where does red sky at night come from
Red sky at morning The rhyme is a rule of thumb used for weather forecasting during the past two millennia. It is based on the reddish glow of the morning or evening sky, caused by haze or clouds related to storms in the region.[2][3][5] If the morning skies are red, it is because clear skies over the horizon to the east permit the sun to light the undersides of moisture-bearing clouds. The saying assumes that more such clouds are coming in from the west. Conversely, in order to see red clouds in the evening, sunlight must have a clear path from the west, so therefore the prevailing westerly wind must be bringing clear skies.
Planetary nebula A mechanism for formation of most planetary nebulae is thought to be the following: at the end of the star's life, during the red-giant phase, the outer layers of the star are expelled by strong stellar winds. After most of the red giant's atmosphere is dissipated, the ultraviolet radiation of the hot luminous core, called a planetary nebula nucleus (PNN), ionizes the outer layers earlier ejected from the star.[2] Absorbed ultraviolet light energises the shell of nebulous gas around the central star, causing it to appear as a brightly coloured planetary nebula.