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MSU AST 115 - Particle Nature of Light and Telescopes

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AST 115 1st Edition Lecture 10Outline of Last Lecture I. Newton’s Universal Law of Gravitationa. Placing a satellite in Earth’s orbitb. WeightlessnessII. Newton’s revisions to Kepler’s lawsa. 1st and 2nd lawsb. 3rd lawIII. Introduction to Chapter 3: Light and Telescopesa. Properties of a waveb. The Electromagnetic Spectrumc. Particle Nature of Lighti. Waves vs. ParticlesOutline of Current Lecture I. Particle Nature of Light continueda. DispersionII. The Doppler EffectIII. Properties or Powers of a Telescopea. Magnificationb. Light-gathering powerc. Resolving powerIV. Telescopes and ObservatoriesCurrent Lecture Particle Nature of Light continuedo Dispersion: the decomposition of light into its component colors by a prism or similar deviseThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Sequence of colors: “ROY G BIV” ; Red, Orange, Yellow, Green, Blue, Indigo, Violet.- Red: longest wave length- Violet: shortest wave length- Wavelength = color- Wavelengths of light are measured in nanometers (nm). One nanometer is equal to 10−9 meter. Ångstroms (Å) = 10−10metero Dispersion in a prism- A prism disperses light into a spectrum Red is refracted the least Violet is refracted the most The Doppler Effecto The pitch (frequency) of a sound wave is affected by the motion of the sound source.o The same occurs for light. The observed wavelength of light is shifted from its normal or rest value.- For relative approach (you are moving towards the source; the source could be moving towards you; or you and the source could be both moving towards each other) = BLUESHIFT- If there is relative recession (you are moving away from the source; the source is moving away from you; or you and the source are both moving away from each other) = REDSHIFTo The Doppler Effect only works for an object that is directly towards or directly away from the source.o The Doppler Effect equation can be used to determine the line-of-sight speed of approach or recession, called the “radical velocity” (RV). Properties or Powers of a Telescopeo 1) Magnification: the ability to make objects look larger and seem closer - [Depends on focal length of objective]M=focal length of objectivefocallength of eyepiece- Example: An 8” diameter telescope → focal length of the objective is F(Obj) 2000 mm. Focal length of the eyepiece F(eyep) is 40 mm.M=2000 mm40 mm=200040=50 xo 2) Light-gathering power = the ability to detect faint objects - [Depends on the area of the objective]- Example: Compare light-gathering power of Keck 10 m telescope to that of Palomar 5 m telescope. Since area ~ diameter2.(10/5)2=(2)2=4o 3) Resolving power: the ability to see fine detail - [Depends on the diameter of the objective, quality of the optics, and status of the atmosphere]- Example: If used on the Moon (no atmosphere), with perfect optics, an 8”Celestron telescope would be able to resolve two stars about 0.7” apart. This is the size of a penny 3 ½ miles away. Examples of Telescopes and Observatorieso Refracting telescopes: telescopes that use lenses at the objective to form an image.- The Yerkes 1 meter refractor (largest refracting telescope ever built)o Reflecting telescopes: telescopes that use a single or combination of curved mirrors that reflect light and form an image.- Newtonian telescope Invented by Sir Isaac Newton Uses a concave primary mirror and flat diagonal secondary mirror- Prime focus telescope No secondary optics used Image is accessed at the focal point of the primary mirror In very large telescopes, an observer can sit inside the telescope inan “observing cage” to directly view the image- Cassegrain telescope: Combination of a primary concave mirror and a secondary convex mirror- Coude telescope: Light from the primary mirror is reflected along the polar axis to additional mirrors  The focus is independent of the telescope’s

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