Prof. James Lowenthal Of Smith College, delivered one of the most sober and timely warnings on light pollution in recent years in his plenary AAS lecture Tuesday, June 2nd.
I had known for some time about the encroaching threat of light pollution on astronomical observations as I'd written on the topic a number of times in the Barbados press. However, nothing in that previous material prepared me for the shock of how things have deteriorated as revealed in Prof. James Lowenthal's plenary lecture at the 236th AAS Meeting last Tuesday with Prof Sandra Cruz-Pol,:
'Satellite Mega Constellations And The Night Sky: OIR Visibility, Impacts & Policy.'
Prof. Lowenthal himself recalls where (White Mountains of New Hampshire) and what he was doing (training undergraduate students) when he first confronted Space X's Starlink in the night sky, which he described as: "deeply impressive, almost beautiful… but it was also a watershed moment and I felt the night sky would never be the same again”.
And it wouldn't be as these man-made celestial intruders, satellite "mega constellations", would be less and less welcome. Indeed, the launch of Starlink angered astronomers around the world and began a conversation about humanity's relationship with the heavens - namely with the ability to observationally access the myriad astronomical objects in the night sky - which might now recede into visual obscurity. As Lowenthal plaintively asked at the conclusion of his talk:
What are the stars and the sky worth?
Who decides?
Why the fuss? As Lowenthal put it, he realized his life as a professional astronomer had changed when he beheld - a year ago- the Starlink formation in the night sky, e.g.
He had actually seen the video earlier in the day but still wasn't prepared for the visual assault on the heavens. It began with a launch of 60 satellites from a Space X spacecraft and will be followed by 26 subsequent launches for a total of 1560 satellites each at an orbit altitude of 300 km. The satellites will then separate and proceed to their individual orbits with altitudes of about 550 km. A close -up of one of the satellites - the "business end" or chassis, is shown in the slide below:
The aspect to process is that a large (8 m long) solar panel is then deployed from each satellite, to reflect sunlight, making each satellite effectively as bright as the brightest stars in the Big Dipper (or brighter than 99 % of all preceding satellites). This is huge, monumental in terms of observational disruptions. If astronomers could make them all vanish with a wave of the hand I am sure they would, but of course we are told they are essential to ensure fast (low latency) internet access, e.g.
But is internet speed THAT important? (E.g. 46 msec from NYC to London) What if a large (o.5 km ) asteroid is on a collision trajectory toward Earth- and say it has the energy of 20 million megatons or enough to wipe out NYC, London or Moscow? But we are unable to detect it because of the interference of Starlink satellites? What then? Let 10-12 million perish in a fireball just to get high speed connections?
The issue of satellites in low Earth orbit (LEO) is especially germane as that is where most of these intruders will be. E.g.
Let's also note that there are already, according to the U.S. Space Surveillance Network, 19,000 objects (with diameter > 10 cm) in such LEOs, but only 2,000 are actually working satellites. The rest are debris but still often enough to yield a nuisance factor. How big a nuisance for the non-debris objects and for how long?
According to Prof. Lowenthal, the visibility of a given (working) satellite depends on 6 factors:
- Orbit altitude
- Orbit inclination
- Time of day
- Time of year
- Latitude
- Attitude, size, albedo (reflectivity) and shape.
In terms of the different impacts related to satellites in low earth orbit (550km) or high Earth Orbit (1300 km) the former are brighter - so will likely be a greater nuisance, but will last usually only 5 years, compared to perhaps 1,000 years for the higher altitude objects. Those latter are also "fainter, slower and less numerous". Nuisance impact on visibility of astronomical objects in any case will be a function of how bright these satellites are relative to celestial objects. The most basic barometer is whether they attain naked eye visibility. Currently, according to Prof. Lowenthal, 420 Starlink (and other) satellites are visible to the naked eye. But the near future could see 10,000 or more vying for attention with stars, planets, planetary moons, comets and even larger asteroids.
Here's the real lowdown on this threat: numerous major observational efforts could be fatally impacted to the point of critical data obliterated by ghost trails from satellites. We are talking about - or rather Prof. Lowenthal and others (in the AAS Committee on 'Light Pollution, Radio Interference Space Debris' ) - the danger of 98 percent or more of observational fields being eroded, pixels completely lost, astronomy at a crossroads of futility and ever diminishing returns. A case in point would be the impacts on the Vera Rubin Observatory which is scheduled to see 'first light' later this year. Its main objective is to image the entire southern sky every few nights. However, it could be impeded in its mission by Starlink satellites operating in southern skies. As Lowenthal explains:
"We are talking about tens of satellites at once, at any moment, during many hours of the night … across your field of view. It’s a terrible collision of technologies”
Lastly, Lowenthal reminds us that there are environmental impacts as well which may not be fully appreciated. For example, migratory birds use the stars to navigate but if artificial "stars" in the form of Starlink satellites dominate the skies they will be diverted, thrown off, from their destinations. This can also have impact on commercial aviation, given we may find more bird strikes on aircraft - possibly with disastrous outcomes.
To read more of Prof. Lowenthal's work in this area readers can check out his findings published in a white paper on which his AAS talk was based.
See also:
Light pollution is getting worse, and Earth is paying the price
https://www.nationalgeographic.com/science/2019/04/nights-are-getting-brighter-earth-paying-the-price-light-pollution-dark-skies/
No comments:
Post a Comment