<p>I'm not sure what language you want to write this script in, but here is one way to calculate the solar longitude using astropy.</p>
<pre><code>import astropy.time
import astropy.coordinates

time = astropy.time.Time(&quot;2023-03-29&quot;)

sun = astropy.coordinates.get_body(&quot;sun&quot;, time=time)
frame = astropy.coordinates.GeocentricTrueEcliptic(equinox=time)

lon = sun.transform_to(frame).lon.value

print(lon)
</code></pre>
<p>Which outputs</p>
<pre><code>8.041066223269443
</code></pre>

CC BY-SA 4.0
2023-03-30T01:01:00.460Z
2023-03-30T01:13:13.640Z
2023-03-30T01:13:13.640Z
Roy Smart
<p>I would like to write a small script to calculate solar ecliptic longitude in relation to different locations and dates. For instance UTC + - 1...2 etc..
I know, solar ecliptic longitude is the position of the sun relative to the vernal equinox, in degrees clockwise 360 degrees over a year..</p>
<p>What do I have to keep in mind?</p>
<p>Thanx a lot!</p>

CC BY-SA 4.0
2023-03-30T08:28:43.053Z
Looking down from above the North Pole, the solar ecliptic longitude increases in the anticlockwise direction. See https://commons.m.wikimedia.org/wiki/File:Ecliptic_with_earth_and_sun_animation.gif
PM 2Ring
CC BY-SA 4.0
2023-03-30T08:34:38.593Z
What do you mean by *"in relation to different locations"*? Typically, the solar ecliptic longitude is calculated relative to the centre of the Earth. There is a small difference to the observed longitude at a given location on the Earth's surface due to parallax and atmospheric refraction. Of course, location (or time zone) is needed to convert local time to UTC.
PM 2Ring
CC BY-SA 4.0
2023-03-30T12:59:12.407Z
Thanx, you helped a lot
Robert
<orbit><solar-system><meteor>
How to calculate solar ecliptic longitude
Robert
# How to calculate solar ecliptic longitude

(Asked by: username_0 on 2023-03-29)

I would like to write a small script to calculate solar ecliptic longitude in relation to different locations and dates. For instance UTC + - 1...2 etc..
I know, solar ecliptic longitude is the position of the sun relative to the vernal equinox, in degrees clockwise 360 degrees over a year..

What do I have to keep in mind?

Thanx a lot!

**Tags:** orbit, solar-system, meteor

> **Comments:**
> **username_1**: Looking down from above the North Pole, the solar ecliptic longitude increases in the anticlockwise direction. See https://commons.m.wikimedia.org/wiki/File:Ecliptic_with_earth_and_sun_animation.gif  
> **username_1**: What do you mean by *"in relation to different locations"*? Typically, the solar ecliptic longitude is calculated relative to the centre of the Earth. There is a small difference to the observed longitude at a given location on the Earth's surface due to parallax and atmospheric refraction. Of course, location (or time zone) is needed to convert local time to UTC.  
> **username_0**: Thanx, you helped a lot  

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## 1 answers

### Answer by username_2 on 2023-03-30. Score: 1 | Accepted answer

I'm not sure what language you want to write this script in, but here is one way to calculate the solar longitude using astropy.
import astropy.time
import astropy.coordinates

time = astropy.time.Time("2023-03-29")

sun = astropy.coordinates.get_body("sun", time=time)
frame = astropy.coordinates.GeocentricTrueEcliptic(equinox=time)

lon = sun.transform_to(frame).lon.value

print(lon)

Which outputs
8.041066223269443


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