The 'Kagami Mochi' New Year decoration

Among the staple New Year decorations is Kagami Mochi.  "Kagami Mochi" literally means 'mirror rice cake'. Two mochmi of different sizes, representing the new and old year, are placed one on top of the other, with an orange on top. They are to welcome good luck and, traditionally, to ward off fires. They are usually placed at or near the family altar in homes. 

They are displayed after Christmas. December 28th is a good day, but the 29th isn't as its considered an unlucky day and its a day of rest traditionally' Likewise, December 31st and January 1st are considered too late to start displaying 'kagami mochi'. Nowadays, many people buy them. The store bought ones are plastic, but they have individually wrapped mochi. Years ago people made the two mochi mounds, like the one in the photo. Bought or made: January 11th is the date for breaking the kagami mochi (but not with a knife as its unlucky) and eating it. 

You can buy them at most supermarkets and shopping centers, and even homeware stores and drug stores.  You can also often find them at the New Year markets at shrines, at this time of year. Prices vary greatly depending on style and size.