101 SKY OBJECTS
WWW.ASTRONOMY.COM 5379 The Lagoon Nebula
The Orion Nebula (see #19) gets some stiff competition for best in class
from the Lagoon Nebula (M8) in Sagittarius. The Lagoon Nebula is visible
to the naked eye on dark moonless nights as a bright patch along the
Milky Way due north of the spout of the Sagittarius Teapot asterism.
The Lagoon Nebula was discovered by Italian astronomer Giovanni
Battista Hodierna in 1654, when he described it as a nebulosa. What
Hodierna likely saw, however, is not what we know today as the Lagoon
Nebula, but rather an embedded open star cluster cataloged separately
as NGC 6523. In fact, most records of the early observations refer to the
open cluster without mentioning the nebula from which it was born.
William Herschel was the first to define the nebula as a separate
object. In 1785, he described it as “an extensive milky nebulosity divided
into two parts.” Irish astronomer Agnes M. Clerke coined the nickname
“the Lagoon Nebula” in her 1890 book The System of the Stars.
When we set our sights on M8, our gaze is taking us some 4,100
light-years away. Under dark skies, 10x50 binoculars can distinguish the
Lagoon’s overall oval shape, as well as the dark slice that cuts the nebula
in half. Telescopes, meanwhile, reveal several of the swirling nebula’s
more complex features.
Hidden within the nebula is another star cluster: NGC 6530. Some of
its young stars sparkle among the rifts of nebulosity. If you plan to seek
it out, expect to spot between two dozen and three dozen luminaries
through most backyard scopes.
Many other stars lie within the Lagoon’s clouds, too. One of the bright-
est is 6th-magnitude 9 Sagittarii, a massive binary system comprising
two extremely close type O stars whose radiation energizes much of the
nebula. Another noteworthy star in the field is Herschel 36, a magnitude
9.5 supergiant just west of the brightest portion of the nebula. — P. H.SERGEY TRUDOLYUBOVPiscium. A 4-inch telescope at low power will show it as a ghostly globe
of uniform light surrounding a bright, starlike nucleus. Moderate magni-
fications give more definition to the central region. Higher powers show
a stellar dappling to the disk, which led John Herschel to mistake this
object for a globular star cluster partially resolved. In 1861, Lord Rosse
“felt confident it was a spiral.” Not until 1893, however, did Welsh astrono-
mer Isaac Roberts finally image it as a “perfect and beautiful spiral.”
With patience, a moderate-sized telescope can bring out the spiral
structure. Even then, the arms are like phantoms, materializing and fad-
ing from view. Larger telescopes will show them well. — S.J.O.
GERALD RHEMANN