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Light and Energy - Week 7 - ASTR 1345

by: Sera

Light and Energy - Week 7 - ASTR 1345 ASTR 1345-004

Marketplace > University of Texas at Arlington > ASTR 1345-004 > Light and Energy Week 7 ASTR 1345

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Notes over Light and Energy for Professor Davis' ASTR 1345 class.
Intro to Astronomy 1
James J Davis
Class Notes
light, Energy, lightandenergy, astronomy, astro, astr1345, notes, spectrum, lightspectrum, visiblelight, telescopes, Davis
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This 5 page Class Notes was uploaded by Sera on Thursday October 13, 2016. The Class Notes belongs to ASTR 1345-004 at University of Texas at Arlington taught by James J Davis in Fall 2016. Since its upload, it has received 7 views.


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Date Created: 10/13/16
Note taker: Sera ASTR 1345 Light and Energy Observational Astronomers  Use telescopes to study actual events and phenomena  Ex. Edwin Hubble, Galileo Galilei Theoretical Astronomers  Use mathematics and physics-based predictions and theories  Ex. Stephen Hawking, Kip Thorne Computational Astronomers  Recreate and test complex physical situations with computers  Ex. Roadrunner Computer (1,700,000,000,000,000 calculations per second) Where Light Comes From  Emitted: an object gives off energy o Depends strongly on temperature  Reflected o Emitted light from one object bounces off of another  Scattered o Chemicals reflect light unevenly White Light  Newton’s Prism o White light (like sunlight) is a combination of all visible colors o A medium of different density will cause light to reflect (bend) Refraction  When light is passed through a medium, the path of it gets deviated  Light only travels in a straight line at the speed of light “The Light Bucket” - The Telescope  A simple refracting telescope o Uses lenses to refract light o Most important astronomical invention  Human vision is unreliable o Light enters the small pupil and is focused light detecting cells o Less incoming light = fainter image o Small details may blur together  The Objective: a telescope’s large lens or mirror o The larger the objective, the more light a telescope can gather  Faint objects appear brighter  Small objects appear larger Note taker: Sera ASTR 1345 o Light is redirected to the eye or camera The Photon  Electromagnetic radiation is “carried” by photons o Objects lose energy by giving off photons (light) o Photons can have a large range of energies  Photons can only travel at the speed of light 8 o Universal constant – c = 3.00x10 m/s Light as Energy  “Lightwave” o Energy rippling through the universe  The energy of a wave is given by its wavelength o Distance between energy peaks o Angstrom (Ǻ) – unit used to measure the wavelength of light  The energy of light is dependent on the light particle’s wavelength o Long wavelength = low energy o Short wavelength = high energy Hot or Not?  Generally, a hot object will produce photons with higher energies than a lower temperature object  Red is actually a “cooler” color, emitted by cooler objects  Blue is emitted by the hottest objects Radio  Largest wavelength radiation o Emitted by particle sin a magnetic field  Radio telescopes are some of the biggest telescopes on Earth  Shows electromagnetically charged gas o Used to confirm black holes  Radio is in: o Wi-Fi o Microwave o Radar o Satellite radio o GPS o Cell Phones o Active Denial System o MRI scanners Infrared (IR)  “Heat energy” o With 3 subclasses Note taker: Sera ASTR 1345 o Glass blocks infrared light well (which is why cars heat up fast in the sun)  Far Infrared (FIR) o Very cold dust (10-100 Kelvin)  440 below zero to 280 below zero F o Would look black in every other wavelength o Dark nebulae clouds  Mid-Infrared (MIR) o Planets, warm dust heated by stars, disks forming planets, and people (100-800 Kelvin)  280 below to 1000 F o Very popular in Astronomy right now  Earth-like planets give off Mid-Infrared and can be seen easier in Mid- Infrared  Near Infrared (NIR) o Giant, cool red stars (800-5000 Kelvin) o Dust is transparent to NIR o NIR penetrates most obstructions o Helps see through dust and most obstructions o Can see through ink, volcanoes to see lava, etc. The Case for Space  The “Great Observatories” program o Telescopes placed in orbit around Earth o Avoid shielding and disturbances from Earth’s atmosphere  Twinkling stars  No daytime  Light population o Infrared, X-Ray, and Ultraviolet light do not penetrate the atmosphere well, but can be detected easier in space  Spitzer o Launched in 2003 o 4 and final observatory o Infrared telescope in space o Captures dim stars, hot gas giant planets, and dust clouds  James Webb Telescope o Hubble’s replacement  Will be launched at some point in the future o Infrared sensitive telescope o 10x the light gathering power of Hubble Visible  Sun’s predominant form of radiation output o Ranges from 3800 Angstrom to 7800 Angstrom Note taker: Sera ASTR 1345  ROY G BIV o Recognized colors in order of decreasing wavelength o Violet – 4000 Angstrom – shortest wavelength – high energy o Green - 5500 Angstrom – easiest for humans to detect o Red – 7000 Angstrom – longest wavelength – low energy o Humans can’t see blue very well, green very well, and red somewhat well  Sun puts out the most energy at 5500 Angstrom which our eyes respond strongly too Hubble  Launched in 1990 o 1 Great Observatory o Visible light telescope  2.4-meter mirror o Not large but extremely sensitive  Will be replaced by the James Webb Telescope Ultraviolet (UV)  3000 Angstrom to 300 Angstrom  Very got gas (10x temp. of the surface of the Sun and up)  Ultraviolet light is mostly blocked by ozone layer in the upper atmosphere UV Photography  Dark pigments absorb damaging UV (melanin)  UV is an “ionizing radiation” which means it can physically break about molecules (including DNA) Mirach  A gargantuan star which blocked other stars with its light when captured by Hubble  When viewed with a UV telescope, it was very small because it was not a very hot star, and thus did not emit a lot of UV radiation, allowing us to see everything around Mirach in the UV spectrum X-Ray  Very short wavelength (10-0.1 Angstrom)  Emitted by very hot gas ~10 million degrees  Sun produces very little amounts of X-Ray radiation, it’s not hot enough to produce a lot, some can be detected in the corona and in areas where there are flares Chandra  Launched in 1999  X-ray telescope  Superhot gas, colliding stars, black holes, galactic superclusters, and neutron stars Note taker: Sera ASTR 1345  Chandra is an incredibly long telescope because X-rays have so much energy, they are hard to stop in order to capture for pictures, so Chandra is long in order to absorb some  energy from X-Ray particles when it interacts with the sides of the telescopes Crab Nebula  In 1054AD a star exploded in a supernova which was visible from Earth for two months, the Crab Nebula was later discovered in the place where the supernova was documented  Spitzer Telescope – captured warm gas lost when the star unraveled  Hubble – captured hot gas blown away by the explosion  Chandra – showed the superheated gas and neutron star at the center of the nebula Gamma  Shortest wavelength (< 0.1 Angstrom)  Produced only by the most violent/energetic processes  Large black holes, nuclear fission, matter-antimatter collisions Compton  Launched in 1991 nd o 2 Great Observatory o Decommissioned  Replaced by Fermi


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