annual showers, a brightening of the night sky from any source means a significant reduction in the number of observable meteors. For example, Brosch et al. (2004) found for the Leonid meteor shower (population index ~ 2) a broad distribution of apparent magnitudes peaking around +5.[1] For a site where the unaided-eye limiting magnitude equalled +5, corresponding to a night-sky brightness ~ 10 times higher than the natural background, approximately 40% of Leonids would be invisible.
The odds of seeing any particular auroral display are similarly decreased as the night-sky background brightens. This phenomenon is readily evident to aurora watchers impacted by the presence of moonlight, which even at relatively small lunar phases can quickly wash out faint auroral displays and those that are close to the horizon. Fainter aurorae (International Brightness Coefficients[2] I and II) have surface brightnesses comparable to that of airglow, and thus would be rendered invisible under a modest amount of sky brightness from any source. If the background were routinely elevated, whether from terrestrial skyglow or the diffuse glow of space objects, it would sharply reduce the potential to see the aurorae at moderately high northern/southern latitudes, reducing the number of nights a year when the phenomenon might be visible.
Figure 2. Starlink trails from objects deployed during Flight 6 are seen in this panoramic view of the night sky. Photo by Mike Lewinski, licensed under CC BY 2.0.
- ↑ Brosch, N., et al. (2004). Meteor light curves: the relevant parameters. Monthly Notices of the Royal Astronomical Society, 355(1), 111. https://doi.org/10.1111/j.1365-2966.2004.08300.x
- ↑ A classification system introduced by Seaton, M. J. (1954) Excitation processes in the aurora and airglow 1. Absolute intensities, relative ultra-violet intensities and electron densities in high latitude aurorae. Journal of Atmospheric and Terrestrial Physics, 4(6), 285, https:// doi.org/10.1016/0021-9169(54)90060-4 and extended in Hunten, D. M. (1955) Some photometric observations of auroral spectra. Journal of Atmospheric and Terrestrial Physics, 7, 141, https://doi.org/10.1016/0021-9169(55)90121-5.
