<p>P is preceding and F is following.</p>
<p>This nomenclature dates from when all observations were visual. I think the point was that the observer didn't want the complication of figuring which way was east or west (and that depends on the convention used), but relied on which object, including the edge of the sun or planet, came into view first (preceding), or last (following).</p>
<p>Similarly if trying to measure right ascension, the observer would use cross hairs or a reticle to measure the time difference for the objects being measured to pass over the same point, which would give the difference in right ascension.</p>
<p>Here is a link to an article from the British Astronomical Association, which supports my answer.  I won't copy/paste as I'm not sure of the copyright position.</p>
<p><a href="https://britastro.org/node/10014" rel="nofollow noreferrer">https://britastro.org/node/10014</a></p>
<p>Alternatively, see page 27 of Norton's Star Atlas, 20th edition.</p>

CC BY-SA 4.0
2021-10-29T21:35:58.000Z
This sounds pretty plausible. Do you have a source? I'd like to read more about this.
Phiteros
CC BY-SA 4.0
2021-10-30T20:56:02.970Z
@Phiteros - done
Dr Chuck
CC BY-SA 4.0
2021-10-31T15:42:24.550Z
It is always okay to *quote* from an article, provided you deal fairly.  You can quote "Because objects exit the field of view on the west and enter on the east, these two directions are sometimes referred to as preceding and following. These terms can also be incorporated into the definition of position angle so, in the above galaxy example, its position angle could be stated as north following/south preceding or, as more usually written, nf/sp." while citing the british Astronomical Association website (as above). No permission is required to make a reasonable quote.
James K
CC BY-SA 4.0
2021-10-29T09:12:50.200Z
2021-10-31T13:13:48.807Z
2021-10-31T13:13:48.807Z
Dr Chuck
<p>In Richard Carrington's drawing of sunspots, he has a compass labeled &quot;N&quot;, &quot;P&quot;, &quot;S&quot;, and &quot;F&quot;. If &quot;N&quot; is North and &quot;S&quot; is South, what do &quot;P&quot; and &quot;F&quot; mean?</p>
<p>Also, why is the compass not oriented in the same way as the lines of longitude/latitude?</p>
<p><a href="https://i.sstatic.net/2vzNj.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/2vzNj.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2021-10-29T04:22:24.670Z
Cool question! Any idea what instrument was Carrington using, and at what focus? Was it a fixed telescope with a coeleostat/siderostat/heliostat or refractor/reflector/Coudé? Source of the image?
uhoh
CC BY-SA 4.0
2021-10-29T04:35:37.540Z
It was in the 1850's; he projected an image of the sun onto a table with paper.
Phiteros
CC BY-SA 4.0
2021-10-29T05:51:08.963Z
I think that it might have been in reference to the way his screen was set up:
https://i.imgur.com/aN8JxfD.png
Phiteros
CC BY-SA 4.0
2021-10-29T06:23:31.803Z
Cool! It must have been hard to draw as the magnified Sun moved so quickly! Side thought: I wonder if he drove the telescope at a strange speed such that the Sun's image was stationary on the wall even though it was moving in the sky?
uhoh
CC BY-SA 4.0
2021-10-29T08:24:37.563Z
[Original article](https://doi.org/10.1093/mnras/20.1.13) and a [nice paper](https://doi.org/10.1088/0143-0807/37/4/045707) about it. (Spoiler: the answer is not there!)
Jean-Marie Prival
CC BY-SA 4.0
2021-10-29T08:26:11.347Z
Thanks for that! I am currently looking through Carrington's book on sunspots, to see if I can find anything.
Phiteros
CC BY-SA 4.0
2021-10-29T08:27:11.343Z
At first I thought the "P" could stand for "Ponante", which is a synonym of West, but then the corresponding East synonym would be "Levante", which does not begin with an "F"...
Jean-Marie Prival
CC BY-SA 4.0
2021-10-29T08:27:46.090Z
The best we could think of was "Past" and "Future", perhaps referring to the sun's rotation or movement across his screen.
Phiteros
CC BY-SA 4.0
2021-10-29T15:37:17.173Z
@Jean-MariePrival : for modern solar conventions (eg. Stonyhurst), west on the sun is to the right of the image ... east is to the left
Joe
<history><sunspots><map>
What do "P" and "F" mean in the compass legend of Carrington's sunspot drawing?
Phiteros
# What do "P" and "F" mean in the compass legend of Carrington's sunspot drawing?

(Asked by: username_0 on 2021-10-29)

In Richard Carrington's drawing of sunspots, he has a compass labeled "N", "P", "S", and "F". If "N" is North and "S" is South, what do "P" and "F" mean?

Also, why is the compass not oriented in the same way as the lines of longitude/latitude?

[![enter image description here](https://i.sstatic.net/2vzNj.png)](https://i.sstatic.net/2vzNj.png)

**Tags:** history, sunspots, map

> **Comments:**
> **username_1**: Cool question! Any idea what instrument was Carrington using, and at what focus? Was it a fixed telescope with a coeleostat/siderostat/heliostat or refractor/reflector/Coudé? Source of the image?  
> **username_0**: It was in the 1850's; he projected an image of the sun onto a table with paper.  
> **username_0**: I think that it might have been in reference to the way his screen was set up: https://i.imgur.com/aN8JxfD.png  
> **username_1**: Cool! It must have been hard to draw as the magnified Sun moved so quickly! Side thought: I wonder if he drove the telescope at a strange speed such that the Sun's image was stationary on the wall even though it was moving in the sky?  
> **username_2**: [Original article](https://doi.org/10.1093/mnras/20.1.13) and a [nice paper](https://doi.org/10.1088/0143-0807/37/4/045707) about it. (Spoiler: the answer is not there!)  
> **username_0**: Thanks for that! I am currently looking through Carrington's book on sunspots, to see if I can find anything.  
> **username_2**: At first I thought the "P" could stand for "Ponante", which is a synonym of West, but then the corresponding East synonym would be "Levante", which does not begin with an "F"...  
> **username_0**: The best we could think of was "Past" and "Future", perhaps referring to the sun's rotation or movement across his screen.  
> **username_3**: @username_2 : for modern solar conventions (eg. Stonyhurst), west on the sun is to the right of the image ... east is to the left  

---

## 1 answers

### Answer by username_4 on 2021-10-29. Score: 9 | Accepted answer

P is preceding and F is following.

This nomenclature dates from when all observations were visual. I think the point was that the observer didn't want the complication of figuring which way was east or west (and that depends on the convention used), but relied on which object, including the edge of the sun or planet, came into view first (preceding), or last (following).

Similarly if trying to measure right ascension, the observer would use cross hairs or a reticle to measure the time difference for the objects being measured to pass over the same point, which would give the difference in right ascension.

Here is a link to an article from the British Astronomical Association, which supports my answer. I won't copy/paste as I'm not sure of the copyright position.

<https://britastro.org/node/10014>

Alternatively, see page 27 of Norton's Star Atlas, 20th edition.

> **Comments:**
> **username_0**: This sounds pretty plausible. Do you have a source? I'd like to read more about this.  
> **username_4**: @username_0 - done  
> **username_5**: It is always okay to *quote* from an article, provided you deal fairly.  You can quote "Because objects exit the field of view on the west and enter on the east, these two directions are sometimes referred to as preceding and following. These terms can also be incorporated into the definition of position angle so, in the above galaxy example, its position angle could be stated as north following/south preceding or, as more usually written, nf/sp." while citing the british Astronomical Association website (as above). No permission is required to make a reasonable quote.  

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