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Astronomy week 2 homework readings

by: Sophie Trent

Astronomy week 2 homework readings Astronomy 106

Marketplace > Western Kentucky University > Astronomy 106 > Astronomy week 2 homework readings
Sophie Trent
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About this Document

These notes cover the readings for part of chapter 5 and all of chapter 6 in the textbook "The Cosmic Perspective" Light, Matter and Telescopes
Richard Gelderman
Class Notes
light, matter and telescopes




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This 13 page Class Notes was uploaded by Sophie Trent on Tuesday February 2, 2016. The Class Notes belongs to Astronomy 106 at Western Kentucky University taught by Richard Gelderman in Spring 2016. Since its upload, it has received 66 views.


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Date Created: 02/02/16
Sophie Trent Monday, February 1, 2016 Astronomy 106 pages 137-143 - 5.1: Light in everyday life • Astronomers study the universe the same way that we see objects. We see the objects because of different ways that light reflects off of the object— We extract information about objects through light that telescopes collect from distant objects. • Radiative energy is the energy that light carries watts: what we measure power in • - 1 watt = 1 joule(s) • power: rate of energy flow • white light: light from the sun/light bulb CMYK: a process in which colors are mixed to then make more colors: cyan, • magenta, yellow and black. these colors are commonly found in your TV and printers. • a spectrum can be produced with diffraction grating or a prism - diffraction grating is a piece of glass/ plastic with a lot of lines close together etched into the surface. • an example is CD disks. When you see the rainbow on the disk— that is diffraction • Light and Matter interact in four ways: - Emission: something that emits or produces visible light 1 Sophie Trent Monday, February 1, 2016 - Absorption: When you go outside in the summer, your skin absorbs the sunlight- making your skin heat up. Opaque matter absorbs. - Transmission: some forms of matter allow light to travel through them— such as glass and water. Transparent matter transmits. - reflection/scattering: light can bounce off of matter, we call this reflection when it goes in the same direction that it did originally. we call it scattering when it goes in different directions. • materials act differently according to different types of light: grass is green because it reflects green light and absorbs all other colors. - 5.2: Properties of Light • What is light? Is light a wave or a particle? these are important questions that scientists are trying to answer • A particle can move or be still-examples can be a baseball, a pen, etc 2 Sophie Trent Monday, February 1, 2016 • wave: a set of outward moving ripples cause by an object hitting another. waves have peaks and troughs - when you throw a rock into the lake - frequency: # of peaks passing a certain point - hertz: Hz: cycles per second - speed: how fast the peaks are going - wavelength x frequency = speed s=wf • what is “waving” when light passes? - scientists call this a field: electric and magnetic - Earth’s gravitational field: gravity - electromagnetic waves: light waves that have vibrations of both electric and magnetic waves - speed of light: 300,000 km/s - the longer the wavelength, the lower the frequency — vice versa - photons have both particles and waves - light is both a particle and a wave— light has photons that contain wavelengths, frequency and energy - the wavelength, frequency and energy of light are related because all photons travel at the same speed of light: 300,000 km/s • What is the electromagnetic spectrum? - the small part of the spectrum of light that we can see - light is often called electromagnetic radiation 3 Sophie Trent Monday, February 1, 2016 - millimeter astronomy: telescopes optimized to detect microwaves with 1 to a few millimeters - sub-millimeter astronomy: science done with wavelengths of tenths of a millimeter - radio waves have very little energy and have no noticeable effect on people 4 Sophie Trent Monday, February 1, 2016 pages 165-185 - 6.1 Eyes and Cameras: Everyday Light Sensors • Within the solar system, we can analyze some matter directly, but most must be gathered through telescopes and cameras. This chapter shows how we see and how eyes work because telescopes are like giant eyes - How do eyes and cameras work? • eyes - the pupil controls how much light enters the eye - the lens bends the light to form the image on the retina - the retina sends the signals to the optic nerve when triggered by light - refraction: a change in the direction that the light is traveling - focus: focal point: point of convergence - light rays that aren't parallel enter the lens from different directions 5 Sophie Trent Monday, February 1, 2016 - image: bending of ray paths on the surface - focal plane: where the image is in focus recording images • - detector: the camera bends the light and brings the image to focus - exposure time: the amount of time that the shutter is open - pixels: picture elements - image processing: what we do to the photo to manipulate it in someway other than its original image - 6.2: Telescopes: Giant Eyes What are the two most important properties of a telescope? • - light collecting area: how much total light a telescope can collect at one time • a 10 meter telescope as a light collecting area of 10 meters • a 10 meter telescope has five times the diameter of a 2 meter telescope. making the light collecting area 5^2=25 times as great - angular resolution: smallest angle over which we tell two dots (or stars) apart - diffraction limit: The angular resolution that a telescope could achieve if it were limited only by the interference of light waves • diffraction: technical term for the effects of interference that limit telescope resolution • a larger telescope may have a smaller diffraction limit- so they can see smaller and more detailed sections of the sky. — and has a better angular resolution • What are the two basic designs of a telescope? - refracting telescope: works a lot like an eye. it uses glass lenses to collect/focus light 6 Sophie Trent Monday, February 1, 2016 - reflecting telescope: uses a curved primary mirror to collect light • The primary mirror reflects onto a secondary mirror that sits in front of it. - nearly all astronomical telescopes are reflecting telescopes • refracting telescopes have the light pass through them - Chromatic aberration: a lens brings different colors of light into focus at different places. - (bottom photo is a reflecting telescope) • What do astronomers do with telescopes? - imaging: creates photos 7 Sophie Trent Monday, February 1, 2016 • many astronomical photos today are made from invisible light— only to be seen the naked eye from special detectors and filters • Astronomical images work similar to those of X-Rays - spectroscopy: astronomers obtain and study spectra • spectrographs: use diffraction gratings and other devices to separate the colors in a spectra- and then recorded with a detector • spectra resolution: the quality of the spectra/image that we see - time monitoring: tracks how an object changes with time • can be as simple as comparing images or spectra obtained at different times. this may require devices that can create multiple and rapid exposures • Light curves: graphs that shoe the intensity of an object over time. - 6.3: Telescopes and the Atmosphere • this section discusses the problems with observing space from Earth. • How does Earth’s atmosphere affect ground-based observations? - the atmosphere scatters sunlight, making it bright during the day over a large area • this is why most astronomical observations take place at night - the atmosphere creates a few problems that affect astronomical observations 8 Sophie Trent Monday, February 1, 2016 • scattering of human-created light (street lights, sky rises, etc) • blurring of images by atmospheric motion most forms of light cannot reach the ground • - light pollution: the light that humans create • this problem has increased as cities grow • lucky for astronomers, many cities are trying to reduce light pollution - turbulence: air currents (like wind) that are continually moving and mixing around in the atmosphere. - adaptive optics: technology to improve the optics of an observation *this is a hard topic to understand. watch this video* • watch?v=gDGvNyVApgg - an atmospheric observation has location criteria. Essentially it must be dark, dry and high. • Why do we put telescopes into space? - we put telescopes into space to avoid the problems created by our atmosphere. 9 Sophie Trent Monday, February 1, 2016 - ^ above is the Hubble Telescope. it’s the most famous and often observes using infrared or ultraviolet wavelengths. - 6.4: Telescopes and Technology • newer technology is making imaging and data recording more efficient • How do we observe invisible light? - Radio telescopes • the most common type of telescope • satellite dishes are essentially a radio telescope • radio waves are really long so the telescope needs to be long enough to absorb the waves - infrared telescopes • most inferred wavelengths don't reach the ground • the higher you go, the better inferred is 10 Sophie Trent Monday, February 1, 2016 • SOFIA: Stratospheric Observatory for Infrared Astronomy - NASA’s infrared observatory - extreme infrared are the longest of infrared wavelengths - Earth’s heat interferes with the reading of infrared wavelengths. so NASA put the Spitzer Space Telescope in space in 2003. - Ultraviolet telescopes • these behave similarly to infrared telescopes because ultraviolet wavelengths are also close to visible light • our atmosphere almost completely absorbs ultraviolet light short ultraviolet rays are called extreme ultraviolet. these behave like x-rays • • the GALEX (Galaxy Evolution Explorer) is a major ultraviolet observatory 11 Sophie Trent Monday, February 1, 2016 - X-Ray Telescopes • specially made mirrors can deflect X-Rays instead of the rays going through the surface (like they normally would at the doctor). - These mirrors are called grazing incidence mirrors because X-Rays graze the surface when the rays are deflected. XMM-Newton has a large light collecting area and thus can obtain more x-rays • - Gamma-Ray Telescope • gamma rays cannot be focused traditionally • Fermi Gamma-Ray Observatory studies the source of light bursts and other gamma-ray sources. They do this with very high resolution and sensitivity 12 Sophie Trent Monday, February 1, 2016 - looking beyond light • cosmic messengers: - neutrino: lightweight type of subatomic particle. This is produced by nuclear reactions- such as nuclear fusion in the sun and the reactions that happen when stars explode - cosmic rays: high-energy subatomic particles. - gravitational waves: different in nature but travel at the speed of light • How can multiple telescopes work together? - Because we have limitations on technology and money, we are limited on how much light we can collect - When we group telescopes together, this will give us a greater image than with just one - VLA (Very Large Array): 27 individual radio dishes that can be moved. With this group, the angular resolution is much better - ALMA (Atacama Large Millimeter Array): combined light from 66 telescopes. 13


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