news@husc6.HARVARD.EDU (USENET News System) (10/17/86)
> > Second, what about Cerenkov(sp?) radiation? If the slower than c > apparant velocity is an effect of the induced radiation from electrons, > why should a particle moving through the intervening vacuum cause > radiation? > From: willner@cfa.harvard.edu (Steve Willner) Path: cfa!willner Cherenkov (should be spelled as you have, but with hacek over the C; becomes Ch in English) radiation occurs when a particle exceeds the speed of light in the current medium of travel. It obviously cannot occur for a particle travelling in vacuum, but it does occur for high energy cosmic rays when they enter the Earth's atmosphere. The Smithsonian Astrophysical Observatory operates a telescope on Mt. Hopkins to observe cosmic gamma rays by Cherenkov radiation of secondary particles. That is, the gamma ray enters the atmosphere and hits an atom, ejecting particles at high energy. These in turn hit more atoms, ejecting more particles. If the gamma ray energy is high enough (above 10**15 eV or so, if I remember correctly), the ejected particles will be going faster than the speed of light in air and will radiate a detectable pulse of light by Cherenkov radiation. ("Detectable" means with a 10-meter diameter collecting dish; you'll never see anything with your eye.) Steve Willner Phone 617-495-7123 Bitnet: willner@cfa1 60 Garden St. FTS: 830-7123 UUCP: willner@cfa Cambridge, MA 02138 USA Telex: 921428 satellite cam
james@reality1.UUCP (james) (10/27/86)
In article <422@husc6.HARVARD.EDU> news@husc6.HARVARD.EDU (USENET News System) writes: >If the gamma ray energy is >high enough (above 10**15 eV or so, if I remember correctly), the >ejected particles will be going faster than the speed of light in air >and will radiate a detectable pulse of light by Cherenkov radiation. >("Detectable" means with a 10-meter diameter collecting dish; you'll >never see anything with your eye.) I seem to recall that on one of the Apollo missions that astronauts reported seeing strange flashes of light. This was a long time ago, and I wasn't even in high school at the time, so I may just be the victim of a modern "old wive's tale". Does anyone else remember anything about this and/or the cause? -- James R. Van Artsdalen ...!ut-ngp!utastro!osi3b2!james "Live Free or Die"
ethan@utastro.UUCP (Ethan Vishniac) (10/27/86)
In article <58@reality1.UUCP>, james@reality1.UUCP (james) writes: > In article <422@husc6.HARVARD.EDU> news@husc6.HARVARD.EDU (USENET News System) writes: > >If the gamma ray energy is > >high enough (above 10**15 eV or so, if I remember correctly), the > >ejected particles will be going faster than the speed of light in air > >and will radiate a detectable pulse of light by Cherenkov radiation. > >("Detectable" means with a 10-meter diameter collecting dish; you'll > >never see anything with your eye.) > > I seem to recall that on one of the Apollo missions that astronauts reported > seeing strange flashes of light. I remember hearing that this was due to the direct stimulation of the optic nerve by cosmic rays, (as opposed to seeing secondary radiation) and that it was a persistent phenomena (i.e. not just on one mission). Is there a biologist here who can comment on the plausibility of this? -- "More Astronomy Ethan Vishniac Less Sodomy" {charm,ut-sally,ut-ngp,noao}!utastro!ethan - from a poster seen ethan@astro.AS.UTEXAS.EDU at an airport Department of Astronomy University of Texas
msellers@mntgfx.mentor.com (Mike Sellers) (02/19/88)
In article <4809@ihlpg.ATT.COM>, tan@ihlpg.ATT.COM (Bill Tanenbaum) writes: > < A stick breaking under foot generates a (sonic) shock wave (chaotic behavior > < due to parts of the stick moving faster than the speed of sound ?) -- I > < don't think there is analogous light behaviour in the everyday world > < (aurora borealis?). > > There is analogous light behavior. It's called Cherenkov radiation. > It occurs when particles travel through a transparent medium faster > than the speed of light in that medium. It occurs in the everyday > world, but not so as you'd notice. > -- > Bill Tanenbaum - AT&T Bell Labs - Naperville IL ihnp4!ihlpg!tan Isn't one instance of this the bluish glow given off by water-bathed nuclear reactors, or more precisely, by the emitted particles moving faster than the speed of light in water? What is the mechanism behind this? Particles travelling faster than c in *any* medium bothers me just a bit ... I mean, what if (physical non sequitor approaching) we found a meduim wherein the speed of light was greater than it is in a vacuum? What consequences could this have? -- Mike Sellers ...!tektronix!sequent!mntgfx!msellers Mentor Graphics Corp., EPAD msellers@mntgfx.MENTOR.COM "Never confuse motion with action." -- Ben Franklin