Who first determined the chemical composition of the sun?

On Thu, 29 Jun 2000, Vicky wrote:

> Who first proposed the chemical composition of the sun, and what did
> they base their supposition on? What were the first theories?

Hello Vicky,

People have been guessing about the chemical composition of the sun from
the earliest cultures until now, and the first people to propose the
composition of the sun are lost to the origins of ancient astronomy.

However, the first modern attempts to discover the composition of the sun
began with Isaac Newton, who discovered that the light from the sun could
be split into its component colors. In 1802, W.H. Wollaston noticed dark
lines crossing the spectrum of the sun, and he proposed (wrongly) that
these lines were the "edges" of the primary colors.

In 1814-15, Josef von Fraunhofer studied the spectrum of the sun and
discovered hundreds of lines - some weak, some strong. He assigned the
strongest lines letter names, but he didn't know their origin.

In the following years, it was noticed that some lines varied their
strength as the sun climbed in the sky, indicating that these lines came
from Earth's atmosphere. Next, it was noticed that when various elements
were burned in the laboratory, they gave off light of unique colors, and
some of these colors (notably those of sodium) matched the dark lines in
the solar spectrum. The mechanism of the creation of these lines, and why
some are dark and some bright, was not known, but various scientists came
to believe that these indicated the sun was made of these materials.

Finally, in 1859, Gustav Kirchhoff discovered laws explaining how spectra
and their lines are formed. He then suggested that the sun's surface was a
glowing liquid or solid, and above this surface was an atmosphere made of
the elements whose lines people had observed.

In the 1870s-1890s, Angstrom and Thalen (Swedes) and Rowland (American)
mapped the many solar lines and determined the elements these referred to.
Also, P.J.C. Janssen and Sir Norman Lockyer discovered lines that matched
no known element, and so this element was given the name "helium", since
it existed in the sun. (It was later discovered on Earth).

The work of all of these scientists, and many others, led to our knowledge
of the composition of the sun. So no single person solved the puzzle --
it took lot of people a long time to get it right.

Thanks for writing!

Sincerely,

Kurtis Williams

(I used the book "Guide to the Sun" by Kenneth Phillips to assist me with
this answer.)

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