I. How is Spectroscopy UsefulII. When You See an Emission and Absorption SpectrumIII. The Structure of AtomsIV. The Bohr ModelV. Molecules have their own Characteristic LinesVI. Other Properties of LightI. The Doppler EffectII. Understanding the Differences Between CrestsIII. TelescopesIV. Great Observatories to KnowI. The Doppler Effecta. The pitch depends on the direction that the sound is coming from and the speed that it is comingb. Same as light (how source of light is moving relative to YOU)c. Depends only on the relative motion of the source and the observerd. The reason we can hear pitch change was because the source of sound was moving relative to usi. When speaker came towards us, it came up, and vice versa when the speaker came away from usii. Sound waves travel through the air, and the wavescompress and spread out as they travel, and as wave come towards it gets “squished” towards ear (pitch goes up)II. Understanding the Differences Between Crestsa. Understand the differences between crest pictures of sound when the source is at rest versus when the source is movingi. Because the source is moving towards the wave crest towards the right (for example), the wave crests are closer together on the rightb. Someone observing from the right (the side at which it is moving towards), the waves will seem shorter. And as the object is moving away, observer behind sees longer than normal wavelengthsi. Red Shift: wavelengths seem longer1. Depends on which direction the source is moving towardii. Blue Shift: wavelengths seem shorter1. Again - depends on which direction the source is moving toward2. If a light source is approaching you, you will observe this and the entire spectrum will shift towards shorter wavelengthsiii. All elements have their fingerprints in terms of their spectral lines, and you can figure what element is present in a given star, but also how fast the star is moving.c. From analyzing a star’s spectrum we can tell what?i. Composition, temperature, color, radial motion (towards/away)ii. To calculate shift n wavelength:1. ∆Lambda / Lambda not (True wavelength) = v (speed of the object) / c (speed of wave)iii. Fun fact: This is how you get caught if you are speeding:1. Radio waves bounce off car and get back to the cop. By looking at difference of the wavelength, the cop can measure your speedd. What speed do radio waves travel at?  SPEED OF LIGHTi. All waves travel at the speed of lightIII. Telescopesa. How we observe the sky – the way the light worksb. It has a large range of frequencies and wavelengths and energies, and for each range of energies we define, we need a different type of telescope to look at itc. Infrared sky:i. You can see through clouds of dust, because dust scatters light away. IR light, wavelengths are longer so it passes through dust cloudsd. Radio Astronomy:i. You can sample parts of very large dishes (which obtained radio waves from astrophysical objects) and you can synthesize a signal and look at things that are fainterii. Dishes used to gather radio waves (i.e. Radio telescopes)iii. The larger the telescope is, the more light it collects, the more fain objects you can see1. So, telescopes have more of a light gathering power than a magnification power (they aren’t PRIMARILY used to magnify stars)e. Two basic types of telescopes:i. Refractory:1. Works like a prism; bends light2. The prism bends the light, curving the lens allows the bending to be different in each part and come to a focus. Use them to focus light coming from far away3. Using refraction of light through glass to observe the skyii. Reflection:1. Gathers light, focuses at point in front of the mirror2. Reflecting light onto primary mirror so top face is coated with mirror surface, light bounces off secondary mirror (another mirror that reelects light off to the side) and so you observe the sky from the side3. Easier to build this kind of telescope4. Modern telescopes are all reflectors:a. Chromatic aberration: property of all lenses; light bends differently depending on wavelength so this needs to be corrected for if using a refractor. There are often too many problems with the fact that:i. Light traveling through lens is refracted differently depending on wavelength (chromatic aberrationii. Light is absorbed (won’t capture as much light)b. Modern telescopes use mirrors rather than lenses for the following reasons:i. Light passing through lenses can be scatteredii. Large lenses can be very heavyiii. Large lenses are more difficult to makeiv. Mirrors can be computer controlled to improve resolutionf. Telescopesize is the MOST IMPORTANT attribute of the telescopei. The larger the telescope is, the more light will be able to travel throughii. Resolving power: If you use a small telescope, images tend to merge into each other. A resolved image is when you can separate out two individual images (you WANT resolution (alpha) to be SMALL!)1. Ability to distinguish objects that are close together is called resolving powera. Angle is alpha = lambda * diameter of telescope2. We want resolution to be good, angle to be small, and that angle is one between two objects that you can tell apart3. So larger the diameter of the telescope, the smaller the angle between the two objectsiii. Atmospheric blurring: can blue images; plays a role in resolution1. Can make a fuzzy picture; the effect of a fuzzy picture is called “seeing”2. Because the atmosphere blurs an image, light gets scattered and bent all over the place, every instant, the image of the star appears at a slightly different position3. A picture that is taken at a light exposure, the star is going to look a given size because light is moving. A picture is given that is BIGGER than actual object, because of blurring.a. A = pi * D^2g. Adaptive Optics:i. Track atmosphere changes with laser, you know what atmosphere is doing to a given beam of lightii. You slightly distort the mirror to compensate atmosphereiii. Done in real time as the atmosphere changesiv. With this on, you can see different t stars within a small region in the sky without the blue of the atmosphereIV. Great Observatories to Knowa. Mauna Kea Observatory (MKO), Hawaii, United Statesb. Arecibo Observatory, Puerto RicoASTRON 89 1st Edition Lecture 11Outline of Last Lecture I. How is Spectroscopy Useful II. When You See an Emission and Absorption SpectrumIII. The Structure of Atoms IV. The Bohr Model V. Molecules have