Toronto background sky

Star data: HYG Database v4.1, David Nash / Astronexus.
Source: https://github.com/astronexus/HYG-Database/tree/c7f7f883fe678cc7680169a50ccd7dcc49b060ce/hyg
License: Creative Commons Attribution-ShareAlike 4.0 International
https://creativecommons.org/licenses/by-sa/4.0/

Adaptation by Astrum: exclude the Sun and stars fainter than visual magnitude 4.8;
select ID, J2000 right ascension, declination, visual magnitude and proper name.
The unchanged coordinates and derived catalogue in /star-catalog.js remain
available under CC BY-SA 4.0. This attribution does not relicense other site code.

Toronto observer: 43 degrees 39 minutes north, 79 degrees 23 minutes west.
Source: City of Toronto, Toronto at a Glance.
https://www.toronto.ca/city-government/data-research-maps/toronto-at-a-glance/

The animated map begins at page-load UTC, precesses J2000 positions to mean-of-date,
then advances hour angle at exactly one degree per active second. North is up,
east is left in a zenith-centered stereographic projection. Stars below the
horizon are excluded. The view is cropped uniformly, without stretching patterns.
Brightness is compressed for legibility; twinkling is artistic. Daylight,
weather, urban sky glow, refraction, proper motion and nutation are not simulated.

Astronomy references:
https://aa.usno.navy.mil/faq/GAST
https://aa.usno.navy.mil/faq/alt_az
https://github.com/liberfa/erfa/blob/master/src/prec76.c
https://github.com/liberfa/erfa/blob/master/src/pmat76.c