The time frame when the Sunlight is no more than 6 levels down below the horizon at either sunrise or sunset. The horizon ought to be Plainly described and also the brightest stars needs to be noticeable less than very good atmospheric situations (i.e. no moonlight, or other lights). Just http://kameronhpuzc.dsiblogger.com/25835353/indicators-on-wallpaper-installers-concord-nc-you-should-know