Use broadcasting to transform many SkyCoords into frames with vector properties

quick_altaz.py

from astropy.coordinates import SkyCoord, EarthLocation
from astropy.coordinates.tests.utils import randomly_sample_sphere
from astropy.time import Time

import numpy as np

# 1000 random locations on the sky
ra, dec, _ = randomly_sample_sphere(1000)
coos = SkyCoord(ra, dec)

# 300 times over the space of 10 hours
times = Time.now() + np.linspace(-5, 5, 300)*u.hour

# note the use of broadcasting so that 300 times broadcast against 1000 positions
aa_frame = coord.AltAz(obstime=times[:, np.newaxis], 
                       location=EarthLocation.of_site('lapalma'))

# calculate alt-az of each object at each time.
aa_coos = coos.transform_to(aa_frame)