神奇的“天眼”

罗崟丹

在中國的神话传说中，二郎神的天眼可观十方。但我们是凡人，没有天眼，却仍然想着可以窥天。

时光倒回到多年之前，一个夏天的傍晚，风轻轻吹过，高高的树上蝉鸣声此起被伏。随着晚霞褪尽，天色暗了下来，各家各户的餐桌上飘散着饭菜的香气。但最吸引孩子们的不是吃什么，而是饭后的娱乐活动。匆匆吃过几口饭之后，孩子们便围坐在一个四四方方的“小盒子”前，急切地等待那里传出期盼的声音和画面。

知道他们在做什么吗？在看电视。人们需要在一个类似锅盖的东西的帮助下，将远方的电视信号传输到电视机上，才可以看到模糊的画面，还需要时不时地调整一下“锅盖”的方向，这样才不会出现时断时续的“雪花”影响人们观看。这个酷似锅盖的东西拥有一个在当时很时髦的名字——“卫星锅”，也被大家亲切地称为“天线锅盖”，实际上它就是一个卫星信号接收器。

卫星信号接收器通过类似锅盖的抛物线形主体，对信号进行反射和聚焦，经过一系列的处理之后，将其发送到电视机上。现如今，这种“卫星锅”早已退出了我们的日常生活，成了记忆里的老物件。但是，与其外形相似的射电望远镜却在天文和相关科学领域大展拳脚，仿佛帮助科学家们生出一只“天眼”，看向地球以外的浩瀚宇宙。

目前世界上最大的“天眼”在中国

2016年，直径达500米的单径射电天文望远镜FAST （Five-hundred-meter Aperture Sphericalradio Telescope）在贵州省平塘县克度镇大窝凼洼地竣工。这是目前为止世界上最大的单孔径望远镜，被称为“中国天眼”。

“建造一个大望远镜”的想法产生于1993年的国际无线电科学联盟大会上。在那个时候，来自宇宙的电波已经呈现逐渐消散的趋势。为了解决天文学中的众多难题，多位科学家提出了建造一台大望远镜的倡议。

将这个望远镜建造在哪里，这是遇到的第一个难题。首先，建造这样一个庞然大物需要足够的土地面积。其次，四周不能有太多居民，一方面，这会影响居民们的日常生活；另一方面，如果有太多电信号，会影响望远镜的信号接收。此外，这种望远镜的仪器精密度极高，对选址的工程地质、气候和海拔等环境要素都有着严苛的要求。

经过反复筛选，在一万多个候选地中，专家们将目光锁定在贵州省平塘县。贵州拥有独特的喀斯特地貌——地下水和地表的其他水系对岩石长年累月冲刷、沉积之后形成的一种独特地貌。神奇的是，它自水中诞生，但并不会积水，为设备的运行和维护提供了优越的条件。另外，下凹式的洼地能够更好地贴合球面望远镜的形态，为其提供良好的支持。此外，平塘周围人烟稀少，需要动迁的居民并不多，造成的影响相对较小。最终，平塘县得天独厚的优势使得它从众多的备选中脱颖而出，成为“中国天眼”的天选之地。

“天眼”最处的设计理念来自美国阿雷西博望远镜

阿雷西搏望远镜是一个固定的，只能扫描一个带状区域的大型望远镜。在它的基础上，“天眼”进行了一系列创新和改进，综合性能提高了约十倍。

首先，光是外表，“天眼”就已经足够吸引人了。“天眼”究竟有多大呢？总工程师王启明曾这样说过：“望远镜反射面总面积为25万平方米，相当于30个标准足球场的规模。”

除了“大”这个特点，“天眼”的每一个细节都表现出科研人员精益求精的精神和创造力：强劲的抗疲劳索网，拥有高达500兆帕的拉力；主动反射面板，使得它能够接收到137亿光年之外的电磁信号，甚至能够达到宇宙的边缘：帮助变位的液压促动器，不仅能够精确定位和运动，还能够进行自我监测：七套接收机，能够以不同的波段观测不同的目标……“天眼”是一个集工业大成之所在，这些高新技术的运用，使“天眼”在很多领域获得了技术奖项。

“天眼”运行至今，已经发现了超过700个优质的脉冲星候选体，为人类探索宇宙奥秘提供了大量实验数据和资源，对人类揭开太空的神秘面纱起到了重大作用。

“圜则九重，孰营度之？惟兹何功，孰初作之？”2 000多年前，屈原在《天问》中如此发问。中国人自古以来就对探索宇宙充满热情，古人仰望星空，想象“天体九重”，发出了“宇宙如何度量与形成”的疑问。现在，科技发展给我们带来更多的探索机会。“中国天眼”是智慧与科技的结晶，如今人们睁开“天眼”，头顶这片无尽天空的神秘面纱正在被更深入地揭开。

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.