1 / 253

ASTRO 101

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

gordon
Download Presentation

ASTRO 101

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ASTRO 101 Principles of Astronomy

  2. Instructor: Jerome A. Orosz (rhymes with “boris”)Contact: • Telephone: 594-7118 • E-mail: orosz@sciences.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_fall2012.html Note the underline: … ast101_fall2012.html … Also check out Nick Strobel’s Astronomy Notes: http://www.astronomynotes.com/

  5. Astronomy Help Room No appointment needed! Just drop by! Where: Room 215, physics-astronomy building. When: • Monday: 12-2, 4-6 PM • Tuesday: 12-1 PM; 4-6 PM • Wednesday: 12-2, 5-6 PM • Thursday: 4-6 PM

  6. Homework • Homework due September 25: 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 25.

  7. Homework • Go to a planetarium show in PA 209: • Wednesday, September 12: 12:00 PM -- 12:30 PM • Thursday, September 13: 12:00 PM – 12:30 PM AND 12:30 PM – 1:00 PM • Friday, September 14: 12:00 PM – 12:30 PM AND 12:30 PM – 1:00 PM • Monday, September 17: 12:00 PM – 12:30 PM AND 12:30 PM – 1:00 PM • Thursday, September 20: 12:00 PM – 12:30 PM AND 12:30 PM – 1:00 PM AND 4:00 PM – 4:30 PM • Friday, September 21: 12:00 PM – 12:30 PM AND 12:30 PM – 1:00 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.

  8. Announcements • Tuesday, September 25: wrap-up and review • Thursday, September 27: exam 1 • Office hours for today are cancelled

  9. 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

  10. 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.

  11. Telescopes

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

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

  14. 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.

  15. 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).

  16. 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.

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

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

  19. 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.

  20. 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.

  21. 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.

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

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

  24. 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.

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

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

  27. Telescopes at other Wavelengths • Recall that there other forms of “light”, including radio waves, X-rays, UV light, etc. • The goal of “collect and detect” is still the same. • However, the technologies used to collect and detect are different at different wavelengths.

  28. Radio Telescopes • Radio telescopes use “mirrors” made from steel plates. • Radio receivers collect the focused radio waves. • The radio telescopes are huge because of the long wavelengths of the radio waves.

  29. Radio Telescopes • Radio telescopes use “mirrors” made from steel plates. • Radio receivers collect the focused radio waves. • The radio telescopes are huge because of the long wavelengths of the radio waves.

  30. Radio Telescopes • The GBT is the largest steerable radio telescope in the world, with a diameter of 100 meters. It is perhaps the largest movable land-based object in the world.

  31. Radio Telescopes • With modern computers and electronics, one can combine the signals from several radio telescopes to “synthesize” a much larger telescope.

  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. To detect these wavelengths, one must go to space.

  33. X-ray Telescopes • For example, X-ray light cannot be reflected like visible light can. X-ray telescopes use “grazing incidence” mirrors to collect X-rays.

  34. Telescopes in Space • The Hubble Space Telescopes observes in the ultraviolet, visible, and infrared

  35. Telescopes in Space • The Hubble Space Telescopes observes in the ultraviolet, visible, and infrared. • It is also above the blurring atmosphere.

  36. Telescopes in Space • The Spitzer Space Telescopes observes in the infrared

  37. Telescopes in Space • The image on the left is at optical wavelengths, and the wavelength on the left is at infrared wavelengths. Different features are seen.

  38. Telescopes at other Wavelengths • For most wavelengths, you need to go into space to observe.

  39. Next: Light Detection

  40. Detection of Light • Once the telescope has collected the light, we need to detect the photons. • A typical detector will not record all of the incoming photons, i.e. the efficiency is less than 100%. • The observing efficiency is proportional to the product of the telescope area and the detection efficiency.

  41. Detection of Light • A bigger telescope gives a higher incoming photon rate. • A more efficient photon detector means more photons are recorded for a given incoming rate.

  42. Detection of Light • The first detector used was the eye. • People simply looked through the telescope and made drawings of what they saw.

  43. Galileo Galilei (1564-1642) • Galileo was one of the first people to use a telescope to systematically study astronomical objects, starting in about 1609.

  44. Galileo showed by observing the patterns of light and shadows that the moon had craters and mountains.

  45. Galileo made very detailed drawings and notes. This page describes his observations of Jupiter and its 4 moons that he discovered.

  46. Galileo observed spots on the Sun. He showed that the Sun rotates about once every 28 days.

  47. Disadvantages of the Eye. • Sometimes your eyes “play tricks” on you, i.e. you hallucinate. • It is hard to be quantitative about some things, for example how bright one star is compared to another. • Unless you are a good artist, it is difficult to share your observations. There is no direct permanent record.

  48. Photography • Certain light-sensitive chemicals (usually silver oxide) are placed on glass plates or on plastic film. • The chemicals are altered when exposed to light, the degree to which depends on the intensity of the light. • A chemical “development” process “freezes” the chemicals in their altered states, making a record of the image. • It is important to note that only about 5% of the exposed light is actually recorded on film. Lots of photons are simply “wasted.”

  49. Photography • Instead of your eye, put a camera on the telescope. There are some practical difficulties, as well as some advantages…

More Related