Chinahand Posted August 31, 2015 Share Posted August 31, 2015 Oh this one is also really cool. Measuring the height of a satellite using parallax. Now, this is something people could do together just on the Isle of Man using either an irridium flare as in the link, but it would also work with the ISS. Someone in Castletown could do an exposure and compare it to someone in Douglas or Ramsey and the parallax differences would be apparent. So Gerry, how far away is the ISS in your dream world? Fancy actually putting this to the test? Link to comment Share on other sites More sharing options...
gerrydandridge Posted August 31, 2015 Author Share Posted August 31, 2015 I could well be doing this wrong but can I ask what assumptions we have to make in order to get a correct distance to the moon via parallax reading. Are we assuming the moons diameter of 3400km is approx 0.56° in the sky My thinking is that the distance is dependable on the width of the moon? See my rather crude drawing. Link to comment Share on other sites More sharing options...
Chinahand Posted August 31, 2015 Share Posted August 31, 2015 You could if you wanted very simply measure the angular width of the moon, but that measurement is not used at all to calculate parallax. Nor is the moon's diameter. All you need is person A to measure the angular position of the moon against a reference star, person B to measure the angular position of the moon against a reference star. If you know how far apart A and B are the angular change will give you the distance to the moon via some pretty simple maths. What don't you understand? Your angle a is a result of people actually measuring an angle, not assuming anything. It is very easy to measure the angle between two objects in the sky using a telescope or sextant. Link to comment Share on other sites More sharing options...
Chinahand Posted August 31, 2015 Share Posted August 31, 2015 Looking at your drawing the moon is in the wrong place - the moon should be where the two lines intersect - there's only one moon! Its position against the stars changes ... ah maybe this is an issue for you Gerry - you don't think the stars are far away. This is a bit of a red herring, but explaining it requires patience! What the two people are doing is measuring the angular position of the moon from their locations and seeing how much it has changed - but actually getting this measurement directly is quite labour intensive - you've got to calculate both person's declination, right ascension, latitude etc. But by using a reference star all these factors which vary for the two people cancel out. It's like asking two people to start at King's Cross and then take a certain number of stations down the Northern Line to get to London Bridge - it is far easier to give that instruction than giving directions from where ever they actually are. You don't need to make that assumption - you can simply do the measurements (give directions from each person's location), but it is a lot easier if you do. Think about it this way - if Polaris was the reference star the two people would both know their telescopes were pointing (basically directly) towards the celestial North when they recorded their results. Other reference stars are more complicated for astronomers at different points on the earth to find - you've got to factor in all the things listed above. Make sense. Gerry, genuinely I am not trying to trick you. You could measure these things yourself it is impossible for a conspiracy to keep this evidence from you. The distance to the moon cannot be kept secret by the illuminati. Link to comment Share on other sites More sharing options...
gerrydandridge Posted August 31, 2015 Author Share Posted August 31, 2015 Looking at your drawing the moon is in the wrong place - the moon should be where the two lines intersect - there's only one moon! Its position against the stars changes ... ah maybe this is an issue for you Gerry - you don't think the stars are far away. Yes I agree 1 moon only, however my thought was along the lines of I hold my thumb out and close 1 eye, then I open it and close the other eye, simulating each eye being each observer, that was why 2 moons, the moon in 1 position for one observer and in another position for another observer. I know the width of my thumb so therefore calculating the arms length should be easy...I am trying to do it in a layman's perspective. The reason being I suspect the entire model is reversed engineered and the tool used to do this was man made mathematics... Yes again we have to assume the distance of the stars, I don't quite see how anyone can take X as a fact on the assumption of Y... Link to comment Share on other sites More sharing options...
Chinahand Posted August 31, 2015 Share Posted August 31, 2015 NO you don't need to know the distance to the stars. Ok lets start again. Image two people looking at a black object stuck a certain distance from a white wall. The two people are standing on a line a certain distance from this object. They don't know how far the line is away from the object. But they do know how far apart they are, D. They also don't know how far away the wall is - but it doesn't matter because the wall is entirely featureless - it is no help to them. Both people measure the angle from the line to the object. One will get x degrees, one will get y degrees. All you need is x, y and D and you can calculate how far away the object is. Now lets put another black mark on the wall. Rather than measuring the angle from the line they measure the angle from the mark on the wall to the object. So they have a, b and D. You can also calculate how far the object is away from the line with these 3 measurements. You do not need to know how far away the wall is. The black mark is just a reference point and it cancels out in the maths. This really isn't complicated. The idea is exactly what is happening with the moon when you measure lunar parallax. Link to comment Share on other sites More sharing options...
gerrydandridge Posted August 31, 2015 Author Share Posted August 31, 2015 Yes that is what I thought, so the photo of lunar parallax that you posted earlier has the positions of the photographers on earth, so we have D, but I see no angle of the moon measurement from their perspective positions (unless I missed it), so we cannot measure the moons distance without these 2 angles....or we have to assume something to get the distance of the moon from the observers... So the way I understand it we need to synchronize an angle measurement of the moon from 2 locations on earth...I don't think many people have gone to such lengths so concealing the distance of the moon is achievable, on searching out this method they all seem to make at least 1 assumption, I find this with other geometrical measurements also. Link to comment Share on other sites More sharing options...
Chinahand Posted August 31, 2015 Share Posted August 31, 2015 No, you are still not getting it. You do have the angles. You have the stars in the image and this gives you the measurements you need. You do not need to assume any angles. You just measure them off the photo. Being really pedantic you do have to ensure the photos are taken at the same time but that isn't difficult with a bit of coordination. You cannot stop two people collecting this information. Only laziness and apathy can stop you doing it. You then directly take the measurements and the results fall out of the maths with no more assumptions than the wall example. Link to comment Share on other sites More sharing options...
wrighty Posted August 31, 2015 Share Posted August 31, 2015 I'm probably being stupid here China, but doesn't this rely on the stars being effectively at infinity? If they're just holes in the black cloth 3000 miles up then you'll have a parallax effect on the star positions too. ETA - I do have a maths degree, but this may be being cancelled out by cider. Apologies if I'm just confused. If so I'm sure I'll see it in the morning Link to comment Share on other sites More sharing options...
Tholtan Posted August 31, 2015 Share Posted August 31, 2015 Are you lot for real? Link to comment Share on other sites More sharing options...
Chinahand Posted August 31, 2015 Share Posted August 31, 2015 @ Wrighty Not really but sort of. As I explained above in the example with the blank wall you don't need to have anything in the back ground to see and measure parallax. It just makes it more visible. The angular measurements would be different from the points of view of the two observers and could be measured even if there was nothing in the background. But in that case you'd have to rely on the observers to be accurate with there measurements. With the Stars there they act as a standard rule and so I don't need to know what the observers measured. Just tell me what the stars are and how far apart the observers were and you can work out the distance to the moon. Link to comment Share on other sites More sharing options...
quilp Posted August 31, 2015 Share Posted August 31, 2015 How far can you go on this stuff ...? Link to comment Share on other sites More sharing options...
doc.fixit Posted August 31, 2015 Share Posted August 31, 2015 to the stars, to the stars.............using paralelxexxll of course Link to comment Share on other sites More sharing options...
Chinahand Posted August 31, 2015 Share Posted August 31, 2015 When ever I think of something which provides an evidence based, experimental method which Gerry could do himself to show that he is wrong to believe the world is flat etc I'll put it up! Link to comment Share on other sites More sharing options...
Tholtan Posted August 31, 2015 Share Posted August 31, 2015 When ever I think of something which provides an evidence based, experimental method which Gerry could do himself to show that he is wrong to believe the world is flat etc I'll put it up! Send him back to basics. https://en.wikipedia.org/wiki/Eratosthenes#Measurement_of_the_Earth.27s_circumference Link to comment Share on other sites More sharing options...
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