2024年12月23日:圣诞树形的极光-（Christmas Tree Aurora） 2024年12月23日:圣诞树形的极光-（Christmas Tree Aurora）--原图下载{mtitle title="圣诞树形的极光"/}Image Credit & Copyright: Jingyi Zhang说明: 在那年的十二月，天空有棵点亮的圣诞树。而这些树形的绿色、蓝色和紫色闪烁极光，则是高层大气中的氧和氮与涌入的成群电子发生反应所致。更精确的来说，碰撞让原子和分子的轨道电子跃迁到激发态，然后在返回基态时释放出可见光。这张主题影像，是在2023年12月摄于冰岛的久比沃古（Djúpivogur）。目前的太阳处在它11年活动周期的最活跃阶段，表面出现大量活跃区和太阳黑子的状态预计会持续到明年。想当然耳，今年全年都处在活动极大期的太阳，所发生的爆发有时会为地球带来壮观的极光。{lamp/}原文：{mtitle title="Christmas Tree Aurora"/}Image Credit & Copyright: Jingyi ZhangExplanation: It was December and the sky lit up like a Christmas tree.Shimmering, the vivid green, blue, and purple auroral colors that formed the tree-like apparition were caused by high atmospheric oxygen and nitrogen reacting to a burst of incoming electrons. Collisions caused the orbital electrons of atoms and molecules to jump into excited energy states and emit visible light when returning to their normal state.The featured image was captured in Djúpivogur, Iceland during the last month of 2023.Our Sun is currently in its most energetic phase of its 11-year cycle, with its high number of active regions and sunspots likely to last into next year.Of course, the Sun has been near solar maximum during this entire year, with its outbursts sometimes resulting in spectacular Earthly auroras.

2024年12月22日:本星际云-（The Local Fluff） 2024年12月22日:本星际云-（The Local Fluff）--原图下载{mtitle title="本星际云"/}Illustration Credit: NASA, SVS,Adler, U. Chicago, Wesleyan说明: 恒星其实并不孤独。在我们的银河系的盘面上，大约有10%的可见物质是名为星际物质（ISM）的云气。然而，星际物质的分布并不均匀， 就连在太阳附近也是支离破碎的。因为星际物质非常稀薄，而且几乎不发光，所以侦测邻近星际物质的工作难度颇高。星际物质之主成分是氢气，因为它会吸收特定波长的光，所以可经由侦测最邻近恒星的星光得知它的存在。上面这幅呈现我们周围20光年内星际物质的暂订分布图，是根据地球轨道上的星际边界探测卫星 （IBEX），目前的观测及粒子侦测数据所建构出来的。这些观测显示，我们的太阳正在穿过 本星际云（Local Cloud），而这团云气则来自天蝎-半人马星协恒星形成区的外泛流。在接下来的一万年内，我们的太阳可能会穿出本星际云。我们对附近的星际物质所知不多，包括分布、起源、及它如何影响太阳和地球等细节都有待釐清。出乎预料的，最近的星际边界探测卫星量测指出，中性星际粒子流通过太阳系的方向正在改变之中。{lamp/}原文：{mtitle title="The Local Fluff"/}Illustration Credit: NASA, SVS,Adler, U. Chicago, WesleyanExplanation: The stars are not alone. In the disk of ourMilky Way Galaxy,about 10 percent of visible matter is in the form of gas called theinterstellar medium (ISM). The ISM isnot uniformand shows patchiness even near ourSun. It can be quite difficult to detect thelocal ISM because it is so tenuous and emits so little light. This mostly hydrogen gas, however, absorbs some veryspecific colors that can be detected in the light of thenearest stars. A working map of the localISM within 20 light-years,based on ongoing observations and particle detections from the Earth-orbiting Interstellar Boundary Exporer satellite (IBEX), is shown here. These observations indicate that ourSun is moving through aLocal Interstellar Cloud as this cloud flows outwards from theScorpius-Centaurus Association star forming region. Our Sun may exit the Local Cloud, also called the Local Fluff, during the next 10,000 years. Much remains unknown about the localISM, including details of its distribution,its origin, and how it affects theSun and the Earth.Unexpectedly, IBEXspacecraft measurements indicate that the direction from which neutral interstellar particles flow through our Solar System is changing.

2024年12月21日:一年份的日落-（A Year in Sunsets） 2024年12月21日:一年份的日落-（A Year in Sunsets）--原图下载{mtitle title="一年份的日落"/}Image Credit &Copyright:Wael Omar说明: 这张堆叠的全景影像，呈现了从2023年4月到2024年3月，西方地平线的日落位置在一年之中的变化。这项精心规划的序列影像工作，从同一位置俯瞰埃及的开罗并摄于每月的21日附近。 不过，在地球上的任何地方，每年日落的最北点（照片右侧）与最南点，皆标记了夏至和冬至的位置。在拉丁语里，“至日”（solstice）意指“太阳”（Sol）和“静止”。在至日这天，太阳于天空中每天的日轨之年度天球旅程，看似伫停并开始反向。 想当然耳，今天的太阳正好位于至点。2024年12月21日的冬至在世界时09:21 UTC降临，此刻标誌了太阳在赤纬上的最南点，并为北半球的天文冬季和南半球的天文夏季拉开序幕。{lamp/}原文：{mtitle title="A Year in Sunsets"/}Image Credit &Copyright:Wael OmarExplanation: A year insunsets, from April 2023 to March 2024, track along thewestern horizon in these stacked panoramic views.Thewell-planed sequenceis constructed of images recordednear the 21st day of the indicated month from the same location overlookingCairo, Egypt.But for any locationon planet Earththe yearly extreme northern (picture right)and southern limits of the setting Sunmark the solstice days.The word solstice is from Latin for "Sun" and "stand still".On the solstice date the seasonal drift of theSun's daily path through the sky appears to pause and reversedirection in itsannual celestial journey.Of course the Sun reaches a stand still on today's date.The21 December 2024 solsticeat 09:21 UTC is the moment ofthe Sun's southernmost declination, thestart of astronomical winterin the north and summerin the south.

2024年12月20日:冷月-（The Long Night Moon） 2024年12月20日:冷月-（The Long Night Moon）--原图下载{mtitle title="冷月"/}Image Credit &Copyright:Giorgia HoferandDario Giannobile(Pictores caeli)说明: 在12月15日那晚，满月彻夜普照。而这轮称为冷月或长夜月的满月，则是最接近北半球冬至的满月，也是2024年的最后满月。 此次满月更遇到最大月球至点。月球至点是指因为周期18.6年的月球轨道进动，导至月出与月落位置的南北範围出现极值。也因此，这轮月亮满相时，月出（或月落）位置位于地平线的最北点。 这张记录12月满月升起的叠合影像，组合后得以呈现冬夜天空中人眼可见的亮度範围。影像里除了色彩缤纷的月晕和飞机凝结尾之外，还有高挂在意大利多罗迈蒂山脉崎岖雪峰上空的冷月。{lamp/}原文：{mtitle title="The Long Night Moon"/}Image Credit &Copyright:Giorgia HoferandDario Giannobile(Pictores caeli)Explanation: On the night of December 15, theFull Moon was bright.Known to some as the Cold Moonor the Long Night Moon, it was the closest Full Moonto the northern winter solstice and thelast Full Moon of 2024.This Full Moon was also at amajor lunar standstill.A major lunar standstill is an extreme inthe monthly north-south range of moonrise and moonset caused by theprecession of the Moon's orbit over an 18.6 year cycle.As a result, the full lunar phase was near the Moon's northernmost moonrise(and moonset) along the horizon. December's Full Moon is rising in this stacked image, acomposite of exposures recording the range of brightness visibleto the eye on the northern winter night.Along with a colorfullunar corona and aircraft contrailthis Long Night Moon shines in a cold skyabove the rugged, snowy peaks of the Italian Dolomites.

2024年12月19日:M2-（Messier 2） 2024年12月19日:M2-（Messier 2）--原图下载{mtitle title="M2"/}Image Credit: ESA/Hubble &NASA,G. Piotto et al.说明: 这个排序在蟹状星云（M1）之后的庞大星团，是18世纪天文学家梅西叶着名“非彗星”星表登录的第二个天体。 而在我们银河系银晕里漫游的球状星团里，M2是其中最庞大者之一。梅西叶当初宣称M2是一团没有恒星的云气，然而这幅令人屏息的哈伯望远镜影像，清楚的解晰出M2中心40光年範围内的恒星。M2的恒星数接近150,000，拥挤在直径约175光年的空间里。这个亦名为NGC 7089、高龄约130亿年的银河系古老成员，位于宝瓶座方向，离我们约55,000光年远。最近的研究发现，M2有一道绵延的恒星流，这种它过去曾受到重力潮汐扰动的特徵结构。{lamp/}原文：{mtitle title="Messier 2"/}Image Credit: ESA/Hubble &NASA,G. Piotto et al.Explanation: After the Crab Nebula,this giant star cluster is the second entry in18th century astronomer Charles Messier's famous list ofthings that are not comets.M2 is one of the largest globular star clusters now known toroam the halo of our Milky Way galaxy.Though Messier originally described it as a nebula without stars, thisstunningHubble image resolves stars across the cluster's central 40light-years.Its populationof stars numbers close to 150,000, concentratedwithin a total diameter of around 175 light-years.About 55,000 light-years distant toward the constellation Aquarius,this ancient denizen of the Milky Way, alsoknown as NGC 7089,is 13 billion years old.An extendedstellar debris stream, a signature ofpast gravitational tidal disruption, was recently found to beassociatedwith Messier 2.

2024年12月18日:NGC 660：极环星系-（NGC 660: Polar Ring Galaxy） 2024年12月18日:NGC 660：极环星系-（NGC 660: Polar Ring Galaxy）--原图下载{mtitle title="NGC 660：极环星系"/}Image Credit & Copyright: Mike Selby说明: 这是那种奇特的星系？具有这种罕见结构的天体称为极环星系，而它则看似拥有2个不同的恒星环。例如在星系NGC 660里，除了有个由明亮恒星、气体和黝黑尘埃构成、近乎垂直指向的环之外，还有另一个类似但较短、斜向左上方伸展的环。极环星系到底如何获得这种引人注目的外观，目前仍然是研究的课题，但主流的理论认为，它们通常是由2个具有不同中心环指向的星系互撞而成。位于双鱼座方向，直径约50,000光年的NGC 660，距离地球约4,000万光年远。这幅主题影像，是在不久前摄于智利的El Sauce天文台。{lamp/}原文：{mtitle title="NGC 660: Polar Ring Galaxy"/}Image Credit & Copyright: Mike SelbyExplanation: What kind of strange galaxy is this?This rare structure is known as a polar ring galaxy, and it seems to have two different rings of stars. In this galaxy, NGC 660, one ring of bright stars, gas, and dark dust appears nearly vertical, while another similar but shorter ring runs diagonally from the upper left. How polar ring galaxies obtain their striking appearance remains a topic of research, but a leading theory holds that it is usually the result of two galaxies with different central ring planes colliding. NGC 660 spans about 50,000 light years and is located about 40 million light years away toward the constellation of the Fish (Pisces). The featured image was captured recently from Observatorio El Sauce in Chile.