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                           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.   
      
                                 2025 September 13   
      
                     Star Trails over One-Mile Radio Telescope   
                Image Credit & Copyright: Joao Yordanov Serralheiro   
      
      Explanation: The steerable 60 foot diameter dish antenna of the   
      One-Mile Telescope at Mullard Radio Astronomy Observatory, Cambridge,   
      UK, is pointing skyward in this evocative night-skyscape. To capture   
      the dramatic scene, consecutive 30 second exposures were recorded over   
      a period of 90 minutes. Combined, the exposures reveal a background of   
      gracefully arcing star trails that reflect planet Earth's daily   
      rotation on its axis. The North Celestial Pole, the extension of   
      Earth's axis of rotation into space, points near Polaris, the North   
      Star. That's the bright star that creates the short trail near the   
      center of the concentric arcs. But the historic One-Mile Telescope   
      array also relied on planet Earth's rotation to operate. Exploring the   
      universe at radio wavelengths, it was the first radio telescope to use   
      Earth-rotation aperture synthesis. That technique uses the rotation of   
      the Earth to change the relative orientation of the telescope array and   
      celestial radio sources to create radio maps of the sky at a resolution   
      better than that of the human eye.   
      
                        Tomorrow's picture: tilts and spins   
        __________________________________________________________________   
      
          Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)   
               NASA Official: Amber Straughn Specific rights apply.   
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                         A service of: ASD at NASA / GSFC,   
                              NASA Science Activation   
                                & Michigan Tech. U.   
      
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