[Just thinking]

Yes please it would be all my pleasure.

I forgot to mention it is just up a little at reply # 54.

[Bored chemist]

Just checking something.
Is there anything special about "the very moment that one of the moons of Jupiter has just alined its edge with the edge of Jupiter", or are you just using it as an event which we can see from Earth or the Moon?

Would it make any difference if we replaced it by a bright flash on the surface of Jupiter?

[Just thinking]

Is there anything special about "the very moment that one of the moons of Jupiter has just alined its edge with the edge of Jupiter", or are you just using it as an event which we can see from Earth or the Moon?

The alinement is very important as seen from our moon as it will act as a timed moment that we on earth can use to coincide with the time delay eg. the moon telescope sees this event and sends to earth a registration of the event as it takes place we will see if the message arrives back on earth about 1-second later as this is the distance of our moon 1 second from the earth if the signal arrived let's say in 0.5 seconds that would mean that light would take 1.5 seconds to reach the moon from earth.

[Just thinking]

Would it make any difference if we replaced it by a bright flash on the surface of Jupiter?

Yes, that would not work as it would require a double journey and that would defeat the purpose of the experiment. One way speed of light.

[Bored chemist]

it would require a double journey

Why?
We could just send a big firecracker to Jupiter .
It would flash and the light would come to us (and the moon) there's no two way journey made by the light, is there?

[Just thinking]

Quote from: Just thinking on Today at 02:20:24

    it would require a double journey

Why?
We could just sens a big firecracker to Jupiter .
It would flash and the light would come to us (and the moon) there's no two way journey made by the light, is there?

No that still won't work as the firecracker on Jupiter would be delivered by a rocket that has a so-called synchronised time that would be relied on to detonate the flash and that time synchronised system is the very thing that we are trying to avoid as it can not be relied on due to the time dilation and distance in space.

[Bored chemist]

There is the same problem with "the very moment that one of the moons of Jupiter has just alined its edge with the edge of Jupiter"
We don't know when and where it happens without bouncing light off Jupiter.

But say we just use the sort of fuse they have on fireworks; you know that it will fire about 15 seconds after you light the fuse.
Isn't that good enough?
As long as we keep a watch for it for a while after we send the signal to light the fuse we will see the flash here, and the camera etc on the moon will see the flash there.
We can still time the interval between when the signals get to us.

[Bored chemist]

The trouble with "the very moment that one of the moons of Jupiter has just alined its edge with the edge of Jupiter"
 is that it depends where you are, so it isn't a good thing to choose as a timing point.

[Just thinking]

The trouble with "the very moment that one of the moons of Jupiter has just alined its edge with the edge of Jupiter"
 is that it depends where you are, so it isn't a good thing to choose as a timing point.

Earth and our moon see Jupiter at the same moment in time as long as Jupiter and our moon are at a 90-degree position as seen from earth and we hear on earth can no what the moon can see at any given time by simple mathematical equations when the moon of Jupiter comes in perfect alignment as seen from our moon at that same very moment we would see the moon of Jupiter in a slightly different position but we still would no when it has reached alignment seen from our moon. When our moon sees that alignment and we would know that moment without the use of light or a synchronised time pice the telescope and system on the moon can send that moment back to us and we can determine the delay of that signal from our moon.

[Just thinking]

There is the same problem with "the very moment that one of the moons of Jupiter has just alined its edge with the edge of Jupiter"
We don't know when and where it happens without bouncing light off Jupiter.

We don't need to bounce light off Jupiter the reflected sunlight is coming from Jupiter and arriving on earth and our moon at the same time provided that Jupiter and our moon are at 90 degrees as seen from earth.

[Just thinking]

But say we just use the sort of fuse they have on fireworks; you know that it will fire about 15 seconds after you light the fuse.
Isn't that good enough?
As long as we keep a watch for it for a while after we send the signal to light the fuse we will see the flash here, and the camera etc on the moon will see the flash there.
We can still time the interval between when the signals get to us.

I think I see what you saying and that is a very good way to go about it. That is if you are suggesting that the telescope on our moon sends the mesage at the very moment of the flash yes we could time that.

[Bored chemist]

Moony.png (5.13 kB . 615x345 - viewed 1811 times)

Earth and our moon see Jupiter at the same moment in time

No, they don't.
Here's a picture.
As they are lined up,  the camera on the moon can't see the moon of Jupiter, but the observer on Earth can see it.

That's why it's a good idea to have a time signal like a flash.

Also, the distance from (Jupiter's moon moon or Jupiter) to either the Earth or the Moon is different.

So your method doesn't even make sense,
https://en.wikipedia.org/wiki/Not_even_wrong

[Bored chemist]

But say we just use the sort of fuse they have on fireworks; you know that it will fire about 15 seconds after you light the fuse.
Isn't that good enough?
As long as we keep a watch for it for a while after we send the signal to light the fuse we will see the flash here, and the camera etc on the moon will see the flash there.
We can still time the interval between when the signals get to us.

I think I see what you saying and that is a very good way to go about it. That is if you are suggesting that the telescope on our moon sends the mesage at the very moment of the flash yes we could time that.

OK, better late than never.
Now, there's another clever trick to simplify things.
Rather than a camera and a signal sent to earth, why not just use a big mirror on the Moon?
If we set it up so that you can see the reflection of Jupiter (using another telescope on Earth) then we don't need to worry about how long the image processing takes.

[Just thinking]

* Moony.png (5.13 kB . 615x345 - viewed 2 times)
Quote from: Just thinking on Today at 03:14:51

    Earth and our moon see Jupiter at the same moment in time

No, they don't.
Here's a picture.
As they are lined up,  the camera on the moon can't see the moon of Jupiter, but the observer on Earth can see it.

That's why it's a good idea to have a time signal like a flash.

Also, the distance from (Jupiter's moon moon or Jupiter) to either the Earth or the Moon is different.

So your method doesn't even make sense,

Jupiter is over 2000 seconds away our moon is only 1 second away and that 1 second can be accounted for or if our moon and Jupiter is at 90 degrees seen from earth it can be cancelled out of the equation. And there are times when the earths moon is in a position that can see jupiter from the same angle.

[Bored chemist]

Moony2.png (9.41 kB . 837x583 - viewed 1873 times)i have another suggestion to make everything easier.
The moon, the Earth and Jupitar are all moving, and two of them are rather awkward to get to.

This is the 21st century. It's easy to get a clock that will measure time intervals to better than a picosecond. That's time for light to travel about a  third of a millimetre.

So, we can set up a "scale model" of your system.
In the lab we have a detector and a mirror a foot apart and (we have a really big lab) 2000 feet away we have a flash light

[Just thinking]

OK, better late than never.
Now, there's another clever trick to simplify things.
Rather than a camera and a signal sent to earth, why not just use a big mirror on the Moon?
If we set it up so that you can see the reflection of Jupiter (using another telescope on Earth) then we don't need to worry about how long the image processing takes.

Well, the image processing time would be known and can be accounted for the amount of time would be very little as an 8-inch telescope will see the image and the camera will handle that light in a fraction of a second. The mirror idea is rather fanciful for a number of reasons such as it would have to be very large as the telescopes on earth or even the Hubble telescope can only see structures on the moon that are of a size far beyond many 10's of meters and that is with very pore clarity.

[Bored chemist]

About 2000 nanoseconds after the flash goes off the light will reach the detector directly. And about 1 nanosecond after that the reflected light will reach the detector.

So the detector will give two signals separated in time by some interval corresponding to how long it takes light to travel from the mirror to the detector (compared to taking the direct path).
And with modern electronics we can measure that accurately.

[Bored chemist]

OK, better late than never.
Now, there's another clever trick to simplify things.
Rather than a camera and a signal sent to earth, why not just use a big mirror on the Moon?
If we set it up so that you can see the reflection of Jupiter (using another telescope on Earth) then we don't need to worry about how long the image processing takes.

Well, the image processing time would be known and can be accounted for the amount of time would be very little as an 8-inch telescope will see the image and the camera will handle that light in a fraction of a second. The mirror idea is rather fanciful for a number of reasons such as it would have to be very large as the telescopes on earth or even the Hubble telescope can only see structures on the moon that are of a size far beyond many 10's of meters and that is with very pore clarity.

The nice thing about a thought experiment is the budget is infinite.

[Just thinking]

* Moony2.png (9.41 kB . 837x583 - viewed 6 times)i have another suggestion to make everything easier.
The moon, the Earth and Jupitar are all moving, and two of them are rather awkward to get to.

This is the 21st century. It's easy to get a clock that will measure time intervals to better than a picosecond. That's time for light to travel about a  third of a millimetre.

So, we can set up a "scale model" of your system.
In the lab we have a detector and a mirror a foot apart and (we have a really big lab) 2000 feet away we have a flash light

This would seem to be a miniature version of my suggestion but in fact it is not the same concept as the smaller version is still reliant on a beam of light and it is the same beam of light that is reflected of the mirror this is one way light travel but we don't know the true time that it left its source. It still is reliant on synchronisation and that is the problem with this type of test.

[Just thinking]

The nice thing about a thought experiment is the budget is infinite.

That is very true I do believe that the mirror on the moon would work if the mirror and the telescope were large but it would be a lot of bad luck if that mirror was to break. Might leave that experiment to china.