Here's why BBC4's only on part time:
On the Freeview digital terrestrial platform, BBC Four is broadcast in a statistically multiplexed stream in Multiplex B that timeshares with the CBeebies channel. As a result, BBC Four broadcasts from 7 pm to about 4 am every day, with an hours down-time and promotions for CBeebies, before CBeebies channel runs from 6 am until 7 pm.
And here's its remit:
It has a schedule dominated by repeats but is required by its licence to broadcast at least 100 hours of new arts and music programmes, 110 hours of new factual programmes and premier 20 international films each year.
Now can I go and watch the Mars programme in peace?