- #1
bothnicum
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How deep in space can current radars reach?
Celestial Reflections: How Far Can Radars Reach in Space?
- Context: Undergrad
- Thread starter bothnicum
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Discussion Overview
The discussion revolves around the capabilities and limitations of radar technology in space, particularly regarding how far radars can reach and the implications of reflected signals from celestial bodies. Participants explore theoretical aspects, practical challenges, and speculative ideas related to radar reflections and gravitational phenomena.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
- Conceptual clarification
Main Points Raised
- Some participants suggest that the effectiveness of radar detection depends on both the size of the object and its distance, with Saturn and its moon Titan cited as examples of distant radar imaging.
- There is a discussion about the time delay in radar reflections, with one participant noting that reflections from Titan indicate events that occurred 2.25 hours prior.
- Speculation arises about the potential for future developments in detecting reflected radiation to provide insights into the past, though this is met with skepticism regarding the practicality of such methods.
- One participant argues that the concept of gravitational reflectors is flawed due to gravity's nature as an attractive force, contrasting it with other forces that can act as both attractive and repulsive.
- Another participant proposes the idea of using clusters of black holes as potential reflectors, suggesting they could bend light similarly to reflective surfaces.
- There is mention of a recent discussion about black holes acting as very weak reflectors, although practical applications of this idea are questioned due to the faintness of such reflections.
- Questions are raised about the existence of toroidal-shaped black holes and their potential reflective properties, though no evidence is provided to support this idea.
Areas of Agreement / Disagreement
Participants express a range of views on the capabilities of radar in space, the nature of gravitational interactions, and the feasibility of using black holes as reflectors. No consensus is reached on these speculative ideas, and multiple competing perspectives remain throughout the discussion.
Contextual Notes
Limitations include the speculative nature of gravitational reflectors, the practicality of detecting faint reflections from black holes, and the unresolved status of toroidal black holes as a concept.
- #2
Nereid
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It's as much a question of 'how big is the object we're trying to get a radar image of?' as it is of 'how far away is object?'
AFAIK, Saturn, its rings and moon Titan hold the record:
http://www.aas.org/publications/baas/v34n3/dps2002/109.htm
http://www.news.cornell.edu/Chronicle/03/10.9.03/Titan_hydrocarbon.html
The distance? >1 billion km
In another sense - radar used to first detect an object within, say, 1 million km - I suspect the difficulty is more to do with 'illuminating the sky' than anything else. The methods used to get radar images of Saturn's rings won't really work if your objective is to spot a large meteor closing fast on the Earth.
AFAIK, Saturn, its rings and moon Titan hold the record:
http://www.aas.org/publications/baas/v34n3/dps2002/109.htm
http://www.news.cornell.edu/Chronicle/03/10.9.03/Titan_hydrocarbon.html
The distance? >1 billion km
In another sense - radar used to first detect an object within, say, 1 million km - I suspect the difficulty is more to do with 'illuminating the sky' than anything else. The methods used to get radar images of Saturn's rings won't really work if your objective is to spot a large meteor closing fast on the Earth.
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- #3
bothnicum
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Thanks for excellent links
So it takes 2.25 hours to get a reflection back from Titan
Reflections are interesting. Reflected signal is allways a signal from the history. Radar reflection from Titan tells (among other thigs) that 2.25 hours back in the history some people were experimenting with a radar.
Reflection of sunlight from Pluto tells something about the Sun approximately 10 hours ago.
Could the developments in detecting reflected radiation reach in the future days or even years?
Research of such reflections would provide us a new approach in search of the past?
So it takes 2.25 hours to get a reflection back from Titan
Reflections are interesting. Reflected signal is allways a signal from the history. Radar reflection from Titan tells (among other thigs) that 2.25 hours back in the history some people were experimenting with a radar.
Reflection of sunlight from Pluto tells something about the Sun approximately 10 hours ago.
Could the developments in detecting reflected radiation reach in the future days or even years?
Research of such reflections would provide us a new approach in search of the past?
- #4
Nereid
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No better than taking a picture now and developing the film tomorrow!
- #5
bothnicum
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Picture taking works only when you know that this is the moment and topic you want to watch later. Same is valid for video.
Instead given that basically all celestial objects are reflective, among the incoming radiation there must be (very) weak signals that are reflections from the Sun or even our planet. And the reflections are there also in the case you didn't bring the camera with you.
From a single reflector at the distance of N light years, we will basically get continuous stream originated 2N years ago. Various distances enables us to "see" over various distances in time.
The question is, are there such reflective surfaces big enough.
If one can speak about gravitational lenses, why can't we assume the existence of gravitational reflectors...
- #6
Labguy
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"If one can speak about gravitational lenses, why can't we assume the existence of gravitational reflectors..."
Because, in most basic terms, of the four forces (Strong Nuclear, EM, Weak Nuclear and Gravity), only the first three are known to act as both a repulsive and attractive forces. Gravity is attractive only. So, if "gravity waves", Gravitons, etc. approach a body they are attractive-only and would interact as such and not "reflect" back off that body. They (it, gravity) might change a property of the other body, such as its motion, and we might be able to detect that change by other means. But, the only "gravity" we could detect from the other body would be the influence of its own gravity/mass.
Because, in most basic terms, of the four forces (Strong Nuclear, EM, Weak Nuclear and Gravity), only the first three are known to act as both a repulsive and attractive forces. Gravity is attractive only. So, if "gravity waves", Gravitons, etc. approach a body they are attractive-only and would interact as such and not "reflect" back off that body. They (it, gravity) might change a property of the other body, such as its motion, and we might be able to detect that change by other means. But, the only "gravity" we could detect from the other body would be the influence of its own gravity/mass.
- #7
bothnicum
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Cluster of black holes as a reflector?
Instead of a reflecting surface, could it be possible to find such a cluster of black holes that bends light like a reflecting surface.
Instead of a reflecting surface, could it be possible to find such a cluster of black holes that bends light like a reflecting surface.
- #8
Nereid
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IIRC, there was some discussion recently about black holes acting like very weak reflectors, so that if you looked at the black hole, you would see a (very faint) image of the Sun - light goes out to the black hole, gets bent 180o, and we see the bent light much later.
In practical terms, this isn't very helpful, at least to what bothnicum is looking for. For a start, the black hole 'reflection' ties you down just as much as photos (you can't vary the time delay - that's fixed by the distance to the black hole). Then there's the small matter of actually seeing the 'reflection' - the Sun, as seen from Earth is mag -26; a black hole reflection would likely be about as faint as the faintest galaxies in the recent Hubble Ultra Deep Field (~30 mag), > 20 orders of magnitude!
In practical terms, this isn't very helpful, at least to what bothnicum is looking for. For a start, the black hole 'reflection' ties you down just as much as photos (you can't vary the time delay - that's fixed by the distance to the black hole). Then there's the small matter of actually seeing the 'reflection' - the Sun, as seen from Earth is mag -26; a black hole reflection would likely be about as faint as the faintest galaxies in the recent Hubble Ultra Deep Field (~30 mag), > 20 orders of magnitude!
- #9
bothnicum
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Toroidal black hole as a reflecftor?
Question 1: Are there any evidence of toroidal shape of a black hole?
Question 2: Could such a black hole act as a reflector in the sense described above?
Question 1: Are there any evidence of toroidal shape of a black hole?
Question 2: Could such a black hole act as a reflector in the sense described above?
- #10
Nereid
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Not that I'm aware of.
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