神奇的“天眼”

羅崟丹

在中國的神話傳說中，二郎神的天眼可觀十方。但我們是凡人，沒有天眼，卻仍然想著可以窺天。

時光倒回到多年之前，一個夏天的傍晚，風(fēng)輕輕吹過，高高的樹上蟬鳴聲此起被伏。隨著晚霞褪盡，天色暗了下來，各家各戶的餐桌上飄散著飯菜的香氣。但最吸引孩子們的不是吃什么，而是飯后的娛樂活動。匆匆吃過幾口飯之后，孩子們便圍坐在一個四四方方的“小盒子”前，急切地等待那里傳出期盼的聲音和畫面。

知道他們在做什么嗎？在看電視。人們需要在一個類似鍋蓋的東西的幫助下，將遠(yuǎn)方的電視信號傳輸?shù)诫娨暀C(jī)上，才可以看到模糊的畫面，還需要時不時地調(diào)整一下“鍋蓋”的方向，這樣才不會出現(xiàn)時斷時續(xù)的“雪花”影響人們觀看。這個酷似鍋蓋的東西擁有一個在當(dāng)時很時髦的名字——“衛(wèi)星鍋”，也被大家親切地稱為“天線鍋蓋”，實(shí)際上它就是一個衛(wèi)星信號接收器。

衛(wèi)星信號接收器通過類似鍋蓋的拋物線形主體，對信號進(jìn)行反射和聚焦，經(jīng)過一系列的處理之后，將其發(fā)送到電視機(jī)上。現(xiàn)如今，這種“衛(wèi)星鍋”早已退出了我們的日常生活，成了記憶里的老物件。但是，與其外形相似的射電望遠(yuǎn)鏡卻在天文和相關(guān)科學(xué)領(lǐng)域大展拳腳，仿佛幫助科學(xué)家們生出一只“天眼”，看向地球以外的浩瀚宇宙。

目前世界上最大的“天眼”在中國

2016年，直徑達(dá)500米的單徑射電天文望遠(yuǎn)鏡FAST （Five-hundred-meter Aperture Sphericalradio Telescope）在貴州省平塘縣克度鎮(zhèn)大窩凼洼地竣工。這是目前為止世界上最大的單孔徑望遠(yuǎn)鏡，被稱為“中國天眼”。

“建造一個大望遠(yuǎn)鏡”的想法產(chǎn)生于1993年的國際無線電科學(xué)聯(lián)盟大會上。在那個時候，來自宇宙的電波已經(jīng)呈現(xiàn)逐漸消散的趨勢。為了解決天文學(xué)中的眾多難題，多位科學(xué)家提出了建造一臺大望遠(yuǎn)鏡的倡議。

將這個望遠(yuǎn)鏡建造在哪里，這是遇到的第一個難題。首先，建造這樣一個龐然大物需要足夠的土地面積。其次，四周不能有太多居民，一方面，這會影響居民們的日常生活；另一方面，如果有太多電信號，會影響望遠(yuǎn)鏡的信號接收。此外，這種望遠(yuǎn)鏡的儀器精密度極高，對選址的工程地質(zhì)、氣候和海拔等環(huán)境要素都有著嚴(yán)苛的要求。

經(jīng)過反復(fù)篩選，在一萬多個候選地中，專家們將目光鎖定在貴州省平塘縣。貴州擁有獨(dú)特的喀斯特地貌——地下水和地表的其他水系對巖石長年累月沖刷、沉積之后形成的一種獨(dú)特地貌。神奇的是，它自水中誕生，但并不會積水，為設(shè)備的運(yùn)行和維護(hù)提供了優(yōu)越的條件。另外，下凹式的洼地能夠更好地貼合球面望遠(yuǎn)鏡的形態(tài)，為其提供良好的支持。此外，平塘周圍人煙稀少，需要動遷的居民并不多，造成的影響相對較小。最終，平塘縣得天獨(dú)厚的優(yōu)勢使得它從眾多的備選中脫穎而出，成為“中國天眼”的天選之地。

“天眼”最處的設(shè)計理念來自美國阿雷西博望遠(yuǎn)鏡

阿雷西搏望遠(yuǎn)鏡是一個固定的，只能掃描一個帶狀區(qū)域的大型望遠(yuǎn)鏡。在它的基礎(chǔ)上，“天眼”進(jìn)行了一系列創(chuàng)新和改進(jìn)，綜合性能提高了約十倍。

首先，光是外表，“天眼”就已經(jīng)足夠吸引人了?！疤煅邸本烤褂卸啻竽?？總工程師王啟明曾這樣說過：“望遠(yuǎn)鏡反射面總面積為25萬平方米，相當(dāng)于30個標(biāo)準(zhǔn)足球場的規(guī)模。”

除了“大”這個特點(diǎn)，“天眼”的每一個細(xì)節(jié)都表現(xiàn)出科研人員精益求精的精神和創(chuàng)造力：強(qiáng)勁的抗疲勞索網(wǎng)，擁有高達(dá)500兆帕的拉力；主動反射面板，使得它能夠接收到137億光年之外的電磁信號，甚至能夠達(dá)到宇宙的邊緣：幫助變位的液壓促動器，不僅能夠精確定位和運(yùn)動，還能夠進(jìn)行自我監(jiān)測：七套接收機(jī)，能夠以不同的波段觀測不同的目標(biāo)……“天眼”是一個集工業(yè)大成之所在，這些高新技術(shù)的運(yùn)用，使“天眼”在很多領(lǐng)域獲得了技術(shù)獎項(xiàng)。

“天眼”運(yùn)行至今，已經(jīng)發(fā)現(xiàn)了超過700個優(yōu)質(zhì)的脈沖星候選體，為人類探索宇宙奧秘提供了大量實(shí)驗(yàn)數(shù)據(jù)和資源，對人類揭開太空的神秘面紗起到了重大作用。

“圜則九重，孰營度之？惟茲何功，孰初作之？”2 000多年前，屈原在《天問》中如此發(fā)問。中國人自古以來就對探索宇宙充滿熱情，古人仰望星空，想象“天體九重”，發(fā)出了“宇宙如何度量與形成”的疑問?，F(xiàn)在，科技發(fā)展給我們帶來更多的探索機(jī)會?！爸袊煅邸笔侵腔叟c科技的結(jié)晶，如今人們睜開“天眼”，頭頂這片無盡天空的神秘面紗正在被更深入地揭開。

The Incredible “Eye of Heaven”

In Chinese mythology， the all-seeing eyeof Erlang Shen could perceive everything，everywhere. As mere mortals， we lack sucha divine eye， yet we find ourselves alwaysyearning for a glimpse of the celestial realm.

Let’s rewind to a time many years past， on a warm summer’s evening. A gentle breeze stirred the air， carryingwith it the songs of cicadas from high in the trees. As the nal blush of sunset receded， darkness fell over the sky，while the delicious scent of home-cooked meals wa ed from every household. Intriguingly， for the children， it wasn’tthe meals that held their attention， but the entertainment that followed dinner. Hurriedly nishing their food， thekids would assemble around a small square device， awaiting the captivating sounds and visuals about to spring forth.

Can you guess what they were doing？ They weretuning in to a television program. At that time， peopleneeded something akin to a “pot lid” to capture distantTV signals into blurry images on screen. From timeto time， they would tweak the direction of this “potlid” to ensure that the intermittent “snowflakes” didnot disrupt their viewing pleasure. This quirky pot lidlikeapparatus was chicly referred to as “satellite dish”，or “antenna pot lid” in its heyday. Essentially， it was asatellite signal receiver.

This receiver， with its parabolic design resembling alid， would re ect and concentrate signals， transmittingthem to a television set a er a series of conversions. Intoday’s world， this kind of satellite dish has disappearedfrom our life and was relegated to the realm ofnostalgic memorabilia. However， ground-based radiotelescopes， which look like satellite dishes， continue tomake remarkable progress in the fields of astronomyand related sciences. They act as if they are the cosmiceyes that grant scientists the ability to peer into the vastuniverse beyond the Earth.

China currently has the world’s largest “Eye of Heaven” or “Tianyan”

Known officially as the Five-hundred-meter Aperture Spherical radio Telescope （FAST）， it was completed in2016 in Dawodang of Kedu Town， Pingtang County， Guizhou Province， with a diameter of 500 meters. It is thelargest single-dish telescope in the world， fondly dubbed as “China’s Tianyan”.

The idea of constructing a gargantuan telescope was initially proposedat the General Assembly of the International Astronomical Union in 1993.Astronomers had been observing a gradual waning in the universe’s radiowaves， and to counter numerous obstacles in the eld of astronomy， severalscientists raised the idea of building a large telescope.

Identifying an ideal location for this telescope was the first hurdle.The structure’s sheer magnitude required a vast area of land. In addition，it was crucial that the site was not heavily populated to avoid disruptingthe residents’ daily life and to prevent excess telecommunication signalsfrom impeding the telescope’s signal reception. Furthermore， the telescoperequired exceptional precision， thereby imposing strict conditions onvarious factors such as the geological features of the site， the climate， andthe altitude.

After rigorous selection from over 10，000potential sites， experts ultimately pinpointedPingtang County in Guizhou Province. Guizhouis characterized by a unique karst topography，formed by prolonged erosion and depositionof underground and surface water on rocks. Remarkably， this landformemerges from the water without retaining it， providing optimal conditionsfor the equipment’s operation and maintenance. Moreover， the concavevalleys in Pingtang perfectly align with the spherical shape of the radiotelescope， o ering robust support. The sparse population in the vicinity ofPingtang and the relatively few residents needing relocation also leads to aminimal impact. These unrivaled advantages of Pingtang set it apart fromother alternative locations， ultimately making it the chosen home for the“China’s Tianyan.”

The design for “Tianyan” was inspired by the Arecibo Telescope in the United States

The Arecibo Telescope is a xed， colossaltelescope limited to scanning a linear area.Scientists made a series of ingenious improvementsand successfully increased FAST’soverall performance tenfold.

The sheer size of “Tianyan” is enough to draw gasps ofastonishment. Just how large is it？ According to the Chief EngineerWang Qiming， the total reflective surface area of the telescope isan impressive 250，000 square meters — equivalent to 30 standardsoccer fields.

But it’s not just its size that impresses;every facet of “Tinayan” is a testamentto the ingenuity of its creators： from therobust anti-fatigue cable net， which boastsa tensile strength of up to 500 gigapascals，to the active reflective panel capable ofreceiving electromagnetic signals from asfar away as 13.7 billion lightyears on thevery edge of the observable universe， to thehydraulic actuators for precision positioning，movement， and self-monitoring， to the sevensets of receivers designed to observe targetsacross different frequency bands. “Tianyan”is truly an engineering marvel， with itscutting-edge technologies earning numeroustechnical awards across various fields.

Since its inception， “Tianyan” hasidentified over 700 high-quality candidatepulsars， providing a treasure trove of data andresources for our exploration of the universe.It has played a significant role in sheddinglight on the mysterious space.

“The celestial sphere is said to consistof nine layers. Who was the pioneer inmeasuring these layers？ And who werethe ingenious individuals responsiblefor constructing them？” More than twomillennia ago， the ancient Chinese poetQu Yuan raised these inquires in his poem“Heavenly Questions”. The Chinese peoplehave maintained a deep fascination withthe cosmos ever since. Our ancestors oncegazed at the starlit sky， wondering aboutthe origin and scale of the “nine layers ofcelestial bodies”. Today， armed with advancedtechnology， we’re better equipped than everfor cosmic exploration. The “China’s Tianyan”represents the pinnacle of wisdom andtechnological prowess. As we open our “eye”to the in nite expanse， we are about to unveilmore cosmic mysteries.