Ontario, CA Night Sky Brightness
Ontario, CA's night sky, measured from orbit
Ontario reads as urban on this dataset's scale. Sky glow overhead most nights. Typically only planets, the Moon, and a handful of the brightest stars are visible. Only 95.3% of the 3,206 cities measured here read darker than Ontario.
Note the source: a satellite reading of upward light, not a visual Bortle scale reading. The two measure related but different things, explained in the Bortle scale guide.
How far Ontario is from a meaningfully darker sky
Eastvale, CA, about 5 miles away as the crow flies, measures in the suburban band, one step darker than Ontario. Actual driving distance will run longer than that straight-line figure.
Eastvale, CA is itself still a measured city, not a designated dark-sky park, this only compares against the 3,206 places this dataset covers.
How Ontario compares nationally
Ontario, CA counts roughly 185,285 residents, among the 3,206 US cities this site tracks. Ontario's position, 3,038 of 3,206, darkest to brightest, comes from the sampling method the methodology guide sets out.