Light and Telescope 10/24/2018. PHYS 1403 Introduction to Astronomy. Reminder/Announcement. Chapter Outline. Chapter Outline (continued)

Transcription

1 PHYS 1403 Introduction to Astronomy Light and Telescope Chapter 6 Reminder/Announcement 1. Extension for Term Project 1: Now Due on Monday November 12 th 2. You will be required to bring your cross staff with you for verification and use during the lab activity on November 12 th. 3. No class and Lab on Monday November 19 th. You can use that time for Term Project 2 or Sunspots lab that will be assigned November 12 th. 4. Term Project 2 will be assigned after November 5 th. Chapter Outline 1. Radiation: Information from Space a) Wave Characteristics b) The Electromagnetic Spectrum c) Dual Nature of Light 2. Optical Telescopes a) Two Kinds of Telescopes b) What Telescope should I buy? c) Telescope Mounts d) Tarleton Telescope 1. What to do with a Telescope? a) Viewing with Eye b) Taking pictures (CCD camera) c) Braking white light in colors 2. Radio Telescopes a) Operation of a Radio Telescope b) Limitations of the Radio Telescope c) Advantages of Radio Telescopes 3. Space Astronomy a) Astronomy in other wavelengths b) Hubble Space Telescope c) New Generation of Space Telescopes Chapter Outline (continued) Recap: Telescopes? A Telescope is an instrument that collects electromagnetic wave of a certain wavelength. There are types of optical telescopes: Refractors and Reflectors Telescope allow us to see a magnified image (Magnification) and details in the image (Resolution). 1

2 Recap: Magnifying Power Ability of the telescope to make the image appear bigger Depends on the ratio of focal lengths of the primary mirror or lens (F p ) and the eyepiece (F e ): Recap: Field of View in a Telescope M = F p /F e RocketMime A larger magnification does not improve the resolving power of the telescope! Skyandtelescope.com Total amount of sky you can see with an eyepiece Reducing the aperture (diameter) of eyepiece increases magnification but also decreases the field of view Recap: Resolving Power Minimum angular distance min between two objects that can be separated. D is diameter of mirror or lens min = 1.22 ( /D) For optical wavelengths, this gives min = 11.6 arcsec / D[cm] Hobby Telescopes Eyepiece Refractor - Lens Jtwastronomy.com Reflector - Mirror Astroshop.eu Telescopes Mounts Telescope require mounts that allow rotation Popular Equatorial Mount No counterweight needed counterweight GeekWrapped.com Starizona.com 2

3 Funding Federal Government (DOE FIPSE) Tarleton State University Manufacturer Astronomical Consultant and Equipment Inc.(ACE) 32-inch (0.8m) Reflector f/ratio= f/7 Remotely Control ACE Software * Observatory CCD Camera Finger Lakes - FOV = 17 x 17 Resolution /pixel Imaging and Photometry UBVRI, Hα, OIII and Neutral Density Astronomical Detectors CCD Camera Makes Digital Images How to Measure and Record Light It is a imaging device The Eye Limited ability The Photographic plate now obsolete Photomultiplier Very limited in capability The CCD (Charge Couple Device) Making Digital Image The Spectrograph Making a Spectrum - Measuring; Chemical Composition Temperature Velocity How does a CCD work? How does a CCD work? 3

4 A CCD Image and Pixel Values Astrophotography Mathworks.com Science from multiple wavelength CCD Images Science from a CCD Image Analyzing a sequence of such image gives us this light curve Brightskies.us Spectrographs/Spectrometer Radio Astronomy Recall: radio waves of ~ 1 cm 1 m also penetrate Earth s atmosphere and can be observed from the ground It is an instrument that allows us to see to colors of white light coming from a star or a hot source: More on this in chapter 7 4

5 Radio Telescopes Comparing Radio and Optical Images Large dish focuses the energy of radio waves onto a small receiver (antenna) Colors in a radio map can indicate different intensities of the radio emission from different locations on the sky Amplified signals are stored in computers and converted into images, spectra, etc. Imagine.gsfc.nasa.gov Why are Radio Telescope so Big? Interference of Light Waves Radio waves are long wavelength waves they give poor resolving power Solution 1: Increase the diameter of the disk min = 1.22 ( /D) But you can make diameter only so big Source: Hewitt Solution 2: Interferometry Radio Interferometry Combine the signals from several smaller telescopes to simulate one big mirror. This holds true even if not the entire surface is filled out. This technique also works in optical range min = 1.22 ( /D) The Very Large Array (VLA): 27 dishes are combined to simulate a large dish of 36 km in diameter. Even larger arrays consist of dishes spread out over the entire U.S. (VLBA = Very Long Baseline Array) or even the whole Earth (VLBI = Very Long Baseline Interferometry)! 5

6 Science of Radio Astronomy Why We Need Space Telescopes? Radio astronomy reveals several features, not visible at other wavelengths: Neutral hydrogen clouds (which don t emit any visible light), containing ~ 90 % of all the atoms in the Universe. Molecules (often located in dense clouds, where visible light is completely absorbed). Wavelength Frequency Radio waves penetrate gas and dust clouds, so we can observe regions from which visible light is heavily absorbed. Need satellites to observe High flying air planes or satellites Space Telescopes The Hubble Space Telescope Launched in 1990 Mirror: 2.5 meters Observers mostly in visible and infra-red Maintained and upgraded by several space shuttle service missions throughout the 1990s and early 2000s Avoids turbulence in Earth s atmosphere Extends imaging and spectroscopy to infrared and ultraviolet The Hubble Space Telescope The Hubble Space Telescope (HST) orbits Earth at an average altitude of 570 km ( 355 mi ) above the surface. In this image, the telescope is viewing toward the upper left. Breath Taking Pics from Hubble 2014: Eagle Nebula and Orion Hubble WFC3/UVIS Breath Taking Pics from Hubble 2017: Supernova 1987A within the Large Magellanic Cloud 6

7 Breath Taking Pics from Hubble 2003: Mars Approaching Earth European Space Telescopes Herschel Space Observatory Launched in 2009 Carried a 3-m mirror and instruments cooled almost to absolute zero Observes in Infrared wavelength wikipedia Image From Herschel Space Telescopes Future Space Telescope (October 2018?) James Webb Space Telescope (JWST) Expected launch year 2018 Mirror: 6.5 meters Will be in solar orbit ~1 million miles from Earth ESA Comparing HST, James Webb and Herschell Comparing Hubble and James Weeb 7

8 Worlds Major Telescpes Non-Electromagnetic Astronomy Radiation from space does not only come in the form of electromagnetic radiation Gravity wave astronomy Gravity waves predicted to be produced by an mass that accelerates, but would be extremely weak and difficult to detect Now gravity waves have been detected LIGO How LIGO Works Laser Interferometer Gravitational Wave Observatory (LIGO) Hanford, Washington Livingston, Louisiana Source: wikipedia Source: wikipedia Acknowledgment The slides in this lecture is for Tarleton: PHYS1411/PHYS1403 class use only Images and text material have been borrowed from various sources with appropriate citations in the slides, including PowerPoint slides from Seeds/Backman text that has been adopted for class. 8