Also, I don't think the first moments are relevant here, only the second?  

Proposed new docstring:
```
The area of the ellipse defined by the second moment, where the major and minor axes used are HWHM (half-width at half-max) measures:

.. math::
    
    \pi HWHM_{maj} HWHM_{min}
```

though the "math" bit is probably just as easy to say:

```area = pi HWHM(maj) HWHM(min)```