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