scholarly journals Navigation, world mapping and astrometry with Galileo's moons

2010 ◽  
Vol 6 (S269) ◽  
pp. 42-48 ◽  
Author(s):  
Kaare Aksnes
Keyword(s):  
Light Curves ◽  
Speed Of Light ◽  
Finite Speed ◽  
The Earth

AbstractGalileo realized that the four moons he discovered, besides supporting the heliocentric system, could also serve as a clock in the sky for longitude determination. Navigation at sea by this method did not prove practical but G. Cassini used it to improve land mapping. O. Rømer discovered that the interval between eclipses of the moons by Jupiter increased or decreased according to whether the Earth moved away from or toward Jupiter. He attributed this to the finite speed of light which he in 1676 determined with an error of about 25%. Timings of the eclipses by Jupiter have served to compute accurate orbits of the moons, notably by means of R. A. Sampson's theory of 1921. Beginning in 1973, light curves of mutual eclipses and occultations between pairs of moons have been made regularly at six years intervals. From these observations very accurate radii and positions of the moons have been obtained.

Influence of displacement currents on the response of helicopter electromagnetic systems

Geophysics ◽  
2005 ◽  
Vol 70 (4) ◽  
pp. G95-G100 ◽  
Author(s):  
Changchun Yin ◽  
Greg Hodges
Keyword(s):  
Phase Shift ◽  
Dielectric Permittivity ◽  
Half Space ◽  
Free Space ◽  
Phase Changes ◽  
Displacement Current ◽  
Speed Of Light ◽  
Finite Speed ◽  
The Earth ◽  
Full Solution

For the purpose of shallow-earth geophysical mapping, progressively higher frequencies have been developed for helicopter electromagnetic (HEM) systems. However, concern has been expressed about the vulnerability of high-frequency EM signals to the influence of the displacement current, especially the phase shift of the HEM signal resulting from the finite speed of light that describes the propagation of the EM wave in free space. In this paper we investigate the influence of the displacement current and the finite speed of light on HEM responses, based on a full solution of the EM field for a conductive, magnetically, and dielectrically polarizable earth half-space and an overlying half-space of air with free-space dielectric permittivity. We calculate the amplitude change and the phase shift of the HEM signal and the change in the apparent resistivity. We find that the displacement current, when both the air and the earth half-space assume the free-space dielectric permittivity, has a small influence on the HEM signal, while substantial influence may occur when the earth is dielectrically polarizable. The finite speed of the EM propagation in free space does not result in significant phase changes in the HEM signal.

scholarly journals SUBLUMINAL OPERA NEUTRINOS

2012 ◽  
Vol 27 (07) ◽  
pp. 1250033 ◽  
Author(s):  
ICHIRO ODA
Keyword(s):  
Special Relativity ◽  
Recent Work ◽  
Causal Structure ◽  
Pion Decay ◽  
Speed Of Light ◽  
The Earth

The OPERA Collaboration has announced to have observed superluminal neutrinos with a mean energy 17.5 GeV, but afterward the superluminal interpretation of the OPERA results has been refuted theoretically by Cherenkov-like radiation and pion decay. In a recent work, we have proposed a kinematical resolution to this problem. A key idea in our resolution is that the OPERA neutrinos are not superluminal but subluminal since they travel faster than the observed speed of light in vacuum on the earth while they do slower than the true speed of light in vacuum determining the causal structure of events. In this paper, we dwell upon our ideas and present some concrete models, which realize our ideas, based on spin 0, 1 and 2 bosonic fields. We also discuss that the principle of invariant speed of light in special relativity can be replaced with the principle of a universal limiting speed.

James Bradley, Sailing on the Thames

Lightspeed ◽  
2019 ◽  
pp. 49-57
Author(s):  
John C. H. Spence
Keyword(s):  
Eighteenth Century ◽  
Experimental Evidence ◽  
The Sun ◽  
Theory Of Relativity ◽  
Speed Of Light ◽  
Astronomical Observations ◽  
The Earth ◽  
Independent Estimate ◽  
The Universe ◽  
At Home

The story of the astronomical observations of James Bradley in the eighteenth century, whose measurements of the small movements of a star throughout the year provided an independent estimate of the speed of the Earth around the Sun relative to the speed of light. His work provided the first experimental evidence in support of Copernicus’s theory that the earth is in motion, and against the idea that it is stationary at the center of the universe. His simple telescope at home, his brilliant idea and perseverance, and his life’s work and influence. The importance of his result for the development of Einstein’s theory of relativity and for theories of the Aether in the following centuries.

Ole Roemer, Who Started It All

Lightspeed ◽  
2019 ◽  
pp. 18-26
Author(s):  
John C. H. Spence
Keyword(s):  
Life Story ◽  
The Sun ◽  
Speed Of Light ◽  
The Earth ◽  
At Home

The story of the first measurement of the speed of light by Ole Roemer in 1676. Galileo had discovered the moons of Jupiter with his new telescope, and proposed using observations of their eclipse every forty-two hours as a universal clock for our planet, since they could be seen from practically anywhere. This would keep track of the time at home, and so give a traveller his or her local longitude. (The King of Spain had offered a prize for longitude determination to avoid disasterous shipwrecks.) Roemer noticed that the eclipses were sometimes a little late, which he concluded was due to the time it took light to get from Saturn to Earth and the movement of the Earth between eclipses. His estimate of the time for light to travel from the Sun to Earth was quite accurate. Roemer’s remarkable life story and many other achievements are told.

Time delay and the effect of the finite speed of light in atom gravimeters

2017 ◽  
Vol 96 (2) ◽  
Author(s):  
Yu-Jie Tan ◽  
Cheng-Gang Shao ◽  
Zhong-Kun Hu
Keyword(s):  
Time Delay ◽  
Speed Of Light ◽  
Finite Speed

scholarly journals Radar determination of the Astronomical Unit

1965 ◽  
Vol 21 ◽  
pp. 177-215
Author(s):  
Irwin Shapiro
Keyword(s):  
Time Delay ◽  
Astronomical Unit ◽  
Speed Of Light ◽  
Comprehensive Review ◽  
A Value ◽  
The Earth ◽  
Lincoln Laboratory ◽  
Data Yield ◽  
Shift Data

A comprehensive review is given of the Earth-Venus measurements made with the Lincoln Laboratory Millstone radar in 1959 and 1961. The time-delay and Doppler shift data yield a value for the Astronomical Unit of 499.0052 ± 0.001 light-sec. Using 299 792.5 km/s for the speed of light leads to an AU of 149 598 000 ± 300 km. With the radius of Earth taken as 6 378.15 km, the solar parallax then becomes 8″.79416 ± 0″.00002. This value is consistent with measurements made at various other laboratories to about one part in 105.

Achieving Human Presence in Space Exploration

2013 ◽  
Vol 22 (4) ◽  
pp. 345-349 ◽  
Author(s):  
Dan Lester
Keyword(s):  
Space Exploration ◽  
Human Cognition ◽  
Speed Of Light ◽  
Human Spaceflight ◽  
Human Presence ◽  
The Earth ◽  
New Perspective ◽  
The Way

One of the primary goals of human spaceflight has been putting human cognition on other worlds. This is at the heart of the premise of what we call space exploration. But Earth-controlled telerobotic facilities can now bring human senses to other worlds and, in that respect, the historical premise of exploration, of boots on the ground, no longer clearly applies. We have ways of achieving remote presence that we never used to have. But the distances over which this must be achieved, by humans based on the Earth, is such that the speed of light seriously handicaps their awareness and cognition. The highest quality telepresence can be achieved not only by having people on site, but also by having people close, and it is that requirement that truly mandates human spaceflight. In terms of cost, safety, and survival, getting people close is easier than getting people all the way there. It is suggested here that to the extent that space exploration is best accomplished by achieving a sense of real human off-Earth presence, that presence can be best achieved by optimally combining human spaceflight to mitigate latency, with telerobotics, to keep those humans secure. This is culturally a new perspective on exploration.

scholarly journals Mach–Zehnder fiber interferometer test of the anisotropy of the speed of light

2009 ◽  
Vol 87 (9) ◽  
pp. 999-1008 ◽  
Author(s):  
Victor de Haan
Keyword(s):  
Optical Fiber ◽  
Phase Difference ◽  
Main Direction ◽  
The Other ◽  
Earth Surface ◽  
Temperature Stabilization ◽  
Speed Of Light ◽  
The Earth ◽  
Better Than ◽  
Phase Differences

Two optical fiber Mach–Zehnder interferometers were constructed in an environment with a temperature stabilization of better than 1 mK per day. One interferometer consisted of a length of 12 m optical fiber in each arm, with the main direction of the arms perpendicular to each other while the other consisted of a length of 2 m optical fiber in each arm, where the main direction of the arms are parallel, and served as a control. In each arm, 1 m of fiber was wound around a ring made of piezo material, enabling the control of the length of the arms by means of an applied voltage. The influence of the temperature on the optical phase difference between the interferometer arms was measured. The temperature change induced a variation of the interaction region of the optical fiber couplers. Further, the influence of rotation of the interferometers at the Earth surface on the observed phase differences was determined. For one interferometer (with the long and perpendicular arms), it was found that the phase difference depends on the azimuth of the interferometer. For the other one (with the short and parallel arms), no relevant dependence on the azimuth has been measured.

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