LASER beam (APOD 31 July 2007)
LASER beam (APOD 31 July 2007)
http://antwrp.gsfc.nasa.gov/apod/ap070731.html
Has anybody ever thought of equiping the Iinternational Space Station with a telescope ?
Has anybody ever thought of equiping the Iinternational Space Station with a telescope ?
Wolf Kotenberg
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Re: LASER beam
I was wondering about this one, but thought it was because (1) we had a space telescope already, and (2) that the movements of the occupants and various docking procedures would 'knock' the telescope.ta152h0 wrote:http://antwrp.gsfc.nasa.gov/apod/ap070731.html
Has anybody ever thought of equiping the International Space Station with a telescope ?
Regards,
Andy.
Andy.
APOD - laser strike at galactic centre
Ref. todays picture and comment regarding the effect of shining a laser at the galactic centre. Forgetting for the moment the distances and hence time frames involved and given that we, with our limited technology, are able to detect water molecules in distant atmospheres, is it not the case that no matter how much the light from the sun "blends" with the laser light, it should be possible for a sufficiently advanced civilisation to distinguish between coherent (laser) light and non-coherent (sun) light?
(With apologies if this is a daft question - I'm a newbie!)
(With apologies if this is a daft question - I'm a newbie!)
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Re: APOD - laser strike at galactic centre
That's the idea.akwaugh wrote:Ref. todays picture and comment regarding the effect of shining a laser at the galactic centre... it should be possible for a sufficiently advanced civilisation to distinguish between coherent (laser) light and non-coherent (sun) light?
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Re: LASER beam
Additionally, the Hubble and other space telescopes have their own pointing priorities, while NASA likes to keep the ISS in certain orientations relative to the sun to help maintain proper temperatures. I imagine this would quite frequently conflict with observations. Also, the ISS orbit was chosen for accessibility to the Russians, and the I believe the Hubble orbit was chosen for observational opportunities. Of course, the future JWST won't be anywhere near either of those.Andy Wade wrote:I was wondering about this one, but thought it was because (1) we had a space telescope already, and (2) that the movements of the occupants and various docking procedures would 'knock' the telescope.
There would be a few small reasons to want a telescope on the ISS, like accessibility for maintenance, but the vibrations of people moving around alone would make it less useful than even a modest independent telescope.
Skylab and the Russian Saylut space stations were equipped with telescopes. Since then robotic space telescopes have eliminated the need.
I'm slightly confused though...how did this question arise from today's APOD?
"Any man whose errors take ten years to correct is quite a man." ~J. Robert Oppenheimer (speaking about Albert Einstein)
that was the poiint
that was the point, to quantify how visible is the laser beam thru the earths atmosphere. Pass the brew, ice cold.
Wolf Kotenberg
A powerful laser will usually be visible (especially in the dark), since even the cleanest air outdoors is loaded with dust and water droplets that will scatter light from the beam. Only in a high vacuum or other 'perfect' environment, would the beam would be practically invisible.
As for the colour of the laser light, I imagine they'd be using a frequency close to whatever frequencies they'd be observing at, since the atmosphere is going to scatter or refract different frequencies of light by differing amounts.
As for the colour of the laser light, I imagine they'd be using a frequency close to whatever frequencies they'd be observing at, since the atmosphere is going to scatter or refract different frequencies of light by differing amounts.
Don't just stand there, get that other dog!
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Causality aside, this was the part that caught my attention. Would there be casualties viewed from somewhere else? Do casualties obey relativity?As for inter-galaxy warfare, when viewed from our Galaxy's center, no causalities are expected.
"Any man whose errors take ten years to correct is quite a man." ~J. Robert Oppenheimer (speaking about Albert Einstein)
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Re: APOD - laser strike at galactic centre
Not necessarily. First of all, there's no way that laser light traveling between stars will stay coherent. Coherence is a property that is lost pretty quickly with distance from the cavity. And simply being nearly monochromatic isn't a guarantee that the source is artificial- natural lasers probably exist, as well as natural narrowband filters. If the sender wants to be sure their signal is recognized as artificial, it's important to modulate it in some way. Low speed data could be transfered with simple AM over huge distances.akwaugh wrote:Ref. todays picture and comment regarding the effect of shining a laser at the galactic centre. Forgetting for the moment the distances and hence time frames involved and given that we, with our limited technology, are able to detect water molecules in distant atmospheres, is it not the case that no matter how much the light from the sun "blends" with the laser light, it should be possible for a sufficiently advanced civilisation to distinguish between coherent (laser) light and non-coherent (sun) light?
Chris
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Re: APOD - laser strike at galactic centre
[quote="Chris Peterson]
Not necessarily. First of all, there's no way that laser light traveling between stars will stay coherent. Coherence is a property that is lost pretty quickly with distance from the cavity. And simply being nearly monochromatic isn't a guarantee that the source is artificial- natural lasers probably exist, as well as natural narrowband filters. If the sender wants to be sure their signal is recognized as artificial, it's important to modulate it in some way. Low speed data could be transfered with simple AM over huge distances.[/quote]
Wrong wrong wrong
Coherence is whenphotons are "in step" and have a definite phase relation. Unrelated to the point you are making. Lasers will not be detected in another solar system, much less galaxy because of "divergence". Divergence is when the the beam spread out over distance.
Take for example this these lasers http://www.dragonlasers.com which are pretty much the best the average person can get. They have a divergence of 1.2mRad.
This means for every meter the beam travels, it will spread by 1.2mm. go ahead and multiply 1.2mm by the number of meters required to travel any where outside this solar system then tell me that a laser can be seen!!!
Sure, you can spend A LOT of money and have a much smaller divergence but given the distances the beam will travel, useless.
Not necessarily. First of all, there's no way that laser light traveling between stars will stay coherent. Coherence is a property that is lost pretty quickly with distance from the cavity. And simply being nearly monochromatic isn't a guarantee that the source is artificial- natural lasers probably exist, as well as natural narrowband filters. If the sender wants to be sure their signal is recognized as artificial, it's important to modulate it in some way. Low speed data could be transfered with simple AM over huge distances.[/quote]
Wrong wrong wrong
Coherence is whenphotons are "in step" and have a definite phase relation. Unrelated to the point you are making. Lasers will not be detected in another solar system, much less galaxy because of "divergence". Divergence is when the the beam spread out over distance.
Take for example this these lasers http://www.dragonlasers.com which are pretty much the best the average person can get. They have a divergence of 1.2mRad.
This means for every meter the beam travels, it will spread by 1.2mm. go ahead and multiply 1.2mm by the number of meters required to travel any where outside this solar system then tell me that a laser can be seen!!!
Sure, you can spend A LOT of money and have a much smaller divergence but given the distances the beam will travel, useless.
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Re: APOD - laser strike at galactic centre
The question I was addressing suggested that the coherence of a laser could be used as a signature of an artificial source. I merely pointed out that coherence would be lost by the time the light reached another system, so that could not be used. This is not wrong, regardless of whether there are other reasons as well that laser communications might be difficult.Dr Evil wrote: Wrong wrong wrong
Coherence is whenphotons are "in step" and have a definite phase relation. Unrelated to the point you are making.
1/R affects all electromagnetic radiation. That doesn't mean it can't be detected, only that the signal gets weaker with distance. A bright, modulated laser beam can certainly be detected even if it has diverged- it's just a question of the sensitivity of the receiver.Lasers will not be detected in another solar system, much less galaxy because of "divergence". Divergence is when the the beam spread out over distance.
Chris
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As noted earlier, laser light loses its coherence quickly with distance, so that cannot be used as an indicator. Natural lasers (which are rare compared with natural masers) are identified by detecting a narrow emission band with a predicted Doppler broadening profile, and at too high an intensity to be explained without some amplification process. I believe all the natural lasers that have been seen are either in the infrared (around 10um) and are the result of CO2 transitions, or in the far infrared (169um) from a hydrogen transition.Qev wrote:I'm curious how astronomers go about detecting naturally-occurring stellar lasers. Are they detecting the coherence of the laser light, or simply the strong peak emission frequency in the stellar spectrum?
Chris
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