Why do images of earth from space not contain satellites and other space junk?
In: Earth Science
The circumference of the earth is about 40,000 Km. At the altitude where satellites orbit (between 500 Km and 2000 KM) above the Earth, the circumference would be closer to 45,000 KM.
A satellite can be about as big as a small school bus. So lets say 5 meters.
there are reported to be 21,000 objects tracked in orbit (and a lot more small debris that cant be tracked).
So, there is about 1 object for every 2 Km of circumference , not to mention that satellites do not all orbit at the equator.
The simple answer is that there is no way to take a picture of the Earth with more than a few in view at any time. The Earth is HUGE.
Space is absolutely huge beyond our comprehension, forgive my French but it’s a Big Ass Sky! If you do the math the chances of hitting a piece of space junk is very slim!
While there is a lot of stuff orbiting the planet, typically there are miles and miles between each object. It’s like driving down a country road in the middle of the night. There’s no one around for miles.
There are (very roughly) 10,000 satellites orbiting the earth. There are about 200,000 Ferraris in the world. Twenty times as many! How many photos of earth contain an identifyable Ferrari?
Space is really big and satellites are really small.
As others have mentioned, the Earth is big – real big compared to a satellite. In order to get a picture of the entire Earth at once you need to be pretty far away – to the order of thousands of kilometers.
Geostationary orbit is about 35,000 kilometers or 22,000 miles away from the earth as an example.
Most satellites or “space junk” are maybe the size of a car. Imagine looking at a car from a mile away. Then ten miles, a hundred miles, a thousand miles.
You can see the Earth because it is huge, but that car floating in the void thousands of miles away? Not a chance.
Photo of International Space station taken from above ISS with Earth in background.
[ISS-Earth in background](https://dm0qx8t0i9gc9.cloudfront.net/thumbnails/video/GTYSdDW/videoblocks-4k-space-station-tilt-shot-in-orbit-around-earth-iss-elements-of-this-image-furnished-by-nasa_rdjdj80iz_thumbnail-1080_01.png)
Everyone else has given great answers, but [here’s an example](https://www.diyphotography.net/cameras-on-the-international-space-station-capture-spacex-starlink-satellite-train-over-an-aurora/) where satellites **were** photographed from the ISS under fortunate conditions!
They’re fucking tiny… Photos taken from geostationary profit that’s high enough to see the whole earth have a resolution of at best 1/3rd of a mile per pixel, meaning youd really need a sat half a mile across to spot at low profit, low earth says that photograph for maps and such are below most other days and statistically it’s near impossible another would be in shot during a photo, shots taken from space stations are wide angle so a sat would have to be within a km or so to be visible and there just isn’t a density of days like that
Space debris and the rising ammount of satellites is a real concern in astronomy, despite being small they have shinny surfaces that reflect the sun and can pollute the observations towards the space. But in the opposite case the Earth is reflecting much more light than any artificial satellite, effectively hiding them just like the sunlight hides all the other stars during the day.
I am one of those newspace satellite engineers, specializing in developing the EO payloads.
The distance argument is the strongest one, but there is also the factor of light. The lighting conditions have to be just perfect, angle of sunlight, the shape and surface on the debris and camera position. The smaller size does not actually matter when there is perfect reflection as that would still fill the pixel up. Think taking a long exposure of the sky, the star is smaller than a pixel but still can be seen in the image. This is true as the background is the void of space, not the case when looking at Earth. It can still happen that the background is well lit and the debris is seen as a dark spot.
A 10cm debris at 300km being imaged at 400km orbit from a satellite that is doing 30cm resolution on earth would surely see it. But most often it would happen over sea or such where the earth image is not of use. Besides, most satellites do 20m – 1000m resolutions, the sub-meter things are very few, and they will have more problems when there are 60000 new satellites up there. But lighting conditions are still important to actually affect the data meaningfully. The problem is much worse for telescopes on ground as they have really high resolution and smallest of the debris can light up with even a fraction of the light. There is a [study](https://astronomy.com/news/2021/04/satellite-skyglow-may-mean-light-pollution-is-unavoidable) that says, they would eventually even reflect man-made light going off earth.
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