Sidebar: Why a Total Eclipse?
The primary message of this article is that nature offers us
opportunities to test our theories, and scientists take advantage of
those opportunities. The circumstances of the solar eclipse were right
for scientists to test Einstein's theory of General Relativity.
In day-to-day life, Newtonian gravity is enough to predict how objects will
behave. In order to see the effects of General Relativity, extraordinary
conditions are needed – either high speeds, close to the speed of light, or
strong gravity. In the early 1900s, the most accessible test for General
Relativity was to watch the behavior of starlight as it passes very near the
Sun.
According to General Relativity, light passing near any object with
mass will be deflected, but only the Sun has enough mass for that
deflection to be detectable from Earth, using the technology available
in 1919. However, in order to observe starlight bending near the Sun,
astronomers had to wait for a total solar eclipse. The best way to
visualize why is to consider what the daytime sky looks like. Clearly
there are stars still shining over the entire sky, but none are visible
during the daytime. This is because the light from the Sun is scattered
by our atmosphere, giving us our familiar blue skies. For the same
reason, astronomers cannot observe starlight near the Sun on just any
day – the Sun is too bright, and the blue sky obscures any
attempted observations.
Therefore, to observe stars near the Sun, astronomers needed to wait for a
total solar eclipse. Only during a total solar eclipse is the light of the Sun
blocked out, making stars visible in the daytime.
However, observations during the eclipse alone, would not tell astronomers if
the starlight had been bent. They also needed images of those same exact stars
without the Sun in the way. Then, by comparing the two images – one
taken without the Sun between the stars and the Earth, and one taken during the
solar eclipse – they could determine if the Sun had any effect on the
starlight. In addition, if the starlight had been bent by the Sun, they could
determine by how much.
|
