For example, the distance between Mercury and Earth can range from 77 million kilometres at their closest point, to 222 million kilometres at their farthest.
From ages 1 to 3, most toddlers sleep about 12 to 14 hours over a 24-hour period. Separation anxiety, or just wanting to be up with mom and dad (and not miss anything), can motivate a child to stay awake. So can the simple toddler style of always saying No!.
While most babies sleep through five or six night a week by the age of six months, according to the study by American psychologists, a third continue to wake much more frequently until they are toddlers. They looked at sleep patterns in 1,200 children from birth to three years and found 'wakers' tended to be boys.