The event of 08-SEP-2002 promises to make another significant step forward in gravitational experiments. Circumstances of the event allow us to measure the component of gravitational refraction which is caused by motion of the Jupiter with respect to the quasar. Since the Jupiter moves during the time when the photons travel through the Solar system, propagation of the photon should be considered in non-stationary gravitation field. The theory of photon propagation in a non-stationary gravitational field developed by S.Kopeikin with co-authors [5]. It was found that coordinates of the Jupiter for computation of gravitational potential at the given point at the photon's trajectory should be taken not at the moment of time when the photon reached the given point, but at the retarded moment of time, which takes into account the fact that gravity propagates with a finite speed. There is a similarity with well known potentials of Lienard-Wiechert introduced in electrodynamics which takes into account the fact that electromagnetic interaction propagates with the speed of c. Retarded potential depends on the constant which has the meaning of propagation of interaction. S. Kopeikin recently showed [4] that measurements of the component of gravitational time delay caused by motion of a gravitating body allows us to measure the speed of propagation of gravity. It is postulated in general relativity that the speed of propagation of gravity should be c, however up to now no direct experiments confirmed this prediction. ( H. Asada [6] argued that such an experiment would measure only speed of light, because ... ). A recent paper of T. van Flandern in Physics Letters A[7] presents a set of arguments in favor of much greater speed of propagation of gravity: 2x1010 c. This paper caused debates[8], and the arguments of T. van Flandern were repelled, but the discussion showed that the absence of experimental measurement of speed of propagation of gravity opens the wide field for speculations. Direct measurement of this speed will be a significant contribution to fundamental physics. Several factors makes event of 08-SEP-2002 unique:
90% of time the sessions is devoted to observing three sources, target 0839+187 and calibrators 0836+182 and OJ287. Three sequences will be observed:
T1 -- C1 -- C1
C1 -- T1 -- C2
T1 -- C2 -- T1 -- C2 -- T1 -- C2 -- T1
Each sequence takes about 1320 seconds and fits one tape pass. Position of these quasars can be found in Master Asrometrical Catalogue mac_20011226 catalogue.
Every 2-3 hours 3-4 sources located in different position on the sky will be observed in order to evaluate troposphere path delay.
| Session code | Date | Sked file | Schedule note | Status |
| grv01t | 2002.02.30 | grv01t.skd | grv01t.txt | correlated |
| grv01c | 2002.08.28 | grv01c.skd | grv01c.txt | correlated |
| grv01 | 2002.09.08 | grav01.skd | grav01.txt | correlated |
Letter to operators before the experiment.
Databases can be accessed through IVS web page, full Mark-4 correlator output files (3-7Gb long) will be accessible via request.
A paper with preliminary results of processing group delay scan be found here.
This experiment made a headline for world news on 08 September 2002: BBC and Russian information agency.
Ed Fomalont and colleagues made a parallel experiment using 10 VLBA telescopes and Effelsberg. They published their results in newspapers: Washington Post, New York Times , Washingotn Times, Izvestia, magazine New Scientist. Their preass release was alsow published in science splashdot, and msncb, and space.com, and AP wire, and Az central. Their results were considered by CNN as world news.