Light-year Light-year The light-year is a unit of length used to express astronomical distances and measures about 9.46 trillion kilometres or 5.88 trillion miles. As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Because it includes the word "year", the term light-year is sometimes misinterpreted as a unit of time. The light-year is most often used when expressing distances to stars and other distances on a galactic scale, especially in nonspecialist and popular science publications. The unit most commonly used in professional astrometry is the parsec
Long-distance running – all-weather tracks, roads and natural terrain, respectively. Typical long-distance track races range from 3000 metres to 10,000 metres (6.2 miles), cross country races usually cover 5 to 12 km (3 to 7½ miles), while road races can be significantly longer, reaching 100 kilometres (60 miles) and beyond. In collegiate cross country races in the United States, men race 8000 or 10000 meters, depending on their division, whereas women race 6000 meters . The Summer Olympics features three long-distance running events: the 5000 metres, 10,000 metres and marathon (42.195 kilometres, or 26 miles and 385 yards). Since the late 1980s,