I wonder what else I can delete from this computer to create space. Does anyone have any suggestions on how to find and delete unnecessary files on a MacBook Pro?
[EDIT: UPDATE] The actual backup only took a bit more than five hours. After triple-checking that the photo files are indeed safely ensconced on the new hard drive, I held my breath and deleted two-hundred twenty-some gigabytes of photo files from the MacBook Pro. After clearing out various files littering the desktop and from the downloads folder, there is now 239gb of hard drive space available on the MacBook.
I think, just to be safe, I shall duplicate the photo backup to another external drive. I lost all my photos from 2006 to 2008, other than those I had uploaded to Flickr, when the hard drive on which they were stored somehow lost all its data. The disk is completely blank. It had worked the last time I had tried it, then I set it away for a couple of years. When I pulled it out several months ago, there was nothing on it. I've tried attaching it to two different Macs and a PC. No matter which device I attach the drive to, I get a "this disk is not readable, would you like to format" message.
This is NOT the disk to which I will be backing up my back-up.