When it passes over the sun, how come it doesn’t cast a massive shadow across the planet akin to an eclipse? Is it just too small or too close to the earth?
In: Physics
The ISS is roughly 120 meters across, while Earth is 12,000,000 meters across. That’s a ratio of 1:10,000. Try seeing the shadow of a pin projected onto a basketball.
[Here’s video of the ISS moving infront of the sun.](https://www.youtube.com/watch?v=qEmD1FP3T6o)
The guy needed a good telescope and slowed it down.
As you can see it looks tiny compared to the sun.
That’s because it’s less than the size of two football fields, is over 400 km up, and orbits the Earth many times a day,
So the shadow is very very small and moving very very quickly.
A objective larger then the slight source will cast a shadow that is larger then itselfe.
An object that is smaller then the light source will cast a total shadow, umbra, that at the same size as the object and then it will decrease in size with distance. There is a max distance of this total shadow and it is the point when the object and light source have the same apparat size. As soon ans the object has a smaller apparent size you will see the light source around it.
The sun radius is 100x the earth radius. ISS is around 100 m long. The result is that the sun is around 7 million times wider then ISS so the shadow will drecreas with dstance
It will alose cast a partial shadow that will get larger and larger but at the same time bloc out less and less light so so it can be the almost undetectable difference. Her is [a image of iss passing in front](http://bartoszwojczynski.com/gallery/full/160430-sun-iss.jpg)[ of the sun](http://bartoszwojczynski.com/gallery/full/160430-sun-iss.jpg) as seen from earth. ISS is the had shadow that looks a bit like a reverse z. ISS only block a small fraction of the sunligt. Compare it area realtive to the sun.You need a solar filter and take pictures so video because it passes the face of the sun in a second.
[Here is an](https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra#/media/File:Diagram_of_umbra,_penumbra_&_antumbra.png)[ image of the Umbra of earth and the sun,](https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra#/media/File:Diagram_of_umbra,_penumbra_&_antumbra.png) The same principle apply for iss
You can show that shadows disappear if the light is larger then the object. Thake a thin string, to outdoor, and hand it up so it is vertical. Look at the shadow it casts on the ground You will see that it is clear when it is close to the string but invisible when it is far away from the string.
If there are electrical or other wires suspended from poles. you see the shadow of the pole but the wires are hard or invisible to see.
So shadows can shrink in size of the light source is larger than the object that cast the shadow.
There is a shadow, however the ISS is so small to completely obscure the sun, so the light can just shine around the ISS. [Wiki has a helpful graphic](https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra#/media/File:Diagram_of_umbra,_penumbra_&_antumbra.png): If you replace the earth with the ISS, we would be in the zone that is marked “Antumbra” in the graphic, so it’s just a very soft shadow.
In addition to that, the ISS moves at a speed of more than 7 km per second, so the shadow is going to be just as fast. That is 7 times as fast as a rifle bullet. So if you want to see it moving on the ground, you would have to use a high-speed camera.
However, you can see the ISS (and other satellites) flying through the sun with a telescope. [Like this shot](https://petapixel.com/assets/uploads/2020/05/isstransit-800×800.jpg)
The ISS does cast a shadow, just not one as large as you might think. Also it travels ridiculously fast – at 17,000 miles per hour – so even if you happened to be directly under it, it would pass by in a fraction of a second.
The ISS is 350 feet end-to-end, and the wingspan of the solar cells is 240 feet. That’s pretty darn big, covering more space than a football field – but it’s tiny compared to the size of the whole Earth.
The moon, in comparison, is 2100 miles in diameter. That’s more than 30,000 times bigger than the ISS. So when it happens to line up with the sun the shadow is much more noticeable.
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