A minor objection to the use of Stark broadening to explain the width of the hydrogen lines
in the gaseous models rests on the fact that the appropriate experiments on hydrogen plasma do not exist.
The chosen segment is centered on the hydrogen line
. It is wide enough that a transmitter broadcasting exactly at the hydrogen frequency could be moving toward or away from Earth by up to 270 kilometers per second and still be picked up despite the resulting Doppler shift.
Run by the SETI Australia Centre, Southern SERENDIP also makes piggyback SETI observations at the hydrogen line
. In addition, two 4-million-channel versions of SERENDIP IV are being built for the University of Western Sydney in Australia and the Institute of Radioastronomy in Bologna, Italy.
Under Pickering's direction, Fleming had followed an empirical approach to classifying stars; she considered the presence or absence of specific lines, such as the hydrogen lines
, in a stellar spectrum.
Any appliance must have its hydrogen lines
cleaned and purged before charging a metal hydride vessel; if not, contamination of the cartridge is almost a certainty.
Its already inconspicuous hydrogen lines
became weaker, whereas lines from elements such as scandium, rubidium, yttrium, zirconium, barium, and tin started to appear.
The hydrogen lines
ofthe Balmer series, and, as Babcock has recently shown, ofthe Paschen series as well, are very strong in the Sun, though the energy required to put an atom into condition to absorb these series is, respectively, 10.16 and 12.04 volts-higher than for any other solar absorption lines.
surface temperature (K) O Blue >25,000 B Blue 11,000-25,000 A Blue 7,500-11,000 F Blue to White 6,000-7,500 G White to Yellow 5,000-6,000 K Orange to Red 3,500-5,000 M Red <3,500 Type Main characteristics Examples O Singly ionised helium, strong ultraviolet continuum 10 Lacertae B Neutral helium lines in absorption Rigel, Spica A Hydrogen lines
at maximum strength Sirius, Vega F Metallic lines become noticeable Canopus, Procyon G Solar-type spectra Sun, Capella K Metallic lines dominate.
Beginning in 1890 Pickering and Fleming expanded Secchi's groups with Roman letters A through O, based primarily on the strengths of the observed hydrogen lines
(P and Q were used for those that did not fit).
At such a high redshift the usual hydrogen lines
are shifted far into the infrared out of sight.