105
See also: Messier objects 87 ■ The Milky Way 88–89 ■ The southern
hemisphere 100–01 ■ Properties of nebulae 114–15 ■ Spiral galaxies 156–61
URANUS TO NEPTUNE
the huge instrument to observe
and record the spiral nature of
some nebulae—now called spiral
galaxies—for the first time. The
first of these spirals that Rosse
identified was M51, later known as
the Whirlpool galaxy. Today, about
three-quarters of all the galaxies
that have been observed are spiral
galaxies. However, these are
thought ultimately to transform
into elliptical galaxies. Formed of
older stars, elliptical galaxies are
dimmer and much harder to spot,
but astronomers believe that they
are probably the most common
galaxy type in the universe.
The nebular hypothesis
In the mid-19th century,
astronomers debated whether
nebulae consisted of gas or stars.
In 1846, Rosse found numerous
stars in the Orion nebula, and
so for a time, the idea of gaseous
nebulae was rejected. However,
although the stars were real,
their presence did not mean that
there was no gas. The gaseous
nature of some nebulae was not
demonstrated until spectroscopic
analysis was used by William
Huggins in 1864. ■The light by which we
recognize the nebulae now
must be merely that which
left their surfaces a vast
number of years ago ...
phantoms of processes
completed long in the Past.
Edgar Allen PoeThe Leviathan Telescope at
Parsonstown held a mirror weighing
3.3 tons (3 metric tons), inside a 54 ft-
(16.5 m-) long tube. The whole structure
weighed about 13 tons (12 metric tons).
Lord Rosse
William Parsons was born
in Yorkshire in 1800 and
became Third Earl of Rosse
on the death of his father in- He was educated at
Trinity College, Dublin, and
at Oxford University, where
he was awarded a first-class
degree in mathematics. He
married in 1836, but only four
of his 13 children survived
to adulthood. Lord Rosse’s
estates were in Ireland,
and this is where he built
his telescopes.
In 1845, after he made
public his findings on nebulae,
Rosse was criticized by John
Herschel, who was convinced
that nebulae were gaseous
in nature. Both men accused
each other of using flawed
instruments. Ultimately,
however, neither succeeded
in demonstrating sufficient
scientific evidence to resolve
conclusively the question
of whether nebulae were
composed of gas or stars.
Key works1844 On the construction of
large reflecting telescopes
1844 Observations on some
of the Nebulae
1850 Observations on
the Nebulae