Oooh .... slight spelling variants ( English c/w US perhaps ) Ephemeris or Emphemeris. Google insists upon the former.
Anyway someone has to keep track of the states of the solar system so NASA's JPL has that job. Originally there were ephemerides : books containing tables of calculations for the positions and times of sky objects. Were used mainly at sea to determine - via looking at the sky positions of something quite obvious - the longitude of the ship ( also need a hopefully accurate clock or three onboard ). So the various world powers kept astronomers for the purpose of producing such tables. An indirect method for sure, but the world does rotate constantly enough that with good instruments one could keep from running aground for instance. However a ship's navigator would get nervous if the conditions prevented sky observations, so it was still a good idea to use the mark-1 eyeball of lookouts.
For E@H, workunits need to know the orientation/position of a given laser interferometer ( with respect to the barycentre ) at the time of an observation. It seems that frame of reference is important in astronomy. The Earth is a rotating platform that moves around the Sun and so an ephemeris is used for that I reckon. I think they went to a GPS time standard some time ago. The interferometer data streams are time-stamped you see.
{ FWIW the barycentre of the solar system is within the radius of the Sun! }
Do you know how a nuclear submarine knows where it is all the time, given that it can stay underwater for a very long time ? The first is using radio signals, GPS and whatnot if it is at or near the surface. But underwater there is a 3 way laser device that measures accelerations via a general relativistic effect and that can be integrated to give a velocity change which in turn can be integrated again to give a position change from some prior independent fix. An acceleration can cause light beams to bend or 'spacetime gets curved'. I doubt whether Einstein would have predicted this obscure application but it comes straight from his theory. GPS needs to account for general relativity ..... so our daily car commute can be governed by it too.
[\long aside on a lazy Saturday]
Cheers, Mike
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
[long aside on a lazy
)
[long aside on a lazy Saturday]
Oooh .... slight spelling variants ( English c/w US perhaps ) Ephemeris or Emphemeris. Google insists upon the former.
Anyway someone has to keep track of the states of the solar system so NASA's JPL has that job. Originally there were ephemerides : books containing tables of calculations for the positions and times of sky objects. Were used mainly at sea to determine - via looking at the sky positions of something quite obvious - the longitude of the ship ( also need a hopefully accurate clock or three onboard ). So the various world powers kept astronomers for the purpose of producing such tables. An indirect method for sure, but the world does rotate constantly enough that with good instruments one could keep from running aground for instance. However a ship's navigator would get nervous if the conditions prevented sky observations, so it was still a good idea to use the mark-1 eyeball of lookouts.
For E@H, workunits need to know the orientation/position of a given laser interferometer ( with respect to the barycentre ) at the time of an observation. It seems that frame of reference is important in astronomy. The Earth is a rotating platform that moves around the Sun and so an ephemeris is used for that I reckon. I think they went to a GPS time standard some time ago. The interferometer data streams are time-stamped you see.
{ FWIW the barycentre of the solar system is within the radius of the Sun! }
Do you know how a nuclear submarine knows where it is all the time, given that it can stay underwater for a very long time ? The first is using radio signals, GPS and whatnot if it is at or near the surface. But underwater there is a 3 way laser device that measures accelerations via a general relativistic effect and that can be integrated to give a velocity change which in turn can be integrated again to give a position change from some prior independent fix. An acceleration can cause light beams to bend or 'spacetime gets curved'. I doubt whether Einstein would have predicted this obscure application but it comes straight from his theory. GPS needs to account for general relativity ..... so our daily car commute can be governed by it too.
[\long aside on a lazy Saturday]
Cheers, Mike
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Mike: Excellent to read
)
Mike:
Excellent to read and very interesting.
Thank you - it was one of the few really interesting post!
Stay save and have a Sunday beer on me.
San-Fernando-Valley
)
And I also concur! Yes, stay safe!
Proud member of the Old Farts Association