Short answers, pulled from the story.
The International Astronomical Union established the light-year as a precise unit of length in 1984. This definition relies on two fixed constants: the speed of light and the Julian year.
Friedrich Bessel measured the distance to star 61 Cygni in 1838. He used a heliometer designed by Joseph von Fraunhofer for his calculations.
Proxima Centauri lies about 4.24 light-years away from Earth. This measurement quantifies the distance between stars within spiral arms or globular clusters.
The Hayden Planetarium specifies a light-month as precisely 30 days of light travel time. Smaller units form by multiplying time units by the speed of light.
MoM-z14 represents the farthest confirmed galaxy discovered as of 2025 at 13.53 billion light-years in light travel distance. The comoving radius of the observable universe extends about 45.7 billion light-years in any direction.