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A light-year is the distance light travels in one Julian year, around 9461 billion kilometres, 5879 billion miles, or 0.3066 parsecs. In round figures, a light year is nearly 10 trillion kilometres or nearly 6 trillion miles. Proxima Centauri, the closest star to Earth after the Sun, is around 4.2 light-years away. [89]
Lunar distance (LD), the distance from the centre of Earth to the centre of the Moon, is a unit of measure in astronomy. The lunar distance is approximately 384,400 km (238,900 mi), or 1.28 light-seconds; this is roughly 30 times Earth's diameter. A little less than 400 lunar distances make up an astronomical unit.
On March 19, 2013, an impact occurred on the Moon that was visible from Earth, when a boulder-sized 30 cm meteoroid slammed into the lunar surface at 90,000 km/h (25 km/s; 56,000 mph) creating a 20-meter crater. [142] [143] NASA has actively monitored lunar impacts since 2005, [144] tracking hundreds of candidate events. [145] [146]
The tornado then crossed the Mississippi River into southern Illinois, debarking trees and deeply scouring the ground in rural areas before hitting the riverside town of Gorham at 2:30 p.m. CST (20:30 UTC), essentially obliterating the entire town. 60 of the 80 homes, all the store fronts, the train depot, and 2 out of the 3 levels of the ...
The angular diameter of the Sun, from a distance of one light-year, is 0.03″, and that of Earth 0.0003″. The angular diameter 0.03″ of the Sun given above is approximately the same as that of a human body at a distance of the diameter of Earth. This table shows the angular sizes of noteworthy celestial bodies as seen from Earth:
The average lunar distance is approximately 385,000 km (239,000 mi), or 1.28 light-seconds; this is roughly 30 times Earth's diameter. Around 389 lunar distances make up an astronomical unit (roughly the distance from Earth to the Sun). Lunar distance is commonly used to express the distance to near-Earth object encounters. [1]
The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to 3.26 light-years or 206,265 astronomical units (AU), i.e. 30.9 trillion kilometres (19.2 trillion miles).
The closest system is Alpha Centauri, with Proxima Centauri as the closest star in that system, at 4.2465 light-years from Earth. The brightest, most massive and most luminous object among those 131 is Sirius A , which is also the brightest star in Earth's night sky ; its white dwarf companion Sirius B is the hottest object among them.