SSkyward
SSeptember 2022
On first looking through Baade’s window
Much have I travell'd in the realms of
gold,
And many goodly stars and clusters
seen;
Round celestial islands have I been
With telescope after telescope to the
night sky hold.
Oft of one wide expanse had I been told
That Galileo ruled as his demesne;
Yet did I never breathe its pure serene
Till I heard Baade speak out loud and
bold:
Then felt I like some watcher of the
skies
When a new star cluster swims into his
ken;
Through his majestic window looks upon
the Milky Way
He star'd at the centre of our galaxy.
Like a diamond shining in the sky, with
a wild surmise—
SSilent, through the mists of space and
time.
(--Keats,
Chapman’s Homer sonnet, adapted for this article.)
Lying in the
western portion of Sagittarius, the archer, is a small region of sky that has
unusual importance for astronomers around the world and which to med is one of
the most beautiful things in the whole sky.
It was most thoroughly studied by the German astronomer Walter Baade
while using the great 100-inch Hooker reflector at Mt. Wilson Observatory in
California while searching for the center of the Milky Way galaxy. Before this time, the location of the Milky
Way Galaxy’s center was not well understood.
Walter Baade had
an interesting and unusual life. In the mid-1930s, he lost his application
papers for United States citizenship. Consequently,
in 1941 he was classified as an enemy alien and was held virtually under house
arrest. Somehow a compromise was reached
and he was allowed to state his address as Mount Wilson observatory. With a
monopoly of observing time on the great 100-inch telescope, he concentrated his
efforts on the Milky Way galaxy.
One of Baade’s
most important projects was a search for a region of the sky that could be
close to the center of the galaxy. He
took good advantage of the wartime blackout over the city of Los Angeles. Intended to help obscure the city from
attacking warplanes from Japan, it also
darkened the sky significantly so that Baade could try to find areas near the
galactic center. Although he did not
find it, he did uncover a small area in Sagittarius relatively free of
dust. This “window” was slightly south
of the main center of the galaxy. The
globular cluster NGC 6522 is at the middle of this area, and NGC 6528 is near
its edge.
Astronomers
still use this window to study stars in the Milky Way’s central bulge. Important information on the internal structure
of the Milky Way is still being better understood by measurements made through
this "window". The window’s shape is irregular in outline and
delimits about 1 degree of the sky, an area of about 2 moon diameters. It is
centered on NGC 6522, which might be, at 12 billion years, the oldest star
cluster in the sky. Baade’s window is the largest of the six areas through
which stars in the Milky Way’s central bulge can be seen. Stars observed through Baade's Window can be
called BW (for Baade’s Window) stars, similarly giant stars can be called BW
giants. OGLE and other observation programs
have successfully detected extrasolar planets orbiting around central
stars in this area.
On a rare clear
evening during the summer of 2022, I gazed at the clusters and stars through
this window. I shall never forget the
exquisite majesty of this distant region which, thanks to Walter Baade, allows
me to peer toward the middle of the enormous Milky Way galaxy which is our
home.
Adam B /Mount Lemmon SkyCenter/University of Arizona
