Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2003 July 31 
Posted on 07/30/2003 10:06:45 PM PDT by petuniasevan
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2003 July 31
Explanation: Posing for this cosmic family photo are the galaxies of HCG (Hickson Compact Group) 87, about four hundred million light-years distant toward the amphibious constellation Capricornus. The large edge-on spiral near picture center, the fuzzy elliptical galaxy immediately to its right, and the spiral near the top of the image are identified members of the group, while the small spiral galaxy in the middle is likely a more distant background galaxy. In any event, a careful examination of the deep image reveals other galaxies which certainly lie far beyond HCG 87. While not exactly locked in a group hug, the HCG 87 galaxies are interacting gravitationally, influencing their fellow group members' structure and evolution. This new image is from an instrument undergoing commissioning on the Gemini Observatory's South Telescope at Cerro Pachon, Chile. It compares favorably with views of this photogenic galaxy group recorded by the Hubble Space Telescope.
Ground-based telescopes such as GMOS-South are rapidly approaching the resolution of HST. This is accomplished through a combination of techniques and technologies, especially Adaptive Optics and Speckle Interferometry, which is the use of a sequence of short-exposure snapshots to obtain images at a telescope's diffraction limit. The reduction of the speckle patterns, which represent the random distribution of atmospheric irregularities, involves computer processing.
Single 150 millisecond speckle interferometry image of a star. Rather than being a single point source (as it would be if there was no atmosphere), or a large blurry disk (as in a long-exposure image), interference between different patches of the telescope mirror and atmosphere produces a "specklegram", with each speckle being the size of a diffraction-limited image. Click HERE for an mpeg movie of 100 successive speckle frames. These images are interpreted and computer processed to yield far sharper images than Earth's atmosphere would naturally allow.
You know, I really do a lot better on 8 hours of sleep.
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