My favorite sub-field of astronomy would be Astrobiology, favorite train would be the SR Class 4DD for its quirkiness and historic value as the only 'double-decker train' to run on UK steels, and my favorite period of time would be the (informal) Precambrian, featuring all the weird, strange and elusive forms, from the Ediacaran biota to the controversial Francevillian forms.
This is just a little list of things I am either working on, or intend to work on soon.
To see WIP articles (when I actually use the sandboxes), see the bottom four links in "Links for quick access".
Lifeform Articles:
Various Neoproterozoic algae-related articles (i.e. Doushantuophyton)