A linefeed for the AO spherical dish (with Radius R=870ft) is placed R/2 feet below the center of curvature. Concentric rings on the dish focus energy at different places on the line feed. ... The picture below is for a plane wave at the center of curvature of the dish. ... The ray goes along line A (blue),hits the dish, reflects back along ray B (magenta), and then intersects the line feed a distance y (red line) from the paraxial point (R/2 feet below the center of curvature). ... Fig top. ...

... Matching the Surface of Best Focus . ... The plug-plates of SDSS project are responsible for locating the optical-fiber plugs spatially and for defining the plug tilt with respect to the surface of best focus. ... Approximately 670 holes are drilled in each plate. ... In the first attempts to match the curvature of the plug-plates to that of the best focal surface, the bending fixture was set upon 3 6.630mm metal supports that were affixed to a table top and spaced 120 apart. ...

... The process was part of an inspection to check for damage to the orbiter, but against the backdrop of planet Earth 300 kilometers below, the pictures themselves are stunning. 11 Hour Star Trails . ... The cause, this time, was not a partial lunar phase -- the Moon was full -- but rather that part of the Moon went into Earth's shadow. Star Clusters Young and Old . ... Galactic or open star clusters are relatively young swarms of bright stars born together near the plane of our Milky Way Galaxy. ...

... The Australia Telescope Compact Array . by Angel Lopez-Sanchez (AAO/UMQ) . Beautiful photo of CSIRO's Australia Telescope Compact Array (ATCA) taken by Angel Lopez-Sanchez - @El_Lobo_Rayado . Five of the six 22-m dishes are seen in one of the most compact hybrid configurations, where two antennas are placed on the short northern spur while the others remain on the regular east-west track. ... today * ATNF | ... ATCA | ...

These pages collect together references to many pictures of the solar system that can be found on the Net. ... Since I originally compiled this list the number of relevant images has grown tremendously. ... http://www.jpl.nasa.gov/pictures/ . ... ftp://dftnic.gsfc.nasa.gov/images/gifs/ . ... http://www.jpl.nasa.gov/galileo/images.html . http://www.jpl.nasa.gov/magellan/images.html . ... http://nssdc.gsfc.nasa.gov/image/planetary/ . ... NASA Image Access Homepage (Planetary Photojournal) . ...

... Tonight's Sky . ... The Magazine . ... Star Atlas . ... An artificial comet holds secrets to Earths life . ... Astronomy for Kids . ... Observing springtime deep-sky objects with a large telescope . ... The planet has extreme temperature swings and perhaps active lava flows. ... A digital supplement to Astronomy magazine. ... Join TravelQuest International with Astronomy and Discover magazines on one of three great tour options surrounding this celestial spectacle . ... Astronomy Magazine . ...

Most of these images were obtained by Mike Bessell, Michelle Buxton, Hwankyung Sung, Ralph Sutherland and Bob Watson at SSO using a 2Kx2K Site CCD behind a Nikon or Hasselblad lens or directly on the 1m telescope. A few images are from the Hubble Space Telescope. Some of the M42 images were obtained with the KPNO 1m and ESO NTT telescope. One image is a mosaic of IRAS images. ... Details of the CCD imaging program at MSSSO. ... antenna.jpg (53KB) . ... ngc6744.jpg (59KB) . ...

... 2006 September 17 . Anticrepuscular Rays Over Florida . ... Although the scene may appear somehow supernatural , nothing more unusual is occurring than a setting Sun and some well placed clouds. ... While enjoying the sunset after visiting NASA's Kennedy Space Center in Florida , the photographer chanced to find that an even more spectacular sight was occurring in the other direction just over the Atlantic Ocean -- a particularly vivid set of anticrepuscular rays . ... About APOD | ...

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... With enough velocity, a spacecraft can break loose from the Earth's gravity and enter an orbit around the Sun, like that of a planet. If it then orbits the Sun with the same period as the Earth--one year--it may keep a fixed position relative to Earth. ... If the distance is just right--about 4 times the distance to the Moon or 1/100 the distance to the Sun--the spacecraft, too, will need just one year to go around the Sun, and will keep its position between the Sun and the Earth. ...

I was wondering what conditions should be met to have the "darkest" sky .. ... Upon the above publication of the Southern Galactic hemisphere, TunГ Tezel started seeking opportunities to create the Northern counterpart image. ... So, the initial quest of having the darkest possible sky have delivered us these two all-sky images of the two galactic hemispheres as seen from Planet Earth. Zoomable and 'full-screenable' fisheye view of the "darkest sky" Southern Galactic Hemisphere image. ...