pynrc.simul.skyvec2ins

skyvec2ins JWST Coronagraph Visibility Calculator

Developed by Chris Stark (cstark@stsci.edu), translated to Python from IDL by Joseph Long (jlong@stsci.edu), Brendan Hagan, Bryony Nickson (bnickson@stsci.edu) and Mees Fix (mfix@stsci.edu)

The allowed pointing of JWST leads to target visibility that depends on ecliptic latitude, and the range of roll angles allowed depends on solar elongation. The allowed PAs for a target can thus be a complicated function of time. As a result, it can be difficult to 1) understand the possible orientations of a given target on the detector, 2) determine the ideal roll angle offsets for multi-roll observations, and 3) determine a group of targets that are simultaneously visible. The JWST Coronagraph Visibility Calculator (CVC) was created to address these issues and assist with creating APT programs and diagnosing scheduling errors.

We stress that the CVC is designed to provide quick illustrations of the possible observable orientations for a given target. As such, the CVC rapidly approximates JWST’s pointing restrictions and does not query the official JWST Proposal Constraint Generator (PCG). The CVC does not include detailed pointing restrictions like Earth and Moon avoidance, etc. Additionally, results may differ from official constraints by a degree or so. Users should treat the results as close approximations.

Functions

ad2lb(alpha_rad, delta_rad)

Convert equatorial coordinates (RA, Dec, i.e. alpha, delta) to ecliptic coordinates (lambda, beta) according to Eq 3 in Leinert et al. 1998.

ei2lb(elong, inc)

Convert alternative ecliptic coordinates (epsilon, i) to ecliptic coordinates (lambda-lambda_sun, beta) according to Eq 12 in Leinert et al. 1998.

lb2ad(lambda_rad, beta_rad)

Convert ecliptic coordinates (lambda, beta) to equatorial coordinates (RA, Dec, i.e. alpha, delta) according to Eq 4 in Leinert et al. 1998.

lb2ei(lmlsun, beta)

Convert ecliptic coordinates (lambda-lambda_sun, beta) to alternative ecliptic coordinates (epsilon, i) according to Eq 11 in Leinert et al. 1998.

skyvec2ins(ra, dec, start_date[, npoints, ...])

JWST coronagraphic target visibility calculator.

sun_ecliptic_longitude(start_date)

Compute ecliptic longitude of sun on a given start date using equations from http://aa.usno.navy.mil/faq/docs/SunApprox.php [broken].