![]() The reader is assumed to be somewhat familiar with the concepts of diffraction theory and the Huygens sources that are used to compute a diffraction pattern. The purpose of this Insights article is to give the reader a brief introduction to the principles behind diffraction-limited focusing. Comparison with spherical lenses and mirrors=the case of imperfect focusing:.What are the focused spot size and focused beam intensity in the case of perfect focusing?.Perfect Focusing by paraboloidal mirror:.He received his PhD from the University of Arizona in 2013, where he helped develop the Magellan AO system and its VisAO camera. Jared Males is a NASA Sagan Fellow at the University of Arizona, where he studies exoplanets with direct imaging and adaptive optics. Follow along as we explore the universe at the limit of diffraction! We are in the middle of a 6-week observing run, and we post a daily update. You can read more about our night of eyepiece observing at the MagAO team's blog. This was a lot of fun for us - professional astronomers almost never get to look through our telescopes with our own eyes. With our own eyes, we saw details as fine as 22 milliarcseconds across, even sharper than if we were using Hubble! A sketch of what Alpha Centauri looked like through the eyepiece by Katie Morzinski, MagAO's Instrument Scientist. The difference was dramatic: we watched as each twinkling blob collapsed into a stable point of light. We pointed the Clay telescope at the Alpha Centauri binary system and turned on the MagAO system. So for our first night, we instead mounted a simple eyepiece in Clio's place and replaced the special beam-splitter with a red filter that passes wavelengths longer than 685 nanometers. We were setting up for our current observing campaign, but our infrared science camera, Clio, wasn't quite ready to go. But just a few weeks ago, we got the opportunity to see the results with our own eyes. Usually, AO systems feed into cameras, which take long-exposure pictures of the night sky. With such a large primary mirror, MagAO achieves resolution as good as 0.02 arcseconds at visible wavelengths -even better than Hubble. A special beam-splitting optic enables us to take visible and infrared images simultaneously. MagAO works at those wavelengths too, but it also corrects visible-light images. Most AO systems built so far work only in the infrared. To correct the turbulence, we use a thin mirror with 585 magnets glued to the back, which serves as the telescope’s secondary mirror We push and pull on the magnets 1,000 times a second to respond to and correct for atmospheric changes. I work on one such system, called MagAO, which is mounted on the 6.5-meter Magellan Clay telescope at Las Campanas Observatory in Chile. MagAO is mounted on Clay, on the right in this image, taken at Las Campanas Observatory in Chile. The twin Magellan telescopes, named Baade and Clay, each have mirrors 6.5 m in diameter. ![]() In other words, AO stops the stars from twinkling. That becomes a possibility or Earthbound telescopes that use adaptive optics (AO), which measures the atmospheric turbulence and then bends a mirror to correct the bent path of the light rays. Now imagine for a moment what it would be like to look through Hubble with your eyes. Since the primary mirror is 2.4 meters across, Hubble can resolve two stars in visible light even if they are just 0.05 arcseconds apart - a factor of 20 better than from the ground. The Hubble Space Telescope is “diffraction limited” - soaring above most of the atmosphere in low-Earth orbit, the telescope’s angular resolution is set by the ratio of the wavelength of light to the diameter of the primary mirror. One way to avoid twinkling is to escape Earth’s atmosphere. Atmosphere-induced twinkling limits astronomical observations to a resolution of (roughly) 1 arcsecond, and amazingly, this is as true on a 10-cm (4-inch) backyard telescope as it is on the 10-meter (33-foot) Keck telescopes in Hawaii. Angular resolution is what enables us to separate a pair - if the stars orbit too closely, they will appear as one. Pretty as they are, those twinkling stars cause astronomers several problems, the main one being the loss of angular resolution.Ĭonsider binary, or double, stars. Yuri Beletsky / Carnegie Observatories inset: Jared MalesĮven on the darkest, clearest night, turbulence in our atmosphere moves the air between us and outer space, bending and shifting starlight. This photo was featured on NASA's Astronomy Picture of the Day. The inset shows an image of the binary star system recorded with MagAO's visible-wavelength science camera. Laird Close (University of Arizona), MagAO's Principal Investigator, observes alpha Centauri A and B at the diffraction limit.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |