Using variables with units

We'll use astropy to unburden us from common calculations (and equally common mistakes when doing them by hand).

astropy has a fair amount of packages, so check of the docs: http://docs.astropy.org/en/latest/



In [1]:

    
kpc_to_km = 3.086E16
distance = 1. # kpc
distance * kpc_to_km









    Out[1]:





3.086e+16



In [2]:

    
type(distance)









    Out[2]:





float



In [3]:

    
import astropy.units as u
distance_q = 1 * u.kpc
type(distance_q)









    Out[3]:





astropy.units.quantity.Quantity



In [4]:

    
distance_q.to(u.km)









    Out[4]:





$3.0856776 \times 10^{16} \; \mathrm{km}$



In [5]:

    
distance_q.to(u.jupiterRad)









    Out[5]:





$4.3161159 \times 10^{11} \; \mathrm{R_{\rm J}}$



In [6]:

    
distance_M = 1 * u.Mpc
distance_q + distance_M









    Out[6]:





$1001 \; \mathrm{kpc}$

Coordinate transformations

Coordinates in astronomy often come in equatorial coordinates, specified by right ascension (RA) and declination (DEC).



In [7]:

    
import astropy.coordinates as coord



In [8]:

    
c1 = coord.SkyCoord(ra=150*u.degree, dec=-17*u.degree)
c2 = coord.SkyCoord(ra='21:15:32.141', dec=-17*u.degree, unit=(u.hourangle,u.degree))

If we wanted this coordinate on the celestial sphere to another system (of the celestial sphere), which is tied to our Galaxy, we can do this:



In [9]:

    
c1.transform_to(coord.Galactic)









    Out[9]:





<SkyCoord (Galactic): (l, b) in deg
    ( 254.64626221,  29.37739278)>