary star problem | 11/3/2009 |
| Q: Can you help with this problem? A visual binary has a period of 100 years, and the semi-major axis ... A: This looks like a fairly basic HW problem, so I will just get you oriented to solving it yourself. ... | |
| Relative and Absolute Time | 11/3/2009 |
| Q: I have no training in astrophysics and very little knowledge about it. However, I am an interested ... A: Okay, you have really two separate issues and I don't want to get them confused - so will stick with ... | |
| astrophysics/ black hole theory | 10/31/2009 |
| Q: I am really in need of help on a theory I am coming up with. I have found most of my answers that ... A: There are several problems with your theory. Let's look at it from the aspect of stellar ... | |
| cmbr | 8/6/2009 |
| Q: sir, what is CMBR? A: "CMBR" refers to the *cosmic microwave background radiation*. That is the 2.7 K temperature "relic ... | |
| boundry of universe | 8/4/2009 |
| Q: sir, what does latest research guide on the subject i mentioned above? is there any boundry of ... A: There is no firm answer yet to whether the universe has a "boundary". This is because more ... | |
| Escape velocity | 5/25/2009 |
| Q: I've always been told Earth's escape velocity is 25,000 mph, but never understood WHY? If a space ... A: Well, there is a non-math explanation but: a) it won't eliminate fully your 3,000 mph belief (that ... | |
| Escape velocity | 5/24/2009 |
| Q: I've always been told Earth's escape velocity is 25,000 mph, but never understood WHY? If a space ... A: You probably have never understood escape velocity - the concept, because it was always presented to ... | |
| Atom formation | 5/13/2009 |
| Q: I was browsing through the WMAP website and found this time line of our universe. ... A: You are correct that the universe had to cool down, a lot actually, in order for atoms to be able to ... | |
| Solar plasma instabilities | 5/10/2009 |
| Q: I am interested in the sort of plasma instabilities that occur in solar conditions (say before solar ... A: Yes, there are a number of instabilities associated with solar plasma, mostly defined in terms of ... | |
| Hall term-Hall MHD | 4/6/2009 |
| Q: Can you elaborate on the meaning and significance of the "Hall term"? Also when is it important and ... A: The "Hall term" arises in one electro-dynamic formulation of Ohm's law often used in solar work, and ... | |
| Theory of relativity | 4/2/2009 |
| Q: Relativity says that an observer can be moving in any way and but it will always observe the same ... A: Theories, once created or proposed - and which stand the test of time, don't get registered in ... | |
| Theory of relativity | 3/31/2009 |
| Q: Relativity says that an observer can be moving in any way and but it will always observe the same ... A: The "relative velocity formula" is actually an equation for the addition of velocities in a ... | |
| Theory of relativity | 3/30/2009 |
| Q: Relativity says that an observer can be moving in any way and but it will always observe the same ... A: Yes, and you can work it out using the relative velocity formula: thus, u = (v1 + v2) / [1 + ... | |
| Number of galaxies | 3/23/2009 |
| Q: Stahl; My brother in law and I were in a discussion about time travel. I had heard (though I don't ... A: Let's order the answers in the order of your questions: i)I think the university you may be ... | |
| expanding universe | 3/18/2009 |
| Q: Philip, If the universe is expanding faster than the speed of light, how does any light get back to ... A: Alas I don't think I can be much more help because getting into metric space and intervals based on ... | |
| expanding universe | 3/18/2009 |
| Q: Philip, If the universe is expanding faster than the speed of light, how does any light get back to ... A: No, the expansion of space to which I referred was the "metric expansion of space" which is quite ... | |
| expanding universe | 3/8/2009 |
| Q: Philip, If the universe is expanding faster than the speed of light, how does any light get back to ... A: The key here is that the contents of the cosmos itself (e.g. galaxies and galaxy clusters) are NOT ... | |
| Hall current in solar flares | 3/6/2009 |
| Q: Can the Hall current exist in solar conditions? Can it trigger solar flare? If so, how? Thanks. A: Yes the Hall current has been proposed to account for some solar flares. The first mention in ... | |
| Supermassive black holes | 3/6/2009 |
| Q: Philip, My understanding of current theory is that supermassive black holes stop "feeding" because ... A: Be aware that most of what you read about exotic astrophysical objects is not even on the level of ... | |
| Proton-Proton Solar Fusion | 3/6/2009 |
| Q: Two protons combine then one turns into a neutron by the release of a positron, electron-neutrino ... A: The difference you are referring to is what is called "the binding energy" of the particular nucleon ... | |
| Speed of light relative | 3/5/2009 |
| Q: I understand some basic physics, and I understand the math behind it, but one question puzzles me ... A: Actually, the two objects of which you speak would not even achieve c as their maximum, but only ... | |
| The powers of a black hole | 3/4/2009 |
| Q: I have heard that black holes have the power to bend and rip space and time. Is this possible? ... A: In actual fact, if one studies a space-time diagram (e.g. Kerr-type) for a black hole. it is not ... | |
| production of energy in stars | 3/3/2009 |
| Q: sir...could you really think that only fusion reactions are responsible for burning of star...rather ... A: Yes, because it is ONLY nuclear fusion reactions that can provide the energy budgets, detailed ... | |
| Flare time scales | 2/26/2009 |
| Q: What is the difference between the different flare time scales: the conductive, radiative, and ... A: The three time scales to which you refer (for LOOP flares of some length, L) can be given in ... | |
| Earth flares | 2/15/2009 |
| Q: Dr Stahl, thank you for your patients in considering my controversial thinking: ... A: Even if you can't provide a model, you should still be able to at least hypothesize based on ... | |
| SID flares | 2/14/2009 |
| Q: I recently downloaded a paper you wrote on "SID flares" and am still confused as to what causes ... A: Verey interesting that you were able to find and DL my paper. Anyway, let's get to your questions in ... | |
| Earth flares | 2/13/2009 |
| Q: Dr Stahl, thank you for your patients in considering my controversial thinking: ... A: Homologous flares, including those that are engendered via CMEs or coronal mass ejections, have been ... | |
| velocity, centripetal acceleration, gravitational acceleration | 2/1/2009 |
| Q: This is home work. The question is what is the speed of a spacecraft in circular orbit at an ... A: When doing any sort of physics problem (or astrophysics!) the first priority is to write down all ... | |
| Earth flares | 1/26/2009 |
| Q: I've been reading the answers to the questions about Earth "flares" and find them intriguing. Isn't ... A: Technically speaking one need not have magnetic reconnection to qualify for a flare. However, one ... | |
| infinity | 1/22/2009 |
| Q: I was reading the latest Scientific American about naked singularities, and as far as I can ... A: First, I am not about to get into any debate over the meaning of “infinite” or “infinity”. I think ... | |
| Surface temperature in gray atmosphere | 1/7/2009 |
| Q: In a previous answer to a question some time ago, dealing with gray atmospheres of stars, you wrote ... A: Okay, the key points - as I noted- were to assume: a) radiative equilibrium, and b) "LTE" or local ... | |
| Polytropic gas spheres | 12/30/2008 |
| Q: Can you tell me what are polytropic gas spheres and how they factor into stellar evolution? Thanks! A: Polytropic gas spheres are basically mathematical entities used for modelling of actual stars. As ... | |
| pop-science | 12/8/2008 |
| Q: Philip A. Stahl, I appreciate the time you took to explain why you declined to answer my previous ... A: These are all excellent questions. Unfortunately, it isn't always easy to discriminate between "pop ... | |
| Speed of cosmic rays | 12/8/2008 |
| Q: I understand that cosmic rays (let's say from the sun) are mainly protons and small atomic nuclei - ... A: Glad to hear this isn't a HW question, since it fits the profile of many problems I used to give in ... | |
| Advance of perihelion in relativity | 12/6/2008 |
| Q: I have been reading the book, Principle of Relativity and in particular one paper by Einstein to do ... A: This is not difficult but does require paying extremely close attention to the units used, as well ... | |
| space travel | 12/2/2008 |
| Q: iam wondering if you could answer these questions for me.the first one is this.how fast is ... A: The question is totally meaningless because you have NO units to go with that number! What is it: ... | |
| why sky is dark at night ? | 11/17/2008 |
| Q: I am not a physicist or something but still interested to know things which are not clear. Learned ... A: Olber's paradox is generally rendered with vastly more complexity than it needs to be, using ... | |
| Big tube from earth... | 10/20/2008 |
| Q: What would happen if you took a big tube and put on end inside the earth's atmosphere and the other ... A: Not likely at all! The air molecules of our atmosphere, remember, are held (more or less) in place ... | |
| Gravitational pull | 9/17/2008 |
| Q: Im trying to figure out the gravitational attraction between Jupiter and the Sun in units of earth ... A: First things first - I have to ask if this is a homework question. If it is, the most I can do is ... | |
| plasma | 9/6/2008 |
| Q: Philip, In the dicta of an article I read recently it listed the various baryonic matter we know of ... A: I think you are confusing two different domains of plasma. You are thinking of "hot plasma" such as ... | |
| more info | 9/5/2008 |
| Q: I recently sent you a question about a rotating pulsar. The whole question is: The Crab Pulsar, ... A: Actually, that value is: 5.3 x 10^8 m/s^2 Not m/s! Remember this is an acceleration, and actually ... | |
| more info | 9/4/2008 |
| Q: I recently sent you a question about a rotating pulsar. The whole question is: The Crab Pulsar, ... A: Okay, the only things we need to know relevant to the question you asked is: the radius, and the ... | |
| Logical Answer | 9/4/2008 |
| Q: While doing a physics problem involving finding the rotational acceleration of a pulsar, I first ... A: I worked out the maximal rotational velocity for the x-ray pulsar Centaurus X-3 using the standard ... | |
| Modern physics | 8/21/2008 |
| Q: Whats the reason for so much high gravity in black hole that light can not escap from black hole.and ... A: The reason for the extremely high gravity arises from the incredible high density of the matter that ... | |
| speed of light | 7/31/2008 |
| Q: I was wondering, did Einstein say NOTHING could go faster than the speed of light (particles etc. ... A: In his paper, 'Does the Inertia of a Body Depend on its Energy Content? (in Annalen der Physik, Vol. ... | |
| White holes -- my favorite astronomical object | 7/3/2008 |
| Q: What about white holes makes their existence impossible? A white hole is the opposite of a black ... A: The 2nd law of thermodynamics or "entropy law" states that the tendency of a closed thermodynamic ... | |
| White holes -- my favorite astronomical object | 7/2/2008 |
| Q: What about white holes makes their existence impossible? A white hole is the opposite of a black ... A: Your question introduces the critical notion of the difference between what is theoretically ... | |
| Binary star problem | 6/4/2008 |
| Q: Can you help me with this problem? Find the mass of the stars Sirius A and Sirius B which form a ... A: Well, what I will do is set this problem up so you can work it out. First, note that for a “true ... | |
| Fermi acceleration | 4/22/2008 |
| Q: My questions seems to have gone to James Gort by mistake. I was really looking for your help here. ... A: Jani First, let's revisit the plasma mirror machine problem you posed last year. As you recall we ... | |
| Double layers | 3/19/2008 |
| Q: Can you elaborate a bit about double layers and what role they might play in solar flares? I have ... A: If you go back to two questions you asked last year, to do with magnetic mirrors in plasmas, you ... | |
| inductance and solar flares | 3/13/2008 |
| Q: I have read that solar flare eruptions can be compared to disruptions of inductive electrical ... A: First, there is no way that the inductance in a flare region can be measured. What is more accurate ... | |
| Transfer equation for brightness temperature | 3/10/2008 |
| Q: What would be the transfer equation for the brightness temperature of radiation in the vicinity of a ... A: The transfer equation for the brightness temperature of radiation in the vicinity of a flare is ... | |
| Normalized Stokes parameters and coherency matrix | 2/28/2008 |
| Q: Help! Can you show me how to do at least one of these problems? Three radio waves from different ... A: Very good! You have solved part (iii) correctly. Just bear in mind that the coherency matrix (also ... | |
| Normalized Stokes parameters and coherency matrix | 2/27/2008 |
| Q: Help! Can you show me how to do at least one of these problems? Three radio waves from different ... A: Well, I am not going to work any of those problems for you, but will set up another example and full ... | |
| radial & transverse star velocities | 2/23/2008 |
| Q: Can you please help with this problem? Barnard's star has a proper motion of 10.31"/ yr. and a ... A: This is a fairly straightforward problem, so I will just point you in the right direction to get you ... | |
| Received spectral power | 2/20/2008 |
| Q: I am hoping this is an astrophysics question, you can help me solve, though it is to do with radio ... A: The normalized Stokes parameters are given as: S[s_i] = S x (s0) (s1) (s2) (s3) where ‘S’ is ... | |
| Equation of motion in a force-field | 2/17/2008 |
| Q: Help! Can you give advice on solving this? Show that: m(dv_z/ dt) = -mu (@B/@z) where @ are ... A: You certainly have a lot of plasma physics problems these days, don't you? The key point to note in ... | |
| Magnetic field problem | 2/15/2008 |
| Q: Can you give advice on solving this problem? Determine the magnetic field of a cylindrically ... A: This problem is actually relatively straightforward. The first thing to note is the force-free ... | |
| Ordiinary and extraordinary waves | 2/13/2008 |
| Q: What is the difference between the X- and O-modes of plasma waves? Btw, I never did receive a notice ... A: Using the graph below, the “O-mode” occurs for the specific case in which the perturbed E –field is ... | |
| Gravitational Shift in Multi-Star Systems | 2/12/2008 |
| Q: I was wondering what would happen to a multi-star system if one star went supernova or for some ... A: Assuming some binary star system, a supernova would herald some form of immensely dense collapsar - ... | |
| cut-off frequency v. resonant frequency | 2/11/2008 |
| Q: For parallel propagation in an EM field, how can one *quantitatively* distinguish the cut-off plasma ... A: In your parallel propagation (3D) case, we assume: w >> W _i (e.g. plasma electron frequency much ... | |
| Number of atoms | 1/31/2008 |
| Q: How do scientists come up with a number of atoms in the universe of 10 to the 80th power? ANSWER: ... A: The estimate of the currently observed cosmological density is a highly complex one and beyond the ... | |
| Number of atoms | 1/30/2008 |
| Q: How do scientists come up with a number of atoms in the universe of 10 to the 80th power? A: More technically, it is the number of *particles* in the *observable* universe (since one ... | |
| Plasma problem | 1/18/2008 |
| Q: Help! I am fit to be distracted with this problem. Can you help? A proton moves in a uniform ... A: Jani I am not going to solve this for you - but rather provide you with what I regard as ample ... | |
| Research | 12/26/2007 |
| Q: I want to pursue research in the field of Astronomy and Astrophysics. I have done my M.Sc. in ... A: Actually - study time isn't much of an issue since the GRE is first and foremost an *aptitude* test. ... | |
| Research | 12/24/2007 |
| Q: I want to pursue research in the field of Astronomy and Astrophysics. I have done my M.Sc. in ... A: Your query presents an intriguing dilemma, and alas, one for which I am unable to offer much help. ... | |
| Jupiter | 11/27/2007 |
| Q: Seeing the size of jupiter and it being a gas giant is it possible for it to someday become a sun A: While Jupiter does, indeed, seem to have ample mass to become a star, the fact is that its total ... | |
| Astrophysics Career | 11/25/2007 |
| Q: I wish to be an astrophysicist. Is it related to daily life? How? ANSWER: Hello, First, it is well ... A: You are correct that most governments will not support astrophysics unless: a) they have a large ... | |
| Astrophysics Career | 11/24/2007 |
| Q: I wish to be an astrophysicist. Is it related to daily life? How? A: First, it is well to recognize that astrophysics is not one uniform discipline but rather a general ... | |
| Velocity of EMR ! | 11/22/2007 |
| Q: I wanted to know that why there is variation in velocity of light when it enter from one medium to ... A: Okay, yes there IS a variation, when light transits from one medium to another. For example, there ... | |
| Loss cone instability and flares | 11/19/2007 |
| Q: Under what conditions might a loss-cone instability lead to a solar flare? A: First, let's go back and review a bit about what a loss cone is and then loss-cone instability. We ... | |
| global warming | 11/18/2007 |
| Q: Has anyone studied the possibility that the weight we are taking off of the earth everyday by ... A: NO one to my knowledge has studied this at all, but it is hard to see why they would. While the ... | |
| Deviation of emr under infulence of gravity | 11/18/2007 |
| Q: Greetings!! can you tell me what was the actual deviation of emr passing by the star, in the famous ... A: In the reference I have ('Gravitation and Spacetime', 2nd ed. by Hans O'Hanion and Remo Ruffini) the ... | |
| Mass of Photon is not equal to ZERO ! | 11/18/2007 |
| Q: Greetings .!!! Ive derived the equation for da mass of photon .. just wnted to make sure that is it ... A: While you are correct that the mass of the photon is non-zero - you're own estimate of it is ... | |
| big bang | 11/14/2007 |
| Q: Firstly I approach this question as one who has little knowledge and appalling maths, but a general ... A: What I think you are referring to is the inflationary aspect of early cosmic expansion. Note that ... | |
| Stars and Elements in the Universe | 11/10/2007 |
| Q: How is energy released in stars and how does this effect the composition of elements in the ... A: Energy is released in stars by the process of nuclear fusion which can take different forms, with ... | |
| Galactic Alignment | 11/1/2007 |
| Q: I've heard the talk of the sun aligning with our galactic center this decade, a rare event. It's ... A: The link you provided had some fascinating information for sure, e.g. clusters of craters of similar ... | |
| Galactic Alignment | 11/1/2007 |
| Q: I've heard the talk of the sun aligning with our galactic center this decade, a rare event. It's ... A: Joe I also seem to recall that an apocalyptic "disaster" was predicted 25 years ago when Jupiter ... | |
| The big rip? | 10/16/2007 |
| Q: The theory of the big rip explains that all matter in the universe is moving away from each other, ... A: The possibility of recollapse of the universe actually hinges on a very critical quantity which we ... | |
| life | 10/10/2007 |
| Q: What got you interested in astrophysics? A: Michelle I think I first became interested in astrophysics not long after I built my first ... | |
| Mean molecular weights of stellar gases | 10/8/2007 |
| Q: How do I show that: i) the mean molecular weight of a pure hydrogen gas in a star is 1/2? ii) the ... A: and thanks for a genuine astrophysics question! In obtaining the mean molecular density we assume ... | |
| forces of nature | 8/10/2007 |
| Q: Is there a relationship between the forces of nature that exist on an astronomical level and those ... A: The only force we know of that exists on the "astronomical scale" is gravitation. Currently, there ... | |
| Gravity in space | 8/9/2007 |
| Q: First who came up with this theory and since moons and planets for that matter dont often rotate on ... A: I think, from your answer - you are really confusing an actual theory (General Relativity) which ... | |
| a career in research in the field of astrophysics | 8/8/2007 |
| Q: but when i get out and have my college money i want to study astrophysics just for the fact i would ... A: Actually - an almost identical question to yours was asked last year, and the answer I gave is evry ... | |
| Brier P-Score for Flare Prediction | 5/16/2007 |
| Q: Can you explain a bit about the Brier P-score for predicting flares and how it would actually work? A: The Brier P-Score is a method of statistical flare forecast evaluation developed in 1950 as a ... | |
| brightness temperature of a supernovae remnant | 5/8/2007 |
| Q: I'm having a little trouble with a problem that I hope you can point me in the right direction with ... A: I think all you really need to solve your problem is a nudge in the right direction with respect to ... | |
| Magnetic helicity | 5/5/2007 |
| Q: What is magnetic helicity and how can we recognize it on the Sun? A: Before going on to magnetic helicity, it is useful to get a general idea of helicity – for example ... | |
| Virial Theorem & Total stellar energy | 4/9/2007 |
| Q: I've read that the virial theorem can be used to show the total energy of a star is negative and ... A: The virial theorem is very important in stellar astrophysics. According to the virial theorem: 2K ... | |
| Static corona? | 4/6/2007 |
| Q: I have read that the assumption of a static corona (no gas expanding into space as solar wind) can ... A: Of course, a static corona seems on first blush to be reasonable but that is why it is necessary to ... | |
| Problem | 4/5/2007 |
| Q: I have been trying to work out this past exam problem but with no success. Can you provide any hints ... A: This problem actually isn't too difficult to work, and is largely a variant on the previous problem ... | |
| Plasma mirror problem | 4/4/2007 |
| Q: Can you help with ideas to solve this problem? Consider a plasma mirror machine of length 2L with ... A: Jani ----------------!-------------- ----------------0-------------- B = (L) B = (-L) ... | |
| Two stream instability | 4/3/2007 |
| Q: Can you tell me under what conditions the two stream instability occurs for plasmas? I understand ... A: Two stream instability is a very common phenomenon in plasmas. It’s usually induced by an energetic ... | |
| gravity | 4/1/2007 |
| Q: how far from the sun's core would you need to be to get 1.1 to 0.9 times Earth gravity? is this out ... A: One can obtain the surface gravity of the Sun (at the photosphere - needed as a reference level) by ... | |
| Alfven waves | 2/10/2007 |
| Q: Can you explain to me how Alfven waves arise? Please use any necessary math to show properties of ... A: Alfven waves are the most important waves propagating in the solar atmosphere, as well as the ... | |
| Magnetic Reynolds number | 12/26/2006 |
| Q: Can you tell me how exactly the magnetic Reynolds number is obtained and what its values is for ... A: The magnetic Reynolds number is a (dimensionless) measure of the degree of coupling between the ... | |
| Maxwell equations applied to solar fields | 12/17/2006 |
| Q: Can you tell me how the Maxwell equations for electromagnetic fields have to be modified for solar ... A: Maxwell’s equations in differential form (much easier to write than in integral form) for free space ... | |
| Big Bang theory | 12/3/2006 |
| Q: Is not the Big Bank Theory more applicable on a galactic scale than a universe wide scale? A: No - if the Big Bang is applicable to anything, it is the cosmos as a whole. First, The 2.7 k ... | |
| Astrophysics problems | 11/28/2006 |
| Q: Can you give assistance in solving the following? Thanks! 1) The lines of the Balmer series crowd ... A: Here are suggested strategies, hints for solving the problems: Problem 1 The Balmer lines are ... | |
| Gray atmosphere and distance modulus | 11/21/2006 |
| Q: In my studies I have come across "gray atmosphere" to with stellar radiation. How do you explain ... A: Modeling stellar atmospheres is a very complex undertaking that often requires we make basic ... | |
| hydrogen absorption lines | 11/15/2006 |
| Q: How are the hydrogen absorption lines formed in a star like the Sun? A: Differences in stellar spectra are actually due mostly to the widely varying temperatures in the ... | |
Philip A. Stahl
Top Expert on this page
Expertise
I specialize in stellar and solar astrophysics. Can answer any questions pertaining to these areas, the spectroscopic analysis of stars – as well as the magneto-hydrodynamics of sunspots and solar flares. Sorry – No homework problems done or research projects! I will provide hints on solutions.
Experience
Have published papers on the relationship between sunspot morphology and solar flares; discovery of SID flares related to this, constructed computerized stellar models; MHD research.
Organizations
American Astronomical Society (Solar physics and Dynamical astronomy divisions), American Geophysical Union, American Mathematical Society, Intertel.
Publications
Solar Physics, Journal of the Royal Astronomical Society of Canada, Journal of the Barbados Astronomical Society, Meudon Solar Flare Proceedings (Meudon, France)
Education/Credentials
B.A. degree in Astronomy; M.Phil. degree in Physics - specializing in solar physics.
Awards and Honors
Postgraduate research award- Barbados government; Studentship Award in Solar Physics - American Astronomical Society
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