<p>You might be comparing an <a href="https://en.wikipedia.org/wiki/Ecliptic_coordinate_system" rel="nofollow noreferrer">ecliptic longitude</a> to a <a href="https://en.wikipedia.org/wiki/Equatorial_coordinate_system" rel="nofollow noreferrer">right ascension</a>.
These are measured around different circles, the ecliptic and the equator respectively.
Their values coincide at the solstices ($\lambda$ 90$^\circ$ or 270$^\circ$, RA 6h or 18h) but generally not elsewhere.</p>

<p>With target body Mars, a geocentric observer location, and output quantities 2 (apparent RA &amp; Dec) and 31 (observer ecliptic lon &amp; lat) selected, JPL HORIZONS gives:</p>

<pre><code>Date__(UT)__HR:MN     R.A.__(a-apparent)__DEC    ObsEcLon    ObsEcLat
2018-Jul-22 00:00     20 38 23.96 -24 58 44.6 305.5424192  -6.2964464
</code></pre>

<p>RA 20h 38m 24s is 309.60$^\circ$, but the quantity to compare is the ecliptic longitude, 305.54$^\circ$.</p>

<p>The Astrodienst ephemeris table, <a href="http://www.astro.com/swisseph/swephinfo_e.htm" rel="nofollow noreferrer">based on JPL DE431</a>, gives ♒ 5$^\circ$ 33', i.e. ecliptic longitude 300$^\circ$ + 5.55$^\circ$ = 305.55$^\circ$, for Mars on 2018-07-22.</p>

CC BY-SA 4.0
2018-07-23T12:13:31.523Z
Yep, you are right, I thought that the RA DEC from Horizons was in the ecliptic plane - which is used in Astrology, but they are not. The 31 (observer ecliptic long & lan) is exactly what Im looking for. Thanks!
Martin Ingvar Kofoed Jensen
CC BY-SA 4.0
2018-07-23T14:14:15.800Z
Note that you can compare the quantities more directly by selecting 'decimal degrees' under the 'angle format' when choosing the output quantities
astrosnapper
CC BY-SA 4.0
2018-07-23T04:56:27.370Z
2018-07-23T05:26:19.790Z
2018-07-23T05:26:19.790Z
Mike G
<p>I have tried to compare the Ephemeris data from Nasa's Horizons with ephemeris 
tables from astro.com. And they do not match. Example:</p>

<p>Date: 22th of July 2018. Body: Mars. Time 00:00 UT
Horizons: 309 degrees (Ephemeris type=Observer)
Astro.com: 305 degrees (<a href="http://www.astro.com/swisseph/ae/2000/ae_2018.pdf" rel="nofollow noreferrer">http://www.astro.com/swisseph/ae/2000/ae_2018.pdf</a>)</p>

<p>But some bodies are matching. Like Mercury and Saturn. </p>

<p>Am I doing something wrong?</p>

<p>Sources:
Nasa Horizons: <a href="https://ssd.jpl.nasa.gov/horizons.cgi#top" rel="nofollow noreferrer">https://ssd.jpl.nasa.gov/horizons.cgi#top</a></p>

<p>Astro.com: <a href="http://www.astro.com/swisseph/swepha_e.htm" rel="nofollow noreferrer">http://www.astro.com/swisseph/swepha_e.htm</a></p>

CC BY-SA 4.0
2018-07-22T14:52:54.683Z
astro-seek state that they get it from horizonz and theirs dont match either. Example: https://horoscopes.astro-seek.com/astrology-ephemeris-planetary-online-ephemerides
Martin Ingvar Kofoed Jensen
CC BY-SA 4.0
2018-07-22T15:02:00.840Z
Astro-seek state that they get their data form Horizonz and theirs matches astro.com com, but not Horizonz (at least when I try to get it through Horizonz). Example: https://horoscopes.astro-seek.com/calculate-astrology-ephemeris-july-2018/?uzel_true=&lilith_true=&presnost=2&barva=p
Martin Ingvar Kofoed Jensen
CC BY-SA 4.0
2018-07-22T15:38:40.520Z
What positions are you giving? I do not see 309 or 305 degrees in either set of data that you give. Actually, I have no idea what the astro.com site is giving. I need to consult an astrologer to know what they are giving, but I do not know any astrologers to ask.
JohnHoltz
CC BY-SA 4.0
2018-07-22T23:52:35.583Z
It is unclear what is being compared here. Normally at least 2 co-ordinate values such as Right Ascension, Declination or an Ecliptic longitude and latitude are needed to specify the position of anything
astrosnapper
CC BY-SA 4.0
2018-07-23T02:54:22.427Z
I'm voting to close this question as off-topic because one of the two sites is non-scientific while the other is the preeminent site regarding the behavior of the solar system.
David Hammen
CC BY-SA 4.0
2018-07-23T05:31:11.670Z
Astrology notation is archaic, but ecliptic longitude is ecliptic longitude. Voting to keep open.
Mike G
CC BY-SA 4.0
2018-07-23T08:16:09.140Z
You got my "leave open" vote, but with an edit suggestion to remove the astrology link.
peterh
<ephemeris>
Ephemeris data mismatch between Nasa Horizonz and Astro.com
Martin Ingvar Kofoed Jensen
# Ephemeris data mismatch between Nasa Horizonz and Astro.com

(Asked by: username_0 on 2018-07-22)

I have tried to compare the Ephemeris data from Nasa's Horizons with ephemeris
tables from astro.com. And they do not match. Example:

Date: 22th of July 2018. Body: Mars. Time 00:00 UT
Horizons: 309 degrees (Ephemeris type=Observer)
Astro.com: 305 degrees (<http://www.astro.com/swisseph/ae/2000/ae_2018.pdf>)

But some bodies are matching. Like Mercury and Saturn.

Am I doing something wrong?

Sources:
Nasa Horizons: <https://ssd.jpl.nasa.gov/horizons.cgi#top>

Astro.com: <http://www.astro.com/swisseph/swepha_e.htm>

**Tags:** ephemeris

> **Comments:**
> **username_0**: astro-seek state that they get it from horizonz and theirs dont match either. Example: https://horoscopes.astro-seek.com/astrology-ephemeris-planetary-online-ephemerides  
> **username_0**: Astro-seek state that they get their data form Horizonz and theirs matches astro.com com, but not Horizonz (at least when I try to get it through Horizonz). Example: https://horoscopes.astro-seek.com/calculate-astrology-ephemeris-july-2018/?uzel_true=&lilith_true=&presnost=2&barva=p  
> **username_1**: What positions are you giving? I do not see 309 or 305 degrees in either set of data that you give. Actually, I have no idea what the astro.com site is giving. I need to consult an astrologer to know what they are giving, but I do not know any astrologers to ask.  
> **username_2**: It is unclear what is being compared here. Normally at least 2 co-ordinate values such as Right Ascension, Declination or an Ecliptic longitude and latitude are needed to specify the position of anything  
> **username_3**: I'm voting to close this question as off-topic because one of the two sites is non-scientific while the other is the preeminent site regarding the behavior of the solar system.  
> **username_4**: Astrology notation is archaic, but ecliptic longitude is ecliptic longitude. Voting to keep open.  
> **username_5**: You got my "leave open" vote, but with an edit suggestion to remove the astrology link.  

---

## 1 answers

### Answer by username_4 on 2018-07-23. Score: 3 | Accepted answer

You might be comparing an ecliptic longitude to a right ascension.
These are measured around different circles, the ecliptic and the equator respectively.
Their values coincide at the solstices ($\lambda$ 90$^\circ$ or 270$^\circ$, RA 6h or 18h) but generally not elsewhere.
With target body Mars, a geocentric observer location, and output quantities 2 (apparent RA & Dec) and 31 (observer ecliptic lon & lat) selected, JPL HORIZONS gives:
Date__(UT)__HR:MN     R.A.__(a-apparent)__DEC    ObsEcLon    ObsEcLat
2018-Jul-22 00:00     20 38 23.96 -24 58 44.6 305.5424192  -6.2964464

RA 20h 38m 24s is 309.60$^\circ$, but the quantity to compare is the ecliptic longitude, 305.54$^\circ$.
The Astrodienst ephemeris table, based on JPL DE431, gives ♒ 5$^\circ$ 33', i.e. ecliptic longitude 300$^\circ$ + 5.55$^\circ$ = 305.55$^\circ$, for Mars on 2018-07-22.

> **Comments:**
> **username_0**: Yep, you are right, I thought that the RA DEC from Horizons was in the ecliptic plane - which is used in Astrology, but they are not. The 31 (observer ecliptic long & lan) is exactly what Im looking for. Thanks!  
> **username_2**: Note that you can compare the quantities more directly by selecting 'decimal degrees' under the 'angle format' when choosing the output quantities  

---

