67 The Carina Nebula
The Orion Nebula (see #19) may be the best-known emis-
sion nebula, but it loses to the Carina Nebula (NGC 3372)
as the most spectacular. Measuring 2° across, the Carina
Nebula looks like an ethereal orchid blossoming, with
many dark rifts dividing it into several distinct “petals.”
Residing about 7,500 to 8,500 light-years from Earth,
the Carina Nebula lies within its namesake constellation,
Carina the Keel. Its southern location (declination –60°)
keeps it below the southern horizon for observers north
of about latitude 30°. But those who can see it are treated
to a great show. Small binoculars are all you need to
begin unlocking this amazing object’s complexities.
Many stars dot the Carina Nebula. Centrally located
is Trumpler 16, one of three associated open clusters.
Trumpler 16 contains some of the most luminous stars
in our galaxy, including its most famous member, the
remarkable star Eta (η) Carinae. A binary, Eta’s total
energy output is some 4 million times that of the Sun.
When Edmond Halley first noted Eta’s appearance in
1677, it shone at 4th magnitude. By 1730, it had increased
to 2nd magnitude, but fell back to 4th over the next half-
century. It generally fluctuated upward until 1843, when
it unexpectedly hit magnitude –0.8. For a brief time that
March, it was the second-brightest star in the night sky.
This so-called Great Eruption may have been caused
by a fierce gravitational tug-of-war that destroyed an
unknown third star in the system. That outburst gave
birth to the Homunculus Nebula, a small but growing
barbell-shaped cloud of gas and dust that today engulfs
Eta, absorbing much of the star’s light.
Another feature within the Carina Nebula worth
exploring is the Keyhole Nebula, a small, dark cloud
silhouetted in front of the brighter background. — P. H.