Pointing telescope: find Alt-Az from RA/Dec, site and time

[fdesvallees]

Hello:

This must be very easy, but I keep getting errors like "AttributeError: 'ICRF' object has no attribute 'at'.
Can you please help?

Thank you
François

[brandon-rhodes]

We usually need to see some sample code to identify what has gone wrong. Can you share the full traceback? Can you share a short script that re-creates the situation you are seeing, that we can run on our own computers to see the same error and investigate solutions to it? Thanks!

[fdesvallees]

Here it is again (slightly modifiled). This is my current understanding of how it should work, but it tells me:

AttributeError: 'ICRF' object has no attribute '_observe_from_bcrs'

Thank you!

from skyfield import api

ts = api.load.timescale()

planets = api.load('de421.bsp')
site = planets['earth'] + api.wgs84.latlon(45, 5)

ra = 16.56
dec = -26

t = ts.now() 

star = api.position_of_radec(ra,dec)
astrometric = site.at(t).observe(star)
apparent = astrometric.apparent()
altaz = apparent.altaz()
print (altaz)

[fdesvallees]

OK, I fixed it. I was missing a Star() constructor. I found it in another example. Thanks anyway Brandon!

François

from skyfield import api 

ts = api.load.timescale()

planets = api.load('de421.bsp')
site = planets['earth'] + api.wgs84.latlon(45, 5)

ra = 16.56
dec = -26

ts = api.load.timescale()
t = ts.now() 

star = api.Star(ra_hours=16.56,dec_degrees=-26)
astrometric = site.at(t).observe(star)
apparent = astrometric.apparent()
altaz = apparent.altaz()
print (altaz)

[brandon-rhodes]

I'm glad you found a fix and that your script is working!