Night

Night or nighttime (sp. night-time or night time) is the period of time between the sunset and the sunrise when the Sun is below the horizon.

This occurs after dusk. The opposite of night is day (or "daytime" to distinguish it from "day" as used for a 24-hour period). The start and end points of time of a night vary based on factors such as season, latitude, longitude and timezone.

At any given time, one side of the planet Earth is bathed in light from the Sun (the daytime) and the other side of the Earth is in the shadow caused by the Earth blocking the light of the sun. This shadow is called the umbra. Natural illumination is still provided by a combination of moonlight, planetary light, starlight, diffuse zodiacal light, gegenschein, and airglow. In some circumstances, bioluminescence, aurorae, and lightning can provide some illumination. The glow provided by artificial illumination is sometimes referred to as light pollution because it can interfere with observational astronomy and ecosystems.

100

Year 100 (C) was a leap year starting on Wednesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Traianus and Frontinus (or, less frequently, year 853 Ab urbe condita). The denomination 100 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

Events

By place

Roman Empire

Europe

Star

A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun. Other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, and the brightest stars gained proper names. Extensive catalogues of stars have been assembled by astronomers, which provide standardized star designations.

For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen into helium in its core, releasing energy that traverses the star's interior and then radiates into outer space. Once the hydrogen in the core of a star is nearly exhausted, almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the star's lifetime and, for some stars, by supernova nucleosynthesis when it explodes. Near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity (chemical composition), and many other properties of a star by observing its motion through space, luminosity, and spectrum respectively. The total mass of a star is the principal determinant of its evolution and eventual fate. Other characteristics of a star, including diameter and temperature, change over its life, while the star's environment affects its rotation and movement. A plot of the temperature of many stars against their luminosities, known as a Hertzsprung–Russell diagram (H–R diagram), allows the age and evolutionary state of a star to be determined.