  Megaconstellations of thousands to tens of thousands of artificial satellites
(satcons) are rapidly being developed and launched. These satcons will have
negative consequences for observational astronomy research, and are poised to
drastically interfere with naked-eye stargazing worldwide should mitigation
efforts be unsuccessful. Here we provide predictions for the optical
brightnesses and on-sky distributions of several satcons, including Starlink,
OneWeb, Kuiper, and StarNet/GW, for a total of 65,000 satellites on their filed
or predicted orbits. We develop a simple model of satellite reflectivity, which
is calibrated using published Starlink observations. We use this model to
estimate the visible magnitudes and on-sky distributions for these satellites
as seen from different places on Earth, in different seasons, and different
times of night. For latitudes near 50 degrees North and South, satcon
satellites make up a few percent of all visible point sources all night long
near the summer solstice, as well as near sunrise and sunset on the equinoxes.
Altering the satellites' altitudes only changes the specific impacts of the
problem. Without drastic reduction of the reflectivities, or significantly
fewer total satellites in orbit, satcons will significantly change the night
sky worldwide.
