Talk:Radio window

What blocks long radio waves?

This article claims that radio waves longer than about 11 meters are blocked. Other articles list the various molecules that absorb light at various shorter frequencies. What blocks long radio waves? --68.0.124.33 (talk) 16:21, 31 October 2008 (UTC)[reply]

Hmm, Radio propagation discusses this question, but from the terrestrial communication point of view, not the astronomical or outer space point of view. It seems to be an omission in the encyclopedia. Jim.henderson (talk) 01:29, 1 November 2008 (UTC)[reply]

Terrestial propogation can reach huge distances with long waves through a process called skywave. This is done by reflecting the radio wave off the ionosphere, possibly with several skips reflecting back and forth between the Earth's surface and the ionosphere. The same phenomenon prevents long waves from reaching the Earth's surface from space, they are simply reflected back into space from the ionosphere. Similarly, Earth ground stations cannot reach space with long waves to communicate with spacecraft.

The physics of it is that the ionosphere forms a conducting layer; radio waves are reflected off it for the same reason microwaves are reflected from the metal walls of a waveguide, or for that matter, light from a mirror. See Reflection (physics)#Mechanism for more information. The real thing that needs explaining is not why long waves are stopped, but why any waves get through at all. SpinningSpark 10:06, 29 December 2021 (UTC)[reply]

Radio window wider than optical window?

The opening of the article states "The radio window is a range of frequencies of electromagnetic radiation that penetrate the earth's atmosphere. This window is significantly wider than the optical and infrared windows." If one defines the window as "a range of frequencies" then the statement that it is "significantly wider" is expected to mean that it has a wider bandwidth. This is patently not true; the radio window has a bandwidth less than 1 THz. The optical window has a bandwidth of around 850 THz. The radio window is wider in terms of wavelengths, but where is that important? Frequency bandwidth, on hte other hand is important in communications because that sets the information transfer rate. In any case the article did not say wavelength.

Does the cited source actually say this directly, or is it something being inferred? The only sense in which the radio window is wider is logarithmically, that is, number of octaves or decades. That may be important to astronomers in some way (I don't know, not my field) but I can't see how. It doesn't provide better imaging; the longer wavelengths mean a poorer resolution than the visible band. SpinningSpark 10:39, 29 December 2021 (UTC)[reply]

Hello and thank you for your most accurate and totally right comments. Indeed, the source I cited [Chaisson, McMillan - Astronomy Today-Pearson (2014), p.114] suggests the radio window is wider than the optical in terms of wavelength range and more specifically when plotted logarithmically, however for some reason I skipped this note. The reason why this feature could be important to radio astronomy eludes me, but the sentence should nevertheless be erased from the article's introduction since it is quite misleading! Thank you again, and if you can, have a look at the related articles I recently updated/created (Optical window, Atmospheric window, Window (optics))--L'OrfeoGreco (talk) 20:10, 29 December 2021 (UTC)[reply]

Thanks for fixing that. I've now managed to see the book at IA. Basically, the radio window is wider because they have drawn it wider, not because it actually is. SpinningSpark 09:24, 31 December 2021 (UTC)[reply]