87
See also: Halley’s comet 74–77 ■ Mapping southern stars 79 ■ Examining
nebulae 104–05 ■ Properties of nebulae 114–15 ■ Spiral galaxies 156–61B
y the 18th century, large
telescopes that could
magnify images by
several hundred times were being
produced. This allowed astronomers
to identify various fuzzy patches
of light, which were called nebulae,
after the Latin word for “cloud.”
French astronomer Charles
Messier was primarily interested in
finding comets, which often look just
like nebulae. A fuzzy object could
only be identified as a comet if it
changed position against the stars
over a period of weeks or months.
Messier therefore compiled a list of
known nebulae to eliminate them
as potential comets. His initial list
was published in 1774 and identified
45 nebulae. The final 1784 versionlisted 80 objects. These nebulae
are now known as Messier objects.
Other astronomers added further
nebulae that were observed by
Messier but not recorded by him
in his catalog, bringing the
total to 110.
With more powerful telescopes,
it has been possible to determine
the nature of the Messier objects.
Some are galaxies beyond the
Milky Way, some are clouds of
gas where stars are forming, and
others are the remains of supernova
explosions or the gas thrown off by
dying stars the size of our sun. ■URANUS TO NEPTUNE
OUR MILKY WAY
IS THE DWELLING
THE NEBULAE
ARE THE CITIES
MESSIER OBJECTS
IN CONTEXT
KEY ASTRONOMER
Charles Messier (173 0 –1817)
BEFORE
150 ce Ptolemy records five
stars that appear nebulous and
one nebula not linked to a star.
964 Persian astronomer
Abd al-Rahman al-Sufi notes
several nebulae in his Book
of Fixed Stars.
1714 Edmond Halley publishes
a list of six nebulae.
1715 Nicolas Louis de Lacaille
identifies 42 nebulae.
AFTER
1845 Lord Rosse observes
that some nebulae have a
spiral structure.
1864 William Huggins
examines the spectra of 70
nebulae, finding that a third of
them are clouds of gas, while
the rest are masses of stars.
1917 Vesto Slipher
identifies spiral nebulae
as distant galaxies.
Messier 31 is also known as the
Andromeda Galaxy. It is the nearest
major galaxy to the Milky Way.