index and sequence name length limit?

What is the limit on the length of a index or sequence's name?

I have some table with long names and I find it confusing when pgsql
truncates the table name when creating indexes or sequences (for serials).

Why does such a limit exist? I would think that since there are
virtually no limits on the size of data that a table or column can hold
there should be no limit on the length of names assigned to
tables/sequences/indexes/etc ... or if that a limit would be rather long
(say 256 characters?).

Jc