PYTS/ASTR 206 – Exploring the Solar System from the Earth1AtzAnnouncements Homework 1 due… Make sure you give it to Kevin before he leaves Late homeworks can be turned in class on TdFb 3df 50% ditTuesday February 3rdfor 50% credit Kevin has set up a facebook page“Shane Byrne's PTYS 206 class”Can use it to organize homework/study groups etc…Eli thSlSt f EthExploring the Solar System from EarthPTYS/ASTR 206 – The Golden Age of Planetary ExplorationShane Byrne – [email protected]/ASTR 206 – Exploring the Solar System from the Earth3In this lecture…In this lecture…z Telescopes and how they work Reflectors and refractors Resolution and magnificationeso ut o a d ag cat o Atmospheric effectsz Spacecraft and how they work Fly-bys, Orbiters & Landers Tricks of the tradePYTS/ASTR 206 – Exploring the Solar System from the Earth4Wh do e se telescopes?zWhy do we use telescopes?PYTS/ASTR 206 – Exploring the Solar System from the Earth5z Why use telescopes?yp To make things bigger When light levels are high Very nearby planets Pirate ships Spying on your neighbors Etc…Phoenix lander is a few m across… but a few 100km away!away! To make things brighter When light levels are low Most of astronomy Far away planets Small objectsPYTS/ASTR 206 – Exploring the Solar System from the Earth6z What have telescopes done for planetary astronomy? Plenty! Heliocentric vs. geocentric solar system Objects visible with the naked eyeSSun Moon Mercury (if you’re lucky) Venus Mars Jupiter Saturn Uranus (barely) – still discovered with a telescope Neptune Discovery of Asteroids Discovery of Kuiper Belt Discovery of moons of other planetsPYTS/ASTR 206 – Exploring the Solar System from the Earth7How do telescopes work?How do telescopes work?z They take light over a wide area and put it into a small areaz We can do this with either refraction or reflectionBigger is better!zBigger is better! Light from distant objects comes in parallel rays The bigger the area of the telescope the more light you can collectHuman eye in daylightThe human eye is like an adjustable-size telescope•Plenty of lightHihHuman eye at night•Iris dilates•Bigger collecting area•You can see fainter thingsPYTS/ASTR 206 – Exploring the Solar System from the Earth8RefractorsRefractorsz Light travels slower in glass than air Waves are extended – so they change directionz Flat sheets of glass produce no net effectRefraction works in reverse when lightRefraction works in reverse when light leave the glass Light hasn’t been concentrated onto a smaller areaPYTS/ASTR 206 – Exploring the Solar System from the Earth9z Curved pieces of glass (lenses) do produce a changeParallel light converges on a single pointthefocal pointParallel light converges on a single point –the focal point Distance between the lens and the focal point – the focal length Depends on the curvature of the lens and its sizePYTS/ASTR 206 – Exploring the Solar System from the Earth10z A refracting telescopeFirst lens (objective) gathers lightFirst lens (objective) gathers light Uses a second lens (eyepiece) to make the light parallel again• So the human eye can use it!Nt ff tzNet effect Telescope lens much bigger than eye so more light gathered Things are brighterMagnifies objectsMagnifies objects Magnification is ratio of focal lengths Magnification = Focal length of objectiveFocal length of eyepiecePYTS/ASTR 206 – Exploring the Solar System from the Earth11z The problem with refractorsThe amount of refraction depends onThe amount of refraction depends on wavelength Red light and Blue light focus in different places Image gets blurred Chromatic aberrationPYTS/ASTR 206 – Exploring the Solar System from the Earth12z The problem with refractors – cont.We need big lenses to gather a lot of lightWe need big lenses to gather a lot of light … but big lenses have long focal lengths Telescopes rapidly get very very unwieldy!PYTS/ASTR 206 – Exploring the Solar System from the Earth13ReflectorsReflectorsz Pioneered by Isaac Newton Flat mirrors don’t focus light Use curved mirrors to concentrate light These mirrors also have a focal lengthPYTS/ASTR 206 – Exploring the Solar System from the Earth14z Why parabolic? Spherical mirrors are easier to make….Spherical mirrors don’t focusSpherical mirrors don’t focus light wellSpherical aberration fivesSpherical aberration fives you a blurry image Other aberrations can also be corrected Coma Astigmatism Defects in the mirror surface should be small Smaller than the wavelength of lightlightPYTS/ASTR 206 – Exploring the Solar System from the Earth15z Focus point is in front of the mirror – usable… but unpopularSeveral designs to get light focused somewhere more convenientzSeveral designs to get light focused somewhere more convenientz Newton’s original design used a flat mirror to redirect focused light to the sidesidez If you want to use your eye then you still need an eyepiecez Magnification is still just the ratio of the focal lengthsPYTS/ASTR 206 – Exploring the Solar System from the Earth16z Other schemes to redirect the focused lightPYTS/ASTR 206 – Exploring the Solar System from the Earth17z Benefits of reflectors You can make the mirrors huge and the focal length short Keck telescopes – mirrors are 10m across? (built in segments) No chromatic aberration All colors behave the samez Plans for a 30m telescope – the CELT California Extremely Large Telescope 3 times the size means 9 times the area!PYTS/ASTR 206 – Exploring the Solar System from the Earth18Th ’ li it t h t f t t l dResolutionResolutionzThere’s a limit to what even perfect telescopes can doz A single point of light gets spread out a little Called the diffraction limitz Resolution – how close can two things be together without joining up.It’s easy to see that there are two separate objects hhere.PYTS/ASTR 206 – Exploring the Solar System from the Earth19zAs things get closer togetherzAs things get closer together we can no longer the individual objectsThe closest angularzThe closest angular-separation they can have and still be separate is the resolutionresolution. Depends on size of telescopeDepends on wavelength ofDepends on wavelength
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