Jan Brown, age 13, of Huntsville, Alabama, for her question:

What do you mean by the cosmos?

Cosmos is one of our favorite words, which explains why we often us it. It is neat and sweet sounding and easy to say. Though small, it conjures up visions of vast heavenly vistas of limitless space and eternity. However, the best way to master a word is to track down its origin. Many of our words are borrowed and adapted from older languages and their wordy ancestors have a great deal to tell us. Cosmos descended to us from an old Greek word and its origin adds an extra dimension of beauty to the poetic little word.

Its original ancestor was a word meaning order and harmony. The thinkers of ancient Greece dreamed of an ideal world governed by smooth running laws, unbounded by time and space. They believed that such an orderly state of harmony existed behind the changing scenery of nature. And the Greeks, of course, had a name for it. The word was the ancestor of our word cosmos. Nowadays, we use cosmos to mean the entire universe, including the far flung galaxies and the oceans of space between them. We probe its cosmic laws and try to fathom its cosmic time. And our name for certain particles that visit us from the cosmos is cosmic rays.