约翰·弗朗茨·恩克Johann Franz Encke

约翰·弗朗茨·恩克的父亲是恩克Michael Encke（1749-1795），汉堡雅各比教堂（圣雅各教堂）的路德宗牧师。他的祖父格奥尔格Friedrich Encke也曾在不来梅附近的阿尔特卢讷贝格担任牧师。他的母亲玛丽·米斯勒（1755-1811）是公务员恩克戈特弗里德·米斯勒和Maria Schramm的女儿。玛丽和恩克Michael Encke共育有九个孩子，三个女儿和六个儿子（尽管一个儿子出生后不久便夭折）。本传记的主人公恩克是倒数第二小的。他最小的弟弟奥古斯特（1794-1860）后来成为普鲁士军队的中将和炮兵总监。

恩克的父亲在他还年幼时就去世了，当时刚被任命为会吏长不久。然而，多亏一位名叫Hipp的学校教师无偿资助他，他才得以继续学业。得益于这位教师的经济支持，恩克于1808年进入汉堡的约翰内乌姆著名学术学校就读中学[12]：-

在这所学校，当时由Johannes Gurlitt（1754-1827）担任校长，他因古典学问而享有盛誉，这位少年学生进步迅速，除了在拉丁文写作方面有相当的能力外，他的希腊文知识足以让他翻译并欣赏品达的抒情诗。

两年后他完成了课程，成为学校最优秀的学生之一。恩克的母亲Marie生病了，所以他最初想成为一名医生。不幸的是，他的母亲在他能进入大学之前就去世了，因此，在Hipp的建议下，恩克决定继续攻读数学。

1811年10月6日，他进入哥廷根大学，师从卡尔·弗里德里希·高斯。卡尔·弗里德里希·高斯对恩克在天文观测方面的才能印象深刻，并试图让他到奥芬（布达的另一个名称，不是布达佩斯的一部分）的一个小天文台担任助手。然而，战争中断了恩克的学业，1813年3月，他入伍对抗拿破仑。他成为一名炮手，最终在汉萨军团中晋升为军士长。他参加了格尔德森林战役（1813年9月18日），此役以法军战败告终。恩克于1814年7月退伍并重返学业，但1816年3月拿破仑从厄尔巴岛逃脱时，他的学业再次中断。这一次，他作为普鲁士军队的炮兵中尉被派往荷兰，但他的部队从未参加滑铁卢战役。

当他回到哥廷根时，奥芬的职位已不再空缺，因此他转而于1816年7月在哥达附近的泽贝格天文台担任助手。卡尔·弗里德里希·高斯不仅支持他申请该职位，而且恩克在服兵役期间就已结识了天文台台长伯恩哈德·冯·林德瑙（1780-1854）。1817年2月，当冯·林德瑙重返政界时，他实际上已成为天文台的台长，尽管名义上不是。1822年，他获得了正式头衔。恩克将时间投入到天文观测以及彗星和小行星轨道的计算中。这为他赢得了一个奖项，也赢得了卡尔·弗里德里希·高斯和弗里德里希·威廉·贝塞尔的认可。

在泽贝格期间，恩克利用1761年和1769年金星凌日的记录，以惊人的精度推导出了太阳视差。恩克在1835年给出的8.571"的值被接受了一些年，但到1860年，被接受的值变成了8.95"。事实上，现在的值是8.8"。他最著名的是以他的名字命名了恩克彗星。这颗彗星不是他自己发现的，而是由Jean-Louis Pons在1818年发现的。事实上，恩克总是称它为Pons彗星。恩克在1818年12月观测到了它，并在1819年1月计算了它的轨道。他发现它是椭圆形的，周期异常短，约为3.6年。恩克将这颗彗星与皮埃尔·梅尚（1786年）、卡罗琳·赫歇尔（1795年）和Pons（1805年）观测到的彗星认定为同一颗。他成功预测了它在1822年的回归。由于他对这颗彗星的研究，他于1824年从皇家天文学会获得了他的第一枚金质奖章（Pons也在同年获得了一枚银质奖章）。让我们注意到，查尔斯·巴贝奇也在1824年从皇家天文学会获得了一枚金质奖章。由于这颗彗星的周期很短，恩克能够多次观测到它。他注意到彗星的周期每次都会稳定减少约三个小时。为了解释这一现象，他提出了存在一种阻力介质——以太——充满行星际空间的理论。当Charles Pritchard撰写恩克的讣告[12]时，恩克对周期减少的错误解释仍然被接受。

1823年，他与Amalie Wilhelmine Becker（1787-1879）结婚，她是Gotha的一位书商、作家和出版商Rudolf Zacharias Becker（1759-1822）的女儿。他们有五个孩子，三个儿子和两个女儿，包括Bertha Henriette 恩克；Heinrich August Encke；Johann Hermann 恩克和Sophie Marie Blase。其中一个儿子后来成为了一名牧师，就像恩克的父亲和祖父一样。

1825年10月11日，在弗里德里希·威廉·贝塞尔的强烈推荐下，他成为了柏林天文台的台长。凭借柏林天文台的台长职位，他当选为柏林科学院的成员，并获得了柏林大学的荣誉博士学位。这很重要，因为战争使他无法在哥廷根毕业。考虑到柏林的天文台不够完善，恩克决定搬到一个新建筑，配备更好的仪器（包括一台大型Fraunhofer折射望远镜）。尽管恩克在就职时被承诺会有一个新的天文台，但如果不是Alexander von Humboldt在1828年向国王Frederick William III呼吁援助，这个承诺不会这么快实现。建设于1832年开始，三年后完成。这座建筑将一直使用到两代人之后，当雅各布·赫尔曼 Struve（1854-1920）在1913年将天文台迁至Babelsberg，距离市中心更远（25公里）。

恩克负责Astronomisches Jahrbuch（天文年历），该年历由其前任恩克 Elert Bode创办，他编辑了五十年。在Bode的领导下，它主要包含星历表，但也有文章和发现公告。恩克致力于改进该出版物：他删除了公告，保留了文章（其中许多是他自己写的），并彻底改进了星历表。在恩克的指导下，Astronomisches Jahrbuch被认为拥有欧洲最好的星历表，并引发了类似出版物如英国Nautical Almanac的许多改革。Royal Astronomical Society认可了恩克的努力，并于1830年授予他第二枚金质奖章。在颁奖仪式上，Royal Astronomical Society的主席Sir James South说：-

[《航海天文年历》应]，像凤凰一样从灰烬中升起，比恩克的[《天文年历》]优越得多，正如恩克的现在比它优越一样。

这句话有点晦涩，因此我们也引用[12]中的内容，其中对此进行了澄清：-

就当今的天文学家而言，恩克可能因其对《柏林星历表》所做的巨大改进而受到最高评价。天文星历表的历史颇为多样和奇特；在皇家天文学会的《回忆录》第四卷中，当学会理事会通过其主席向恩克颁发金质奖章，以表彰他在改进《柏林星历表》中所起的作用时，可以找到对此的简要叙述。我们自己的《航海天文年历》，在当时，即1830年，已经落后或大大落后于天文学家的需求；但在谈到外国星历表的优点时，理事会的报告如下：“已投票授予恩克教授金质奖章，以表彰其卓越的《柏林星历表》。详述这部著名著作的优点将是多余的，它远远超越所有竞争对手，必须被视为唯一一部与当前科学需求相称的星历表。”在颁发奖章时，主席Sir James South补充说：“有了《柏林星历表》，天文台几乎不需要任何一本书；没有它，则需要每一本书。”然而，如果不补充说，刚刚关于1830年《柏林星历表》所说的话，同样可以真实地用于1834年至今的《航海天文年历》，那将是不忠实的，尽管在其他方面可能没有必要；尽管如此，最初的推动来自恩克和柏林。

恩克参与了海王星的发现。他最初反对使用望远镜搜索海王星，但最终允许他的两名学生恩克 Gottfried Galle和Heinrich d'Arrest进行搜索，使用恩克在1830年至1859年间印刷的夜空图。海王星在1846年恩克55岁生日前夕的午夜前被发现。恩克被从生日聚会上叫出来确认这一发现，成为第三个看到海王星的人，至少知道自己在看什么。作为台长，恩克将这一发现通报给了Astronomisches Nachrichten（天文新闻）。恩克在这份通知中没有提到d'Arrest，他后来在生活中为此感到后悔。

通过观测，他在 1837 年发现了土星外环中的 恩克 环缝（或 恩克 缝）。1838 年，他成为军事学院研究委员会的成员，并于 1844 年获得柏林大学天文学教授的称号。1846 年，他成为历法委员会的成员。多年来，他当选为许多外国科学院院士。恩克 还在 1851 年推导出一种计算小行星轨道摄动的方法，这比 卡尔·弗里德里希·高斯 以前的方法更为方便。

为了了解恩克的性格，我们引用[12]中的话：-

恩克在柏林担任教授的四十年代里，将自己的心智形态和倾向印刻在许多学生身上，这些学生为天文学知识的进步做出了卓越贡献。没有什么比学生对他赞誉有加、充满爱戴更能证明一位教师的真正价值了。他们既看到他的弱点，也看到他的长处。恩克的情况正是如此。他们一致而坚定地证明他极其坦率和真诚；他们说，他工作不懈，娱乐极少；他举止朴素，所有习惯都有节制。他对助手和协作者要求严格，但为自己树立了更严格的榜样。这样一个人，全神贯注于工作，与外界隔绝，有时可能说话唐突、简短，甚至不慎；这些言论，由于直率或真实，偶尔会冒犯他人，使恩克陷入麻烦。然而，随着年岁增长，他的举止变得更加温和，言辞更加柔和；在他了解和信任的人面前，这位老人有时会回顾自己的一生，并敦促他喜爱的学生从他的经验中吸取节制和自律的教训，无论是在评判他人的工作方面，还是在他们认为自己有责任要求自己完成的工作量方面。

1859年11月，他中风了。这次中风较轻，但在1863年2月第二次更严重的中风后，他决定退休。他与一个女儿和妻子搬到了柏林附近的施潘道。威廉·朱利叶斯·福斯特于1865年接替他担任天文台台长。恩克于同年去世，享年七十四岁。

关于查尔斯·普里查德为恩克所写讣告的版本[12]，见THIS LINK。

Johann Franz Encke's father was Johann Michael Encke (1749-1795), a Lutheran clergyman at the Jacobikirche (St James church) in Hamburg. His grandfather, Georg Friedrich Encke, had also been a pastor, in Altluneberg, near Bremen. His mother Marie Misler (1755-1811), was the daughter of Johann Gottfried Misler, a civil servant, and Maria Schramm. Marie and Johann Michael Encke had nine children together, three daughters and six sons (though one son died soon after birth). Encke, the subject of this biography, was the second youngest. His youngest brother, August (1794-1860), became Lieutenant General and Inspector of Artillery for the Prussian military.

Encke's father died when he was still young, shortly after having been made an archdeacon. He managed to continue his studies, however, thanks to a schoolteacher named Hipp, who supported him without accepting any payment. Thanks to his financial support, Encke was able to attend secondary school in Hamburg in the prestigious Academic School of the Johanneum in 1808 [12]:-

At this College, then under the directorship of Johannes Gurlitt (1754-1827), who enjoyed a high reputation for classical learning, the boy-student rapidly advanced, and in addition to considerable ability in Latin composition, his knowledge of Greek was sufficient to enable him to translate and enjoy the Lyrics of Pindar.

He completed the course two years later, standing out as one of the best students in the school. Encke's mother Marie was sick, so he initially wanted to become a doctor. Tragically, his mother died before he could enter university, so, under Hipp's advice, Encke decided to pursue further studies in mathematics.

On 6 October 1811, he enrolled in Göttingen University to study under Carl Friedrich Gauss. Gauss was impressed with Encke's talents in astronomical observation and tried to have him work as an assistant in a small observatory in Ofen (another name for Buda, not part of Budapest). However, war interrupted Encke's studies and, in March 1813, he enlisted to fight against Napoleon. He became a gunner, and eventually reached the rank of sergeant major, in the Hanseatic Legion. He fought in the battle of Göhrde forest (18 September 1813), which resulted in a defeat for the French forces. Encke was discharged in July 1814 and returned to his studies, but he was again interrupted in March 1816, when Napoleon escaped from the island of Elba. This time as a lieutenant of artillery in the Prussian army, he was dispatched to the Netherlands but his unit never participated in Waterloo.

When he came back to Göttingen, the position at Ofen was no longer available, so he instead went to work as an assistant at Seeberg Observatory, near Gotha, in July 1816. Not only did Gauss support his application for the position, but Encke had met the director of the observatory, Bernhrd von Lindenau (1780-1854), during his time in military service. In February 1817, when von Lindeau returned to politics, he became director of the observatory in all but name. He obtained the formal title in 1822. Encke dedicated his time to astronomical observations and the computation of orbits of comets and minor planets. This earned him a prize, but also the recognition of both Gauss and Friedrich Wilhelm Bessel.

During his time in Seeberg, Encke used the records of the transits of Venus (from 1761 and 1769) to derive the solar parallax with surprising accuracy. Encke's value of 8.571", given in 1835, was accepted for some years but by 1860 the accepted value became 8.95". In fact the present value is 8.8". He is most famous for giving his name to Encke's comet. The comet was not discovered by himself, but by Jean-Louis Pons in 1818. In fact, Encke always referred to it as Pons's comet. Encke observed it in December 1818 and computed its orbit in January 1819. He found it to be elliptical with an extraordinarily short period of about 3.6 years. Encke identified the comet with the ones observed by Pierre François-André Méchain (1786), Caroline Herschel (1795) and Pons (1805). He successfully predicted its return in 1822. For his work on the comet he received his first Gold Medal from the Royal Astronomical Society in 1824 (Pons also received a silver medal in the same year). Let us note that Charles Babbage also received a Gold Medal from the Royal Astronomical Society in 1824. Because of the comet's short period, Encke was able to observe it a number of times. He noticed the comet's period suffered a steady decrease of about three hours each time. To explain this phenomenon, he theorised about the existence of a resisting medium, an ether, which filled interplanetary space. When Charles Pritchard wrote Encke's obituary [12], Encke's incorrect explanation for the decrease in period was still accepted.

In 1823, he married Amalie Wilhelmine Becker (1787-1879), the daughter of a bookseller, writer and publisher in Gotha named Rudolf Zacharias Becker (1759-1822). They had five children, three sons and two daughters, including Bertha Henriette Encke; Heinrich August Encke; Johann Hermann Encke and Sophie Marie Blase. One of the sons would later become a clergyman, like Encke's father and grandfather had been.

On 11 October 1825, he became the director of the Berlin observatory following a strong recommendation from Wilhelm Bessel. Berlin with the directorship, he was elected a member of the Berlin Academy of Sciences and received an honorary doctorate from the University of Berlin. This was significant since the war had stopped him from graduating at Göttingen. Considering the observatory in Berlin to be inadequate, Encke decided to move to a new building, equipped with better instruments (including a large Fraunhofer refractor). Though Encke had been promised a new observatory when he took office, the promise would have not been realised so soon were it not for Alexander von Humboldt, who in 1828 appealed for aid to King Frederick William III. The construction started in 1832 and finished three years later. The building would be in use until two generations later, when Hermann Struve (1854-1920) moved the observatory to Babelsberg in 1913, further away (25 km) from the city centre.

Encke was in charge of the Astronomisches Jahrbuch (Astronomical Yearbook), founded by his predecessor, Johann Elert Bode, who edited it for fifty years. Under Bode, it had contained mostly ephemerides, but also articles and announcements of discoveries. Encke worked to improve the publication: he dropped the announcements, kept the articles (writing many of them himself) and radically improved the ephemerides. The Astronomisches Jahrbuch was, under Encke's direction, considered to have the best ephemerides in Europe, and was the cause of many reforms in similar publications like the British Nautical Almanac. The Royal Astronomical Society recognised Encke's efforts and gave him a second Gold Medal in 1830. In the ceremony, the President of the Royal Astronomical Society, Sir James South, said:-

[The Nautical Almanac should], rising, like a phoenix, from its ashes, be as much superior to Encke's [Astronomisches Jahrbuch] as Encke's is now superior to it.

This quote is a little obscure, so we also quote from [12] where things are clarified:-

By astronomers of the present day it is possible that Encke may be most highly estimated for the vast improvements which he introduced into the Berlin Ephemeris. The history of astronomical ephemerides is not a little varied and curious; a concise account of it will be found in the fourth volume of the 'Memoirs' of the Royal Astronomical Society, on the occasion of the council of the Society presenting Encke, through their President, with a gold medal, for the part which he had taken in the improvement of the Berlin Ephemeris. Our own 'Nautical Almanac', at that day, viz. in 1830, had fallen or had remained greatly behind the requirements of astronomers; but in speaking of the merits of the foreign Ephemeris, the report of the Council runs as follows: ''A gold medal has been voted to Professor Encke for the superb 'Ephemeris of Berlin'. It would be superfluous to dwell upon the merits of this well-known work, which, far outstripping all rivalry, must be considered as the only Ephemeris on a level with the present wants of the sciences." On presenting the medal, Sir James South, the President, adds, "With the 'Berlin Ephemeris', an observatory scarcely wants a single book; without it, every one." It would, however, be disloyal, though in any other aspect it may be needless, not to add that what has just been said of the Berlin Ephemeris of 1830, may with equal truth be predicated of the 'Nautical Almanacs' from 1834 to the present date; nevertheless the first impulse came from Encke and Berlin.

Encke was involved in the discovery of the planet Neptune. He initially opposed the use of the telescope for the search of Neptune, but he eventually gave permission to Johann Gottfried Galle and Heinrich d'Arrest, two of his students, to carry it out, using a chart of the night sky printed by Encke between 1830 and 1859. Neptune was found just before midnight on Encke's 55th birthday, in 1846. Encke was taken out of his birthday party to confirm the discovery and became the third person to see Neptune, at least knowing what he was looking at. As Director, Encke communicated the discovery to Astronomisches Nachrichten (Astronomical News). Encke did not mention d'Arrest in this notice, something he would come to regret later in life.

Through observations, in 1837, he found Encke's division (or Encke's gap) in the outer ring of Saturn. In 1838, he became a member of the Board of Studies of the Military College, and in 1844, he earned the title of Professor of Astronomy at the University of Berlin. In 1846, he became a member of a Calendar Commission. Over the years, he was elected to many foreign academies. Encke also derived a method to calculate perturbations on the orbits of minor planets in 1851, which was more convenient than Gauss's previous method.

For a look at Encke's character we quote from [12]:-

Encke, during the forty years of his professorship at Berlin, impressed the form and bent of his mind upon many pupils, who have ably contributed their share in the progress of astronomical knowledge. There is no greater proof of the real worth of a teacher, than when his pupils speak well and lovingly of him. They see the man in his weakness and in his strength. So it fared with Encke. They bear strong and uniform testimony to his eminent frankness and truthfulness; his labours, they say, were incessant, his recreations few; he was simple in his manners, and in all his habits temperate. Towards his coadjutors and assistants he showed a severe judgment, but he set them a severer example. A man such as this, absorbed in his work, and shutting himself away from the outer world, was likely to be sometimes abrupt, or laconic, or even incautious, in his utterances; these utterances, from their bluntness or their truthfulness, occasionally gave offence, and involved Encke in trouble. As age, however, grew upon him he became more gentle in his manners, and softer in his address; and in the presence of those whom he knew and trusted, the old man would sometimes review his own life, and urge his favourite pupils to draw from his own experience lessons of moderation and self-restraint, both in passing their judgments on the labours of others, and in the amount of labour which they felt it their duty to exact from themselves.

In November 1859, he suffered a stroke. It was minor, but after a second, more serious, one in February 1863 he decided to retire. He moved to Spandau, near Berlin, with one of his daughters and his wife. Wilhelm Julius Foerster succeeded him as director of the Observatory in 1865. Encke died that same year, at the age of seventy-four.

For a version of Charles Pritchard's obituary of Encke [12], see THIS LINK.