# Astronomy/distance to stars

Question
Is there any truth to this statement I read today in a discussion group?

some astronomers feel that it is possible that the entire universe could fit into an area within a 200 light-year radius from the earth! Therefore, there is no guarantee that the actual distances in space are as great as we have been told, and light from the farthest point in the universe could have reached us in only a few hundred years

I have never heard any professional astronomer have/express that belief, and more importantly, I have never seen anyone produce any evidence of this.

We have many different techniques for measuring distances to stars, galaxies, and across the Universe.  We have to use different techniques to calculate distances across the Universe because of the scale of it.  Just as we have cars to get us to close places, and airplanes to get us to faraway places, we have different tools depending on what we want to do.

FIrstly, I think this 200 light-year radius idea is related to a technique called parallax, which uses trigonometry to calculate the distance to a star.  It is a well-tested, robust technique, but it does have a limit on how far it can be used.  Some have said that it only works to 200 light-years, so everything beyond that is not trustworthy.  New advances in this technique, though, allow us to go much much further than that "limit", tens of thousands of light-years further, so right there that belief would be wrong.

However, other techniques such as redshift, allow us to measure distances much further across the Universe.  Redshift uses something called the Doppler Effect, a well known physical principle, something we experience for sound all the time.   When you hear a police car or ambulance drive by, but when you look based on the sound, it is in a different position from what you expected based on the sound.  That is because sound takes time to travel to us from the source (the siren), and in the meantime, the car has continued to drive away, so there is a lag or delay.  The further away the car is, the bigger this delay is (you've probably noticed this with airplanes too).  This effect also works with light.  If a galaxy is speeding away from us, there will be a delay in the light reaching us, and we can measure that delay.  This is a basic physical principle that we experience every day, and it allows us to measure the distances to galaxies that are billions of light-years away!

I hope this helps.

Peace,

Astronomy

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##### Expertise

I'm happy to answer any general questions about Astronomy, Astrophysics, and Cosmology. I'm also happy to take general, specific, and detailed questions related to supernovae, Baryonic Acoustic Oscillations, the Cosmic Microwave Background, dark matter, dark energy, and the Big Bang Theory. I'm also happy to chat about Astronomy/Astrophysics education and careers, and philosophy and science.

##### Experience

I am a professional research astronomer/astrophysicist/cosmologist. My research focuses on studying supernovae and using them to measure the properties of the Universe, such as how fast it is growing and what it is made of. I also frequently give talks to school groups and the public, and am a regular guest on various radio stations.

Organizations
Current Research Fellow at Mt. Stromlo Observatory, the Australian National University, and in the Department of Astronomy, University of California, Berkeley.

Publications
Lots of journals, including the Astrophysical Journal, the Astronomical Journal, and Nature. I am currently in the middle of writing my first popular book.

Education/Credentials
B.A. Philosophy, University of Notre Dame, Notre Dame, IN USA B.A. Theology, University of Notre Dame, Notre Dame, IN USA B.Sc. Physics, University of Notre Dame, Notre Dame, IN USA Ph.D. Astrophysics, Mt. Stromlo Observatory, the Australian National University, Canberra, ACT, Australia