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Unformatted text preview: hydrogen fusion Unusual things happen in the Sun’s core. —-—--—---~ 0 Conditions are extreme. 0 Protons normally repel each other. 0 in solar core, protons forced so close that the attractive strong nuclear force binds them (fusion) 9 In a nucleus, the strong nuclear force is 137 times stronger than repulsive electromagetic force. Proton-proton chain is a 3- step process. ———_ 0 Deuterium nucleus (1 p, In) combines with another proton to form Helium-3 (2p, 1n). 0 Two Helium-3 nuclei combine to yield a Helium-4 nucleus (2p, 2n) and 2 p. ‘ Energy is released in each step. 9 1g H becomes (L993 g end—products. . 0.007 g becomes energy!!! .......... v Neutrino Proton—proton chain. 1H l is the mass number which given number of particles in the H stands for , so this tells you there is/are __ proton(s) in the nucleus. Q Positron The Sun generates energy from hydrogen fusion. ° Energy is released when protons come together. 1L ‘ One proton transforms into a neutron, S, {f9 releasing a positron (positively charged *3 electron) and a neutrino (very unreactive). ' Positron (antimatter) meets an electron and is annihilated (E=mc2) E=energy, m=particle masses, c=speecl of light To produce the Sun’s energy : 0 600 miliiou tons of protons converted to helium each second 0 4 million tons of mass becomes energy 0 At this rate the Sun will last 14 trillion years!!! 0 NO!!! Fusion only occurs in core where conditions are extreme. Step 1 1H + 1H —% 2H + positron (6*) + neutrino (v) Step 2 2H + 1H Heal-{e + photon (U'l’fly) top 3 W 7 Gamma ray . Neutron 2151 There are proton(s) and neutron(s) in this nucleus. 3“He There are proton(s) and neutr:on(s) in this nucleus. 'He There are proton(s) and neutron(s) in this nucleus. 3He + “He —) “He +>1H + 1H + photon Stellar Properties (Part 2) I 3. LUMINOSITY: How much energy is radiated? The energy emitted every second by a star depends on its temperature and its size. This isn’t quite so straight forward; since what we observe on Earth depends on the distance to the star. Here what astronomers do: 1. Take spectrum. 2. Classify the star (OBAFGKM) and from the width of the spectral lines—estimate its luminosity class (indicates whether this is a large or small star). This analysis will allow you to estimate the star’s absolute magnitude (ND—how bright the star would appear at a standard distance of 10 parsecs (32.5 LY). 3. This analysis allows astronomers to compare the amount of energy radiated by each star so they can be compared. Results: There are stars emitting one millionth the Sun’s enerfl to a few million times the Sun’s energy. 4A. DISTANCE—Stellar Parallax 1. Observe the positions of stars over a year. 2. Measure parallax angle (p). 3. Use formula to solve for distance, d = l/p. d in parsecs, p in arcseconds Results: This method only works for stars <1000 parsecs (Hipparcos satellite). Actually from the ground it is more like < 50 parsecs due to atmospheric blurring. 4B. DISTANCE—Spectroscopic Parallax 1. Take spectrum. 2. Classify spectral type and luminosity class. This is most easily expressed as absolute magnitude, M. 3. Measure the apparent magnitude (in) using a telescope. The apparent magnitude is how bright a star appears from the Earth. Very easy to measure! 4. Use the equation relating apparent and absolute magnitudes to distance. Remember: the smaller the magnitude value, the brighter the star. m — M = Slog d — 5 solve for distance, d (m — NI) is called the distance modulus Results: A distance can be estimated if the star is bright enough to get good spectral infomation. This method is used for the vast ma‘ori of stars in our a1 Annie Cannon & others scrutinized 350,000 spectra 0 Systematic progression in appearance of spectra (Lab #8) due to surface temperature 0 OBAFGKM—Oh, be a fine guy/gal kiss me 0 Sun is a GZ star 0 (F9, G0, G1, G2, ...G9, K0, K1, etc.) (3) Relating magnitude (brightness) to luminosity (total energy) 0 Sirius looks bright because it is relatively close, 8 LY away * Spica looks bright because it is a powerhouse—260 LY away but 100 times more luminous than Sirius There is a relationship between distance, luminosity (spectrum), and bow bright star appears(0bservation) from Earth. Vulusal ‘ i gen-m i Pol-rim “ l 1mm ‘ gallium il = l'. 1":ltl-l' l'g'.. 40—25411—15 —1a -5 o 5 to is an 'as' Apmnlmaflnihldlimv) - meme: an Pmlmirg corn-pamsn a Full moon Apparent magnitude is how bright Ill object appears from Earth. (observation) A smaller magnitude indicates a brighter object. (4b) m—M=5]ogd—5 0 m = apparent magnitude, observe 0 M = absolute magnitude (5: measure of luminosity), it is the apparent magnitude a star has at the standard distance of 10 pc. from spectrum spectral type (Lab 8) (In-M) is called the distance modulus ...
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