<p>This radius of the observable universe is measured by the <a href="http://en.wikipedia.org/wiki/Comoving_distance" rel="nofollow">comoving distance</a> which is the same in every direction. Using <a href="http://www.astro.ucla.edu/~wright/CosmoCalc.html" rel="nofollow">CosmoCalc</a> (a common tool for astronomers measuring cosmological parameters) you get 46 Gly for the comoving radial distance. </p>

CC BY-SA 3.0
2014-09-06T16:26:50.887Z
2014-09-06T16:26:50.887Z
Aaron
<p>I have found two answers for the radius of the observable universe.  Wikipedia (and other places, including this site) say approximately 46 billion LY.  I am researching this to study for the National Science Bowl, and their question database says 200 yottameters, which is about 23 billion LY (half the size that wikipedia says). There are other places which cite 200 yottameters as the radius.  Which is the more accurate answer?  </p>

CC BY-SA 3.0
2014-09-06T16:19:25.020Z
Please cite sources that list each of these distances.
Aaron
CC BY-SA 3.0
2014-09-06T20:11:52.837Z
Assuming @Aaron is right (and I have no reason to think otherwise), someone could have found 23 billion light-years by assuming that 46 billion light-years was a diameter, and not a radius.
HDE 226868
<distances><observable-universe>
What is the radius of observable universe- 46 billion LY or 200 yottameters?
Lily
# What is the radius of observable universe- 46 billion LY or 200 yottameters?

(Asked by: username_0 on 2014-09-06)

I have found two answers for the radius of the observable universe. Wikipedia (and other places, including this site) say approximately 46 billion LY. I am researching this to study for the National Science Bowl, and their question database says 200 yottameters, which is about 23 billion LY (half the size that wikipedia says). There are other places which cite 200 yottameters as the radius. Which is the more accurate answer?

**Tags:** distances, observable-universe
> **Comments:**
> **username_1**: Please cite sources that list each of these distances.  
> **username_2**: Assuming @Aaron is right (and I have no reason to think otherwise), someone could have found 23 billion light-years by assuming that 46 billion light-years was a diameter, and not a radius.  

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## 1 answers

### Answer by username_1 on 2014-09-06. Score: 3

This radius of the observable universe is measured by the [comoving distance](http://en.wikipedia.org/wiki/Comoving_distance) which is the same in every direction. Using [CosmoCalc](http://www.astro.ucla.edu/~wright/CosmoCalc.html) (a common tool for astronomers measuring cosmological parameters) you get 46 Gly for the comoving radial distance.


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