Total Solar Eclipse

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图注： This not to scale diagram shows what happens during a total solar eclipse. The Moon orbits the Earth, but its orbit is slightly tilted with respect to the Earth’s orbit around the Sun. During the new moon lunar phase, the Moon lies between the Earth and the Sun, but due to the Moon’s tilted orbit around the Earth, the Moon normally lies above or below the Sun at this point. However twice a year the Moon’s orbit lines up in such a way that the Moon can lie in a direct line between the Earth and Sun. During each of these periods (each of which last roughly a month) solar (and lunar) eclipses can occur. The Moon is about 400 times smaller than the Sun, but is 400 times closer to the Earth than the Sun. Hence the Sun and Moon have approximately the same angular size when viewed from the Earth. This means that it is possible for the Moon to completely cover the Sun when viewed from Earth. This is known as a total solar eclipse. Here we see a schematic of such and eclipse. The Moon casts a shadow on the Earth known as the umbra. This is a roughly circular shadow a few hundred kilometres across although its shape can be severely distorted when the eclipse is at the edge of the illuminated part of the Earth. Any region within the umbra will see the Moon completely cover the Sun and thus will experience a total solar eclipse. Outside of the umbra there are regions where the Moon will cover part of the Sun. This partial shadow is known as the penumbra. Regions in the penumbra will experience a partial solar eclipse. An eclipse is a dynamic event with the Moon moving in its orbit and the Earth rotating. Hence the umbra and penumbra move across the Earth’s surface together. The path the umbra takes across the Earth is known as the path of totality. Let’s consider one particular region that lies in the path of totality: except in rare cases where an eclipse begins at sunrise, a region that experiences totality will first see the Moon cover part of the Sun and gradually move across Sun until it is totally covered. From outside the Earth this would appear as the penumbra moving over this particular region followed by the umbra moving over this region. Once the Moon moves so that it no longer completely covers the Sun, totality ends and the umbra moves away from this particular region. The Moon will continue to uncover the Sun until (unless the Sun sets before the end of the eclipse) the Sun is completely uncovered. From outside the Earth this would appear as the umbra moving away from our particular region and the edge of the penumbra approaching and eventually passing over the region. Outside of the path or totality there is a much broader region that will lie in the penumbra but will be missed by the umbra. Such regions will not experience a total solar eclipse during this event, only a partial solar eclipse.
来源： Aneta Margraf/IAU OAE

词汇表: 月相 , 月球 , 新月 , 日偏食 , 半影 , 日食 , 太阳 , 日全食 , 本影
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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Lynx Constellation Map

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图注： Lynx is a northern constellation and thus the whole constellation is visible at some point in the year throughout the northern hemisphere. The whole constellation is also visible in equatorial regions of the southern hemisphere with parts of the constellation visible in southern temperate regions. Lynx is best viewed in the evenings in the northern hemisphere winter and southern hemisphere summer. The y-axis of this diagram is in degrees of declination with north as up and the x-axis is in hours of right ascension with east to the left. 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. The blue line at the bottom right of the diagram marks the ecliptic. Neither the constellation boundaries, nor the line marking the ecliptic, 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 , 星座 , 赤纬 , 黄道 , 双子座 , 狮子座 , 赤经（RA） , 巨蟹座
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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Corvus Constellation Map

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图注： The constellation Corvus with its bright stars and surrounding constellations. Corvus is surrounded by (going clockwise from the top): Virgo, Crater and Hydra. Corvus is a southern constellation and thus the whole of the constellation is visible in the southern hemisphere at some point in the year. The whole constellation is also visible from temperate and equatorial regions of the northern hemisphere. Corvus is best viewed in the evenings in the northern hemisphere late spring and southern hemisphere late autumn. The y-axis of this diagram is in degrees of declination with north as up and the x-axis is in hours of right ascension with east to the left. 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. The blue line at the top left marks the ecliptic. Neither the constellation boundaries, nor the line marking the ecliptic, 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 , 星座 , 赤纬 , 黄道 , 赤经（RA）
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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Canis Minor Constellation Map

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图注： The constellation Canis Minor with its bright stars and surrounding constellations. Canis Minor is surrounded by (going clockwise from the top): Gemini, Monoceros, Hydra and Cancer. Canis Minor has relatively few bright stars but its brightest star Procyon is the eight brightest star in the sky. Canis Minor spans the celestial equator and thus part of the constellation is visible from the whole Earth at some point during the year. The whole constellation is visible to all but the most arctic and antarctic regions. The y-axis of this diagram is in degrees of declination with north as up and the x-axis is in hours of right ascension with east to the left. 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. The blue line in the top right of the diagram marks the ecliptic. Neither the constellation boundaries, nor the line marking the ecliptic, 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 , 天赤道 , 星座 , 赤纬 , 黄道 , 赤经（RA）
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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Crater Constellation Map

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图注： The constellation Crater with its bright stars and surrounding constellations. Crater is surrounded by (going clockwise from the top): Leo, Sextans, Hydra, Corvus and Virgo. Crater is a southern constellation so the whole of the cluster is visible at some point in the year from the whole of the southern hemisphere.The whole constellation is also visible from temperate and equatorial regions of the northern hemisphere. The constellation is best viewed in the evening in the northern hemisphere spring and southern hemisphere autumn. The y-axis of this diagram is in degrees of declination with north as up and the x-axis is in hours of right ascension with east to the left. 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. The blue line at the top left of the diagram marks the ecliptic. Neither the constellation boundaries, nor the line marking the ecliptic, 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 , 星座 , 赤纬 , 赤经（RA）
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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