help

Distance Light Travels in a Year in Space

-- David | April 10, 2023

Question:

I’m aware that the speed of light in a vacuum is constant. Space has lots of stuff in it, dust, gravitational fields vast enough to bend light, and things we are not aware of, and not a vacuum. Yet we measure distance in light years – what am I missing ?
Appreciate your help, this has been bothering me for a while !

-- David

Answer:

It is true that matter in a medium through which light propagates will increase the length of a light year relative to that in a vacuum. Since space is very close to a perfect vacuum, with just a few hydrogen atoms per cubic meter, the length of a light year in space is very close to its vacuum value.

-- Jeff Mangum

Facebook
Pinterest
Twitter
Linkedin

The National Radio Astronomy Observatory is a facility of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
	Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.
	The U.S. National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..."
	AUI collaborates with the scientific community and research sponsors to plan, build, and operate cutting-edge facilities. We cultivate excellence, deliver value, enhance education, and engage the public.