双语小知识

□ 曹 燕

双语小知识

□ 曹 燕

Galactic Hub 银心

It’s a good jaunt from the suburbs to downtown — a journey into bright lights, heavy traffic, and non-stop action. That’s especially true of the“downtown” region of the Milky Way— the galaxy’s core. It’s populated by some bright, massive stars that race around at high speeds. And those stars are packed together much more tightly than the stars out where we live, in the galactic suburbs.

从郊区到闹市是次不错的短途旅行——一场进入绚丽灯光、繁忙交通，以及永不停止活动的旅程。银河系的“闹市区”——“银心”尤其如此。这里被诸多以高速运转的、明亮而巨大的恒星所占据。这些恒星的拥挤程度远比我们所居住的银河系“郊区”大得多。

S S T空间望远镜（S pitzer S pace Telescope）红外照相机下的银河系中心，来源：NASA

The very heart of the Milky Way contains a black hole that’s about four million times the mass of the Sun. Gas or debris occasionally funnel into the black hole, causing a short flare-up before they disappear from view.

在银河系中心包含着一个大约四百万倍于太阳质量的黑洞。气体和碎片偶尔漏入其中，在消失前短暂地闪耀一下。

Thousands of stars orbit within a few light-years of the black hole. Most of them are fairly old and feeble. But there’s also a cluster of hot, young stars that are many times heavier than the Sun, and many thousands of times brighter. Some of these stars get so close to the black hole that they can whip around it at millions of miles per hour.

在距黑洞几光年范围内，有几千颗恒星围绕其运动，其中大多数衰老而虚弱，但也有一群炽热、年轻的星球，它们比太阳重许多倍、亮几千倍。很多恒星距离黑洞如此之近，使得它们以数百万英里每小时的高速度转动着。

A ring of cold gas also encircles the black hole. It’s probably about 10 lightyears across, give or take. It’s possible that the ring could fragment into smaller clumps, which could then collapse to give birth to new stars.

一条寒冷气体环同样围绕于黑洞，直径差不多10光年左右，气体环有可能会碎裂成更小的团块，团块塌缩后将诞生新恒星。

Many more stars lie not far outside the ring, including a couple of other big, bright clusters. So do ribbons of hot gas that are sculpted by strong magnetic fields, and much more— all part of our galaxy’s dynamic downtown.

许多恒星位于寒冷气体环以外不远处，包括几个巨大而明亮的星团，还有一条条被强磁场塑造而成的炙热气体带，以及其他一些物质，共同组成银河系的闹市区。

Far, Far Away 很远很远

It’s a long way from Earth to the center of the galaxy. But the exact distance is uncertain — measurements vary by several thousand light-years.

地球距离银河系中心很远，但到底有多远还不能精确地测定，因为用不同的测量方法得出的结果相差了几千光年。

The most accurate method of measuring astronomical distances is called parallax. To understand how it works, hold out a finger and look at it with first one eye, then the other. The finger appears to shift against the background. The angle of the shift reveals how far the finger is from your eyes.

测量天文距离最精确的方法叫作视差法。用一根手指就能弄明白视差法是怎么回事：伸出一根手指，先用一只眼睛注视它，之后再换作另一只，这根手指先后在背景中呈现出不同位置，两个位置间的夹角就能揭示这根手指距离眼睛有多远。

Astronomers determine parallax by looking at an object when Earth is on opposite sides of the Sun. The change in position causes a target to shift a tiny bit compared to the background of more-distant objects.

天文学家们是这样运用视差法的：他们在地球刚好运行到太阳两端时观测同一目标，在由更远的天体所构成的背景中，观测目标发生了微小的位移。

As the distance increases, though, the angle gets smaller. Eventually, it gets so small that it’s almost impossible to measure. That’s especially true when you’re looking through Earth’s atmosphere, which blurs the view. New technology has sharpened the view, but there’s still a lot of wiggle room in the measurements.

当然，观测目标距离越远，位移夹角便越小。最终，夹角小得难以测量，当你透过地球那令人视线模糊的大气层观测时就更是如此了。新技术已经锐化了视野，但在提高测量精度方面仍有余地。

因为地球绕日公转，在地球上观测恒星会出现视差。如上图，每年1月份和7月份，在地球上观测同一颗恒星会产生微小的位置位移，被观测的恒星离我们越近，视差就越大。来源：ESA

Another technique looks at how certain stars change in brightness. There’s a relationship between the length of each brightness cycle and the star’s true brightness. But clouds of dust between Earth and the center of the galaxy absorb a lot of light, complicating the measurements.

另外一种方法是观测某些恒星亮度的变化。亮度变化周期的长度与恒星的真实亮度间具有联系。但地球与银河系中心之间的尘埃云吸收掉很多光线，使得测量更加复杂。

So when you take all the difficulties into account, different studies yield a distance of between about 24,000 and 28,000 light-years away — a long jaunt any way you look at it.

总之，把所有这些困难都考虑进去，不同研究得出的地球与银心距离在24,000到28,000光年之间，不管怎么看这都是很远的距离了。

（责任编辑 张长喜）