Computing sub-solar point

Question

I am just getting started with PyEphem. My immediate task is, given a date and time compute the sub-solar point on Earth with latitude-longitude values. I'll dig into PyEphem to work this out but if someone has already done this, I'd appreciate sample code.

Answer 1

I went looking for the same answer as the OP. Many posts "mention" how PyEphem is the way to go but without providing the actual example.

Here is my working example to calculate the subsolar point. Mapping everything to a longitude between -180 and + 180 degrees.

greenwich = ephem.Observer()
greenwich.lat = "0"
greenwich.lon = "0"
greenwich.date = datetime.utcnow()
sun = ephem.Sun(greenwich)
sun.compute(greenwich.date)
sun_lon = math.degrees(sun.ra - greenwich.sidereal_time() )
if sun_lon < -180.0 :
  sun_lon = 360.0 + sun_lon 
elif sun_lon > 180.0 :
  sun_lon = sun_lon - 360.0
sun_lat = math.degrees(sun.dec)
print "Subsolar Point Sun Lon:",sun_lon, "Lat:",sun_lat

I am no expert in PyEphem and there may be a better approach - but my testing so far has this work for my purposes.

p.s. yes.. Greenwich above is not actually set to the actual lat/lon... it's really only the Longitude of 0.0 that's needed to get the appropriate Sidereal time we need.