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Astro Final 3
| Question | Answer |
|---|---|
| A galaxy full of hydrogen gas-spiral arms | each spiral arm has a different doppler velocity with respect to us. Longer wavelengths get through "stuff" easier |
| Molecules also emit spectral lines | Electronic, Vibrational, Rotational |
| Electronic spectral lines of molecules | (optical and UV) high energy, temp. Similar to individual atoms. NOT superposition of two atoms. They share electrons which changes energy level structure |
| Vibrational spectral lines of molecules | (IR) moderate energy, temp |
| Rotational spectral lines of molecules | (radio) low energy, temp. Ground state:J=0, quantized, rotational angular momentum different from spin angular momentum |
| Vibrational energy states | All these are quantized. IR wavelengths. The vibration frequency/period is quantized. scissoring, rocking, wagging, twisting |
| Rotational energy states | A molecule can be "spun-up" (excited) from a lower energy state (slow rotation/low angular momentum state) to a higher energy state (fast rotation/high angular momentum state). Faster spin means more energy. Rotational states are quantized |
| When does Rotational energy state transition happen | the excitation to a higher energy rotational quantum state can happen by absorbing a photon of the right energy OR by a collision that transfers the right amount of KE |
| Rotational energy states J and E | The rotational angular momentum/energy levels are quantized. E=0 for J=0, energy levels increase with J |
| J in rotational energy states | rotational quantum number (0,1,2....) J=0 for ground, rotational E=0. For rotational transitions delta J=+-1 |
| B in rotational energy states | rotation constant. (each mol is different since moment of inertia is different. B can be given in units of K or Hz but you need to use it with units of J |
| Para | H nuclear spins anti-parallel, I=0 |
| Ortho | H nuclear spins parallel, I=1 |
| Molecular gas is | Cold (20-50K), dense by ISM standards (but air is still 100 billion times denser), sites of current and future star formation, H2 is the most abundant molecule followed by CO which is 10^-4 times less abundant than H2 |
| Plotting spectral lines | spectral lines from molecules generally occur in the radio regime, so we cannot see them. We build radio receivers/spectrometers that scan across frequency/wavelength and measure how much signal they detect. This is made into a plot |
| The doppler effect and spectral lines | spectral lines SHOULD be infinitesimally narrow since they are quantized and SHOULD absorb and emit at only one specific wavelength/frequency. The Heisenberg uncertainty principle does give the lines a "natural" line width, but still VERY narrow |
| The doppler effect causes | the infinitesimally narrow spectral lines to broaden |
| Doppler effect and superposition | its a superposition of all spectra in the resolution element. In each resolution element, we see a number of unresolved atoms/molecules some of which have redshifted motion and some of which have blue shifted motion. |
| Heat and Doppler shift | heat increased, more spread out doppler shift, peak broader |
| What is the sun? | An ordinary star. A great big ball of fusing gas, mostly made of Hydrogen. The sun is constantly changing. The sun in an active object |
| Core density of the sun | is 100,000 times denser than air (and about 20x the density of iron) |
| Surface temperatures of the sun | 2000-50,000 degrees |
| Average density of the sun is | 1,100 times denser than air (~water) |
| The sun is | 99.85% of Mass of entire solar system. A regular star. Not solid but hot dense gas. A plasma. Most atoms are ionized |
| To astronomers, everything that isn't H or He is | a "metal". Metals are given the element label Z |
| The sun converts | gravitational energy to thermal energy to radiation energy because the sun is contracting |
| Radiation zone of the sun | energy is transported via photons since the plasma is made of bare electrons and protons which don't absorb photons as easily as atoms. So the plasma is optically thin. very low opacity so basically travels at the speed of light |
| Convection zone of the sun | Energy is transported by convection bubbles since the electrons have recombined with protons to form H atoms (which can absorb photons) Hence the gas becomes optically thick and energy transport by radiation is no longer effective |
| The photosphere of the sun | is the "surface" of the sun. Not a discrete surface but a range of depths from which radiation can escape. The layer that we "see" when we look at the sun. Where most absorption lines come from. Don't see photons from lower depths b/c opacity too high |
| Granulation | caused by convection. "bubbling" of the sun |
| The photosphere is where we measure | spectral lines from |
| The chromosphere | gas extends far beyond photosphere. Opacity is low, all radiation escapes. Not very bright since the gas density is low. Best observed during an eclipse. Small. Reddish colour from H alpha emission |
| The chromosphere continued | Hard to see the emission lines against bright background of photosphere. Density decreases with altitude but temperature increases from 4500K at the photosphere to 100,000K in the upper chromosphere |
| Upper levels of chromosphere merge with | lower levels of the corona (transition zone) |
| The Corona | Above chromosphere the temperature continues to rise, maximizes at a few thousand km above photosphere at 1 million K, continues to extend millions of miles above photosphere at this high temperature. STRONG X-RAY EMISSION |
| The corona continued | Thins out to the solar wind. T increases with distance because: Corona and chromosphere heated in different manner than photosphere, Corona most likely heated by magnetic disturbances in the photosphere that shock heat the corona gas |
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