Lensing Definition and 88 Threads

It is known that light from stars bend near surface of sun due to its mass. Similarly light will bend near Earth's surface (may be insignificant due to less mass). My question is that sunlight that strikes Earth's surface travels a straight path from sun or a curves near Earth's surface ?

I have been trying to work this out for the last couple of weeks, but I just keep getting the Newtonian deviation in angle for a path of a photon traveling from x=-∞ to x=∞. At first I tried putting the actual path into a computer simulation, transforming back and forth between the hovering...

On the subject of gravitational lensing there seems to be two rather different phenomena. The "arc" phenomena seems rather plausible to me, if light is affected by gravity which is natural then there should be able to get that kind of behaviour. But the multiple imaging stuff, seems rather...

Dear all, so far I have only studied weak lensing. Therefore I understand little about multiple images.The light paths, by Fermat's principle, have to correspond to stationary points of the (proper) time delay. Minima, maxima saddle points. Basics are nicely reviewed here [p.14]...

Do the new optical and time shifting versions of 3D cloaking present a challenge to gravitational lensing as a valid proof of gravity ? Am curious if the time shifting constituent of the theories can mimic the redshifting observed in arcs and lenses also. Seems that with the findings of...

Hello all, Would like to get some feed-back on some questions I had about special/general relativity and a thought experiment. In the case of gravitational lensing, an obvious case being the Earth is lined up with the sun which is lined up with a distant star. From Earth the star is seen...

Hi, The recent Astronomy Picture of the Day: http://apod.nasa.gov/apod/ap111221.html Has the following caption: ...the gravity of a luminous red galaxy (LRG) has gravitationally distorted the light from a much more distant blue galaxy. I was under the impression that the more...

Hello, could someone point out to me 1) Ironclad evidence of correlated light curves - and I mean a correlation that is beyond doubt - among lensed quasars 2) Morphological correspondence - e.g. corresponding jets - in images of lensed quasars. I can find sketchy cases which may be...

Can gravitational lensing also be explained by the refraction of light from a more distant object through a gradient of radiant heat and dense cool space? Same difference? Or completely separate and unrelated? If unrelated, how can this optical phenomenon be determined as a result of...

I wasn't sure whether this was the right place to post this since it isn't really coursework, but it seems like it could be. My problem is with the deflection angle of light for several point masses. The deflection for a point mass can be described as: \frac{4GM}{c^{2}\xi} where \xi...

Hi. I am trying to make my way through http://www.mathpages.com/rr/s8-09/8-09.htm one step at a time if I have too. I already got stuck once, where it says: The paper makes it sound like these two variables are constant, but the way it should be defined is "Let t1 be the time...

The basic question is: will a photon traveling through a vacuum lose some of its energy due to interactions with gravity from a massive body? Gravitational lensing implies that the photon will change its initial direction but is its energy conserved (i.e. differences in blueshift/redshift...

Let us assume that two light rays are started at the same time symmetrically (towards the left and towards the right side of the star) which are diffracted due to the gravitational effect of a star and they meet each other at the same place behind the star. The meeting is the same event...

Fermat's principle states that light travels the path of stationary time, I've read up on this from several sources and I've come to realize that this means that it will travel paths of extrema, (maxima, minima & saddle points). For minima, refraction is often given as an example (minizing...

Forgive what might strike you as an excessively elementary question, as well as irrelevant, but... Well, at least I guarantee that it is not any classroom project! Imagine a mass of pretty clean helium (yeah, *I* know, but this is an academic exercise! :smile: It gets worse; read on!)...

Hi I'm new to the forums. I have a question I hope you guys can help me understand. When gravitational lensing produces multiple images of the same object, do they undergo any red/blue shift? And if so, is the frequency shift the same for each image?

I've been puzzled by this. If light of different frequencies (like ultra violet to infra-red) would experience different refraction angles in the presence of a powerful gravity field. I understand that light has zero rest mass but has effective mass given the fact it's in motion. What I'm...

Hello. In the attached a diagram there are 2 stars on the left, the upper star is the apparent position as veiwed from Earth and the lower star the true position. The central star is the Sun Could anyone give or direct me to an equation for the angle by which the light is deflected aº in...

Gravitational lensing displaces the apparent direction of a star outwards away from a gravitational source. Do you think it would be possible to see the same star at least twice simultaneously, one either side of this gravitational source? Even more likely, if the gravitational source was great...

Actually i want know about the lensing of light from accretion disc around a black hole(kerr and schwarschild). Is the lensing is strong for radie near minimum inner radius of accretion disc. I want know how the accretion disc will look like for a distant observer. Can somebody give me some...

Observer O sees object S in the imaginary position S', because of the gravitational lensing caused by the heavy mass M. Question 1. If O is positively charged and S is negatively charged, in what difrection acts the coloumb force - S or S' ? Question 2. If S is massive (but is still much...

I'm interested in the deflection angles of light rays passing by extremely dense gravitational objects, specifically black holes. First, I'd like to find the formula for the deflection angle of an incoming light ray. My googling (as well as a textbook from college, Hartle's "Gravity") states...

What is the extent of gravitational lensing? i mean, if every single star, black hole, galaxy ect is lensing light in all directions it would surely make the true nature/structure of the universe far different than is observable, right? we could be seeing the same object in two completely...

Does anyone know where I could find (online) a derivation of the deflection angle in gravitational lensing: alpha = 4GM/Rc^2 Thank you

Does gravitational lensing cause diffraction patterns, such as those seen by single, double, etc slit diffraction? In other words, would x-rays from object X get bent "less" than say microwaves or infrared? Would this happen if the light was passing between binary stars only, or could it...

I was wondering whether one has examined the spectrum of gravitational lensed light (nice description on wikipedia : http://en.wikipedia.org/wiki/Gravitational_lensing ). Have there been indications on some red or blue shifts in the light from different parts of the observed ring? Does anyone...

Does anyone know if gravitational lensing confirms the existence of Dark matter?

Light that has traveled millions of years is gravitationaly (lensed) around a body, if there is any frequency dependant light travel time ,would it not show up as if it had been split by a prism when it was lensed around said body, or would the various frequencies recombine?

Light having to travel through a gravitational field deflects towards the mass and thus increases the length and duration of its journey (traveling through more curved space-time takes more proper time than traveling through less curved space-time) I understand that unlike in refraction, light's...

I read that when a galaxy comes in the path of light coming from a quasar, its path bends slightly resulting in the formation of a giant luminous arc (called einstein ring). The phenomenon is called gravitational lensing. Can someone tell me something more about gravitational lensing ? Please...

Gravitational lensing (GL), first mooted in 1924, is now a technique being used by astronomers to detect dark matter. Lensing depends on the bending of light by the gravity of a mass concentration, such as a galaxy or galaxy cluster. In glass, it is the spatial gradient of the optical path...

Hi I was wondering where in the universe is gravitational lensing that i can see first hand through my telescope. Thanks!:biggrin:

Why does light bend when it encounters a black hole or a star? Does a black hole have a refractive index? It must depend on its mass if it does. A star can produce an effect knows as gravitational lensing which bends light in much the same way as an optical lens bends light, how does this...

I was wondering... Why doesn't Gravitational Lensing ever create a ring when bending light from an obstructed star? It seems to always create 2,3 or 4 clones of the star. I can't get my head around this, maybe I'm missing something fundamental? Your posts are appriciated. Regards, Sam

I have heard of two physical phenomena: 1. A photon traveling from one location to another, goes the path that takes the shortest time. (More correctly, the quickest paths has the highest probability amplitude) 2. Time is slowed down in a gravitational field. Is this how gravitational...

Ok I have this idea and i need you all to bash it so i can see what's wrong with it. Ok imagine a very very large black hole at distances like 10 billion light years, imagine that there could be black holes larger than we can fathom and imagine how many stars would lie behind such an anomaly...

I have been searching for alternatives to BBT and the doppler effect to explain everything, and have been dissapointed to find a lot of crackpots out there. I have recently found this website: http://www.geocities.com/newastronomy/Index.htm and the thing makes all kinds of sense (to my...

Gravitational Lensing - question An article published today at http://spaceflightnow.com/news/n0402/11lens/ stated that "Einstein's general theory of relativity predicts there should be an odd number of images, yet almost all observed lenses have only 2 or 4 known images." How and Why does...