def METHOD_NAME(ts):
    e = api.load('de421.bsp')
    o = e['earth'] + api.wgs84.latlon(36.7138, -112.2169)
    a = o.at(ts.utc(2014, 2, 9, 14, 50)).observe(e['mars'])
    with assert_raises(ValueError, 'it is not useful to call .altaz'):
        a.altaz()