Using astropy to convert pandas columns-CodePudding

I have a pandas dataframe that includes the columns _RA2000 and _DEJ2000, thus:

and I'd like to convert them to degrees, as they appear in the RAJ2000 and DEJ2000 columns. I should be able to do it with astropy, but if I try the first one:

from astropy import units as u
from astropy.coordinates import SkyCoord
c = SkyCoord('23 58 36.30073', 'icrs', unit=(u.hourangle))

I get

ValueError: Invalid character at col 0 in angle 'icrs'

So my questions are:

why is the string I've inputted causing the error, and
how can I apply SkyCoord to the pandas columns?

CodePudding user response：

You need to do the conversion for both coords simultaneously and supply the frame as a keyword argument:

import pandas as pd
from astropy import units as u
from astropy.coordinates import SkyCoord

df = pd.DataFrame({'_RAJ2000': ['23 58 36.30073 ',  '23 58 19.66200 ',  '23 58 17.43747 ',  '23 58 10.18153 ',  
                                '23 57 42.51840 ',  '23 56 32.18853 ',  '23 56 30.99313 ',  '23 56 06.29927 ',
                                '23 55 33.67007 ',  '23 55 14.54907 ',  '23 54 19.62527 ',  '23 52 46.54273 ',
                                '23 52 02.17560 ',  '23 51 50.76387 '],
                   '_DEJ2000': [' 03 07 21.9650',  ' 14 36 42.0370',  ' 15 16 40.3390',  ' 11 20 06.6370',
                                ' 06 19 41.0660',  ' 07 30 53.1500',  ' 07 21 08.8880',  ' 11 24 22.3520',
                                ' 04 37 36.1520',  ' 10 59 36.1680',  ' 08 15 14.7020',  ' 01 57 15.8870',
                                ' 02 36 10.4110',  ' 03 53 50.8780']})

df = pd.concat(
    (df, SkyCoord(df._RAJ2000, df._DEJ2000, frame='icrs', unit=(u.hourangle, u.deg)).to_table().to_pandas()),
    axis=1).rename(columns={'ra': 'RAJ2000', 'dec': 'DEJ2000'})

Result:

           _RAJ2000        _DEJ2000     RAJ2000    DEJ2000
0   23 58 36.30073    03 07 21.9650  359.651253   3.122768
1   23 58 19.66200    14 36 42.0370  359.581925  14.611677
2   23 58 17.43747    15 16 40.3390  359.572656  15.277872
3   23 58 10.18153    11 20 06.6370  359.542423  11.335177
4   23 57 42.51840    06 19 41.0660  359.427160   6.328074
5   23 56 32.18853    07 30 53.1500  359.134119   7.514764
6   23 56 30.99313    07 21 08.8880  359.129138   7.352469
7   23 56 06.29927    11 24 22.3520  359.026247  11.406209
8   23 55 33.67007    04 37 36.1520  358.890292   4.626709
9   23 55 14.54907    10 59 36.1680  358.810621  10.993380
10  23 54 19.62527    08 15 14.7020  358.581772   8.254084
11  23 52 46.54273    01 57 15.8870  358.193928   1.954413
12  23 52 02.17560    02 36 10.4110  358.009065   2.602892
13  23 51 50.76387    03 53 50.8780  357.961516   3.897466

CodePudding user response：

You can also do this using the Angle class if you just want to use astropy to parse the coordinate strings

>>> from astropy.coordinates import Angle
>>> Angle(['23 58 36.30073 ',  '23 58 19.66200 '], unit='hourangle').to_value('deg')
array([359.65125304, 359.581925  ])

>>> Angle([' 03 07 21.9650',  ' 14 36 42.0370'], unit='deg').to_value('deg')
array([ 3.12276806, 14.61167694])