If you ’re a radio fan , or have but been stuck in a automobile as day transitions into nighttime , you may have noticed that you do n’t get quite as clear sign in the hours of darkness .

Before you get into that it ’s a plot of ground by inverse lamia ( possiblyin conjunction with the saucer the great unwashed ) for make radio listeners go to bed , you should bed that it ’s actually the effect of a prerequisite by the Federal Communications Commission ( FCC ) to power down or turn off at nighttime , and the FCC in turn are required to do this by the laws of physic .

It all has to do with wavelengths and the ionosphere . During the daytime , AM signals primarily circularise close to the ground ( known asground wave propagation ) and follow the curves of the Earth . In the daylight hr , AM signals send off by radiocommunication station can cover around 162 kilometers ( 100 Admiralty mile ) before you will struggle to get wind the signal .

As good as this is , at dark the power of prospicient waves to propagate large space becomes a problem , thanks to theionosphere . Between 80 and 600 kilometers ( 50 - 373 miles ) above the Earth , particles in the Earth ’s ambience are bombarded withExtreme Ultraviolet ( EUV ) and x - ray solar radiation , ionise them as they do so . The ionospheregrows and shrinks(on your side of the major planet ) reckon on the sentence of daytime .

At nighttime , the stratum reflects AM radio receiver signal ( get laid as " skywave " propagation ) to a much greater degree than during the day , tolerate the sign to be carried for hundreds of naut mi further than during the mean solar day . While this may sound like good news program , it is what ’s known as a " pain in the buns " for any communication regulators out there , or people who desire to listen to anything other than an indiscernible mess of static .

" Because of this variety in signal propagation from day to dark , if every AM place kept its daytime operating power at night , monumental hinderance would result , " the FCCexplains on their website .

so as to compensate for this , and " in recognition of the strong-arm Pentateuch that regularize AM radio multiplication " , the FCC requires that certain station lower their power at sundown , so that the place does not interfere with others .

" Other stations , which can not cater the necessary trade protection at night to other AM stations , are presently certify to function during the daytime hours only , " they add .

So that ’s why , thanks to the laws of physics , your favorite AM station might close down at dark . But to be fair , it is the laws of physics that appropriate you to listen in the daytime , so allow ’s not get too mad at the rule which govern our macrocosm .