Twilight is the time between dawn and sunrise or between sunset and dusk, during which sunlight scattering in the upper atmosphere illuminates the lower atmosphere, and the surface of the earth is neither completely lit nor completely dark. The sun itself is not directly visible because it is below the horizon. Owing to the distinctive quality of the ambient light at this time, twilight has long been popular with photographers and painters, who refer to it as the "blue hour", after the French expression l'heure bleue. Twilight is technically defined as the period between sunset and sunrise during which there is natural light provided by the upper atmosphere, which receives direct sunlight and scatters part of it towards the earth's surface.The collateral adjective for twilight is crepuscular; it is most frequently encountered when applied to certain insects and mammals that are most active during that time.
The Moon is Earth's largest natural satellite and the nearest major celestial object. Observing the Moon can be accomplished by using a variety of instruments ranging from the naked eye to large telescopes. For most people, the Moon is the only celestial object upon which surface features can be discerned with the naked eye (some people with good eyesight can see large sunspots on the surface of the Sun using handheld solar filters). the Moon can be viewed even with the naked eye, however it may be more enjoyable with optical instruments. The primary lunar surface features detectable to the naked eye are the lunar maria or "seas", large basaltic plains which form the familiar "Man in the Moon" and other figures seen by many people who take a glance at a full moon. The maria cover about 35% of the surface.