Editing Viking 1 (section)

== Test of general relativity ==
{{main|Introduction to general relativity}}
[[File:Cassini-science-br.jpg|thumb|right|150px|High-precision test of general relativity by the ''[[Cassini-Huygens|Cassini]]'' space probe (artist's impression)]]
[[Gravitational time dilation]] is a phenomenon predicted by the theory of [[general relativity]] whereby time passes more slowly in regions of lower [[gravitational potential]]. Scientists used the lander to test this hypothesis, by sending radio signals to the lander on Mars, and instructing the lander to send back signals, in cases which sometimes included the signal passing close to the Sun. Scientists found that the observed [[Shapiro time delay|Shapiro delay]]s of the signals matched the predictions of general relativity.<ref>{{cite journal
|display-authors=  6
|author=  Reasenberg, R. D.
|author2=  Shapiro, I. I.
|author3=  MacNeil, P. E.
|author4=  Goldstein, R. B.
|author5=  Breidenthal, J. C.
|author6=  Brenkle, J. P.
|author7=  Cain, D. L.
|author8=  Kaufman, T. M.
|author9=  Komarek, T. A.
|author10=  Zygielbaum, A. I.
|date=December 1979
|title= Viking relativity experiment – Verification of signal retardation by solar gravity
|journal= Astrophysical Journal Letters
|volume= 234
|pages= L219–L221
|bibcode= 1979ApJ...234L.219R
|doi= 10.1086/183144
|doi-access=  free
}}</ref>