Transcript Day-21
Astronomy 1010-H Planetary Astronomy Fall_2015 Day-21 Course Announcements • How is the sunset/sunrise observing going? • SW-chapter 6 posted: due Fri. Oct. 23 • Exam-2 will be returned on Friday • 1st Quarter Observing night: Tuesday, Oct. 20; 7:30pm The refracting telescope uses two lenses Since the eye already has a lens, the eyepiece is needed to bring the light rays back to parallel for the eye to see Large refractors can be very long and bulky The Largest Lens is 40” Built in the late 1890’s, it is the last great refracting telescope. Lenses and refractors suffer from Chromatic Aberration This applies to camera lenses, your eye, telescopes and anything else that uses a lens to focus light Correcting for Chromatic aberration can be expensive The compound lens takes two lenses of different materials and combines them to correct for color distortion Color separation is useful in a prism so that we can obtain a spectrum of light Since it is meant to be separated we don’t call it an aberration. Instead, it is called dispersion A diffraction grating works on interference of light waves Diffraction is much more efficient at separating light into its colors than dispersion Unfortunately, diffraction also leads to problems Look closely enough at stars and they aren’t just points of light but rings, too Refractors have many problems They suffer from chromatic aberration They are large and bulky and difficult to maneuver Even the best glass cuts off the IR and UV wavelengths Reflecting telescopes use mirrors. There are primary and secondary mirrors. Focal length is determined by the path the light takes reflecting off the mirrors. Reflection is the bouncing of light off a surface i r Mirrors do not suffer from chromatic aberration and they do not cut off long or short wavelengths A concave mirror focuses light to a focal point Telescope mirrors are made so that the focus is a plane instead of a point Reflecting Telescopes Suffer From Spherical Aberration There are several types of reflecting telescopes LSST Site – Artist Concept LSST Site – 1st Blast – March 2011 Steward Observatory Mirror Lab LSST M1 in polishing build-up Coming “soon” The 30m Tele. MATH TOOLS 6.1 The light-gathering power of a telescope is proportional to the square of the aperture size. A telescope’s magnification depends on the focal lengths of the objective lens or mirror and the eyepiece.