Three generations of stars may exist based on metallicity.

以金属度划分，恒星有三个世代。

One clue comes from the metallicity of the disc's constituent stars.

一条线索来自于主盘内恒星的金属丰度。

Different theories predict how this metallicity gradient changes over billions of years.

已有几种不同的理论对金属丰度梯度在亿万年间如何变化作了推测。

Metallicity is a measure of the relative abundance in a star of elements other than hydrogen and helium.

金属丰度是对恒星内除氢和氦之外元素的相对丰度的度量(天文学中比氦重的元素都叫金属。——译者注)。

The metallicity of a star measures the amount of "metals" it has —that is, any element heavier than helium.

恒星的金属度用于表征它含有的“金属”的量——其实是所有比氦重的元素的量。