How to make a computer turn itself on at a scheduled time?

[Josef Lowder]

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How can one make a computer turn itself on at a scheduled time? 

While I leave my computer on 24x7, I'd like to set up my wife's 
computer to come on at 6 am so it will be all ready for her to 
check her email in the morning before she leaves for work, and 
then (with power management) have it turn itself off an hour after 
she stops using it (when she leaves to go to work for the day). 
No sense having it run 24x7 when she only uses it for about a 
half hour every day. 

Yes, of course she can turn it on and off, but it would be great 
to make this automatic.