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Cosmological Problems
In article ,
(Phillip Helbig (undress to reply)) writes: Visible light is about 0.4 to 0.7 microns (400 to 700 nm (nanometers), That range is what the human eye can see. In practice, the term "visible" often refers to light detectable by instrumentation suitable for visible light, say from 300 nm (the atmospheric cutoff) to 1000 nm (the intrinsic silicon limit). there is a bit of overlap between HST and JWST. JWST's short-wavelength limit is 600 nm. Its prime range is roughly 1000 to 3000 nm, and the long limit is 28000 nm (=28 microns). JWST is more or less a normal reflecting telescope, with a CCD as detector. Detectors are actually infrared hybrid arrays, not CCDs. They are based on the "HAWAII-2RG" technology: http://www.teledyne-si.com/products-...d-fpa-products You can easily search for "Planck focal plane" on the web and find an image showing lots of horns and other radio-astronomy stuff. Planck has I think "had" for that last word above. a wide frequency range, with frequencies from 30 GHz to 857 GHz, corresponding to wavelengths between a centimetre and about a third of a millimetre, the latter being about 300 microns. Typical traditional ground-based radio astronomy is in the GHz range and below, so wavelengths from centimetres to metres. Frequencies up to 15 GHz (wavelength 2 cm) were pretty common even when I was in school. Nowadays, the VLA https://public.nrao.edu/telescopes/vla/ makes images up to 50 GHz, and ALMA https://public.nrao.edu/telescopes/alma/ goes up to 950 GHz (though I don't think the highest frequencies are 100% operational yet). https://space.mit.edu/home/tegmark/movies.html In the plots, as usual, larger angular scales are on the left, smaller ones on the right. Yes, very nice. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#13
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Cosmological Problems
On 1/2/2019 8:09 AM, Steve Willner wrote:
In article , (Phillip Helbig (undress to reply)) writes: Visible light is about 0.4 to 0.7 microns (400 to 700 nm (nanometers), That range is what the human eye can see. In practice, the term "visible" often refers to light detectable by instrumentation suitable for visible light, say from 300 nm (the atmospheric cutoff) to 1000 nm (the intrinsic silicon limit). (In the same fashion, this silicon is a 'metal' of course!) ... Typical traditional ground-based radio astronomy is in the GHz range and below, so wavelengths from centimetres to metres. Frequencies up to 15 GHz (wavelength 2 cm) were pretty common even when I was in school. Nowadays, the VLA https://public.nrao.edu/telescopes/vla/ makes images up to 50 GHz, and ALMA https://public.nrao.edu/telescopes/alma/ goes up to 950 GHz (though I don't think the highest frequencies are 100% operational yet). 950 GHz sounds like an interesting LNA design problem! Is there any pointer to the solutions they use? (Other metals than silicon, undoubtedly..) -- Jos |
#14
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Cosmological Problems
I wrote:
In practice, the term "visible" often refers to light detectable by instrumentation suitable for visible light, say from 300 nm (the atmospheric cutoff) to 1000 nm (the intrinsic silicon limit). In article , Jos Bergervoet writes: (In the same fashion, this silicon is a 'metal' of course!) Heh. (Silicon is a semiconductor, not a metal, for anyone who is confused.) I reported how the language is used in practice. Human language is not always logical. I don't think I've seen silicon described as a metal, but it wouldn't shock me. Actually, come to think of it, doesn't silicon become a metal at very high pressure? 950 GHz sounds like an interesting LNA design problem! Is there any pointer to the solutions they use? (Other metals than silicon, undoubtedly..) There must be some design documents, but I don't know where. There should also be descriptions in the literature. Try an ADS search. My courses in radio astronomy were a long time ago, and the technology has changed. I don't think there is any amplification at the incoming frequency, though. In most radio telescopes, the signal is mixed down to an intermediate frequency and amplified there. In the old days, they would have used klystrons or something, but I doubt they do now. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
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Cosmological Problems
[[Mod. note -- I apologise for the delay in posting this article
(the delay was caused by a mistake on my part). This article was received by the s.a.r moderation system on 2019-02-06. -- jt]] On Tuesday, February 5, 2019 at 10:44:44 AM UTC-5, Steve Willner wrote: I wrote: In practice, the term "visible" often refers to light detectable by instrumentation suitable for visible light, say from 300 nm (the atmospheric cutoff) to 1000 nm (the intrinsic silicon limit). In article , Jos Bergervoet writes: (In the same fashion, this silicon is a 'metal' of course!) Heh. (Silicon is a semiconductor, not a metal, for anyone who is confused.) I reported how the language is used in practice. Human language is not always logical. I don't think I've seen silicon described as a metal, but it wouldn't shock me. Actually, come to think of it, doesn't silicon become a metal at very high pressure? I suspect Jos was hinting at the astro view of metals, IOW, there is hydrogen and helium, while the rest are metals. Ed |
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