<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  

---

## 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

```


---

