The forum discussion centers on the observation of the hydrogen 21 cm line and its implications for measuring hydrogen speed in space. Participants clarify that the observed frequency range of 200 MHz to 15 MHz is due to cosmological redshift, not just intergalactic hydrogen. The discussion emphasizes that defining "speed" relative to Earth is problematic due to the complexities of redshift components: cosmological, gravitational, and Doppler effects. Ultimately, the speed of distant hydrogen gas clouds cannot be accurately defined without a clear reference frame.
PREREQUISITESAstronomers, astrophysicists, and students interested in cosmology, particularly those studying hydrogen's role in the universe and the complexities of measuring cosmic phenomena.
Because the hydrogen atoms being measured are in gas clouds in our own galaxy, whose velocities relative to Earth are not going to be very fast when compared with the speed of light.Jaaanosik said:why we do not measure 'fast' hydrogen atoms.
My understanding was the measurements in the 200MHz-15MHz as per wiki page include Doppler effect in combination with the other factors.PeterDonis said:But until post #23, you did not tell us what "hydrogen atoms" you were even talking about. Not until post #23 did you actually give us a reference that showed specific measurements of particular hydrogen gas clouds--and then they turn out to be hydrogen gas clouds in our own galaxy, whose measured power spectrum, as shown in the "previous post" on physicsopenlab (linked to at the top of the one you referenced), peaks at about 1420 MHz, exactly as expected for the 21 cm hydrogen line with no cosmological redshift. Yet in your OP, you talked about frequencies ranging from 200 MHz down to 15 MHz, which cannot possibly be from the measurements discussed in the physicsopenlab article.
Have nothing to do with the actual measurements you referenced in post #23.Jaaanosik said:the measurements in the 200MHz-15MHz as per wiki page
And at this point that question has been sufficiently answered, and enough time has been spent on it. Thread closed.Jaaanosik said:The title: "Hydrogen line observation frequency range and space Hydrogen speed?
points towards the question trying to resolve the speed of hydrogen in space.