Reference Terms
from Wikipedia, the free encyclopedia
Light-year
A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance light travels in a vacuum in one year. While there is no authoritative decision on which year is used, the International Astronomical Union (IAU) recommends the Julian year. A light-year is equal to 9,460,730,472,580.8 km (about 9.461 Pm; 5,878,625,373,183.61 statute miles; about 63,240 astronomical units or about 0.3066 parsecs. The exact length of the light-year depends on the length of the reference year used in the calculation, and there is no wide consensus on the reference to be used. The figures above are based on a reference year of exactly 365.25 days (each of exactly 86,400 SI seconds). A few examples of distances for light to travel are: Reflected sunlight from the Moon's surface takes 1.3 seconds to travel the 4.04 × 10-8 light years to Earth. It takes 8.3 minutes for light to travel from the Sun to the Earth (a distance of 1.58 × 10-5 light-years). The most distant space probe, Voyager 1, was 13 light hours (only 1.5 × 10-3 light years) away from Earth in September 2004. It took Voyager 27 years to cover that distance. The nearest known star (other than the Sun), Proxima Centauri is 4.22 light years away. The center of our galaxy, the Milky Way, is about 26,000 light years away.
Related Stories
1
2
Space & Time News
October 16, 2025
Oct. 15, 2025 — 3I/ATLAS, a mysterious interstellar object racing toward the Sun, is baffling scientists with its speed and origin. Some researchers suggest it could even be alien-made, drawing comparisons to probes ...
Oct. 14, 2025 — High above the Sun’s blazing equator lie its mysterious poles, the birthplace of fast solar winds and the heart of its magnetic heartbeat. For decades, scientists have struggled to see these regions, hidden from Earth’s orbit. With the upcoming ...
Oct. 12, 2025 — A colossal northern asteroid impact billions of years ago likely shaped the Moon’s south polar region and explains its uneven terrain. Researchers found that the South Pole-Aitken Basin formed from a glancing northern strike, revealing deep ...
Oct. 12, 2025 — ESA’s Mars orbiters have observed comet 3I/ATLAS, only the third interstellar comet ever discovered. The faint, distant object revealed a glowing coma as it was heated by the Sun. Researchers are still studying the data to understand its makeup ...
Oct. 9, 2025 — Mars may look calm, but new research reveals it’s a world of fierce winds and swirling dust devils racing at hurricane-like speeds. Using deep learning on thousands of satellite images from European orbiters, scientists have discovered that ...
Oct. 6, 2025 — ESA has inaugurated a powerful new 35-meter deep space antenna at its New Norcia site in Western Australia, marking a major boost to Europe’s ability to communicate with spacecraft exploring the ...
Oct. 3, 2025 — Researchers have designed a new type of gravitational wave detector that operates in the milli-Hertz range, a region untouched by current observatories. Built with optical resonators and atomic clocks, the compact detectors can fit on a lab table ...
Sep. 30, 2025 — A new boron-rich compound, manganese diboride, delivers much higher energy density than current solid-rocket materials while remaining stable until intentionally ignited. Its power comes from an unusual, strained atomic structure formed during ...
Sep. 18, 2025 — Astronomers have long relied on supercomputers to simulate the immense structure of the Universe, but a new tool called Effort.jl is changing that. By mimicking the behavior of complex cosmological models, this emulator delivers results with the ...
Sep. 18, 2025 — Faint hydrogen signals from the cosmic Dark Ages may soon help determine the mass of dark matter particles. Simulations suggest future Moon-based observatories could distinguish between warm and cold dark matter, providing long-sought answers about ...
Sep. 17, 2025 — A new AI model from NYU Abu Dhabi predicts solar wind days in advance with far greater accuracy than existing methods. By analyzing ultraviolet solar images, it could help protect satellites, navigation systems, and power grids from disruptive space ...
Sep. 15, 2025 — The booming space industry has filled the skies with rockets and satellites, but this rapid expansion comes with a hidden danger: slowing the recovery of the ozone layer. Rocket launches and burning space debris release chlorine, soot, and metals ...
Latest Headlines
updated 12:56 pm ET
Oct. 16, 2025 — Ryugu’s samples reveal that water activity on asteroids lasted far longer than scientists thought, possibly reshaping theories of how Earth gained its oceans. A billion-year-old impact may have ...
Oct. 16, 2025 — Researchers discovered a new field of ancient tektites in South Australia, revealing a long-forgotten asteroid impact. These 11-million-year-old glass fragments differ chemically and geographically ...
Oct. 16, 2025 — CO₂ ice blocks on Mars may dig gullies as they slide and sublimate in the thin atmosphere. In lab experiments, scientists recreated these eerie, worm-like movements under Martian conditions. The ...
Oct. 15, 2025 — Scientists at TU Wien have uncovered that quantum correlations can stabilize time crystals—structures that oscillate in time without an external driver. Contrary to previous assumptions, quantum ...
Oct. 15, 2025 — Scientists at the University of Hawaiʻi have discovered why it rains on the Sun. Solar rain, made of cooling plasma, forms rapidly during solar flares, a mystery now solved by modeling time-varying ...
Oct. 15, 2025 — Astronomers are investigating a strange class of exoplanets known as eccentric warm Jupiters — massive gas giants that orbit their stars in unexpected, elongated paths. Unlike their close-orbiting ...
Oct. 15, 2025 — Researchers analyzing pulsar data have found tantalizing hints of ultra-slow gravitational waves. A team from Hirosaki University suggests these signals might carry “beats” — patterns formed by ...
Oct. 14, 2025 — Scientists imaged the heart of the OJ 287 galaxy, uncovering a curved plasma jet around what appears to be two merging supermassive black holes. The ...
Oct. 14, 2025 — New observations from the James Webb Space Telescope hint that the universe’s first stars might not have been ordinary fusion-powered suns, but enormous “supermassive dark stars” powered by ...
Oct. 12, 2025 — Complex, intelligent life in the galaxy appears vanishingly rare, with the nearest possible civilization perhaps 33,000 light-years distant. Yet despite the odds, scientists insist that continuing ...