Solar absorption lines

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图注： This is a high resolution spectrum of light from our Sun showing visible region of the electromagnetic spectrum. The absorption lines are visible clearly as narrow black regions. The visualization shown here was created to mimic a so-called echelle spectrum, with wavelength increasing from left to right along each strip, and from bottom to top. Each of the 50 horizontal strips covers 6 nanometers, for a complete spectrum across the visible range from 400 to 700 nanometers. This spectrum was created from a digital atlas observed with the Fourier Transform Spectrometer at the McMath-Pierce Solar Facility at the National Solar Observatory on Kitt Peak, near Tucson, Arizona (‘Solar Flux Atlas from 296 to 1300 nm" by Robert L. Kurucz, Ingemar Furenlid, James Brault, and Larry Testerman: National Solar Observatory Atlas No. 1, June 1984). Note: NSO/Kitt Peak FTS data used here were produced by NSF/NOAO.
来源： N.A. Sharp/KPNO/NOIRLab/NSO/NSF/AURA
来源链接

词汇表: 天体物理学 , 可见光谱 , 光谱线 , 吸收线

授权许可： 知识共享许可协议 署名 4.0 国际 (CC BY 4.0) 知识共享许可协议 署名 4.0 国际 (CC BY 4.0) 图标

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An Encounter With Halley's Comet

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图注： This image shows the solid core, or nucleus, of Halley’s Comet, captured in 1986 by the European Space Agency spacecraft Giotto during its flyby of the comet in the inner Solar System. The nucleus appears irregular and potato-shaped, measuring roughly 15 kilometers (about 9 miles) across, and is composed of a mixture of ice, dust, and rock. Unlike the glowing fuzzy cloud (coma) and long tail that make comets visible from Earth, the nucleus itself is dark and difficult to see until a spacecraft passes close enough to take detailed images. Halley’s Comet is one of the best-known comets because it returns to the inner Solar System approximately every 76 years, allowing generations of astronomers to observe it repeatedly. The material that is released from the nucleus as the comet warms near the Sun forms a glowing coma and long tails of gas and dust, and over many returns leaves trails of debris that produce meteor showers on Earth, such as the Eta Aquarids in May and the Orionids in October.
来源： NASA/ESA/Giotto Project
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词汇表: 彗发 , 彗星 , 彗核 , 哈雷彗星

授权许可： 公共领域 公共领域 图标

文件 ( 图像 1.45 MB)

Detailed View of Charon, Moon of Pluto

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图注： Charon is the largest natural moon of the dwarf planet Pluto. This detailed image was taken by NASA’s New Horizons spacecraft in 2015 during its historic mission through the outer Solar System. Charon’s surface shows a fascinating mix of light and dark regions, including vast canyons, broad plains, and impact crater. With a diameter of about 1,200 kilometers, Charon is more than half the diameter of Pluto, making it unusually large compared to its parent body. Charon's mass is roughly 12% of that of Pluto. Because Pluto and Charon are so close in mass, the center of mass of the system (the point both Pluto and Charon orbit) is not within Pluto but between Pluto and Charon. This is in contrast to systems like the Earth and its Moon where the center of mass lies within the larger body, the Earth in this case. Scientists think the Pluto-Charon system may have formed by a collision of two objects that then separated and began to orbit each other. By studying Charon and the smaller moons that circle Pluto, astronomers gain insight into how moons form and how distant icy bodies evolve over billions of years.
来源： NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker
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词汇表: 卫星 , 冥王星

授权许可： 公共领域 公共领域 图标

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Apparatus for determining the gravitional constant

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图注： Observations of the motions of the planets around the Sun, or the Moon around the Earth, could not yield the gravitational constant, as in those cases, the mass of the central body is not initially known. Measuring the gravitational constant required a situation where the masses involved had been determined independent of measuring their gravitational attraction. The device shown here was built by John Michell (1724–1793), but Michell died before he could perform the experiment. Henry Cavendish (1731–1810) inherited the device, modified it so as to suppress external disturbances, and successfully completed the experiment. Cavendish's report to the Royal Society was under the title of "Experiments to determine the density of the Earth" as, from knowledge of the gravitational constant, the gravitational acceleration at Earth's surface and the Earth's radius, one can determine the Earth's mass and its mean density. From the modern perspective, what is now known as the "Cavendish experiment" is seen as a way of determining Newton's gravitational constant G. The image shows a cross-section of the apparatus, which Cavendish had further isolated from environmental influences by putting it into a separate room and inside a wooden box. The devices allowing Cavendish to illuminate, observe and manipulate the experiment from the outside are pictured as well. The core of the experiment is a torsion balance using two small lead spheres. The restoring force of the torsion pendulum is deduced from its natural oscillation frequency in the absence of the large masses. The gravitational attraction of the small lead spheres to their larger counterparts can then be determined by measuring how far it makes the torsion pendulum masses deviate from their null position. The image is a slightly modified (cropped, contrast and brightness adjusted) version of Fig. 1 in Cavendish's article in the Philosophical Transactions of the Royal Society, Volume 88 (December 1798), pp. 469–526 [DOI: 10.1098/rstl.1798.0022]. The permission of the Royal Society to publish this image under a CC BY licenses gratefully acknowledged.
来源： Henry Cavendish in Philosophical Transactions of the Royal Society, DOI: 10.1098/rstl.1798.0022
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词汇表: 引力常数 , 万有引力
分类： 物理学

授权许可： 知识共享许可协议 署名 4.0 国际 (CC BY 4.0) 知识共享许可协议 署名 4.0 国际 (CC BY 4.0) 图标

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