移过天空的天王星和卫星

移过天空的天王星和卫星

ByNASA中文

2021年11月30日 In Motion: Uranus and Moons Video Credit: David Campbell (U. Hertfordshire), Bayfordbury Observatory Explanation: What’s that moving across the sky? A planet just a bit too faint to see with the unaided eye: Uranus. The gas giant out past Saturn was tracked earlier this month near opposition — when it was closest to Earth and at its brightest. The featured video captured by the Bayfordbury Observatory in Hertfordshire, UK is a four-hour time-lapse showing Uranus with its four largest moons in tow: Titania, Oberon, Umbriel and Ariel. Uranus’ apparent motion past background stars is really dominated by Earth’s own orbital motion around our Sun. The cross seen centered on Uranus is called a diffraction spike and is caused by light diffracting around the four…

哈勃的行星状星云视图揭示了复杂的结构

哈勃的行星状星云视图揭示了复杂的结构

ByNASA中文

NGC 6891 is a bright, asymmetrical planetary nebula in the constellation Delphinus, the Dolphin. This Hubble image reveals a wealth of structure, including a spherical outer halo that is expanding faster than the inner nebula, and at least two ellipsoidal shells that are orientated differently. The image also reveals filaments and knots in the nebula’s interior, surrounding the central white dwarf star. From their motions, astronomers estimate that one of the shells is 4,800 years old while the outer halo is some 28,000 years old, indicating a series of outbursts from the dying star at different times. NGC 6891是一个明亮的、不对称的行星状星云，位于海豚座。这张哈勃图像揭示了丰富的结构，包括一个比内星云膨胀得更快的球形外晕，以及至少两个方向不同的椭球壳。这张照片还揭示了星云内部围绕中央白矮星的丝状和结状结构。根据他们的运动，天文学家估计其中一个椭球壳有4,800年的历史，而外晕大约有28,000年的历史，这表明垂死的恒星在不同的时间发生了一系列的爆发。 Hubble studied NGC 6891 as part of efforts to gauge the distances to nebulae, and to learn more about how their structures formed and evolved. NGC…

飞马LL星的不寻常螺旋结构

飞马LL星的不寻常螺旋结构

ByNASA中文

2021年11月29日 The Extraordinary Spiral in LL Pegasi Image Credit: NASA, ESA, Hubble, HLA; Processing & Copyright: Jonathan Lodge Explanation: What created the strange spiral structure on the upper left? No one is sure, although it is likely related to a star in a binary star system entering the planetary nebula phase, when its outer atmosphere is ejected. The huge spiral spans about a third of a light year across and, winding four or five complete turns, has a regularity that is without precedent. Given the expansion rate of the spiral gas, a new layer must appear about every 800 years, a close match to the time it takes for the two stars to orbit each other. The star system that created it is most commonly…

丘泽彗星的高耸悬崖

丘泽彗星的高耸悬崖

ByNASA中文

2021年11月28日 A High Cliff on Comet Churyumov-Gerasimenko Image Credit & Licence: ESA, Rosetta spacecraft, NAVCAM; Additional Processing: Stuart Atkinson Explanation: This high cliff occurs not on a planet, not on a moon, but on a comet. It was discovered to be part of the dark nucleus of Comet Churyumov-Gerasimenko (CG) by Rosetta, a robotic spacecraft launched by ESA that rendezvoused with the Sun-orbiting comet in 2014. The ragged cliff, as featured here, was imaged by Rosetta in 2014. Although towering about one kilometer high, the low surface gravity of Comet CG would likely make it an accessible climb — and even a jump from the cliff survivable. At the foot of the cliff is relatively smooth terrain dotted with boulders as large as 20 meters…

M101

M101

ByNASA中文

2021年11月27日 Messier 101 Image Credit: NASA, ESA, CFHT, NOAO; Acknowledgement – K.Kuntz (GSFC), F.Bresolin (U.Hawaii), J.Trauger (JPL), J.Mould (NOAO), Y.-H.Chu (U. Illinois) Explanation: Big, beautiful spiral galaxy M101 is one of the last entries in Charles Messier’s famous catalog, but definitely not one of the least. About 170,000 light-years across, this galaxy is enormous, almost twice the size of our own Milky Way. M101 was also one of the original spiral nebulae observed by Lord Rosse’s large 19th century telescope, the Leviathan of Parsontown. Assembled from 51 exposures recorded by the Hubble Space Telescope in the 20th and 21st centuries, with additional data from ground based telescopes, this mosaic spans about 40,000 light-years across the central region of M101 in one of the highest definition…

黑洞碰撞可能发生光爆炸

黑洞碰撞可能发生光爆炸

ByNASA中文

In a first, astronomers may have seen light from the merger of two black holes, providing opportunities to learn about these mysterious dark objects. 天文学家们首次看到了来自两个黑洞合并产生的光线，为了解这些神秘的黑暗物体提供了机会。 This artist’s concept shows a supermassive black hole surrounded by a disk of gas. Embedded in this disk are two smaller black holes that may have merged together to form a new black hole. 这幅艺术家的概念图展示了一个被气体盘包围的超大质量黑洞。在这个气体盘中嵌入了两个较小的黑洞，它们可能合并在一起形成了一个新的黑洞。 When two black holes spiral around each other and ultimately collide, they send out gravitational waves – ripples in space and time that can be detected with extremely sensitive instruments on Earth. Since black holes and black hole mergers are completely dark, these events are invisible to telescopes and other light-detecting instruments used by astronomers. However, theorists have come up with ideas about how a…

大折射镜与月食

大折射镜与月食

ByNASA中文

2021年11月26日 Great Refractor and Lunar Eclipse Image Credit & Copyright: Laurie Hatch Explanation: Rain clouds passed and the dome of the Lick Observatory’s 36 inch Great Refractor opened on November 19. The historic telescope was pointed toward a partially eclipsed Moon. Illuminated by dim red lighting to preserve an astronomer’s night vision, telescope controls, coordinate dials, and the refractor’s 57 foot long barrel were captured in this high dynamic range image. Visible beyond the foreshortened barrel and dome slit, growing brighter after its almost total eclipse phase, the lunar disk created a colorful halo through lingering clouds. From the open dome, the view of the clearing sky above includes the Pleiades star cluster about 5 degrees from Moon and Earth’s shadow. Notable APOD Submissions: Lunar…

在地球影子的边缘

在地球影子的边缘

ByNASA中文

2021年11月25日 At the Shadow’s Edge Image Credit & Copyright: Jean-Francois Gout Explanation: Shaped like a cone tapering into space, the Earth’s dark central shadow or umbra has a circular cross-section. It’s wider than the Moon at the distance of the Moon’s orbit though. But during the lunar eclipse of November 18/19, part of the Moon remained just outside the umbral shadow. The successive pictures in this composite of 5 images from that almost total lunar eclipse were taken over a period of about 1.5 hours. The series is aligned to trace part of the cross-section’s circular arc, with the central image at maximum eclipse. It shows a bright, thin sliver of the lunar disk still beyond the shadow’s curved edge. Of course, even within the…

哈勃见证了奔跑者星云中气体碰撞的冲击波

哈勃见证了奔跑者星云中气体碰撞的冲击波

ByNASA中文

Mounded, luminous clouds of gas and dust glow in this Hubble image of a Herbig-Haro object known as HH 45. Herbig-Haro objects are a rarely seen type of nebula that occurs when hot gas ejected by a newborn star collides with the gas and dust around it at hundreds of miles per second, creating bright shock waves. In this image, blue indicates ionized oxygen (O II) and purple shows ionized magnesium (Mg II). Researchers were particularly interested in these elements because they can be used to identify shocks and ionization fronts. 在这张哈勃拍摄的名为HH 45的赫比格-哈罗天体图像中，堆积的、发光的气体和尘埃云闪闪发光。赫比格-哈罗天体是一种罕见的星云，当新生恒星喷出的热气体以每秒数百英里的速度与周围的气体和尘埃碰撞，产生明亮的冲击波。在这张图片中，蓝色表示电离的氧（O II），紫色表示电离的镁（Mg II）。研究人员对这些元素特别感兴趣，因为它们可以用来识别冲击波和电离锋线。 This object is located in the nebula NGC 1977, which itself is part of a complex of three nebulae called The Running Man. NGC 1977 – like its companions NGC…

NASA、SpaceX发射DART：首次保卫地球的测试任务

NASA、SpaceX发射DART：首次保卫地球的测试任务

ByNASA中文

影像来源：NASA 美国东部时间周三凌晨1点21分，NASA的双小行星重定向测试（DART）由SpaceX猎鹰9号火箭在加利福尼亚州范登堡太空基地东四号航天发射中心发射，这是世界上首个全面测试保护地球免受小行星或彗星威胁技术的任务。 DART只是NASA更大的行星防御战略的一部分，它由位于马里兰州劳雷尔的约翰霍普金斯应用物理实验室（APL）建造和管理，DART将撞击一颗对地球没有威胁的已知小行星。它的目标是稍微改变该小行星的运动，其方式可以用地面望远镜准确测量。 DART将展示航天器可以自主导航到目标小行星并有意与其发生碰撞——一种称为动能撞击的偏转方法。该测试将提供重要数据，帮助更好地为可能对地球构成冲击危险的小行星做好准备。LICIACube是一颗由意大利航天局（ASI）提供的立方体卫星，与DART一起运行，将在DART撞击前发射，以捕捉撞击和由此产生的喷射物质云的图像。 在DART撞击大约四年后，欧洲航天局的Hera项目将对这两颗小行星进行详细的调查，特别关注DART撞击留下的陨石坑，并精确确定小行星Dimorphos的质量。 “DART正在把科幻小说变成科学事实，它证明了NASA为所有人的利益而进行的积极主动和创新。”NASA局长比尔·纳尔逊说。“除了NASA研究我们的宇宙和我们的地球的所有方法外，我们还致力于保护我们的家园，而这项测试将有助于证明一种可行的方法，如果发现有一颗危险的小行星朝向地球，可以保护我们的地球免受其害。” 凌晨2点17分，DART与火箭的二级分离。几分钟后，任务操作人员收到了第一个航天器遥测数据，并开始将航天器定向到一个安全的位置，以部署其太阳能电池阵列。大约两小时后，航天器成功地展开了它的两个28英尺长的太阳能电池阵列。它们将为航天器和NASA的进化型氙气推进器——商用离子发动机提供动力，这是正在DART上测试的若干技术之一，以便将来应用于太空任务。 “DART的核心是一项准备任务，它也是一项团结的任务。”位于华盛顿的NASA总部科学任务局副局长托马斯·左布臣说。“这项国际合作涉及DART、ASI的LICIACube、ESA的Hera调查和科学团队，它们将对这项开创性的太空任务采取后续行动。” DART的单程旅行是前往Didymos小行星系统，该系统包括一对小行星。DART的目标是小卫星Dimorphos，它的直径约为530英尺（160米）。这颗小卫星围绕着直径约为2560英尺（780米）的Didymos运行。 由于Dimorphos围绕Didymos运行的相对速度要比这对绕太阳运行的行星慢得多，因此在双星系统中DART的动力学影响比单个小行星围绕太阳运行轨道的变化更容易测量。 “我们还没有发现任何重大的小行星撞击地球的威胁，但我们继续寻找我们知道仍有相当大的群体有待发现。我们的目标是提前数年至数十年发现任何可能的撞击，这样就可以利用我们目前拥有的技术，像DART那样的能力来使它偏移。”NASA总部的行星防御官员林德利·约翰逊说。“DART是NASA工作的一个方面，目的是让地球做好准备，以防我们遇到小行星灾害。与此同时，我们正在准备近地物体测量任务，这是一个基于太空的红外望远镜，计划在本十年晚些时候发射，旨在加快我们发现和描述距离地球轨道3000万英里以内的潜在危险小行星和彗星的能力。” 该航天器将在2022年9月26日至10月1日之间拦截Didymos系统，故意以大约每秒4英里（每秒6公里）的速度撞向Dimorphos。科学家们估计，这种动力撞击将使Dimorphos围绕Didymos的轨道缩短几分钟。研究人员将使用地球上的望远镜精确测量这一变化。他们的结果将验证和改进科学的计算机模型，这些模型对于预测作为小行星偏转可靠方法的动力撞击的有效性至关重要。 “看到你在‘纸上的文字’阶段成为现实并发射到太空后所参与的事情，这是一种难以形容的感觉。”安迪·程说，他是约翰霍普金斯大学APL的DART调查负责人之一，也是提出DART想法的人。“这仅仅是第一幕的结束，DART的调查和工程团队在接下来的一年里还有很多工作要做，为主要的事件──DART对双态生物的动力学影响做准备。但今晚我们要庆祝！” DART的唯一仪器，Didymos侦察和小行星光学导航相机（DRACO），将在一周后启用，并提供航天器的第一批图像。DART在未来10个月内将继续在地球绕太阳运行的轨道之外运行，直到Didymos和Dimorphos离地球的距离为680万英里(1100万公里)。 一个复杂的制导、导航和控制系统，与称为小体机动自主实时导航（SMART Nav）的算法一起工作，将使DART航天器能够识别和区分这两颗小行星。然后，该系统会将航天器引导至 Dimorphos。这一过程将在撞击前大约一小时内发生。 约翰霍普金斯APL管理NASA行星防御协调办公室的DART任务，作为该机构行星任务计划办公室的一个项目。 NASA为该任务提供了多个中心的支持，包括南加州的喷气推进实验室、马里兰州格林贝尔特的戈达德太空飞行中心、休斯顿的约翰逊航天中心、克利夫兰的格伦研究中心和弗吉尼亚州汉普顿的兰利研究中心。此次发射由NASA的发射服务项目管理，该项目位于该机构位于佛罗里达州的肯尼迪航天中心。SpaceX是DART任务的发射服务提供商。 有关DART任务的更多信息，请访问： https://www.nasa.gov/dartmission 参考来源： https://www.nasa.gov/press-release/nasa-spacex-launch-dart-first-test-mission-to-defend-planet-earth