https://www.astro-init.top/index.php?action=history&feed=atom&title=2018%E5%B9%B4USAAAO%E9%95%BF%E9%97%AE%E9%A2%98%E7%AC%AC3%E9%81%93 2026-05-01T08:15:58Z 本wiki的该页面的版本历史 MediaWiki 1.32.2 https://www.astro-init.top/index.php?title=2018%E5%B9%B4USAAAO%E9%95%BF%E9%97%AE%E9%A2%98%E7%AC%AC3%E9%81%93&diff=1795&oldid=prev 2020-03-09T14:01:16Z

<p></p> <table class="diff diff-contentalign-left" data-mw="interface"> <col class="diff-marker" /> <col class="diff-content" /> <col class="diff-marker" /> <col class="diff-content" /> <tr class="diff-title" lang="zh-Hans-CN"> <td colspan="2" style="background-color: #fff; color: #222; text-align: center;">←上一版本</td> <td colspan="2" style="background-color: #fff; color: #222; text-align: center;">2020年3月9日 (一) 14:01的版本</td> </tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l13" >第13行：</td> <td colspan="2" class="diff-lineno">第13行：</td></tr> <tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"></td></tr> <tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>(c) [5 pt] The mean bolometric luminosity per unit volume emitted by stars in the universe today is about</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>(c) [5 pt] The mean bolometric luminosity per unit volume emitted by stars in the universe today is about</div></td></tr> <tr><td class='diff-marker'>−</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>$$3 × 10^8 L_{sun}<del class="diffchange diffchange-inline">�</del>/Mpc^3$$. How long would it takes stars at this rate to fuse all the hydrogen and helium in</div></td><td class='diff-marker'>+</td><td style="color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>$$3 × 10^8 L_{sun}/Mpc^3$$. How long would it takes stars at this rate to fuse all the hydrogen and helium in</div></td></tr> <tr><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>the universe? Compare to the present age of the universe.</div></td><td class='diff-marker'> </td><td style="background-color: #f8f9fa; color: #222; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>the universe? Compare to the present age of the universe.</div></td></tr> </table>

Jingsong Guo https://www.astro-init.top/index.php?title=2018%E5%B9%B4USAAAO%E9%95%BF%E9%97%AE%E9%A2%98%E7%AC%AC3%E9%81%93&diff=1794&oldid=prev 2020-03-09T14:01:01Z

<p>创建页面，内容为“==英文题目== 3. [15 pt] Suppose that at some time in the very recent past all the hydrogen and helium (baryon density $$ρ_b = 4.2 × 10^{−31} g/cm^3$$ , abou…”</p> <p><b>新页面</b></p><div>==英文题目==<br /> <br /> 3. [15 pt] Suppose that at some time in the very recent past all the hydrogen and helium (baryon density<br /> $$ρ_b = 4.2 × 10^{−31} g/cm^3$$<br /> , about 75% hydrogen (=1 baryon) by mass and 25% helium (=4 baryons) by mass)<br /> in the universe had been instantly fused into iron in stars, and the released energy thermalized into black<br /> body radiation. (Note that the binding energy per nucleon of $$_{26}^{56}\textrm{Fe}$$ is 8.8 MeV and that of $$_{4}^{2}\textrm{He}$$ is 7.1 MeV.)<br /> <br /> (a) [5 pt] Calculate the current temperature of this black body radiation.<br /> <br /> (b) [5 pt] At what wavelength would the black body spectrum peak, and what region of the electromagnetic<br /> spectrum would this be?<br /> <br /> (c) [5 pt] The mean bolometric luminosity per unit volume emitted by stars in the universe today is about<br /> $$3 × 10^8 L_{sun}�/Mpc^3$$. How long would it takes stars at this rate to fuse all the hydrogen and helium in<br /> the universe? Compare to the present age of the universe.</div>

Jingsong Guo