| 1. | There is a curious feature in the spectra of spiral galaxies .
在旋涡星系的光谱中有一种奇妙的特征。 |
| 2. | Spiral galaxies are considered to be gravitationally bound configurations of stars .
旋涡星系被认为是由恒星组成的引力束缚系统。 |
| 3. | But almost all spiral galaxies are much older than 2 billion years
但是几乎所有旋涡星系的年龄都超过了20亿年。 |
| 4. | The mystery arises when one considers how a spiral galaxy rotates
当人们考虑旋涡星系是如何转动的时候难题就来了。 |
| 5. | New stars are constantly forming out of gas and dust in spiral galaxies
在旋涡星系中不断由气体和尘埃形成新的恒星。 |
| 6. | This spiral galaxy is called m81 which is about 11 . 7 million light years away
这旋涡星系名为m81 ，距离我们约有1 , 170万光年。 |
| 7. | Grand design spiral
宏象旋涡星系 |
| 8. | Dwarf spiral galaxy
矮旋涡星系 |
| 9. | Face - on spiral
正向旋涡星系 |
| 10. | Smaller groups of stars called globular clusters often surround spiral galaxies
称作球状星团的小型恒星团体经常环绕在旋涡星系周围。 |
