重庆寸滩保税港区官网:我们如何猜出银河系的样子的？

好像我们看到的也只是过去的宇宙的模样，所以最好用一个以时间为轴的立体图像描述我们所处的宇宙，况且宇宙中有这么多大的星体，更具广义相对论，光线到我们这里不知道已经被弯曲过多少次了，所以很难从银河系内知道银河系的确切模样，有点身在庐山中的味道！

不确切地说是根据观察河外星系的形状和记录银河系中恒星位置推测出来的。最早是恒星计数方法，现在主要通过旋臂示踪天体，例如21cm氢发射区（最主要）。

另外，银河系并不具有“蝶形外观”，据说是“碟子形的”，但是现在有新的证据表明银河系是棒旋星系，而非先前所认为的旋涡星系。

给段英文，你能看懂就看。
Because we live inside the Milky Way, it is very hard for us to determine its shape and size. It is clearly planar, but estimating it's exact shape and our position inside it was not done until the early 20th century.
Not only do we have a bad angle, but we also have to deal with dust in the plane of the galaxy. This dust obscures our view of most of the Milky Way.

The Milky Way's shape was first determined through studying globular clusters
Globular clusters are spherical clusters of up to 106 stars (usually Pop II), typically outside the plane of the galaxy.
The distance to globular clusters is measured with Cepheid and RR Lyrae variable stars.
These variables change their brightness in a periodic way. Their outer layers are unstable, so they pulsate. As they expand and cool, the opacity drops, so light can escape more easily and the outer layers are no longer supported. As the star contracts, it heats up, and the opacity goes up. Thus the outer layers become more strongly supported, so the star begins expanding again.
The period of variation depends on the luminosity of the star. If we can measure the period and the apparent brightness, we can determine the distance.
Cepheids are high luminosity stars, so they can be seen out to great distances.
In measuring Cepheid and RR Lyrae distances in globular clusters, we find that they are centered on a point 8.5kpc (8500 pc) away, in the direction of Sagittarius. Shapley reasoned that this must be the center of the galaxy.
Strong radio sources (H2 clouds and ionized hydrogen regions) show the presence of spiral arms in our galaxy.
The Milky Way thus appears to be a spiral galaxy, and we are on one of the spiral arms.
From observations of our own and other spirals, we know that spirals have a central bulge, a disk, and a halo.
The disk has mainly Pop I stars. In addition, about 10% of the disk mass is in the form of gas and dust. Thus, there is active star formation in the disk.
Stars don't stay in spiral arms. The arms are waves of extra density in the gas of the disk. The Sun has moved in and out of spiral arms dozens of times.
Since there is extra gas, most star formation occurs in the arms. Since high luminosity O and B stars explode in a short time, they don't have time to leave the spiral arm. Thus, spiral arms are where all of the very brightest stars are.
The disk also has open clusters: loosely bound groups of young stars, like the Pleiades. These are probably stars that formed together and haven't yet dispersed.
Most of the 1011 stars in our galaxy are in either the disk or the bulge.
The halo has many fewer stars. Many halo stars are in globular clusters.
By looking at the main sequence cutoff (maximum age of the brightest main sequence stars), we find that most globular clusters are 1010 years old.
Halo stars orbit radially, while disk stars orbit in roughly circular orbits within the disk.
The bulge is a combination of young and old stars. Active star formation is occuring, but most of the stars are very old. Many old bulge stars (and globular clusters) have high metallicity, implying that star formation was very early and very active.
别问我这都什么意思，我不懂啊，你就知道天文学家们有数学方法就行了。

有数千亿恒星的银河系被认为像一个盘子，100000光年宽，中间有个突起，带6条螺旋形的臂。我们不能发射探测器到银河之外，来给银河系拍照。但是我们可以给附近天文学家认为应该和银河系类似的星系拍照，来了解我们的银河系从外部看起来会是什么样子的。另外银河系的样子还可以根据银河系内恒星的分布来推断的。

有个星系的代号是 NGC 4565，也被称作 Needle Galaxy。最先于 1785 被观测到。我们正好对着它的窄边，离我们大约3千万光年。

这个漂亮的螺旋形星系叫 Messier 83，离我们1千5百万光年，是我们银河系的二分之一大。其中螺旋形的臂清晰可见。

你知道天球吗？银河系在天球有投影，根据这个投影就可以知道，银河系的形状。

有数千亿恒星的银河系被认为像一个盘子，100000光年宽，中间有个突起，带6条螺旋形的臂。我们不能发射探测器到银河之外，来给银河系拍照。但是我们可以给附近天文学家认为应该和银河系类似的星系拍照，来了解我们的银河系从外部看起来会是什么样子的。另外银河系的样子还可以根据银河系内恒星的分布来推断的。

有个星系的代号是 NGC 4565，也被称作 Needle Galaxy。最先于 1785 被观测到。我们正好对着它的窄边，离我们大约3千万光年。

这个漂亮的螺旋形星系叫 Messier 83，离我们1千5百万光年，是我们银河系的二分之一大。其中螺旋形的臂清晰可见。

有数千亿恒星的银河系被认为像一个盘子，100000光年宽，中间有个突起，带6条螺旋形的臂。我们不能发射探测器到银河之外，来给银河系拍照。但是我们可以给附近天文学家认为应该和银河系类似的星系拍照，来了解我们的银河系从外部看起来会是什么样子的。另外银河系的样子还可以根据银河系内恒星的分布来推断的。

有个星系的代号是 NGC 4565，也被称作 Needle Galaxy。最先于 1785 被观测到。我们正好对着它的窄边，离我们大约3千万光年。

这个漂亮的螺旋形星系叫 Messier 83，离我们1千5百万光年，是我们银河系的二分之一大。其中螺旋形的臂清晰可见。