查看“中性氢”的源代码

*the neutral hydrogen (H i) in the interstellar medium (ISM) is in two phases - a warm and a cold phase. 
:*The warm neutral medium (WNM) has typical temperatures of ∼ 10000 K 
:*he cold neutral medium (CNM) has typical temperatures < 300 K (20-50%) 
:*The WNM is mostly detected in emission and the CNM in absorption.
:*H i self-absorption (HISA) clouds are unique places where we can study the structure and the physical properties of the CNM at the same time.(mixed with H2[[分子氢]]

==optical depth==

==Spin temperature==