Walter Baade was a German national working at Mt. Wilson Observatory in California when World War II broke out. He was allowed to remain in the United States during the war, but was barred from working on any defense projects. This allowed him to fully utilize the large 100" Hooker telescope at Mt. Wilson (the largest in the world until 1948) while many other astronomers were occupied with military projects. His studies were aided considerably by the "blackout" of nearby Los Angeles each night that made it harder for enemy aircraft to locate and bomb the city. Those of us who live in suburban or urban areas can only dream of having all lights turned off every night!
Baade made a number of important discoveries during his years at Mt. Wilson. His most enduring achievement was noting that the cores of spiral galaxies are dominated by yellow or reddish stars, while the spiral arms are predominantly blue or white. He labeled the yellow and red stars "Population II" and the blue and white stars in the spiral arms "Population I." We now know that these two main "populations" of stars are distinguished not only by color, but also by age, temperature, and size.
This differentiation between Population I and Population II stars is easily seen in this image of NGC 4216, the bright spiral "edge on" galaxy in the center of this image. Note how the yellow core, and the bluish stars in the spiral arms. NGC 4216 is flanked on each side by a smaller edge on galaxy, giving the field a dramatic "tricycle" effect. The companion galaxies are NGC 4206 (left) and NGC 4222 (right). The distance of NGC 4216 is 55 million light years (based on its measured redshift). NGC 4216 is located in the Virgo Galaxy Cluster. This image reveals many fainter galaxies, visible as small fuzzy patches.
Galaxy Trio in Virgo
Date Taken:May 25, 2005
Location Taken: Conditions of Location:FWHM 1.87
Equipment Used:Takahashi TOA-130 5" apochromat refractor telescope, SBIG ST-10XME CCD camera, Optec TCF-S focuser, Astrodon RGB filters
Processing Used:8x600 sec luminance, 4x200 sec RGB, guided, processed in Maxim DL and Photoshop
Distance from Location:55 million light years
Constellation:Virgo (the "virgin")
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