<p><code>pc</code> is the abbreviation for <a href="https://en.wikipedia.org/wiki/Parsec" rel="nofollow noreferrer">parsec</a>, a common unit of distance objects outside the Solar system. In order to compress the scales, they have also taken the logarithm (to base 10) of the distances in parsecs. So the scale in the figure on the x-axis in the radial (<code>r</code>) direction from the central black hole spans from 1e-5 to 100 parsecs. The z-axis, which is perpendicular or normal to the plane of the galaxy and the accretion disk, spans from 1e-5 to 1000 parsecs.</p>

CC BY-SA 4.0
2019-07-08T02:39:17.370Z
Oh, I knew about parsecs. So that's kind of saying "the distance in parsecs has been log'ed"?
Jim421616
CC BY-SA 4.0
2019-07-08T02:31:31.980Z
2019-07-08T02:31:31.980Z
astrosnapper
<p>In this diagram of the regions and approximate scale of an AGN:</p>

<p><a href="https://i.sstatic.net/dYrG2.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/dYrG2.png" alt="enter image description here"></a></p>

<p>which is from <a href="https://arxiv.org/pdf/1709.00019.pdf" rel="nofollow noreferrer">this paper</a>, what do the x and y scales <code>log(z/pc)</code> and <code>log(r/pc)</code> mean? I'm guessing <code>z</code> is the z-direction ('upwards') and <code>r</code> is radius, but what is the meaning of the pc bit?</p>

<quasars><active-galaxy>
Regions and size of an AGN
Jim421616
# Regions and size of an AGN

(Asked by: username_0 on 2019-07-08)

In this diagram of the regions and approximate scale of an AGN:

[![enter image description here](https://i.sstatic.net/dYrG2.png)](https://i.sstatic.net/dYrG2.png)

which is from [this paper](https://arxiv.org/pdf/1709.00019.pdf), what do the x and y scales `log(z/pc)` and `log(r/pc)` mean? I'm guessing `z` is the z-direction ('upwards') and `r` is radius, but what is the meaning of the pc bit?

**Tags:** quasars, active-galaxy

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## 1 answers

### Answer by username_1 on 2019-07-08. Score: 1 | Accepted answer

`pc` is the abbreviation for [parsec](https://en.wikipedia.org/wiki/Parsec), a common unit of distance objects outside the Solar system. In order to compress the scales, they have also taken the logarithm (to base 10) of the distances in parsecs. So the scale in the figure on the x-axis in the radial (`r`) direction from the central black hole spans from 1e-5 to 100 parsecs. The z-axis, which is perpendicular or normal to the plane of the galaxy and the accretion disk, spans from 1e-5 to 1000 parsecs.

> **Comments:**
> **username_0**: Oh, I knew about parsecs. So that's kind of saying "the distance in parsecs has been log'ed"?  

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