Twilight was asked to help clean up Canterlot library, not really sure why Celestia asked her to wear the outfit as well. Celestia can be so odd, but it makes her happy.

The art is for  Laurenrivers' new mouse pad
art by me.
Twilight Sparkle and Celestia ©2010 Lauren Faust and Hasbr
Library ©3000 BC Humanity
Fire ©beginning of time with oxygen
Torches ©20,000 BC Humanity
Hourglass ©16th Century CE some body in Europe
Dust Pan ©1897 Lloyd Ray
French Maid Outfits ©19th century Victorian era