Seasons

图像
为 OAE 制作

图注： This diagram shows the Earth at the June solstice which is known as the summer solstice in the Northern Hemisphere and the winter solstice in the Southern Hemisphere. The Earth’s axis of rotation is tilted from the axis of the Earth’s orbit around the Sun by 23.4°. Here we see light from the sun represented as parallel lines, in the diagram the Sun would lie far off the right-hand edge. Five lines are marked with angles. These lines hit the Earth at special latitudes. From top to bottom these lines hit the Earth at the North Pole, the Tropic of Cancer, the Equator, the Tropic of Capricorn and the Antarctic Circle. The lines are shown hitting the Earth at the longitude where it is currently noon. For the last four lines, the angles marked show the angle above the horizon (the altitude) which the Sun appears in the sky at at local noon. At the June solstice, the Sun will appear directly overhead at local noon on every point on the Tropic of Capricorn. By contrast the Sun reaches a maximum altitude of 0° at local noon on every point in the Antarctic Circle. This means the Sun never rises and every point south of the Antarctic Circle experiences a long Polar Night. By contrast the Sun never sets on this day north of the Arctic Circle and the regions here experience a Polar Day. The at the North Pole the Sun will remain at a constant altitude all day. This altitude will be the angle 180°-156.6° (23.4°). The altitude the Sun appears at is important as it defines how spread out the Sun’s rays are on the Earth’s surface. Look at the thick, faint parallel lines in the background. Notice how at the Tropic of Cancer the area the lines intersect with the Earth’s surface perpendicularly and the line only covers a small part of the Earth’s surface. Now look at a line near the Tropic of Capricorn and see that this intersects with the Earth at a grazing angle and the line is spread out, covering a much wider area of the Earth’s surface. This means that a given amount of light from the Sun that hits the Tropic of Cancer is more concentrated and the same amount of light hitting the Tropic of Capricorn would be more spread out. This leads to more energy per unit area from the Sun hitting the Tropic of Cancer and less energy per unit area hitting the Tropic of Capricorn. This means it will be warmer at the Tropic of Cancer than at the Tropic of Capricorn. It is thus summer at the Tropic of Cancer and winter at the Tropic of Capricorn. Six months later this situation will be reversed and it will be summer at the Tropic of Capricorn and winter at the Tropic of Cancer.
来源： Maria Cristina Fortuna/IAU OAE

词汇表: 赤道 , 二至点 , 夏至 , 冬季 , 冬至 , 北极圈 , 南极圈 , 北回归线 , 南回归线 , 北极

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 1.09 MB)

Also available in black and white
文件 ( 图像 400.17 kB)
PDF 文件 ( 477.01 kB)

Latitude and Longitude

图像
为 OAE 制作

图注： Two views of the Earth, one viewing the Northern Hemisphere, one viewing the Southern Hemisphere. The Earth rotates around its axis, an imaginary line that runs through the Earth from the North Pole to the South Pole. The Equator is an imaginary line that is the same distant from both the North Pole and the South Pole. The positions of two cities, Rome in the Northern Hemisphere and Sydney in the Southern Hemisphere are marked here with red dots. Arrows indicate the two spherical coordinates latitude and longitude. Latitude marks the position north or south of the equator. Here we can see Rome has the letter N in its latitude as it is in the Northern Hemisphere and Sydney has the letter S in its latitude as it is in the Southern Hemisphere. Latitude can vary from 90° N at the North Pole to 0° at the Equator to 90° S at the South Pole. Longitude measures the position around the equator. While the choice of the zero point for latitude as the equator seems obvious, the choice of the zero point for longitude is more subjective. By convention the zero point in longitude is the prime meridian which passes through the Royal Greenwich Observatory in the UK. This is marked here as a solid line originating at the North Pole. Longitude is measured in degrees east or west of the prime meridian. As both Rome and Sydney lie to the east of Greenwich, they have the letter E as part of their longitude. Moving west to east, longitude varies from 180° W on the other side of the world from the prime meridian to 0° on the prime meridian before reaching 180° E again on the other side of world from the prime meridian. This diagram shows the Earth at the December solstice. Two views are presented, one viewing the Northern Hemisphere and one viewing the Southern Hemisphere about nine hours later. The shaded region shows the night side of the Earth, with the day side being lighter. As it is the December solstice, the Sun appears overhead at the Tropic of Capricorn. This is a line of constant latitude at 23°26′09.3″ S. Six months later, at the June solstice, the Sun will appear to be overhead at the Tropic of Cancer at 23°26′09.3″ N. As the Sun appears over the Tropic of Capricorn more of the Southern Hemisphere is illuminated than the Northern Hemisphere. Indeed below the Antarctic Circle (the Polar Circle around the South Pole) the Sun does not set at this time of year leading to a Polar Day. Conversely, north of the Arctic Circle (the Polar Circle around the North Pole) the Sun does not rise at this time of year, leading to a Polar Night.
来源： Maria Cristina Fortuna/IAU OAE

词汇表: 地球自转 , 赤道 , 纬度 , 经度 , 极圈 , 地轴 , 回归线 , 极昼 , 极夜 , 北回归线 , 南回归线 , 热带地区 , 北极 , 南极
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 434.22 kB)
PDF 文件 (PDF file 449.61 kB)

Also available in black and white
文件 ( 图像 433.51 kB)
PDF 文件 ( 358.89 kB)

Aquila Constellation Map

图像

图注： The constellation Aquila with its bright stars and surrounding constellations. Aquila is surrounded by (going clockwise from the top): Sagitta, Hercules, Ophiuchus, Serpens Cauda, Scutum, Sagittarius, Capricornus, Aquarius and Delphinus. Aquila is most notable for its brightest star Altair. This forms one vertex of the prominent Summer Triangle asterism that is visible in northern hemisphere summer evenings. Aquila spans the celestial equator and thus some part of it is visible from all of the Earth at some point in the year. It is most visible in the evenings in the late northern hemisphere summer and late southern hemisphere winter. 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 lower right of the diagram is 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 IAU/Sky & Telescope
来源链接

词汇表: 视星等 , 摩羯座 , 天球坐标 , 天赤道 , 星座 , 赤纬 , 黄道 , 赤经（RA） , 宝瓶座 , 星宿（星群）
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 95.28 kB)
PDF 文件 (PDF file 175.09 kB)

Piscis Austrinus Constellation Map

图像

图注： The constellation Piscis Austrinus with its bright stars and surrounding constellations. Piscis Austrinus is surrounded by (going clockwise from the top): Aquarius, Capricornus, Microscopium, Grus and Sculptor. Piscis Austrinus is a southern constellation and thus the whole constellation is visible at some point in the year throughout the southern hemisphere. The whole constellation is also visible to some equatorial regions of the northern hemisphere with parts of the constellation visible to the remaining equatorial and some temperate northern hemisphere regions. Piscis Austrinus is best viewed in the evening in the northern hemisphere autumn and southern hemisphere spring. 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 lines joining the stars, nor the ecliptic, 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 , 摩羯座 , 天球坐标 , 星座 , 赤纬 , 黄道 , 赤经（RA） , 宝瓶座
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

文件 ( 图像 81.19 kB)
PDF 文件 (PDF file 155.49 kB)

Microscopium Constellation Map

图像

图注： The constellation Microscopium with its brighter stars and surrounding constellations. Microscopium is surrounded by (going clockwise from the top): Capricornus, Sagittarius, Telescopium, Indus, Grus and Piscis Austrinus. Microscopium is a faint constellation with relatively few bright stars. Microscopium is a southern constellation and thus the whole constellation is visible at some point in the year throughout the southern hemisphere. The whole constellation is also visible in equatorial and some temperate regions of the northern hemisphere with parts of the constellation visible from other northern temperate regions. Microscopium is best viewed in the evening in the northern hemisphere autumn and southern hemisphere spring. 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. Neither the constellation boundaries, nor the line marking the ecliptic, nor the lines joining the stars appear on the sky. The ecliptic is marked with a blue line in the top right.
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 , 摩羯座 , 天球坐标 , 星座 , 赤纬 , 黄道 , 赤经（RA） , 人马座
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

文件 ( 图像 77.31 kB)
PDF 文件 (PDF file 147.46 kB)