How long is winter to a groundhog?

Winter is just as long to a groundhog as to us, but supposedly, groundhogs can predict the season changes.

According to the legend, if the groundhog on leaving its burrow does not see his shadow, it will leave the burrow , which it means that winter will soon end. If, however, it "sees his shadow" and is frightened, it will go back into the Burrow, meaning that winter will last six more weeks.