In an attempt to express absolute certainty, one often hears the expression that "I am as sure as I am certain that the sun will rise tomorrow". Of course, with each sunrise, we have an even more majestic sunset. Aside from signalling the end of the day, the setting sun helps accentuate many features of the atmosphere during the few minutes it approaches and later dips below the horizon including rich and colorful patterns in the lower parts of the atmosphere which invariably are immune to our eyes and yet produce vivid colors and patterns on film emulsion. An equally dramatic experience involves the rising moon and which is often characterized with a "bloody" red or dark orange appearance.

Although most people associate the setting of the sun with the end of day and the beginning of darkness, we also have civil, nautical and astronomical twilight which are also used to indicate the end of day and absence of light. Civil twilight technically occurs when the sun is between 0 and 6 degrees below the horizon; it is when people first sense "complete" darkness and car headlights must be turned on in most places of the world. Similarly, nautical twilight is defined to occur when the sun is between 6 and 12 degrees below the horizon and, as the term suggests, someone at sea would not be able to distinguish the horizon during this time, thus rendering the use of sextants, for example, useless. Finally, astronomical twilight is when the sun is at least 12 degrees below the horizon and signals the start of the greatest possible darkness that one can expect during the evening (barring the possible influence of the moon in the sky) and is of great interest, for example, to astrophotographers.