Real stars, real distances
The three destinations are actual stars. Proxima Centauri, the closest to the Sun, is about 4.2 light-years away. Tau Ceti — the system at the heart of the mission in Project Hail Mary — sits around 11.9 light-years out. And 40 Eridani, the star of Rocky's homeworld Erid, is roughly 16.3 light-years from us. A light-year is the distance light travels in a year, so even light itself takes years to make these trips.
How long it really takes
At the speed of light, Tau Ceti is a 11.9-year journey and 40 Eridani about 16.3 years — and nothing with mass can actually reach light speed. The story's astrophage engine cruises at roughly 92% of light speed on average, which puts Tau Ceti near 13 years and Erid near 18. Compare that to a real spacecraft: a Voyager-class probe at about 61,000 km/h would need on the order of 200,000 years just to reach Tau Ceti. The gap between science fiction and today's rockets is staggering.
Why the times are a simplification
These are classical estimates — distance divided by speed — and they deliberately ignore relativity. Near light speed, time dilation means the crew aboard would experience far less time than the years counted here, which is exactly why interstellar fiction leans on it. The tool is built for wonder and a sense of scale rather than mission planning, pairing real astronomy with an original ship and a fictional drive.
For fun and scale: real distances with a simplified, non-relativistic model.
Frequently asked questions
How far are Tau Ceti and 40 Eridani?
Tau Ceti is about 11.9 light-years away and 40 Eridani (Rocky's star) about 16.3 light-years. Proxima Centauri, the nearest star, is about 4.2.
Are the travel times exact?
No. They're classical distance-over-speed estimates and ignore relativistic time dilation, so treat them as a fun sense of scale, not a precise mission time.