THE USM SOUTHWORTH PLANETARIUM
207-780-4249     www.usm.maine.edu/planet
70 Falmouth Street     Portland, Maine  04103
43.6667° N                   70.2667° W
Altitude:   10 feet below sea level
Founded January 1970
Julian date:  24586323.5
"Oh leave the Wise our measures to collate
One thing at least is certain, light has weight
One thing is certain and the rest debate
Light rays, when near the Sun, do not go straight."
                 -Sir Arthur Eddington

THE DAILY ASTRONOMER
Thursday, May 30, 2019
100 Years and One Day Ago on the Space-Time Continuum

Sir Arthur Eddington and Astronomer Royal, Sir Frank Dyson, each lead an
expedition to different locations in the Southern Hemisphere in order to
observe a total solar eclipse on May 29, 1919.     They did not embark on
these expeditions merely to observe the spectacle of a total solar
eclipse.   Instead, they were seeking to confirm a startling prediction
made by Einstein's Theory of General Relativity:   that the path of
starlight is distorted by massive objects.  Or, more precisely, by the
space-time distortions caused by the presence of massive objects.

As Einstein's theory had been published less than 5 years earlier, none of
its tenets had yet been tested.   The first "test" was designed to observe
the positions of stars around the totally eclipsed Sun.    Einstein's
theory predicted that the star light around the Sun would experience a 1.75
arc-second deflection.  Isaac Newton's model also predicted that light
would experience a deflection.  However, the Newtonian deflection was about
half of that value.    Eddington and Dyson were hoping to observe a 1.75
arc-second deflection in the stars close to the solar eclipse so as to
provide the first observational evidence in support of the General Theory.

Despite some unsettled weather, Eddington's team captured more than a dozen
photographic plates of the total solar eclipse.  As totality lasted about
six minutes, 51 seconds, they had ample time to capture these images.  (The
longest possible totality duration is 7 minutes, 31 seconds.)   Their
measurements determined that some stars showed deflections of about 1.75
arc-seconds, in agreement with Einstein's prediction.    While some other
astronomers criticized the observations as being insufficiently precise and
therefore unable to confirm the deflection, Eddington nevertheless
announced his results later that year to the astonishment of the world.
The well regarded physicist Albert Einstein was suddenly elevated to the
status of global celebrity.  The following New York Times headline on
November 10, 1919, succinctly summarized the reaction the Eddington
experiment results elicited.


[image: Einstein_theory_triumphs.png]

One hundred years and a day ago, Eddington and Dyson conducted an
experiment that would lend credence to a theory that profoundly altered our
view of the Universe.   Suddenly, the cosmos no longer seemed like a finely
calibrated clockwork mechanism, but was, instead, composed of a strangely
malleable structure known as the "space time."   Scientists realized that
space and time were not disparate aspects of the universe, but were
conjoined in one continuum and both could be altered by gravity.

We mark the first centennial of our introduction to a Universe far stranger
than humans could ever have imagined.