The Astronomy Book

163

Hydrogen and helium

together make up 98

percent of all of the

matter throughout the

galaxy that is made

of atoms (this omits

dark matter, the

nature of which

is not understood).

See also: The sun’s spectrum 112 ■ The characteristics of stars 122–27 ■

Nuclear fusion within stars 166−67 ■ Energy generation 182–83

ATOMS, STARS, AND GALAXIES

the spectral classes of stars and

their surface temperatures. She

also showed that the variation

in absorption lines between

star spectra was due to varying

amounts of ionization at different

temperatures, and not to varying

abundances of chemical elements.

Payne knew that the intensity

of absorption lines in star spectra

could give only crude estimates of

chemical elements, so other factors

needed to be taken into account,

such as the ionization states of the

atoms of different elements. Using

her knowledge of atomic physics,

she determined the abundances

of 18 elements found in the spectra

of many different stars. She found

that helium and hydrogen were

vastly more abundant than on

Earth, making up nearly all the

matter in stars.

Astronomers’ reaction

In 1925, Payne’s thesis was sent

to the astronomer Henry Russell for

review. Russell declared that Payne’s

results were “clearly impossible,”

and pressured her to include a

statement saying that the levels of

hydrogen and helium she had found

were “almost certainly not real.”

Four years later, however, Russell

conceded that Payne was right.

Payne’s discoveries were

revolutionary. First, she established

that most stars are chemically

similar. Second, she demonstrated

how to determine the temperature

of any star from its spectrum. Third,

she showed that hydrogen and

helium are dominant elements in

the universe—a key step toward

the Big Bang theory. ■

Cecilia Payne-

Gaposchkin

Cecilia Payne was born

in Wendover, England, in

1900. At age 19, she won
      a scholarship to Newnham
      College, Cambridge, where
      she studied botany, physics,
      and chemistry. After attending
      a lecture by Arthur Eddington,
      she switched to astronomy.
      In 1923, she left for the US to
      join a new graduate course in
      astronomy at Harvard College
      Observatory. Within two
      years, she had produced her
      revolutionary doctoral thesis,
      Stellar Atmospheres. Much
      of her research focused on
      variable stars and novae
      (exploding white dwarfs).
      This work helped explain the
      Milky Way’s structure and
      the paths of stellar evolution.
      In 1931, she became a US
      citizen and in 1934 married
      Russian astronomer Sergey
      Gaposchkin. In 1956, she was
      made professor of astronomy
      at Harvard University, the
      first female professor at
      Harvard. She died in 1979.

Key works

1925 Stellar Atmospheres

1938 Variable Stars

1957 Galactic Novae

Hydrogen:

74 percent

Helium:

24 percent

Oxygen: 1 percent

Other 1 percent:
carbon 0.45; neon 0.13;
iron 0.11; nitrogen 0.096;
silicon 0.065; magnesium
0.058; sulfur 0.044

If you are sure of

your facts, you should

defend your position.

Cecilia Payne-Gaposchkin