揭秘太阳的“雀斑”——黑子

古人认为它们是太阳神脸上生的麻子，抑或太阳内的星辰，现代人猜想它们和UFO以及各种超自然现象密不可分——这种神秘物质就是太阳黑子，它们能量巨大，也会时不时给人类的生活带来麻烦，让我们随本文一起揭开太阳黑子的面纱吧。

The Aztecs[1] thought that their sun god had pockmarks on his face. The ancient Chinese referred to them as stars inside the solar orb. One Renaissance astronomer argued that they were actually undiscovered planets. Today, some believe their appearance is linked to UFO sightings and paranormal activity. Others offer them as an alternative explanation for human-caused climate change. The rest of us wonder if they’re the reason for dropped cell phone calls or static-plagued radio stations.

We’re talking about sunspots, those peculiar dark areas that pop up regularly on the surface of the sun. They usually appear in pairs or in groups on either side of the sun’s equator. Sunspots vary tremendously in size, ranging from less than 200 miles across to many times the size of the Earth. Some small sunspots may last for less than an hour, but larger ones can last up to six months. Some sunspots—such as one in 2004 that measured 20 times the size of our planet—are big enough to be seen by the naked eye.

Astronomers in ancient China noticed sunspots several thousand years ago. The I-Ching or Book of Changes, which dates back to the 12th century B.C., mentions the phenomenon. The first written record of a sunspot sighting dates to 28 B.C., when it was noted that “the sun was yellow at its rising and a black vapor as large as a coin was observed at its center.” On the other side of the world, the Aztecs, who ruled Mexico before the Spanish arrived in the 1500s, also paid a lot of attention to the sun. As we discussed, their creation myth featured a sun god with a pockmarked face.

In Europe, people had a harder time accepting the existence of sunspots. That was because everyone—including the Catholic Church—accepted Greek philosopher Aristotle’s idea that the heavens were perfect and unchanging. Instead, when a large sunspot appeared for eight days in A.D. 807, they dismissed the phenomenon as the passage of the planet Mercury across the sun.

However, after the telescope was developed in the early 1600s, the Italian astronomer Galileo and others clearly saw that the sun had dark spots. Astronomer and Catholic priest Christoph Scheiner tried to come up with an explanation that didn’t contradict Church teachings; he argued that the spots actually were undiscovered planets that orbited very close to the sun and were visible only when the planets were in front of the sun. Despite Scheiner’s attempts, Galileo correctly figured out that sunspots were part of the sun itself by closely studying the movement of sunspots over time. By the mid-1700s, European astronomers were recording and compiling their observations of sunspots on a daily basis.

As scientists accumulated more and more data, they began to notice that sunspot activity developed a pattern. In 1843, astronomer S.H. Schwabe was the first to describe the 11-year sunspot cycle.

Since then, scientists used have used an array of tools—including giant solar telescopes that were specially cooled to observe the sun’s light without being distorted by its heat—to learn more about the physics of sunspots.

Sunspots occur because the sun isn’t a hunk of rock like the Earth and the inner planets, but a ball of continually circulating hot gases that doesn’t move in one piece. The interior and the exterior of the sun rotate separately; the outside rotates more quickly at the equator than at the solar north and south poles. Over time, all that messy and uneven movement twists and distorts the sun’s main magnetic field in the same way that your bed sheets get wrinkled and bunched up when you toss and turn in your sleep. The bunched up spots—actually twists in the magnetic field lines—have so much magnetic power that they push back the hot gases beneath them and prevent the heat from rising directly to the surface. In other words, they become sunspots.

Because sunspots are cooler than the rest of the sun’s surface, they look darker. At the same time, the hot gases blocked by these sunspots flow into the areas around them, making those areas even hotter and brighter than normal. This contrast makes sunspots stand out even more.

Sunspots’ Effect on Earth

Sunspots are connected with other solar events like flares and coronal mass ejections (CMEs). A solar flare is a sudden release of energy from the sun, while a CME actually shoots hot plasma from the sun into space. The precise mechanisms that trigger flares and CMEs are not yet known, but the bigger the group of sunspots, the more intense such solar weather tends to be.

Flares and CMEs can send enormous amounts of energy and charged particles hurtling into collision with the Earth’s atmosphere, where they can cause magnetic storms that disrupt or alter radio and cell phone communication and can wreak havoc with electrical grids. In 1989, for example, a power surge triggered by solar energy damaged transformers that were part of the Hydro-Quebec power system. That surge left 6 million people in Canada and the northeastern U.S. without electricity for more than nine hours.

The increase in radiation that accompanies a solar flare is a theoretical health hazard to spacewalking astronauts, crew and passengers in high-flying aircraft, but there isn’t any evidence that people have actually gotten sick from such exposure.

It’s unclear if there’s a link between solar weather and changes in the Earth’s climate, because our planet’s climate is influenced by so many other factors—from volcanic eruptions to man-made emissions of greenhouse gases. In the 1600s and 1700s, when there was almost no sunspot activity, coincided with a period of cold temperatures and severe winters in Europe and North America. However, scientists haven’t been able to determine if the two phenomena were actually related, though they think that a decrease in the sun’s ultraviolet emissions may have triggered the change in climate.

UFO watchers and paranormal enthusiasts also see links between the unknown and increased sunspot activity, but there may be more of a correlation with the intensity of a person’s belief in mystical phenomena.

阿兹特克人觉得那是他们的太阳神脸上生的麻子;古代中国人把它们叫做太阳内部的星辰;还有一位文艺复兴时期的天文学家提出：它们其实是尚待发现的行星。如今，一些人认为它们的出现与UFO和超自然活动有关;还有人把它们认作是人为引起的气候变化的另一种表现;我们剩下的人则怀疑它们是手机信号中断和无线电台静电干扰的罪魁祸首。

我们所说的就是太阳黑子，那些定期突然出现在太阳表面的奇特黑色区域。通常它们会在太阳赤道的一侧成对或成群出现。黑子的大小差别巨大，小的直径不到二百英里，大的比地球还大很多倍。一些小的太阳黑子可能只存在不到一小时(就消失了)，而大的黑子可以持续存在六个月之久。一些黑子，比如2004年出现的大小为地球20倍的那个，大到我们可以用肉眼就能观察到。

早在几千年前，中国古代的天文学家们就注意到了太阳黑子现象。公元前12世纪的《易经》提到了这一现象。首次观测太阳黑子的书面记载是在公元前28年，当时的记载是“太阳初升时呈黄色，中间可见硬币大小的一团黑色雾气。”在地球的另一端，16世纪西班牙入侵前一直统治着墨西哥的阿兹特克人也很注重察太阳。正如我们上文提到的，他们的创世纪神话中就有生了麻子脸的太阳神的形象。

在欧洲，人们接受太阳黑子却经历了艰难的过程。那是因为当时的每个人，包括天主教派，都接受了希腊哲学家亚里士多德的观点，即认为上天是完美无缺并恒定不变的。于是，当公元807年一个巨大的太阳黑子出现并持续了八天时，他们并未放在心上，只是觉得那是因为水星路过太阳所致。

然而，17世纪早期望远镜发明之后，意大利天文学家伽利略和其他天文学家都清楚地观测到了太阳上的黑色阴影。天文学家、天主教牧师克里斯托夫•沙因尔努力想给出一种不违背教会教义的解释，他坚称这些黑点实际上是尚待发现的行星，它们紧紧地围绕着太阳运转，并且只有挡在太阳前面时才可以被观测到。尽管沙因尔努力辩解，伽利略在连续观察并仔细研究太阳活动之后，还是正确地指出：太阳黑子是太阳自身的组成部分。到了18世纪中叶，欧洲的天文学家们开始逐天记录并编纂他们对太阳黑子的观测情况。

随着科学家们积累了越来越多的数据，他们开始注意到太阳黑子的活动是遵循着一定规律的。1843年，天文学家S.H. 施瓦贝第一个描述了太阳黑子11年一次的周期。

自那时起，科学家们便运用了一系列工具——包括巨型太阳望远镜——来认识太阳黑子的更多物理特性，巨型太阳望远镜经过特殊处理，能滤过并冷却太阳的热量，这样观察太阳光的时候就不会被其热量所干扰。

太阳黑子的产生是因为太阳与地球和内行星那样由大块岩石组成的构造不同，太阳是一团由不停环绕运动的热气构成的球体，并且并不整体运动。太阳的内部和外部各自旋转;其外部的赤道部位比南北极转速要快。久而久之，这种混乱、不平衡的运动逐渐改变、扭曲了太阳的主要磁场，就好像你在床上睡觉时，翻来覆去使床单变皱和鼓起来一样。这些鼓起的区域(实际上是磁力线上的扭曲)的磁力特别大，于是它们将底下的热气推回来，并阻止热量直接升到太阳表面。换句话说，它们就成了太阳黑子。

因为太阳黑子比太阳表面的其他区域温度要低，所以它们看起来颜色更黑。同时，被这些太阳黑子阻挡的热气涌入它们周边的区域，使得这些区域变得比平时温度更高，颜色更明亮。这种对比便衬托得太阳黑子更为突出。

太阳黑子对地球的影响

太阳黑子与其他太阳现象，如耀斑和日冕物质抛射也有着一定关联。太阳耀斑是太阳能量的突然释放;而日冕物质抛射实际上是太阳上灼热的等离子体向宇宙空间的散射。引发耀斑和日冕物质抛射的确切机理尚不可知，但是黑子群的规模越大，此类太阳活动就越为剧烈。

耀斑和日冕物质抛射能够释放巨大的能量和无数带电的粒子，并与地球的大气层猛烈碰撞，从而引发磁暴，干扰或更改无线电或手机通信信号，并可对电力系统造成严重破坏。例如在1989年，太阳能量释放引发的能量激增就造成了魁北克水电系统变压器的损坏，从而导致加拿大和美国东北部地区的600万人口遭遇长达九个多小时的电力中断。

理论上而言，伴随太阳耀斑产生的辐射能增加对太空漫步的宇航员、高空飞行的飞机上的机务人员和乘客也会造成一种健康危害，但目前还没有证据表明这种辐射能可以致病。

太阳活动与地球气候变化的关系目前还有待论证，因为地球气候同时受到许多其他因素的影响——从火山爆发到人为温室气体的排放。在17和18世纪，太阳活动几乎为零，欧洲和北美地区恰恰就出现了低温和严寒天气。然而，尽管科学家们认为太阳散发紫外线的减少可能会引发气候变化，他们尚不能确定这两种现象存在确定的因果关系。

UFO的观测者和超自然现象爱好者们也认为太阳黑子活动的增加与这类未知现象有关，但也许这与人们对神秘现象的相信程度更为相关吧。