黑体辐射

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图注： 不同温度黑体的辐射曲线。x 轴表示波长，y 轴表示黑体表面每平方米在每个波长下每秒发射的能量。 温度越高的物体，波长越短，发出的最大能量光也越蓝。尽管图中最冷的天体发出的红光达到峰值，但其他较热的天体发出的红光都比最冷的天体多。
来源： IAU OAE/Niall Deacon

词汇表: 黑体辐射 , 电磁辐射 , 波长
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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黑体辐射--紫外线灾难

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图注： 不同温度黑体的辐射曲线。x 轴表示波长，y 轴表示黑体表面每平方米在每个波长下每秒发射的能量。 温度越高的物体，波长越短，发出的最大能量光也越蓝。尽管图中最冷的天体发出的红光达到峰值，但其他较热的天体发出的红光都比最冷的天体多。 虚线显示的是现代量子力学之前的经典理论所预测的辐射量。对于任何温度高于零的黑体，这一预测在较短波长处都趋于无穷大，被称为 "紫外线灾难"。
来源： IAU OAE/Niall Deacon

词汇表: 黑体辐射 , 电磁辐射 , 波长
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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Annual Parallax

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图注： Distance determination has historically been a challenge for astronomy. One of the primary ways to measure distance is to use annual parallax. The Earth orbits around the Sun over the course of a year meaning that it moves from one side of the Sun (shown here as position A) to the other side of the Sun (position B) over the course of six months. It then moves back to its original position over the remaining six months. This movement subtly changes the perspective an observer on Earth sees the night sky from. This is similar to the change in viewing perspective you may get when viewing a scene from your left eye and then your right eye. The change of viewing perspective causes nearby objects to shift in position in your vision. The annual motion of the Earth around the Sun changes the perspective of the observer enough to shift the observed positions of celestial objects. How big this effect is depends on the distance to the celestial object. Nearby stars will have bigger shifts in observed position than more distant stars. The positional shift is known as the trigonometric or annual parallax (which we will call α here) and is defined as the shift in position of a star compared to what an observer at the center of the Solar System (the Sun) would see. In this diagram we see the star viewed from perspectives six months apart (positions A and B). When observed from position A the star’s shift in position will be α while when observed at position B it will be –α. Thus the relative difference in the stars position between being observed at position A and position B will be 2α. The size of the trigonometric or annual parallax in arcseconds is approximately 1 divided by the distance in parsecs. An arcsecond (often represented by a ″ symbol) is the angular diameter a one-metre-long stick would have when viewed from 206 km away. A parsec (often abbreviated to pc) is 3.26 light years or 30.86 trillion kilometres. This is 206,265 astronomical units (the typical distance between the Earth and the Sun). No other star is closer than 1 pc to the Sun so all stars in the sky have trigonometric parallaxes less than one arcsecond. While trigonometric parallaxes have long been used to measure the distances to objects in our Solar System or nearby stars, recent advances have pushed the boundaries of these distance measures further. The Gaia satellite has pushed the boundaries of parallax measurements to over a thousand parsecs. Arrays of radio telescopes can also very accurately measure the positions of very distant objects and thus their trigonometric parallax. Note the Earth and Sun are not to scale here and the Earth’s axial tilt is not accurately represented.
来源： Aneta Margraf/IAU OAE

词汇表: 角直径 , 周年视差 , 天文单位 , 视差
分类： 观测天文学

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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Chamaeleon Constellation Map

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图注： The constellation Chamaeleon with its bright stars and surrounding constellations. Chamaeleon is surrounded by (going clockwise from the top): Carina, Volans, Mensa, Octans, Apus and Musca. Chamaeleon lies close to the south celestial pole and this the whole of the constellation is visible from the whole southern hemisphere at some point in the year. All or part of the constellation can be seen from equatorial regions of the northern hemisphere. The whole constellation is circumpolar for all but the most equatorial regions of the southern hemisphere. Chamaeleon is best viewed in the evenings in the northern hemisphere spring and southern hemisphere autumn. This diagram maps an area around the south celestial pole. Here lines of constant right ascension converge. The right ascension values of these lines are marked on the x-axis above and below the diagram. The solid circle around the pole marks a line of -80° declination with the larger, incomplete circles above it marking -70° and -60° declination respectively. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labeled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. Neither the constellation boundaries, nor the lines joining the stars appear on the sky.
来源： Adapted by the IAU Office of Astronomy for Education from the original by the IAU and Sky & Telescope
来源链接

词汇表: 视星等 , 天球坐标 , 拱极星 , 星座 , 赤纬 , 赤经（RA） , 南天极 (SCP)
分类： 肉眼天文学

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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Lunar Phase Equator

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图注： The phases of the Moon when viewed from the Equator. Here west is up, north is left and east is down. The Moon orbits the Earth every 29.5 days. It is tidally locked to the Earth meaning its rotation period is the same as its orbital period and the same side of the Moon always faces the Earth. At any particular time, half of the Moon is illuminated by the Sun and half is in shadow. Over the course of the Moon’s orbit around the Earth every part of the Moon is illuminated for half of the orbit and is in shadow for the other half of the orbit. When the Moon sits between the Earth and the Sun its illuminated half faces away from the Earth and we only see the half that is in shadow. This phase of the Moon is known as new moon. As the Moon moves in its orbit, a small but growing sliver of the illuminated half of the Moon begins to be seen from the Earth. This illuminated sliver appears on the western side of the Moon’s face when viewed from Earth. This phase is known as waxing crescent moon. By a quarter of the way through the Moon’s orbit around the Earth the Moon appears 90° away from the Sun and half of the Moon’s illuminated half points toward the Earth. This phase is known as first quarter moon. As the orbit continues more than half of the Moon seen from Earth is now illuminated with a dark crescent. This phase is known as waxing gibbous moon. Once we reach the halfway point in the Moon’s orbit round the Earth the Moon is now on the opposite side of the Earth from the Sun and we see all of the Moon’s illuminated half. As the whole of the side of the Moon that faces the Earth is now illuminated this is referred to as full moon. For the remaining half of the Moon’s orbit the half of the moon that faces the Earth begins to move into shadow. Hence the illuminated portion of the Moon that we see from Earth begins to shrink or wane. The western edge of the face of the Moon when viewed from Earth begins to appear dark and this grows through subsequent phases. The phases are repeated in reverse order: waning gibbous, third quarter, waning crescent and finally back to new moon. The perspective for this diagram is with west up, north left and east down. When the moon is viewed looking west, for example viewing the waxing crescent just after sunset, the view of the Moon would be rotated by 180°. Note the surface features of the Moon are illustrative and do not accurately represent the Moon’s true surface.
来源： Aneta Margraf/IAU OAE

词汇表: 满月 , 月相 , 新月 , 弦月 , 残月 , 亏凸月 , 蛾眉月 , 盈凸月 , 新月 , 凸月
分类： 肉眼天文学

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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