Celestial Coordinates

图像
为 OAE 制作

图注： Here we see how celestial coordinates map positions on the celestial sphere. The celestial sphere is an imaginary, hollow sphere that surrounds the Earth. Celestial objects appear to be attached to the inside of the celestial sphere, and the planets, Sun, and Moon appear to move slowly across it. The celestial sphere has a spherical coordinate system similar to the latitude and longitude we see on the Earth. The celestial equator is the projection of the Earth's equator onto the celestial sphere while the north and south celestial poles are the projections of the Earth's north and south poles onto the celestial sphere. Declination is similar to latitude on the Earth in that it marks the angle above and below the celestial equator. Declination is zero on the celestial equator, is positive to the north of the celestial equator and negative to the south of it. It is commonly measured in degrees and sometimes in radians. Right Ascension is similar to longitude as it marks the angle around the celestial equator. As with longitude the zero point of right ascension (shown here as a dashed line) is a matter of choice. Traditionally the zero point of right ascension was the position of the Sun at the northern hemisphere vernal equinox (spring equinox) in March. It is positive and increases to the east, unlike longitude on Earth which is defined as east or west of the prime meridian. It is most commonly measured in hours, minutes and seconds or occasionally in degrees or radians. The ecliptic marks the Sun's path across the celestial sphere when viewed from the Earth. The Earth rotates within the celestial sphere. This leads to objects like stars or galaxies, which appear static on the celestial sphere, rising and setting when viewed from the Earth but remaining in the same position on the celestial sphere. The Earth's axis precesses within the celestial sphere. This slowly moves the celestial equator and the celestial poles meaning that the traditional celestial coordinate system changes slowly over time meaning that stars and galaxies that do not move will have positions that change. Astronomers have used coordinate systems defined by the position of the celestial poles and equator at a fixed point in time. Now celestial positions are most commonly measured on a fixed coordinate system defined by the position of the celestial poles and equator on the 1st of January 2000.
来源： Maria Cristina Fortuna/IAU OAE

分类： 肉眼天文学 , 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

文件 ( 图像 517.83 kB)
PDF 文件 (PDF file 203.59 kB)

Also available in black and white
文件 ( 图像 501.79 kB)
PDF 文件 ( 202.13 kB)

Lunar Phase Equator

图像
为 OAE 制作

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

文件 ( 图像 1.27 MB)
PDF 文件 (PDF file 451.94 kB)

Also available in black and white
文件 ( 图像 168.11 kB)
PDF 文件 ( 414.51 kB)

Mensa Constellation Map

图像

图注： The constellation Mensa with its brighter stars and surrounding constellations. Mensa is surrounded by (going clockwise from the top): Dorado, Hydrus, Octans, Chamaeleon and Volans. Mensa is a faint constellation with relatively few bright stars. Mensa lies close to the south celestial pole and thus the whole constellation is visible at some point in the year throughout the southern hemisphere. The whole constellation is visible to a thin strip of the northern hemisphere around the equator with parts of the constellation visible to some other northern equatorial regions. Mensa is circumpolar in temperate, antarctic and some equatorial regions of the southern hemisphere. Mensa is best viewed in the evenings in the northern hemisphere winter and southern hemisphere summer. The Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way, lies in Mensa and the neighboring constellation Dorado. The outline of the Large Magellanic Cloud is marked here as a roughly circular loop in green. 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 circle to the right marking -70° declination. 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 , 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

文件 ( 图像 135.16 kB)
PDF 文件 (PDF file 172.00 kB)

Chamaeleon Constellation Map

图像

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

文件 ( 图像 141.46 kB)
PDF 文件 (PDF file 166.96 kB)

Hydrus Constellation Map

图像

图注： The constellation Hydrus with its bright stars and surrounding constellations. Hydrus is surrounded by (going clockwise from the top): Eridanus, Phoenix, Tucana, Octans, Mensa, Dorado, Reticulum and Horologium. Hydrus is a southern constellation and thus the whole constellation is visible in the southern hemisphere at some point in the year. As it lies close to the celestial south pole, only a small part of the northern hemisphere near the equator can see the whole of Hydrus, with other northern equatorial regions able to see parts of the constellation. Hydrus is best viewed in the evenings in the northern hemisphere winter and southern hemisphere summer. 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 circle to the right marking -70° declination. 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 , 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

文件 ( 图像 126.70 kB)
PDF 文件 (PDF file 165.65 kB)