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ASTRO 101

ASTRO 101. Principles of Astronomy. Instructor: Jerome A. Orosz (rhymes with “ boris ” ) Contact:. Telephone: 594-7118 E-mail: j orosz@mail.sdsu.edu WWW: http://mintaka.sdsu.edu/faculty/orosz/web/ Office: Physics 241, hours T TH 3:30-5:00.

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ASTRO 101

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  1. ASTRO 101 Principles of Astronomy

  2. Instructor: Jerome A. Orosz (rhymes with “boris”)Contact: • Telephone: 594-7118 • E-mail: jorosz@mail.sdsu.edu • WWW: http://mintaka.sdsu.edu/faculty/orosz/web/ • Office: Physics 241, hours T TH 3:30-5:00

  3. Text: “Discovering the Essential Universe, Fifth Edition”by Neil F. Comins

  4. Course WWW Page http://mintaka.sdsu.edu/faculty/orosz/web/ast101_fall2013.html Note the underline: … ast101_fall2013.html … Also check out Nick Strobel’s Astronomy Notes: http://www.astronomynotes.com/

  5. Homework • Homework due September 19: Question 4 from Chapter 3 (What are the three main functions of a telescope?) • Write down the answer on a sheet of paper and hand it in before the end of class on September 19.

  6. Homework • Go to a planetarium show in PA 209: • The days and times of the shows will be (all shows last less than 1 hour): • Thursday,  September 5  :  5 PM • Friday,    September 6  :  2 PM • Monday,    September 9  :  1 PM and 5 PM • Tuesday,   September 10 :  1 PM and 5 PM • Wednesday, September 11 :  5 PM • Thursday,  September 12 :  5 PM • Friday,    September 13 :  3 PM • Get 10 points extra credit for homework part of grade. • Sign up for a session outside PA 209. • Hand in a sheet of paper with your name and the data and time of the session.

  7. Coming Up • This week: Chapter 3 (Telescopes and light) • Tuesday, September 24: wrap-up, review • Thursday, September 26: Exam #1

  8. Fall 2013 Astronomy Help Room No appointment needed! Just drop by! Where: Room 215, physics-astronomy building (PA-215). When: All semester long, at the following days and times: • Monday: 12 – 2 PM; 5 – 6 PM • Tuesday: 12 – 2 PM; 5 – 6 PM • Wednesday: 12 – 2 PM; 5 – 6 PM • Thursday: 1 – 2 PM; 3 – 6 PM

  9. In the News… • http://www.latimes.com/science/sciencenow/la-sci-sn-harvest-moon-video-20130918,0,525553.story • http://24timezones.com

  10. Coming Up: • The 4 forces of Nature • Energy and the conservation of energy • The nature of light • Waves and bundles of energy • Different types of light • Telescopes and detectors

  11. Light is a form of energy.Why is this important?With very few exceptions, the only way we have to study objects in Astronomy is via the light they emit.

  12. What is the nature of light?Light can be thought of as awave in an electric fieldoras discrete particles of energy…

  13. What is the nature of light? Image from Nick Strobel’s Astronomy Notes (http://www.astronomynotes.com) Light can be thought of as a wave. The wavelength (usually denoted with a l) is the distance from crest to crest.

  14. What is the nature of light? Image from Nick Strobel’s Astronomy Notes (http://www.astronomynotes.com) Light can be thought of as a wave. The frequency (usually denoted with n) is the number of crests that pass a given point each second.

  15. What is the nature of light? Light can be thought of as a wave. The frequency (usually denoted with n) is the number of crests that pass a given point each second.

  16. What is the nature of light? The velocity of the wave is the wavelength times the frequency: The velocity of light in vacuum is constant for all wavelengths, regardless of the relative velocities of the observer and the light source.

  17. What is the nature of light? Image from Nick Strobel’s Astronomy Notes (http://www.astronomynotes.com) The above animation shows waves with different wavelengths moving with the same speed. Their frequencies are different.

  18. What is the nature of light?Light can be thought of as awave in an electric fieldoras discrete particles of energy…

  19. What is the nature of light? Light can also behave like discrete particles called photons. The energy of a photon depends on the frequency (or equivalently the wavelength): The value of h is constant for all situations.

  20. What is the nature of light? Photons of higher energy have higher frequencies and shorter wavelengths, since

  21. Different “types” of light.What light can tell us.

  22. Visible light • White light is made up of different colors

  23. Visible light • Different colors correspond to different frequencies (or wavelengths). • The colors of the rainbow are ROY G BIV: red orange yellow green blue indigo violet.

  24. Visible light • In the visible, • red has the longest wavelength, the smallest frequency, and the lowest energy. • violet has the shortest wavelength, the highest frequency, and the highest energy.

  25. The Electromagnetic Spectrum • Visible light is only a tiny fraction of the Electromagnetic Spectrum. • For example, there is invisible radiation with wavelengths longer than red light that heats the thermometer.

  26. The Electromagnetic Spectrum • As we go to wavelengths slightly longer than visible (i.e. smaller frequencies and lower energies), we find infrared radiation, which is basically perceived as heat. • As we go to longer wavelengths still, we find microwave radiation, which is often used to pop popcorn.

  27. The Electromagnetic Spectrum • At the longest wavelengths, corresponding to the smallest frequencies and the lowest energies, we have radio waves, including AM/FM, shortwave, TV, etc.

  28. The Electromagnetic Spectrum • Visible light is only a tiny fraction of the Electromagnetic Spectrum. • If we go to shorter wavelengths (higher frequencies and energies), we find ultraviolet light. With higher energies, UV photons can damage skin cells.

  29. The Electromagnetic Spectrum • As we go even shorter in wavelength (higher in frequency and energy), we get X-rays. With their high energies, X-rays can be used to image our insides. • As the shortest wavelengths and the highest energies, we have gamma rays. Gamma rays are sometimes used to sterilize food.

  30. The Electromagnetic Spectrum • Visible light is only a tiny fraction of the Electromagnetic Spectrum.

  31. The Electromagnetic Spectrum • Gamma rays, X-rays, UV light, visible light, infrared radiation, microwaves, and radio waves are all different manifestations of electromagnetic energy. • The range in wavelengths typically encountered span a factor of 1014. • All forms of electromagnetic radiation travel with the same velocity.

  32. The Earth’s atmosphere is transparent to visible light, some infrared, and the radio. It is opaque to UV, X-rays, and gamma rays.

  33. Coming Up: • The 4 forces of Nature • Energy and the conservation of energy • The nature of light • Waves and bundles of energy • Different types of light • Telescopes and detectors

  34. With very few exceptions, the only way we have to study objects in Astronomy is via the light they emit.So we need to collect photons, and detect them.

  35. Telescopes

  36. Telescopes • A flat surface reflects incident light at the same angle. • A curved surface can focus light.

  37. Telescopes • Glass alters the path of light. • A curved piece of glass can focus light.

  38. Telescopes • A telescope uses mirrors or lenses to collect and focus light. • The area of the lens or mirror can be considerably larger than the area of the eye’s pupil, hence much fainter objects can be seen.

  39. Telescopes • A refracting telescope uses a large lens to bring the light to a focus, as in Figure (a). • A reflecting telescope uses curved mirrors to bring the light to a focus, as in Figure (b).

  40. Telescopes • The largest lenses that can be built have a diameter of about 1m, and have very long focal lengths. • A lens must be held by its edges, and large lenses sag under their own weight. Also lots of light is lost in the glass. • For these and more reasons, all modern telescopes use mirrors.

  41. Telescopes • Using an objective mirror, plus some additional mirrors and lenses, light is collected and focused to a point. • This is a Newtonian telescope.

  42. Telescopes • Using an objective mirror, plus some additional mirrors and lenses, light is collected and focused to a point. • This is a Cassegrain telescope.

  43. Telescopes • A telescope’s main job is collecting photons. • The light gathering power is proportional to the area of the mirror or lens. The area of a circle is • If you double the diameter of the mirror, the light gathering power goes up 4 times.

  44. Telescopes • Modern mirrors can be made thin. Their shapes are maintained using pistons under computer control. • The Gemini telescope in Hawaii has primary mirror 8.1m in diameter.

  45. Telescopes • Modern mirrors can be made thin. Their shapes are maintained using pistons under computer control. • The Gemini telescope in Hawaii has primary mirror 8.1m in diameter. • These thin mirrors are cast in special rotating ovens.

  46. Telescopes • Mirrors can also be made out of smaller segments. • The Keck telescopes in Hawaii have primary mirrors 10m in diameter.

  47. What a Telescope Does • A Telescope is used to collect photons, so you can see fainter objects.

  48. Seeing Detail • What does the next line say? • If you can read this, thank a teacher. • Why is so hard to read? • Why do binoculars help? • It is hard to read because the angular size is small. The binoculars magnify the angular size.

  49. What a Telescope Does • A telescopes magnifies angular sizes.

  50. What a Telescope Does • A telescopes magnifies angular sizes and allows you to see more detail.

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