At present, we do not have anything even like a heuristic model of astrotourism spending that can suggest how the monetary value of nighttime darkness scales with metrics such as night sky quality. But we raise the alarm that a global rise in night sky brightness from satellites and space debris (collectively, “space objects”) will be akin to a rising tide that lifts all boats. It seems reasonable to expect that such increasing worldwide night sky brightness will tend to diminish the value of all "dark-sky" sites, particularly those that are now thought of as pristine such as dedicated dark-sky parks and preserves. This will impact millenia-old human observations of the Milky Way, meteor showers and more, which we elaborate on and attempt to quantify below. This is also yet another way that satellites and space debris will impact Indigenous sky traditions and storytelling, which have had an increasing role in recent years in astrotourism tours and stargazing initiatives at International Dark Sky Parks designated by the International Dark-Sky Association.[1]
2.3. Rising diffuse night sky brightness from satellites and space debris
Concerns raised to date about the impact of large satellite constellations on the night sky have tended to focus on the streaks or trails of light they produce, whether observed visually as discrete, moving points of light or recorded on various electronic detectors. However, we are only beginning to examine the contribution of space objects in elevating the global diffuse brightness of the night sky[2], much as the collective light of millions of individual stars too faint to detect by the human eye yields the familiar, glowing clouds of the Milky Way. A recently published study estimates that, prior to the first SpaceX launch in 2019, these objects yielded an increase of "approximately 10 per cent … over the brightness of the night sky determined by natural sources of light", equivalent to a zenith luminance contribution of 20 μcd m-2. Coincidentally, the IAU and the International Committee on Illumination consider an astronomical observatory site whose night-sky brightness exceeds 10% above background at zenith angles ≤ 70° to be light-polluted.[3]
According to the Union of Concerned Scientists, as of 1 April 2020 there were a total of 2666 satellites in orbit around Earth, of which 1918 were in LEO.[4] Assuming the number above for the total steady-state number of new LEO satellites in space in the 2020s, the total would reach about 50,000 satellites. If the population of debris objects increases according to the current size distribution, then the number of LEO objects in 2030 should be a factor of about 25 times higher than it is now. That would yield an average zenith luminance contribution from space objects of around 500 μcd m-2, or 250% above the natural background. As we detail below, if this scenario were fully realized, it would cause significant degradation of detail in visual observations of the Milky Way, a diminution of the number of stars visible to the unaided eye by a factor of about two, the disappearance of roughly half of the meteors in major annual events like the Leonid meteor shower, and the inability to view faint auroral displays.
- ↑ National Parks Are Embracing Indigenous Astronomy, Outside Online, 12 July 2021 (https://www.outsideonline.com/adventure-travel/national-parks/national-parks-indigenous-stars/).
- ↑ Kocifaj, M., Kundracik, F., Barentine, J. C. & Bará, S. (2021). The proliferation of space objects is a rapidly increasing source of artificial night sky brightness. Monthly Notices of the Royal Astronomical Society: Letters, 504(1), L40. https://doi.org/10.1093/mnrasl/slab030.
- ↑ Cayrel R., et al. (1980). Guidelines for minimizing urban sky glow near astronomical observatories. CIE 001-1980.
- ↑ Geospatial World, How many satellites orbit Earth and why space traffic management is crucial (https://www.geospatialworld.net/blogs/how-many-satellites-orbit-earth-and-why-space-traffic-management-is-crucial/, accessed 23 August 2021)
