am/pm

Dear to whom may it concern,
Can I write the first letter of am/pm in this way? Or it is necessary to write the first of letter am/ pm in capital letter?
[color=red]The train arrives at 8.am
The train arrives at 8.Am

With the marvelous regards
Mitra584

Yours are not quite right. These are all possible:

8 am
8 a.m.
8 AM
8 A.M.

Dear Dozy,
:))Thank you very much indeed.
Regards
Mitra584