This picture shows a comparison of images of the same region of the sky obtained with the Hubble Space Telescope Advanced Camera for Surveys (right) and the Subaru 8 meter telescope's Supreme camera. The region is an area from the GOODS North field. Both images are color composites obtained by combining three monochromatic images taken through blue, visible and infrared filters.
The "seeing" of an astronomical object is a parameter that measures the sharpness of observations from the ground. The stability of the atmosphere is directly correlated with this parameter. The more stable the atmosphere, the smaller the "seeing," and hence, the sharper the image. The ground image of this region of the GOODS field was obtained during average atmospheric conditions for the Subaru telescope, with a seeing of roughly 0.8 arcseconds. A value of 0.8 arcseconds is typical of what an observer would find during most nights at this telescope. However, the "seeing" can get very good, as low as 0.4 arcseconds. Such nights, unfortunately, are very rare. For comparison, the theoretical "seeing" of the Advanced Camera for Surveys is about 0.08 arcseconds.
Credit: NASA, Mauro Giavalisco, Lexi Moustakas, Peter Capak, Len Cowie and the GOODS Team.