In a message dated 10/30/2003 8:44:28 PM US Mountain Standard Time, [EMAIL PROTECTED] writes:
> > > Anyone? > > > > > > > > > > > > -- Ronn! :) > > > > > > >Hydrogen absortion line that was used by the Vegan broadcast in Contact? > > > > A bit more general than that. Radiation with a wavelength of 21cm or a > frequency of 1420 MHz corresponds to the energy difference between the two > hyperfine states of the neutral hydrogen atom: i.e., to the energy > difference between the states when the spins of the proton and the electron > are parallel and when they are antiparallel (the spinning charged particles > generate a magnetic field which in one case is aligned in the same > direction around both particles, so they repel each other, and in the other > case is aligned in opposite directions, so they attract each other). It > has been used for several decades to map the location of clouds of neutral > hydrogen (HI) in the spiral arms of our Galaxy, and so to map the spiral > arms of the Galaxy. Beginning about 1980 or so, Tully and Fisher realized > that the Doppler broadening of the 21-cm line from distant spiral galaxies > due to the rotation of the distant galaxy (the HI regions on one side of > the galaxy would be moving toward us while those on the opposite side would > be moving away from us, and the more the difference in the velocities, the > wider the line), and that the rotational velocity of a spiral galaxy is > related to its size, hence to its overall luminosity, so measuring the > broadening of the 21-cm line in distant spiral galaxies could give us a way > to measure its true brightness, and then by comparing that to the apparent > brightness, provide a way to measure its distance. > > Many astronomers interested in SETI have suggested that, since the 21-cm > line is a universal standard because hydrogen is the most common element in > the Universe, it would be reasonable for ETs interested in broadcasting a > signal which they wanted to be detected by other intelligent beings to > broadcast a signal a bit on one side or the other of the 1420 MHZ so it > might be detected accidentally by radio astronomers on other planets > looking for, say, Doppler broadening of the 21-cm line from natural > sources, as I described above . . . > > Um... Me savy movie. William Taylor -------------------- (And I bet this was his _short_ version.) _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
