help

Why Can We See Stars That Are Billions of Light Years Away?

-- | April 18, 2014

Question: I can’t get seem to find a thoughtful yet scientific answer to this question, I was hoping you could help. I hope this doesn’t sound dumb, I don’t mean it to be. When we look at the night sky, we see a blanket of stars. They seem very close together and crowed in the sky. I know some of them may not even still exist, just the light still coming from them over millions of light years away, in some cases. But how is it that we can see stars that appear to be so close together but in fact are at least light years away from one another, with the naked eye from earth, no less? And stars from one side of the night time horizon to the other have to be billions of light years apart, right? How can we see objects so far away with the naked eye? If we use our suns size and scale it to stars we see in the sky, millions of light years away we should not be able to see them at all, right? I just don’t get it! Is there some phenomenon I’m not understanding? — Tim

Answer: For the most distant objects, such as galaxies and quasars, what you are seeing is not just the light from a single star, but light from a galaxy full of stars. Now, the most distant galaxies cannot be seen with the unaided eye, though. That is why we build large optical telescopes (basically, the equivalent of a really-big and sensitive eye!).

Jeff Mangum

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.