  SiTian is an ambitious ground-based all-sky optical monitoring project,
developed by the Chinese Academy of Sciences. The concept is an integrated
network of dozens of 1-m-class telescopes deployed partly in China and partly
at various other sites around the world. The main science goals are the
detection, identification and monitoring of optical transients (such as
gravitational wave events, fast radio bursts, supernovae) on the largely
unknown timescales of less than 1 day; SiTian will also provide a treasure
trove of data for studies of AGN, quasars, variable stars, planets, asteroids,
and microlensing events. To achieve those goals, SiTian will scan at least
10,000 square deg of sky every 30 min, down to a detection limit of $V \approx
21$ mag. The scans will produce simultaneous light-curves in 3 optical bands.
In addition, SiTian will include at least three 4-m telescopes specifically
allocated for follow-up spectroscopy of the most interesting targets. We plan
to complete the installation of 72 telescopes by 2030 and start full scientific
operations in 2032.
