Star without parallax_mas using from_dataframe for hipparcos

[lirw1984]

Great project, thanks!

I have a suggestion, or maybe it can be called a bug.

Since 1.7, use pandas to load the Hipparcos star catalog as a Pandas dataframe, then use Star.from_dataframe to get a specified star. It is very convenient. BUT, the parallax_mas is ignored (ps: I am using v1.10).

from skyfield.api import Star, load
from skyfield.data import hipparcos

with load.open(hipparcos.URL) as f:
    df = hipparcos.load_dataframe(f)

barnards_star = Star.from_dataframe(df.loc[87937])
print(barnards_star)

giving the following result:
Star(ra_hours=17.963601536666665, dec_degrees=4.66828815, ra_mas_per_year=-797.84, dec_mas_per_year=10326.93, epoch=2448349.0625)

While the parallax of HIP87937 is 549.01mas.

So in the method Star.from_dataframe, I suggest to add one line to use parallax value:

    @classmethod
    def from_dataframe(cls, df):
        epoch = 1721045.0 + _unwrap(df['epoch_year']) * 365.25
        return cls(
            ra_hours=_unwrap(df['ra_hours']),
            dec_degrees=_unwrap(df['dec_degrees']),
            ra_mas_per_year=_unwrap(df.get('ra_mas_per_year', 0)),
            dec_mas_per_year=_unwrap(df.get('dec_mas_per_year', 0)),

            # add the following one line to use parallax value
            parallax_mas=_unwrap(df.get('parallax_mas', 0)),

            epoch=epoch,
        )

[brandon-rhodes]

I agree, and I'm not sure how that got left out. Would you like to offer a pull request to get credit for the line of code, or should I add it myself?

[lirw1984]

I agree, and I'm not sure how that got left out. Would you like to offer a pull request to get credit for the line of code, or should I add it myself?

I am not sure how to do that. I am a newer to use github. Please do it by you. Thanks.

[brandon-rhodes]

The next version of Skyfield that's released will include the fix. Thanks!