Image 1 Caption: The
Solar eclipse of May 29, 1919
(a total solar eclipse)
from a reprocessed image by
1919 Solar Eclipse Expedition.
The
corona and a large
prominence are seen.
The background stars
are in the
constellation
Taurus.
The background stars, in fact,
belong (at least mostly) to the
open star cluster
Hyades
which is close in angle to the
bright red
naked-eye star
Aldebaran
(which is NOT a member of the
Hyades and
is much closer to Sun).
Neither Aldebaran
nor brighter members of the
Hyades
are in the image.
Image 2 Caption:
"Negative photograph
of the
1919 solar eclipse
taken from the report of
Sir Arthur Eddington (1882--1944)
on the 1919 Solar Eclipse Expedition
to verify Albert Einstein's (1879--1955)
prediction of the bending of light
around the Sun: i.e., of
gravitational lensing
by the Sun."
(Somewhat edited.)
Because it is a
negative photograph,
bright is dark and dark is bright.
We are seeing
near side of the Moon
in its nighttime (it's
the white
circle)
during a total solar eclipse.
The sky is
whitish
and the solar corona
is black.
Features:
- Albert Einstein's (1879--1955)
theory of general relativity
presented in 1915
(Wikipedia: History of general relativity)
predicted
that light rays
should be bent by gravity:
an effect we now call
gravitational lensing.
- In years immediately after
1915, there was
high interest in quantitatively testing
gravitational lensing.
The only light rays
which would be sufficiently bent for such a test were
those that pass very close to the
Sun coming from
background stars.
These stars could only be
observed during a total solar eclipse.
The
1919 solar eclipse
was highly favorable for the
test since it had very long period of
totality
6 minutes 50.75 seconds
(which permitted
long exposures
to photographically image
faint stars)
and a large number of faint background
stars to image in
the Hyades.
Observing a large number of
faint background
stars
permitted multiple tests which in turn allow for good
statistical inference
in making the test.
The 1919 solar eclipse
was also after the end of
World War I (1914--1918)
which was convenient for everyone.
- Observations for the test were
carried out by what we now call the
1919 Solar Eclipse Expedition
led by Sir Arthur Eddington (1882--1944)
(a cosmologist among other things)
and
Sir Frank Watson Dyson (1868--1939)
(an expert on solar astronomy and solar eclipse
observations).
Dyson
was Astronomer Royal
which meant director of the
Royal Greenwich Observatory
before 1972.
By the by,
Sir Frank Watson Dyson
has NO known relation to physicist
Freeman Dyson 1923--2020,
but their families both
originated in West Yorkshire
where the surname
Dyson is common, and so
they probably are related way back.
- Image Caption 3: Clockwise:
Albert Einstein's (1879--1955),
Paul Ehrenfest (1880--1934),
Willem de Sitter (1872--1934),
Hendrik Lorentz (1853--1928),
and
Sir Arthur Eddington (1882--1944)
in the office of
de Sitter,
Leiden University,
Leiden,
the Netherlands,
1923.
- Two teams from
1919 Solar Eclipse Expedition
were sent to make the observations
on the eclipse path:
one to Sobral, Creara
in Brazil
and the other (which was led by
Eddington personally) to
Principe,
an island
of the west
coast of
Africa.
Useful observations were obtained at both locations.
- To within observational error,
the observations of the
1919 Solar Eclipse Expedition
were consistent with
gravitational lensing
(as predicted by general relativity)
and inconsistent with
a Newtonian physics
prediction of
light bending by
gravity
and the prediction of NO
light bending by
gravity.
Of course, the results did NOT prove
general relativity
absolutely, but they were strong evidence for it and showed that is passed
a falsification test
that the other hypotheses did NOT.
The reasonable leading
physicist of that
time would conclude that
general relativity
was the best available theory
of gravity and most did so.
Circa 2020,
general relativity is still the
best available theory
of gravity and it has passed many more
falsification tests and failed none.
It may well be the true
emergent theory of
gravity at the macroscopic scale: i.e.,
the macroscopic limit
of quantum gravity---for which
there is NO verified theory as of now.
- The results of the
1919 Solar Eclipse Expedition
were announced at a meeting of the
Royal Society
(the United Kingdom's
national academy of sciences)
on 1919
Nov06.
The announcement made Einstein
world famous.
Before he his fame was mostly only among
physicists.
- Later of observations of
gravitational lensing
to circa 1960
generally confirmed
the predictions of
general relativity, but
did NOT improve the
accuracy/precision
of the
1919 Solar Eclipse Expedition
(see Gilmore & Tausch-Pebody 2020, p. 10--11).
This was probably largely because
total solar eclipses used
were less favorable than the highly favorable
1919 solar eclipse
(see Gilmore & Tausch-Pebody 2020, p. 10--11).
Since 1960,
the predictions of
general relativity for
gravitational lensing
have been verified to very high
accuracy/precision.
- There is a sorry story to add.
In 1980, an
article
in the history of science
genre
(also relevant to the
philosophy of science)
alleged that
the results of the
1919 Solar Eclipse Expedition
suffered from
confirmation bias
and did NOT really verify
general relativity.
Many people, including yours truly,
were vaguely aware of the allegation and vaguely thought it must
be somewhat true if for NO other reason than later analysis should be better than
earlier analysis.
By 1980, of course, the
allegation had NO
affect on people's confidence in
general relativity
which had been been verified to
very high
accuracy/precision
by many other tests.
Vaguely believing the allegation simply meant one vaguely believed that people
in 1919 believed in something that
was true for inadequate reasons.
It is always possible to
believe true things for inadequate/wrong reasons.
In fact, the 1980
article was wrong
(see Gilmore & Tausch-Pebody 2020, and references therein).
There was NO
confirmation bias
by
Eddington
and
Dyson
and their results were as good as they thought they were.
Of course, they and everyone else knew that they
could have had systematic errors
of which they were unaware.
But, in fact, all the verifications of
general relativity
since then show there were NO
systematic errors.
The 1980
article's allegation
of confirmation bias
can be relegated to a footnote
in the history of the
history of science.
Images:
- Credit/Permission: ©
ESO,
Heidelberg-Koenigstuhl State Observatory,
Sir Frank Watson Dyson (1868--1939),
Arthur Eddington (1882--1944),
Charles Rundle Davidson
(1875--1970),
2019
(uploaded to Wikimedia Commons
by User:Jmencisom,
2019) /
Creative Commons
CC BY-SA 4.0.
Image link:
Wikimedia Commons: File:Highest resolution image of the 1919 solar eclipse.tif.
- Credit/Permission:
Sir Frank Watson Dyson (1868--1939),
Sir Arthur Eddington (1882--1944),
Charles Rundle Davidson
(1875--1970),
1919
(uploaded to Wikimedia Commons
by User:Fastfission,
2005) /
Public domain.
Image link: Wikimedia Commons:
File:1919 eclipse negative.jpg.
- Credit/Permission: ©
H. van Batenburg,
1923
(uploaded to
Wikimedia Commons
by User:Vysotsky,
2014) /
CC BY-SA 3.0.
Image link: Wikimedia Commons:
File:PhysicistsinLeiden.jpg.
Local file: local link: 1919_solar_eclipse_expedition.html.
File: Relativity file:
1919_solar_eclipse_expedition.html.