July 16th, Lecture 5.docx

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Astronomy & Astrophysics
Marija Stankovic

July 16 , Lecture 5, AST201H1 Transition: How do we get knowledge about astronomical data. All we know about the universe is from the light we receive. What happens at the micro-level. What happens between the atoms. Nucleus, made of protons and neutrons, electrons. Move around the nucleus. Very specific. Specific amount of energy, specific orbital. From one level to another, it can only happen if the electron has the energy to the correspond to the difference between which that transition happens. The further away from the nucleus, the energy goes up. Possible transitions (on the slide) are different/ highlighted for different colors. Number of these orbitals, the energy (how far the space). Circular representation, more horizontal representation (cut the circle and level it out). Each transition, whether it happens in emission or absorption, correspond energy, wavelength, and frequency. Light of how many colors approaches. All of these different wavelengths. Of all these photons, only the green one will have that specific energy. Allow electron to move from lower to higher. Absorption. Gain the energy to move from lower level to higher level. All other light aside from the green. Later, the green light is re-emitted. Another type of representation, strips of colors. More of what we get from astronomical data. Spectrum. How do we get these bright lines? Emitted certain energy, is certain wavelength and frequency, all we get is the spikes, thus color. The dark lines are absorbed. Hit with all the colors, see the background of rainbow colors that continue, but dark lines are interrupted when absorbed. The set of spectral lines that we see in the star’s spectrum depends on the star’s: Chemical Composition. Chemical fingerprints This is why we call spectral lines  chemical composition Energy levels of molecules: Made of atoms. Molecules have additional energy levels, because they can vibrate and rotate. Many more energy levels. If look at spectrum of molecules, there are more black lines. The large number of rotational or vibrational energy levels can make the spectra of molecules very complicated. Many of these molecular transitions are in the infrared and radio part of EM Spectrum. Interpreting an Actual Spectrum (insert slide) Spike up = emission Going low = absorption Low-Density Gases Mass per unit volume. Density equals mass divided by volume. Within a certain volume, certain amount of matter, if you have more matter compared to the same volume where you have way less matter, higher density. Water has higher density to Gas. Compare within the same area, small in size but can be more massive. Density and area are related to the mass. Cat’s Eye Nebula. A planetary nebula. Give away emission lines (insert slide). Gas that is fairly hot. When something is hotter, it moves faster. Has more energy. Has more energy, electrons are already going to be on excited levels, and what they produce are the emission levels. Peaks at very specific wavelengths. Low density gas (not a lot of interactions, no chance to interact  each atom emits or absorbs light independently of the others. Hot gas. Atoms more excited, electrons can go to higher levels, particles will be more excited. Lines are higher (amount of light are high). Warm gas. Amount of light that comes is not as strong Cool gas, less electrons are higher levels, not as many transitions. So less light comes. Temperature decreases, less and less light comes. Low density gases produce emission spectra. Dense objects. Solid objects. Sun, way more particles than interstellar mediums. (Insert slide) A gradient, a continuous graph. Peak at certain point and drop down. Dense objects emit some light at all wavelengths. The particular continuous spectrum emitted by dense objects is called a blackbody spectrum. We have a certain blackbodies (stars), but these are the type of objects that absorb all the light that comes into them. Most dense objects
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