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Telescopes and Spacecraft

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

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  1. Telescopes and Spacecraft Astronomy 311 Professor Lee Carkner Lecture 7

  2. 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)

  3. How Do Telescopes Work? • Telescopes: • Light gathering ability (not magnification) is the most important attribute of a telescope • telescopes make faint things brighter

  4. Lenses • 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)

  5. Lenses and Refraction

  6. 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

  7. Refracting Telescope

  8. Giant Refractor at Yerkes Observatory

  9. 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)

  10. 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 --

  11. Cassegrain Reflecting Telescope

  12. 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

  13. 5 meter Hale Telescope at Mount Palomar

  14. The Hobby-Eberly Telescope

  15. 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

  16. 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

  17. 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

  18. 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

  19. The Electromagnetic Spectrum

  20. 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

  21. 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 --

  22. More Telescope Taxonomy • Ultraviolet (UV) -- high energy radiation, causes sunburn • Example -- • X-ray -- very high energy • Example -- • Gamma Ray -- the highest energy • Example --

  23. The VLA

  24. Hubble Space Telescope

  25. Spacecraft • 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:

  26. 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)

  27. 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

  28. Mars Least Energy Orbit to Mars Time to get to Mars • aEarth = 1 AU • aMars =1.5 AU Sun Earth Spacecraft Orbit

  29. Summary • 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

  30. Summary • 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)

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