The difference between day and night?

An old rabbi once asked his disciples how they could tell when the night ended and the day was on its way back. "Could it be" asked one student, "when you see an animal in the distance and you know whether it's a sheep or a dog?"

"No", replied the Rabbi.

"Could it be",  asked another, "when you look at a tree in the distance and can tell whether it is a fig tree or a peach tree?"

"No", said the Rabbi."Well then, when is it?" his pupils wanted to know.

"It is when you can look at the face of any man or woman and see that he is your brother or she is your sister. Because if you cannot do this, no matter what time it is, it is still night."
From: Tales of the Hasidim.