I'm starting to question my sanity. This wikipedia article claims a ship with a constant acceleration of 1g will cross 100000 light-years in 24 years by traveller's clock: https://en.wikipedia.org/wiki/Space_travel_using_constant_acceleration Numerous calculators over the web give you the same value (example: http://nathangeffen.webfactional.com/spacetravel/spacetravel.php). I get a sense something is wrong here. Are they using the acceleration measured in observer's frame? But that's nonsensical, it's not what "constant acceleration" means by any sane definition, right? Aren't proper acceleration, traveller's time and observer's distance connected with a simple newtonian s=½at²? The result is about 622 years, not 24. Am I missing something?