物理学者探索百年地球到太阳距离终于确定

2012年10月10日，分类：资料；

历经数百年探索之后，天文学家终于达成一致：这是从地球到太阳的距离：149597870700米。大约93000000英里。

太阳是离地球有多远？只是，你知道，很，很远，但我想问的是一个具体的测量的距离？

在今年九月份国际天文学联合会上，这个问题的答案总算是出来了。

中学时光

当你计算，你是怎么决定从地球上的位置来衡量吗？你是如何决定的道路上地球的轨道将作为焦点的测量点？

你如何解释太阳庞大规模，它的气浪、烟雾、火焰的衍射范围吗？

地球到太阳的平均距离，也被称为1个天文单位，自17世纪以来，天文学家一直是一个争论的主题。

第一次精确测量地球与太阳之间的距离，是由天文学家和工程师乔瓦尼·卡西尼在1672年《自然》杂志上的记录。

卡西尼号从巴黎相比，火星对他的测量，由他的同事让更丰富的观测记录，从法属圭亚那。

结合他们的计算，天文学家们能够确定的第三个测量地球和太阳之间的距离。

对估计绵延8700万英里-这实际上是非常接近的值天文学家假设今天。*（PI）/ K 天（即 365.2568983

但火箭科学只是得到了一个更直接一点。默默无闻，自然报告，重新定义了国际天文学联合会天文数字，一旦和所有-或者，至少，有一次和现在。根据联盟的一致表决，这里是地球的官方的，科学的，固定距太阳的距离：149597870700米。大约93000000英里。

对于天文学家来说，复杂性，固定性的变化将意味着一个新的便利时，他们计算的距离（更不要说解释这些距离的学生和非火箭科学家）。这将意味着沟临时数字，有利于更加统一的计算能力。这将意味着一个更正确地考虑广义相对论的测量。（甲米在这种情况下，定义为 “在距离旅游由光在真空中在1/299，792458的第二个” -和，因为光的速度是恒定的，天文单位将不再取决于观察者的位置与上太阳能系统）。新的单位也会更准确的太阳，正在逐渐失去质量，因为它辐射能量的状态。（高斯常数是太阳质量的基础上。）那么，为什么花了这么长的时间天文学界同意在一个标准的测量？因为，除其他事项外，这个故事中提到米，位于同样的原因。传统可以将自己强大的力量，广泛使用的旧部- 自1976年以来一直在 -意味着将需要一个新的变化轻微而全面的。计算是基于对老机组。计算机程序是基于老机组。直率也不是没有诸多不便。

定义1AU是地球到太阳的距离，那么金星是 0.72±0.01 AU，而火星是 1.52±0.04AU；

英文原文如下，节选自http://www.theatlantic.com/

How far away from Earth is the sun? Not just, you know, very, very far, but in terms of an actual, measurable distance? When you’re calculating, how do you decide which location on Earth to measure from? How do you decide which spot on the path of Earth’s orbit will serve as the focal point for the measurement? How do you account for the sheer size of the sun, for the lengthy reach of its fumes and flames?

The measurable, mean distance — also known as the astronomical number — has been a subject of debate among astronomers since the 17th century. The first precise measurement of the Earth/sun divide, Nature notes, was made by the astronomer and engineer Giovanni Cassini in 1672. Cassini, from Paris, compared his measurements of Mars against observations recorded by his colleague Jean Richer, working from French Guiana. Combining their calculations, the astronomers were able to determine a third measurement: the distance between the Earth and the sun. The pair estimated a stretch of 87 million miles — which is actually pretty close to the value astronomers assume today.

But their measurement wasn’t, actually, a number. It was a parallax measurement, a combination of constants used to transform angular measurements into distance. Until the second half of the twentieth century — until innovations like spacecraft, radar, and lasers gave us the tools to catch up with our ambition — that approach to measuring the cosmos was the best we had. Until quite recently, if you were to ask an astronomer, “What’s the distance between Earth and the sun?” that astronomer would be compelled to reply: “Oh, it’s the radius of an unperturbed circular orbit a massless body would revolve about the sun in 2*(pi)/k days (i.e., 365.2568983…. days), where k is defined as the Gaussian constant exactly equal to 0.01720209895.”

Oh, right. Of course.

But rocket science just got a little more straightforward. With little fanfare, Nature reports, the International Astronomical Union has redefined the astronomical number, once and for all — or, at least, once and for now. According to the Union’s unanimous vote, here is Earth’s official, scientific, and fixed distance from the sun: 149,597,870,700 meters. Approximately 93,000,000 miles.

For astronomers, the change from complexity to fixity will mean a new convenience when they’re calculating distances (not to mention explaining those distances to students and non-rocket scientists). It will mean the ability to ditch ad hoc numbers in favor of more uniform calculations. It will mean a measurement that more properly accounts for the general theory of relativity. (A meter in this case is defined as “the distance traveled by light in a vacuum in 1/299,792,458 of a second” — and since the speed of light is constant, the astronomical unit will no longer depend on an observer’s location with the solar system.) The new unit will also more accurately account for the state of the sun, which is slowly losing mass as it radiates energy. (The Gaussian constant is based on solar mass.)

So why did it take so long for the astronomy community to agree on a standard measurement? For, among other things, the same reason this story mentions both meters and miles. Tradition can be its own powerful force, and the widespread use of the old unit — which has been in place since 1976 — means that a new one will require changes both minor and sweeping. Calculations are based on the old unit. Computer programs are based on the old unit. Straightforwardness is not without its inconveniences.

But it’s also not without its benefits. The astronomical unit serves as a basis for many of the other measures astronomers make as they attempt to understand the universe. The moon, for example, is 0.0026 ± 0.0001 AU from Earth. Venus is 0.72 ± 0.01 AU from the sun. Mars is 1.52 ± 0.04 AU from our host star. Descriptions like that — particularly for amateurs who want to understand our world as astronomers do — just got a little more comprehensible. And thus a little more meaningful.