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I know that this is never going to happen, because those telescopes have much more important things to look for ...

But I was just wondering if we still did it, what would the best result look like? Would it look like

  • a lighter pixel in a dark background
  • those pictures of ISS taken in front of the Sun or the Moon
  • could we get something a lot better than these, like a good resolution and being able to identify Starman as well

I am thinking about the best case scenario like best orbit position for Starman too

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The angular resolution of the Hubble and James Webb telescopes are about the same - both are around $0.05$ to $0.1$ arc seconds or about $4 \times 10^{-7}$ radians.

If we express the angle $\theta$ in radians then the distance subtended by that angle at a distance $r$ is just $r\theta$. Starman is about fifty million kilometres away, and at that range $4 \times 10^{-7}$ radians corresponds to a distance of around $5 \times 10^{7}\ \mathrm{km} \times 4 \times 10^{-7} = 20\ \mathrm{km}$. So neither telescope will be able to see the Tesla as anything other than a point of light.

According to Ars Technica the closest Starman will come to Earth in the next century in 2047 when he will be about five million kilometers away. But even at this distance the resolution of the telescopes would only be $2\ \mathrm{km}$.

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    $\begingroup$ FWIW: That same article says, "in order to resolve more than a dot, Starman would have to make a pass within 37,000 miles (60,000km) of a telescope 10m (33 feet) in diameter." $\endgroup$ Feb 18 at 18:31
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    $\begingroup$ @SolomonSlow it brings it home to you just how big space is! :-) $\endgroup$ Feb 18 at 18:50
  • $\begingroup$ The article's author has posted an answer as well :-) $\endgroup$
    – uhoh
    Feb 18 at 20:00
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    $\begingroup$ @JohnRennie - "I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space." ;-) $\endgroup$ Feb 19 at 12:22
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    $\begingroup$ @T.J.Crowder I very nearly added the quote to my answer, but chickened out at the last minute :-) $\endgroup$ Feb 19 at 12:23
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Hubble is one of the few telescopes that could possibly image Starman, as a dot. James Webb will have far more sensitivity. It's a really small space rock in a really big space. You can take a look at https://www.whereisroadster.com/ which has information on how big of a telescope it would take to see it, and to resolve it, updated in realtime. The answer right now is:

A telescope about 7,223 ft (2,202 m) in diameter would be required to resolve the Upper stage from Earth. A smaller one could see him as an unresolved dot, about 13.9 ft (4.2 m) in diameter, in ideal conditions.

Hubble, being outside of the atmosphere, is better than the small unresolved dot scenario. There are telescopes right now on the ground that if they pointed at it and spent an hour of imaging time could probably find it, but those telescopes aren't likely to be used for this purpose, their primary purpose being scientific pursuit.

To get an idea of what something might look at, I suggest looking at the Hubble pictures of 2014 MU69. Starman is of a comparible side, but would be moving faster than 2014 MU69.

enter image description here

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