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Telescopes and Spacecraft. Astronomy 311 Professor Lee Carkner Lecture 7. How Do We Learn About The Solar System?. View from Earth: View remotely: Other methods: find pieces of solar system that have visited us (meteorite). How Do Telescopes Work?. Telescopes:

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Telescopes and Spacecraft

Astronomy 311

Professor Lee Carkner

Lecture 7

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How Do We Learn About The Solar System?

  • View from Earth:

  • View remotely:

  • Other methods:

    • find pieces of solar system that have visited us (meteorite)

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How Do Telescopes Work?

  • Telescopes:

  • Light gathering ability (not magnification) is the most important attribute of a telescope

    • telescopes make faint things brighter

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  • If you point an empty tube at an object, you may be gathering lots of light, but it doesn’t get to your eye

  • Lenses bend light (refraction) and focus all of the light incident on the front to a point (focus) a certain distance behind the lens (focal length)

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Refracting Telescope

  • If you put a second lens (eyepiece) behind the first lens(objective), you can magnify the image

  • Magnification is equal to the ratio of the focal lengths

    • mag.= f.l. objective / f.l. eyepiece

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Refractors and Reflectors

  • It is hard to make large refracting telescopes

  • A curved mirror can be used to gather and focus the light instead (reflecting telescope)

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Reflecting Telescopes

  • A curved mirror (the primary mirror) reflects light so that it is focused

  • Problem: The focal point is between the mirror and the sky

  • Cassegrain Telescope --

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Path of Light

  • Light beams enter from infinity and are initially parallel

  • The eyepieces then magnifies the point image by taking the divergent rays from the focal and making them parallel again

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What Can a Telescope Do?

  • Imaging --

  • Photometry –

  • Spectroscopy --

    • A spectrum is the amount of light at each wavelength.

      • The shape of the spectrum tells you about the temperature, composition and motions of the object

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Types of Detectors

  • Eye -- limited ability to do photometry or spectroscopy, data is difficult to analyze (must write down what you see)

  • Photographic plate --

  • Charge Coupled Device (CCD) -- more sensitive and easier to use than a plate, allows you to store and reduce data electronically

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Telescope Misconceptions

  • Magnification is the most important property of a telescope

  • Astronomers peer through an eyepiece

  • Telescopes stick out of the dome

  • Telescopes fold up like a giant pirate’s spyglass

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The Electromagnetic Spectrum

  • Every photon (light particle) has a wavelength which places it in the electromagnetic spectrum

  • The wavelength relates to energy

    • long wavelength --

    • short wavelength --

  • We see different wavelengths of visible light as colors

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Observing at Different Wavelengths

  • Planets, stars and galaxies produce radiation at many different wavelengths in many different ways

  • Many types of light don’t penetrate the Earth’s atmosphere and need to be observed from orbit

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Telescope Taxonomy

  • Radio and Millimeter -- penetrates atmosphere and everything else

    • Example:

  • Infrared (IR) -- we feel as heat

    • Example:

  • Optical -- what our eyes can see

    • Example --

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    More Telescope Taxonomy

    • Ultraviolet (UV) -- high energy radiation, causes sunburn

      • Example --

  • X-ray -- very high energy

    • Example --

  • Gamma Ray -- the highest energy

    • Example --

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    • Since the 1960’s we have sent probes to study the planets close up

    • Types of spaces probes:

      • Fly-by --

        • Example:

      • Orbiter --

        • Example:

      • Lander --

        • Example:

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    Getting to The Planets

    • Spacecraft don’t zoom around the Solar System like in science fiction

      • Use small thrusters to maneuver (remember Newton’s First Law -- Inertia)

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    Least Energy Orbit

    • Once the spacecraft is out of the Earth’s gravity well, a little nudge with the thrusters will send it on its way

    • Easiest way to get to a planet is a least energy orbit

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    Least Energy Orbit to Mars

    Time to get to Mars

    • aEarth = 1 AU

    • aMars =1.5 AU





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    • Refracting Telescopes use a lens to bend light to a focus

    • Reflecting Telescopes use a mirror to reflect light to a focus

      • Most large research telescopes are reflectors

    • Astronomers today record and analyze data digitally

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    • To observe the entire electromagnetic spectrum you need many different types of telescopes, some of them in space

    • Spacecraft have allowed close up study of the planets

      • Spacecraft reach their destinations by using the gravity of the Sun (or sometimes planets)