Chris Durkin, age 13, of Staten Island, N.Y., for his question:

WHO INVENTED THE CALENDAR?

Today's calendar has 365 days in each year. It is a record of the days, weeks and months of the year. Each fourth year, to correct a bit of additional time, an extra day is added. Last year, 1976, was such a year  and it was called leap year.

The Egyptians were first to measure a year accurately. When a new moon appeared every 29 or 30 days, they called it a month. Twelve of these months became a year.

Ancient calendar makers knew that time was divided into days and years. Days were separated into light and darkness, so it was easy to tell how long they were, but it   were, but it was not as easy to figure the length of the year. Finally they decided the year must be the amount of time it takes the earth to revolve around the sun.

The Egyptian calendar was 11 days short of the time it took the earth to go around the sun. When the Greeks, Babylonians and Hebrews borrowed this calendar they added an extra month if they found the year too short or the seasons coming at the wrong time.

In 46 B.C. the Julian or Old Style calendar appeared. Then the Gregorian calendar. Named for Pope Gregory XIII, this calendar dropped 10 days from the year in 1582 and moved all of the months ahead. This was called the New Style calendar.

Some people are still not too happy with the present calendar and would like to see it changed. One proposal is for the world Calendar which has been submitted to the United Nations for approval.

This calendar contains 364 days with an extra day at the year's end which would be world holiday. Any date would always fall on the same day each year.    (Changes in our calendar continue today. As you know, there has recently been legislation that has changed such favorite holidays as Washington's Birthday and Memorial Day. As time passes and as the subject is discussed, there may be additional changes.