金星凌日

2012年6月6日，最值得期待的天文現象金星凌日即將精彩上演。金星凌日是一種極為罕見的天象，凌日時，地球、金星、太陽在一條直線上，從地球上可以看到金星像一個小黑點一樣在太陽表面緩慢移動。據悉，我國大部分地區都能觀測到這次凌日的全過程。如果錯過這一次，就要再等105年。你還猶豫什么？

The Travails1) of Le Gentil 勒讓蒂的辛勤探索

Imagine your country is sending you on a quest to resolve one of the era's biggest questions in science. At this moment in history， the solution， the technology， and the alignment2) of planets have come together. For your part of the mission， all you have to do is record the instant3) when the edge of one small circle touches the edge of a second larger circle.

Such were the fortunate circumstances of Guilliaume Hyacinthe Jean Baptiste Le Gentil. The French astronomer eagerly set sail for India to witness the 1761 transit of Venus， a rare celestial4) alignment in which the silhouette5) of Venus appears to pass directly across the Sun.

Upon Le Gentil's arrival， the intended destination was occupied by hostile English troops， so his ship turned back to sea， where he could not effectively use a telescope. He missed the 1761 transit of Venus. Committed to his task， Le Gentil hung around the Indian Ocean for eight years awaiting the next transit of Venus. He returned to India to view the 1769 transit of Venus， but on the morning of the transit a \"fatal cloud\" momentarily brought brief yet harsh6) weather to the normally placid7) region， and he missed it again! Le Gentil was numb8) with dejection9).

想象一下：國家派你去探索以解決這個時代最大的科學問題之一。在歷史上的這一時刻，(解決問題所需的)方案、技術和星球的排列都已齊備。而你在這次任務中所要完成的全部事情，就是在一個小圓的邊緣切入比它大的另一個圓的邊緣時，將這一瞬間記錄下來。

這正是吉亞姆· 亞森特·讓·巴蒂斯特·勒讓蒂當年所處的有利境況。這位法國天文學家迫不及待地揚帆前往印度，去見證1761年的金星凌日——一種罕見的天體排列現象。該現象出現時，金星的黑色輪廓似乎直接穿過太陽。

勒讓蒂到達印度時，原定的目的地已被敵對的英國軍隊所占領，他的船只好返回大海，可是望遠鏡在海上的觀測效果十分不理想。他錯過了1761年的金星凌日。一心想要完成使命的勒讓蒂在印度洋上漂泊了八年，等待下一次金星凌日的出現。1769年，他返回印度觀測這一年的金星凌日，可是就在凌日的那天早上，通常都很寧靜的天空突然冒出一片“要命的烏云”，轉瞬之間陰云遍布、天昏地暗，時間雖短卻讓他又一次錯過了時機！勒讓蒂絕望到了極點！

Centuries of Intrigue10) 數百年的吸引力

Transits of Venus occur in pairs eight years apart， with a span of more than a century between each pair. The telescope was in its infancy for the pair of transits prior to Le Gentil's effort. In the early years of the 17th century， Johannes Kepler showed the relationship between a planet's orbital period and its distance from the Sun. Kepler then derived tables of unprecedented11) accuracy that predicted the motions of the planets， including transits of Venus in 1631 and 1639. Poring12) over one such table， the young English astronomer Jeremiah Horrocks caught one of Kepler's mistakes within weeks of the 1639 transit of Venus and mathematically predicted its imminent13) appearance. Horrocks projected14) an image of the 1639 transit of Venus and noted the planet's size and path—the first time in recorded history.

What surprised Horrocks' contemporaries15) most was how small Venus appeared relative to the Sun. Rather than being a disappointment， though， this size discrepancy16) should be recognized as a stunning visual comparison. A planet the size of Earth， Venus' diminutive17) profile highlights the immensity of the distant Sun， which could hold the volume of a million Earths!

Mathematics served science well when Edmond Halley announced one could quantify the distance to the Sun merely by having observers from widely separated locations time the duration of the transit of Venus， which Halley would not live to see. For Venus to slice across the Sun takes about 6 hours， and observers needed to time that event to the second.

金星凌日以兩次凌日為一組，每次間隔八年，而每兩組之間的間隔卻長達一百多年。在勒讓蒂觀察之前的那組金星凌日發生之時，望遠鏡的發展還處于初期。17世紀初期，約翰尼斯·開普勒描述了行星的軌道運行周期及其與太陽之間的距離的關系。在此基礎上，開普勒得出了一些空前準確的數據表，預測了各個行星的運動，其中就包括1631年和1639年的金星凌日。一位年輕的英國天文學家杰里邁亞·霍羅克斯在仔細研究了其中一個表格后，發現了開普勒的一個錯誤，這時距1639年的金星凌日僅有數周的時間，他利用數學運算預測到了凌日的逼近。霍羅克斯用投影法繪制了一幅1639年金星凌日的圖像，并標明了金星的大小和運行軌跡——這是有史記載以來的第一次。

最令霍羅克斯同時代的人感到驚訝的是，金星相對太陽竟顯得那么渺小。然而，這種體積上的差異不應成為人們失望的理由，反而應當被人們視為一種絕妙的直觀比較。金星的大小和地球差不多，金星輪廓的渺小更加反襯出遙遠的太陽的巨大——太陽的體積相當于一百萬個地球那么大。

數學對科學有著很好的作用，埃德蒙·哈雷就曾宣布只需用一個辦法就可以計算出地球到太陽的距離，那就是在廣泛分布的地點讓不同的觀測者測定金星凌日的持續時間，而這卻是哈雷在世無法看到的。因為金星劃過太陽需要大約六個小時，而觀測者需要將這一時間測定精確到秒(編注：這在當時是無法做到的)。

Black Drop Effect 黑滴效應

Unfortunately， the limitations of the telescopes and other factors gave rise to a hindrance18) called the \"black drop effect\". When the edge of Venus appears just about to touch the inside edge of the Sun， an annoying ligament19) suddenly appears between the well-defined edges. This distortion20) confounded21) the accurate timing of the transit by a few seconds， and Halley's vision of accuracy plummeted22). The effect can be simulated by holding your nearly-pinched thumb and index finger together in front of a bright light. Before they touch， a dark meniscus23) seemingly joins the two digits.

When the 19th century pair of transits rolled around24)， astronomers hoped the new tools of photography could help them to discern25) the exact instant of internal contact， which had been plagued26) previously by the black drop effect. Jules Janssen developed a \"photographic revolver\"， a precursor27) to motion picture cameras， which captured a series of images near the critical moment. Again， ambitious expeditions set out to far-flung28) locales to await and to time the duration of the 1874 and 1882 transits of Venus. Alas， photography proved to have its limitations as well， and the accuracy in practice was again not what Halley had suggested was achievable.

In ensuing29) decades， developments like radar helped astronomers refine the true distance to Venus， and the transit method became a historical artifact. Nonetheless， the 2004 transit of Venus piqued30) the world's curiosity， and for the first time spacecraft could peer at the celestial phenomenon with unprecedented clarity.

遺憾的是，望遠鏡的局限和其他因素導致了一個(測定準確時間的)障礙——“黑滴效應”。當金星邊緣即將碰觸到太陽內緣時，原本清晰的邊緣中間會突然出現一道討厭的韌帶狀黑暈。這一扭曲現象會給金星凌日的準確計時帶來幾秒的誤差，這樣一來，哈雷所預見的精確性就大打折扣了。這種效應可被模擬呈現，你只需將大拇指和食指在強光前似觸非觸地接觸，在這兩根手指碰觸到之前，一道黑色的彎月狀光暈似乎已將二者連接起來。

當19世紀的這組凌日如期發生時，天文學家們希望新的照相儀器能夠幫助他們看清凌日內切的精確瞬間，在此之前，這個問題一直深受黑滴效應的困擾。朱爾斯·詹森研制出一種“照相旋轉裝置”——這應該算是電影攝像機的前身吧——用來捕捉凌日內切前后的一系列圖像。于是，雄心勃勃的探索再次開始了，人們前往眾多相隔遙遠、四處分散的觀測點，等待著1874和1882年這組金星凌日的到來，以測定其精確的持續時間。遺憾的是，事實證明照相技術也有其局限性，實踐中的數據精確性再次沒能達到哈雷設想能達到的那種精確性。

在之后的幾十年時間里，雷達之類的技術發展使得天文學家們能夠修正地球與金星距離的確切數值，凌日測距法已成為歷史產物。然而，2004年的金星凌日仍然激起了全世界人們的好奇心，人類第一次可以通過宇宙飛船以前所未有的清晰度觀看這一天文奇觀。

The Future of Transits 金星凌日的前景

While transits of Venus were historically significant， today the spectacle illustrates how astronomers seek to answer one of the biggest questions in modern science: Are there distant worlds capable of sustaining life? A transit of Venus illustrates the method by which astronomers are now searching for planets in the \"habitable zone\" around distant stars. Here on Earth we have a front row seat to a planetary transit on June 5~6， 2012. As we watch the planet Venus pass across the face of the Sun， the Sun's total brightness dips31) by a fraction of a percent. The decrease is not perceptible to the human eye， but it is certainly measurable by sensitive instruments. NASA's Kepler Mission is looking at over 150，000 distant stars simultaneously to detect periodic yet discrete32) dips in stellar brightness， which hint at the presence of companion planets transiting their host stars. Early results from the Kepler Mission suggest there may be over 50 billion planets in the Milky Way， of which 500 million would reside in the so-called habitable zone. A new quest using the transit method has just begun.

在歷史上，金星凌日曾有其重要意義，而在今天，這一奇觀仍能幫助天文學家嘗試解決現代科學中的一個重大問題：有沒有適合生命生存的遙遠世界？金星凌日可以詮釋天文學家們現在是運用何種方法在遙遠的恒星周圍的“可居住帶”尋找行星的。2012年6月5日至6日，我們在地球上就可以坐在前排有利位置觀看一場行星凌日的演出。當我們看著金星緩緩穿過太陽表面，太陽的整體亮度就會減弱極小一點兒。這種亮度減弱是人的肉眼所看不到的，但通過精密儀器肯定是可以測出的。美國宇航局的開普勒計劃同時在觀測超過十五萬顆遙遠的恒星，以探測恒星亮度定期卻又短暫的減弱，這種減弱說明正有行星穿過其恒星。開普勒計劃早期監測到的結果表明，在銀河系中可能存在五百多億顆行星，其中有五億顆可能位于所謂的可居住帶。一種運用凌日測距法而進行的新的探索才剛剛開始。

Participate in 2012 Transit of Venus 觀測2012年的金星凌日

The last transit of Venus in our lifetimes occurs June 5~6， 2012， with the date and time dependent on your location. With some preparation， you can safely witness the 2012 transit of Venus yourself.

Popular \"eclipse shades\" are useful， but because the one-arc33) minute diameter of Venus is near the limit of the human eye's capability， the best views will be filtered and magnified. Experienced observers can use solar filters over the large， front end of their telescopes， or project an image onto a surface. A rear screen projection is a favored viewing technique， allowing a group of people to gather around the projected image while enclosing the path of the Sun's rays. Be safe， but seize the opportunity.

Unlike Le Gentil， a \"fatal cloud\" should not doom you. The beleaguered34) astronomer would have marveled at the capacity of our population to rally around his longtime objective， regardless of weather. If inclement35) weather occurs， or if you are in the zone where the transit is not visible， you can watch webcasts of the 2012 transit of Venus broadcast live from atop the Big Island of Hawaii.

The 2012 transit of Venus is also an opportunity to celebrate the Sun and marvel at its magnificence. During the preceding several years the Sun has been at a low point in its 11-year cycle of activity. However， as it rises from the depth of visual dullness， you will likely be able to see through filtered telescopes some emerging solar features like sunspots36).

As the 2012 transit of Venus concludes， envision how the 2117 and 2125 pair of transits might differ from our seemingly modern events. What new inventions or unforeseeable changes in world culture will transform the 22nd century experience? We will have to wait 105 years to find out， which is more incentive not to miss this last transit of Venus in our lifetimes.

我們這一生所能見到的最后一次金星凌日發生在2012年6月5日至6日，具體日期和時間取決于你所處的地理位置。做點兒準備，你就可以親眼安全觀測到2012年的金星凌日。

常用的“觀測日食的減光裝置”都可以使用，但由于金星1弧分的視直徑(編注：1弧分是1弧度的60分之一)已幾乎接近人類視力的極限，必須經過過濾和放大方可得到最佳觀測結果。有經驗的觀測者可在望遠鏡較大的前端放置陽光過濾裝置，或者將圖像投射到一個平面上。使用背投式投影是一種很好的觀測方法，它可以使一群人圍在一起觀看投射的影像而又能遮擋太陽光線。(觀測時)既要注意安全，又要抓住時機。

和勒讓蒂不同的是，現在即使有一片“要命的烏云”也不會讓你有扼腕嘆息之感。如果那位倒霉的天文學家看到我們那么多人能夠聚集在一起無視天氣狀況也能觀看他長期期待的目標，肯定會驚嘆不已。如果遭遇惡劣天氣或者身處觀測不到凌日的區域，你還可以觀看從夏威夷大海島上空發出的2012年金星凌日的網絡現場直播。

2012年的金星凌日也是一個禮贊太陽、仰慕太陽光輝的大好時機。在先前的幾年時間里，太陽一直處于其11年活動周期的低點。然而，一旦它從視覺疲勞的深淵中升起，你就會通過過濾的望遠鏡觀測到諸如太陽黑子之類的新出現的太陽特征。

在2012年金星凌日結束之時，可以設想一下2117和2125年那組凌日將會和我們目前看似比較現代的事件有何不同。又有什么新發明或者什么無法預見的世界文化變革將會改變人類22世紀的凌日體驗呢？我們將不得不等待105年才可以揭曉答案，這也更加促使我們不要錯過我們今生最后一次的金星凌日。

1.travail [#712;traelig;ve#618;l] n. 艱苦勞動，辛勤努力

2. alignment [#601;#712;la#618;nm#601;nt] n. 成一直線；直線排列；隊列

3.instant [#712;#618;nst#601;nt] n. 瞬息，頃刻，剎那；(某一)時刻

4.celestial [s#601;#712;lesti#601;l] adj. 天的，天空的，天上的

5.silhouette [#716;s#618;lu#712;et] n. (淺色背景上的)黑色輪廓像

6.harsh [hɑ#720;#643;] adj. 嚴酷的，嚴峻的

7.placid [#712;plaelig;s#618;d] adj. 寧靜的，平靜的

8.numb [n#652;m] adj. 麻木的；失去感情的

9.dejection [d#618;#712;d#658;ek#643;n] n. 沮喪，情緒低落，泄氣

10.intrigue [#618;n#712;tri#720;ɡ] n. 吸引力

11.unprecedented [#652;n#712;pres#618;dent#618;d] adj. 無前例的，空前的，前所未聞的；絕無僅有的

12.pore [p#596;#720;(r)] vi. 專心閱讀；鉆研(over)

13.imminent [#712;#618;m#618;n#601;nt] adj. 臨近的；即將發生的；逼近的

14.project [pr#601;#712;d#658;ekt] vt. 作……的投影線(或圖)；用投影法制作(地圖、天體圖等)

15.contemporary [k#601;n#712;tempr#601;ri] n. 同時代的人；(幾乎)同年齡的人

16.discrepancy [d#618;s#712;krep#601;nsi] n. 差異，不符合，不一致

17.diminutive [d#618;#712;m#618;nj#601;t#618;v] adj. 極小的，小型的，超常微小的

18.hindrance [#712;h#618;ndr#601;ns] n. 起妨礙作用的人(或事物)；阻礙者；障礙物

19.ligament [#712;l#618;ɡ#601;m#601;nt] n. 維系物，聯結物，紐帶

20.distortion [d#618;#712;st#596;#720;#643;n] n. 扭歪，扭曲，變形

21.confound [k#601;n#712;fa#650;nd] vt. 混淆

22.plummet [#712;pl#652;m#618;t] vi. (價格、水平等)驟然下跌，徒然變差

23.meniscus [m#601;#712;n#618;sk#601;s] n. 彎月形物，新月形物

24.roll around: 規律發生

25.discern [d#618;#712;s#604;#720;n] vt. 識別，區別

26.plague [ple#618;ɡ] vt. <口> 使煩擾，困擾

27.precursor [pri#720;#712;k#604;#720;s#601;(r)] n. (從中產生變化的)產物母體，前身，前體

28.far-flung: 分布廣的；覆蓋面大的；遙遠的

29.ensue [#618;n#712;sju#720;] vi. 接著發生

30.pique [pi#720;k] vt. 激起，引起(好奇心或興趣)

31.dip [d#618;p] vi. 下降；(尤指短暫或小幅度地)減少

32.discrete [d#618;#712;skri#720;t] adj. 分離的，互不連接的；不相關聯的

33.arc [ɑ#720;k] n. 弧

34.beleaguered [b#618;#712;li#720;ɡ#601;d] adj. 身陷困境的

35.inclement [#618;n#712;klem#601;nt] adj. 險惡的；嚴寒的；狂風暴雨的

36.sunspot [#712;s#652;nsp#594;t] n. 【天】(太陽)黑子