Moonrise and sunset rays are a rare phenomenon that occurs when rays of sunlight filter through cracks in crater walls and mountains to cast a peak of light across the dark bottom of the crater. They occur rarely and only during sunrise and sunset when the angle of sunlight is very low. The rays can range from thin slivers of light to triangular patches of illumination. They differ from lunar rays in which debris from impact craters is scattered across the face of the Moon. A true ray of moonlight has been defined as one that crosses 3 degrees of longitude while being less than, on average, ¼ of a degree of width of latitude. They can occur at both dawn and dusk. Due to the geometry involved, they are usually short-lived and occur within a window of opportunity of only 2 to 3 hours. Although rays of moonlight were first observed more than 150 years ago, they only recently gained popularity after a report about them was published. in an astronomy journal. Amateur astronomers have since discovered several craters where sunrise or sunset rays shone through a crumpled or broken crater wall and created these light shows that lasted only a few hours. Rays of moonlight can be detected by scanning along the lunar terminator and if you're lucky, you might spot one. For those who prefer not to leave everything to chance, the “CalSKY” website can calculate sunrise and sunset times along with the angle of the sun to determine which lunar craters will show light rays and when. After entering your geographical coordinates, you must enter the date, time and duration you wish to observe. CalSKY will then generate a list of craters showing rays, including the date and time of visibility along with a map showing the crater and the observer in the center of the sheet of paper and extending westward. wall.Vogel RayA dawn ray crosses Vogel's floor, starting as a thin triangle of light that progressively thickens.Walter RayWalter's Ray is a fairly dramatic ray of light that crosses Walter's floor at sunset. A diffuse wedge of light is projected onto the floor from a crack in the wall. A small crater near the opening resembles a tiny crown, casting three spiky shadows across the floor toward the central peak. A complete list of craters with lunar sunset and sunrise rays can be obtained from the Robinson Lunar Observatory website at http:// www.lunar-occultations.com/rlo/rays/rays.htm Although not have any scientific value, the rarity of these events, combined with the short period of time in which they are visible, make these real challenges for the avid lunar observer. So if the sky is clear, go catch some rays!