Chapter 6 Optics and Telescopes Telescopes, and the detectors to go with them, are important in ASTR 1100, so the important points are covered here. 1.

Slides:



Advertisements
Similar presentations
Chapter 6: Telescopes – Portals of Discovery. Visible light is only one type of electromagnetic radiation emitted by stars Each type of EM radiation travels.
Advertisements

Optics and Telescopes Chapter Six. Telescopes The fundamental purpose of any telescope is to gather more light than the naked eye can In many cases telescopes.
Chapter 5 Telescopes. 5.1 Optical Telescopes The Hubble Space Telescope 5.2 Telescope Size The Hubble Space Telescope 5.3 Images and Detectors Diffraction.
NOTES: Reflection and Refraction Principle of reflection: the angle of incidence equals the angle of reflection--for all mirrors. A parabolic mirror creates.
Light and Telescopes Please pick up your assigned transmitter
Telescopes: Augmenting the Eye Text, Chapter 4 Thanks to: howstuffworks.com bbc/science.
Telescopes Analyzing electromagnetic spectra to search for understanding of celestial objects.
Chapter 6 Optics and Telescopes
Chapter 6 Telescopes: Portals of Discovery. 6.1 Eyes and Cameras: Everyday Light Sensors Our goals for learning How does your eye form an image? How do.
Optics and Telescopes Chapter 5 Survey of Astronomy om astro1010-lee.com.
1 Earth’s Atmosphere & Telescopes Whether light is absorbed by the atmosphere or not depends greatly on its wavelength. Earth’s atmosphere can absorb certain.
Optics and Telescopes Chapter Six.
Astronomy 101 Section 020 Lecture 6 Optics and Telescopes John T. McGraw, Professor Laurel Ladwig, Planetarium Manager.
Astro 201: Sept. 16, 2010 New: Copies of Lecture Notes and HW are now on d2l, and should be faster to download. HW #3 on line, due Tuesday Midterm #1:
Telescopes (Chapter 6). Based on Chapter 6 This material will be useful for understanding Chapters 7 and 10 on “Our planetary system” and “Jovian planet.
Reading Unit 28, Unit 29, Unit 30 Will not be covered by the first exam.
This Set of Slides This set of slides deals with telescopes. Units covered: 26, 27, 28, 29, and 30.
Optics and Telescopes Chapter Six.
Telescopes. Optical Telescopes Ground based and on satellites Observations are recorded using a camera instead of the human eye most times. – This is.
Telescopes. Magnification (make things look bigger) easy to make a telescope with good magnification Collection of large amounts of light (see fainter.
Telescopes & Light. The Powers of a Telescope Light Gathering Power Light Gathering Power : Astronomers prefer *large* telescopes. A large telescope can.
Chapter 17 Optics 17.1 Reflection and Refraction
Land Based Telescopes. Telescopes: "light buckets" Primary functions: 1. ___________ from a given region of sky. 2. ______ light. Secondary functions:
Chapter 5 Telescopes: “light bucket”. Telescopes have three functions 1.Gather as much light as possible: LGP ∝ Area = πR 2 LGP ∝ Area = πR 2 Why? Why?
4. Telescopes Light gathering power and resolution Optical and radio telescopes Limitations of Earth’s atmosphere and satellite missions. Instruments (prism.
ISNS Phenomena of Nature The Eye The eye consists of pupil that allows light into the eye - it controls the amount of light allowed in through the.
Chapter 6: The Tools of the Astronomer. Telescopes come in two general types Refractors use lenses to bend the light to a focus Reflectors use mirrors.
How do Astronomers know what they know? Almost everything we know about Astronomy was learned by gathering and studying light from distant sources Properties.
Chapter 3 Light and Telescopes. What do you think? What is the main purpose of a telescope? Why do stars twinkle?
Telescopes. Act as “electromagnetic radiation catchers” Capture as much as possible Focus Magnifies images Telescopes that “catch” visible light are called.
Observatories and Telescopes Mauna Kea, Hawaii (14,000 ft) Why do telescopes need to be located at high altitude and dry climate ?
New Improved Eyes Telescopes and “Invisible” Astronomy.
© 2010 Pearson Education, Inc. Chapter 6 Telescopes: Portals of Discovery.
Optics and Telescopes. Optics and Telescopes: Guiding Questions 1.How do reflecting and refracting telescopes work? 2.Why is it important that professional.
Studying for the Exam Relevant chapters: E, 1, 2 & 3 To prepare for the exam it is helpful to … –review readings –review lecture notes online (esp. concept.
© 2004 Pearson Education Inc., publishing as Addison-Wesley Telescopes.
Telescopes: Portals of Discovery
Astronomical Tools. Essential Questions 1.What is Light? 2.How do telescopes work, and how are they limited? 3.What kind of instruments do astronomers.
Telescopes  Device used to collect Light and to Magnify Distant Objects  Plans made by Rodger Bacon 13 th Century  Galileo improved the Device.
Optics and Telescope Chapter Six. ASTR 111 – 003 Fall 2007 Lecture 06 Oct. 09, 2007 Introducing Astronomy (chap. 1-6) Introduction To Modern Astronomy.
Tools of Astronomy.
Chapter 6 Telescopes: Portals of Discovery. 6.1 Eyes and Cameras: Everyday Light Sensors Our goals for learning How does your eye form an image? How do.
is transparent ERAU Astronomical Observatory Meade inch Schmidt Cassegrain Reflecting Telescope.
Optics and Telescopes Chapter Six. Introducing Astronomy (chap. 1-6) Introduction To Modern Astronomy I Ch1: Astronomy and the Universe Ch2: Knowing the.
THE EARTH AS AN OBSERVATORY. Learning Outcomes To understand that the Earth’s atmosphere is transparent to some electromagnetic radiation and opaque to.
Units to cover 25, Types of Spectra Kirchoff ’ s Laws: –If the source emits light that is continuous, and all colors are present, we say that this.
Telescopes. Light Hitting a Telescope Mirror huge mirror near a star * * * small mirror far from 2 stars In the second case (reality), light rays from.
Telescopes Lecture. Standards Understand how knowledge about the universe comes from evidence collected from advanced technology (e.g., telescopes, satellites,
Light & Telescopes (Chapter 5) All of what we know and understand about the stars is the result of observation and analysis of light.
14 Sep 2000ASTR103, GMU, Dr. Correll1 ASTR 103--Week 3.
1 Earth’s Atmosphere & Telescopes Whether light is absorbed by the atmosphere or not depends greatly on its wavelength. Earth’s atmosphere can absorb certain.
Refraction P 7.2 LIGHT TELESCOPES AND IMAGES. You should understand that the wave speed will change if a wave moves from one medium into another a change.
Chapter 21: Stars, Galaxies, Universe Section 1: telescopes
Telescopes Mr. Hibbetts Special thanks to Dr. Dan Bruton, Astronomy and Physics SFA.
Chapter 24 Sec. 1 Light Sec. 2: Tools of Astronomy
The Very Large Array (VLA) in New Mexico. Observations at wavelengths other than visible light are revealing previously invisible sights Visible light.
Studying for the Exam Relevant chapters: E, 1, 2 & 3 To prepare for the exam it is helpful to … –review readings –review lecture notes online (esp. concept.
Universe Tenth Edition Chapter 6 Optics and Telescopes Roger Freedman Robert Geller William Kaufmann III.
Telescopes. Light Hitting a Telescope Mirror huge mirror near a star * * small mirror far from a star In the second case (reality), light rays from any.
Refracting Telescopes 24.2 Tools for Studying Space  A refracting telescope is a telescope that uses a lens to bend or refract light.  Focus The most.
다양한 창문을 통한 우주 내용 왜 다양한 창문 ? 왜 다양한 창문 ? 대기의 영향 대기의 영향 망원경의 성능 망원경의 성능 관측에서 얻는 정보 관측에서 얻는 정보 중요 망원경들 중요 망원경들 차세대 망원경들 차세대 망원경들.
Telescopes I. Refraction: Refraction is the _____________ of light as it passes through glass. II. Reflection: Reflection occurs when light _____________.
Telescopes & Light. History Hans Lippershey Middleburg, Holland –invented the refractor telescope in 1608 Galileo –the first to use a telescope in astronomy.
© 2014 Pearson Education, Inc. Telescopes Portals of Discovery.
Optics and Telescopes Chapter Six. Some Guiding Questions 1.Why is it important that telescopes be large? 2.Why do most modern telescopes use a large.
Chapter 6 Telescopes: Portals of Discovery
Telescopes & Light.
4. Telescopes Light gathering power and resolution
Optics and Telescopes Chapter Six.
Telescopes Lecture.
Presentation transcript:

Chapter 6 Optics and Telescopes Telescopes, and the detectors to go with them, are important in ASTR 1100, so the important points are covered here. 1. Telescopes are simply extensions of the eye. They gather more light than the eye does because of their large apertures. Magnification is a consequence of different focal lengths for the telescope lens/mirror and eyepiece. 2. More important are the devices used by astronomers to image the sky as well as spectra of astronomical objects. The human eye just won’t do !

Telescopes take advantage of the optical properties of lenses or mirrors, i.e. refraction or reflection.

The bending of a beam of light by refraction in glass. Properly figured surfaces on a convex lens bring the light beam to a focus.

Telescopes can be thought of as “light buckets.” They gather light in proportion to their collecting aperture surface area, D 2, be it lens, mirror, radio dish, or an array of hexagonal mirrors. Thus, a 16-inch telescope has four times the light gathering power as a 8-inch telescope.

Light from distant objects enters telescopes in a plane parallel beam.

Basic Optical Principles: Each point in a distant object is the source of a spherically expanding wave front, but the light arrives as the telescope as plane parallel wave fronts, lightly distorted by Earth’s atmosphere. An ideal telescope would focus the incident wave fronts to a single point, the focus, irrespective of wavelength and position on the wave front.

A prism (upper right) shows how it is possible to deflect a beam of light, albeit with some dispersion resulting from the wavelength dependence of n λ. A thin lens (lower right) can be thought of as simply a series of small prism segments deflecting the light to a single point, the focus, a distance f from the lens. A convex lens (a) focuses light in a converging beam, while a concave lens (b) defocuses light in a diverging beam.

A simple refracting telescope consisting of two lenses: a primary lens and an eyepiece lens. The resulting magnification is given by the ratio of the focal lengths:

e.g. old Burke-Gaffney telescope. Original effective focal length of the 0.4m telescope was f(telescope) = 4780 mm. When used with an eyepiece labelled as having a focal length of 40 mm, In other words, that combination produced a magnification of 119½ power (119½  ).

DAO Director Jim Hesser modelling Galileo’s telescope.

Examples:

Chromatic aberration occurring in glass optics is a serious problem for refracting telescopes, which is why reflectors are superior.

The advantages/disadvantages of telescope types. Refracting telescopes: (i) suffer from chromatic aberration that requires a doublet main lens rather than a single lens, (ii) four surfaces need to be figured, (iii) beyond ~40 inches, a lens sags under its own weight. Reflecting telescopes: (i) spherical mirrors suffer from spherical aberration, parabolic mirrors do not, (ii) parabolic mirrors suffer from “coma,” that requires special shaping of the mirrors, (iii) mirrors need only be figured on one side, (iv) mirrors can always be supported from the back, (v) the material of mirrors need not be transparent since it will be aluminized, (vi) composite mirrors can be built to do the job of one large mirror.

A mirror system focuses light without suffering from chromatic aberration.

A modern view of the Plaskett Telescope.

Reflecting telescopes also suffer from light aberration.

Telescope resolution is established by the diameter of the collecting aperture, the larger the better, except for the effects of atmospheric seeing. The diffraction image of a star is surrounded by the “Airy disk” in excellent seeing.

Larger Size = Better Resolution, θ Up to a point. Atmospheric seeing is the limit for ground- based telescopes. For θ in radians, For θ in arcseconds,

These devices are also telescopes.

Image Scale of a Telescope. The image scale of a telescope links the angular separation of objects in the sky to their linear separation on an image obtained with the telescope. As illustrated below using the “chief ray” from an object passing through the centre of the lens, by geometry: The image scale is therefore defined as: For θ in arcseconds rather than radians, and y in mm:

Example. The ST8 CCD camera at the old BGO operated at an effective telescope focal length of f = 4924 mm. The image scale for the CCD camera was therefore: It seems, at first sight, that one could achieve arbitrarily large separations between image points merely by increasing “f.” But images of Jupiter (θ = 49".7 near opposition) have a size, X, given by: The value corresponds to ~66 18-micron pixels on the ST8, for 2  2 binning. In other words, the size of the detector elements governs the resolution.

Earth’s atmosphere is opaque to gamma rays, X-rays, ultraviolet light, some infrared light, microwaves, and long wavelength radio waves, so observations in these spectral regions can only be done from space.

Chandra X-Ray Orbiting Telescope

Compton Gamma-Ray Observatory

COBE Satellite

Hubble Space Telescope (from Shuttle)

Many modern telescope mirrors are equipped with adaptive optics.

Adaptive optics “off.”

Adaptive optics “on.”

James Webb telescope mirror test.

Keck telescope “mirror,” full scale.

A CCD chip (used for imaging).

The inner workings of a CCD camera.

CCD images of the same field: negative image in B&W (left) and colour image (right).

A photographic image of the same field for comparison.

Telescope spectrographs (used to image spectra of stars and galaxies) must include a prism or grating.

Spectrograph on the DAO Plaskett Telescope.

Modern observing is done from “warm” rooms equipped with computers to control telescope and imaging devices.

Telescopes are housed in domed structures to protect them from the elements. DAO Plaskett Telescope Dome.

DAO 1.2-meter Telescope Dome.

Victoria, B.C., from Little Saanich Mountain (DAO).

Mount Baker from the DAO.

Astronomical Terminology Refractor. A telescope that uses lenses to focus light. Reflector. A telescope that uses mirrors to focus light. Light Gathering Power. A measure of the collecting area of a telescope’s primary element. Atmospheric Window. A region of the electromagnetic spectrum in which Earth’s atmosphere is transparent. Optical Telescope. A telescope designed to gather light in the optical band. Radio Telescope. A telescope designed to gather light at radio wavelengths. Seeing. The fluctuating effect on telescope images caused by turbulent bubbles in Earth’s atmosphere randomly deflecting light paths from the source. CCD = Charge-Coupled Device. An ultrathin wafer of silicon divided into a 2-dimensional array of picture elements (pixels) that collect electrons produced by light falling on the element.

Sample Questions 1. “Twinkle, twinkle, little star. How I wonder what you are.” Explain why stars twinkle. Answer: From ground-level we observe stars through Earth’s atmosphere, where convection and air density differences create small bubbles of air that generate random scattering of the starlight and produce “seeing,” the irregular wobbling and intermittent size changes in star images that we call twinkling.

2. Why are the world’s largest telescopes located on high mountains?

Answer. Earth’s atmosphere is very detrimental to astronomical observations. Thermal currents in the atmosphere make seeing blurry, water vapour absorbs infrared frequencies, and light pollution at the surface limits deep sky observing. Placing telescopes on mountaintops reduces thermal currents and situates telescopes above 90% of the water vapour and well above urban light pollution.