A light-day is a measure of distance: how far light, traveling about 186,000 miles per second, moves in 24 hours. That equals roughly 16.1 billion miles, or 25.9 billion kilometers. Voyager 1, launched in 1977 and traveling for nearly five decades, is expected to reach this unprecedented mark for a human-made object on Nov. 18, 2026, at 5:16 a.m. Eastern time. The milestone describes its distance from Earth, not the time it takes the spacecraft to travel there.
Light-based distance units help make vast space distances easier to grasp. Light takes about 1.3 seconds to travel from Earth to the Moon, eight minutes and 20 seconds to reach Earth from the Sun, and between three and 22 minutes to cross the changing distance between Earth and Mars. The same delays apply to radio signals, so messages exchanged with spacecraft at Mars can take minutes each way. Voyager 2, which followed a different route to visit Uranus and Neptune, is projected to reach one light-day from Earth in November 2035. The milestone underscores both the enormous scale of interplanetary space and the communication delays faced as spacecraft venture farther away.
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Voyager 1’s team completed power-saving equipment swaps that will keep its remaining science instruments operating longer despite the probe losing about four watts each year. A 48-hour communications pause on Oct. 20 ended on its own before engineers sent troubleshooting commands. (jpl.nasa.gov)
![The lithium hypothesis of obesity [video]](https://hntoday.pixelshot.io/screenshots/20261031/99348d6522c847df_tn.jpeg)
The video is titled “The lithium hypothesis of obesity.” The provided page contains no information about the hypothesis or its evidence. (youtube.com)
The linked paper’s title proposes that Alzheimer’s disease may begin in the nose and be caused by aluminosilicates. Its contents could not be accessed, so the claim cannot be verified from the provided text. (sciencedirect.com)
William Nordhaus, a Yale economist who won the 2018 Nobel Prize for incorporating climate change into economic analysis, died at 85 after battling brain cancer. He spent more than 50 years at Yale as a professor and university leader. (news.yale.edu)
A large Harvard study found that men reporting 21 or more ejaculations per month had a lower prostate cancer risk than men reporting 4 to 7. The observational results show an association, not proof that ejaculation prevents cancer. (health.harvard.edu)
Trump administration staffing cuts, grant cancellations and pressure on universities are straining the federal research system, despite overall research spending remaining near $200 billion. The losses threaten U.S. advantages in defense, medicine and technology as global rivals advance. (nytimes.com)
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