<p>I have a working implementation of <a href="http://www.stjarnhimlen.se/comp/tutorial.html" rel="nofollow noreferrer">Schlyter's method</a> for calculating the Sun's position.   I would like to know how Schlyter got the 3.24587E-5_deg in the following calculation for Mercury.</p>

<pre><code>N =  48.3313_deg + 3.24587E-5_deg   * d    (Long of asc. node)
</code></pre>

<p>I could not find this number in JPL Horizons.   I'm guessing it's the difference between the N at two epochs divided by number of days between the two epochs, but I'm not sure.</p>

CC BY-SA 3.0
2018-03-04T23:55:21.653Z
@barrycarter Schlyter in that article used a date before 2000 as the observation date.  Could that be why the sign is different?   Also, if I took 0.12534081 deg/Cy from your rate tables divided by the avg no. of days in a century (3650.2425), I get 3.4338E-5.   Not quite 3.24E-5, but close.   Any idea how to get deg/Cy from JPL Horizons for any object in its catalog?
jp2g
CC BY-SA 3.0
2018-03-05T04:56:06.023Z
@barrycarter thanks.   If you repost the above as an answer, I'll accept it.
jp2g
<ephemeris>
Where to get rate of change for calculating ephemeris from JPL Horizons
jp2g
# Where to get rate of change for calculating ephemeris from JPL Horizons

(Asked by: username_0 on 2018-03-03)

I have a working implementation of Schlyter's method for calculating the Sun's position.   I would like to know how Schlyter got the 3.24587E-5_deg in the following calculation for Mercury.
N =  48.3313_deg + 3.24587E-5_deg   * d    (Long of asc. node)

I could not find this number in JPL Horizons.   I'm guessing it's the difference between the N at two epochs divided by number of days between the two epochs, but I'm not sure.

**Tags:** ephemeris
> **Comments:**
> **username_0**: @barrycarter Schlyter in that article used a date before 2000 as the observation date.  Could that be why the sign is different?   Also, if I took 0.12534081 deg/Cy from your rate tables divided by the avg no. of days in a century (3650.2425), I get 3.4338E-5.   Not quite 3.24E-5, but close.   Any idea how to get deg/Cy from JPL Horizons for any object in its catalog?  
> **username_0**: @barrycarter thanks.   If you repost the above as an answer, I'll accept it.  

---

## 0 answers

