adjust_time_to_hour_angle

specsim.transform.adjust_time_to_hour_angle(nominal_time, target_ra, hour_angle, longitude=None, max_error=<Quantity 0.01 arcsec>, max_iterations=3)

Adjust a time to a specified target hour angle.

The input nominal time will be adjusted to the closest time where the specified hour angle is achieved, using either a positive or negative adjustment. For example to observe Polaris from KPNO on MJD 55100 at its maximum elevation (hour angle = 0):

>>> where = observatories['KPNO']
>>> night = astropy.time.Time(55100, format='mjd', location=where)
>>> polaris = astropy.coordinates.ICRS(ra=37.95 * u.deg, dec=89.25 * u.deg)
>>> when = adjust_time_to_hour_angle(night, polaris.ra, 0 * u.deg)
>>> print('MJD %.3f' % when.mjd)
MJD 55100.401

Parameters:

nominal_timeastropy.time.Time

Nominal time that will be adjusted. If it does not have an associated location, the longitude parameter must be set.

target_raastropy.units.quantity.Quantity

Target right ascension to use for calculating the hour angle.

hour_angleastropy.units.quantity.Quantity

Desired target hour angle after the adjustment, expressed as an angle.

longitudeastropy.units.quantity.Quantity

The longitude to use for calculating the hour angle. When the value is None, the location associated with nominal_time is used.

max_errorastropy.units.quantity.Quantity

The desired accuracy of the hour angle after the adjustment, expressed as an angle.

max_iterationsint

The maximum number of iterations to use in order to achieve the desired accuracy.

Returns:

astropy.time.Time

Adjusted time, which will be within max_error of target_ra, or else a RuntimeError will be raised.

Raises:

RuntimeError

The desired accuracy could not be achieved after max_iterations.