In modern astronomy, a constellation is a specific area of the celestial sphere as defined by the International Astronomical Union (IAU). These areas had their origins in Western-traditional asterisms from which the constellations take their names. There are 88 officially recognized constellations, covering the entire sky.Thus, any given point in a celestial coordinate system can unambiguously be assigned to a constellation. It is usual in astronomy to give the constellation in which a given object is found along with its coordinates in order to convey a rough idea in which part of the sky it is located. For example, saying the Horsehead Nebula is near Orion's Belt in the constellation Orion immediately locates it just south of the ecliptic and conveys that it is best observable in winter from the Northern Hemisphere.