The Time ontology defines concepts related to temporal descriptions of images A period of time that occurs every week An instant of time that is defined by a date and a time A class for special annual occasions such as christmas, new year's eve, etc. A generic class for seasons A period of time that occurs every day A day in a week (Sunday to Saturday) A generic class for time instants and periods A period of time that occurs every year A period of time A generic class for months A period of time can be covered by another period of time. A period of time can be covered by another period of time. A period of time can overlap with a period of time. The autumn season The summer season The winter season The spring season The time of day immediately following sunset [Wordnet] Midday Noon is the time exactly halfway through the day. [Wikipedia] Sunrise, also called sunup in some American English dialects, is the time at which the first part of the Sun appears above the horizon in the east. Sunrise should not be confused with dawn, which is the (variously defined) point at which the sky begins to lighten, some time before the sun itself appears, ending twilight. Dawn is the first light of day [Wordnet] Sunup The word morning referred originally to the sunrise, but has been extended to mean the whole early part of the day, from dawn to noon. [Wikipedia] Day Daylight or day is the time after sunrise and before sunset while it is light outside. [Wordnet] Dark Dark period of the day (roughly from sunset to dawn). The time after sunset and before sunrise while it is dark outside [Wordnet] Informally, the evening refers to the period in which the daylight is decreasing, between the afternoon and night; it extends from the latter portion of the daylight (before sunset) until dark (after sunset). [Wikipedia] Point at which darkness falls, some time after the Sun itself sets (which begins twilight) [Wikipedia] Sunset, also called sundown in some American English dialects, is the time at which the Sun disappears below the horizon in the west. It should not be confused with dusk, which is the (variously defined) point at which darkness falls, some time after the Sun itself sets (which begins twilight). Sundown Afternoon is the time of day after 12:00 (noon), and follows morning each day. It nevertheless comes before night, and its use is often quite subjective. [Wikipedia]