Since the earliest times, the natural cycles of the sun and moon have been used to measure intervals of time. Solar cycles define days, years and seasons while the moon marks off “moonths.”

There are two major lunar cycles, the best known being the 291/2-day synodic month during which the moon goes from new moon to new moon. (“Synodic” refers to the meeting of the sun and moon). Less apparent is the 271/3-day sidereal (star) month, which is based on the moon’s position as seen against the background stars.

If Earth wasn’t orbiting the sun, synodic and sidereal months would be equal. But since we are moving, the synodic month takes longer.

In a sidereal month, the moon travels 360 degrees (one complete circle) around Earth before repassing the same background stars. During this time, however, Earth has traveled nearly one-twelfth of the way around the sun, meaning the moon must travel nearly 390 degrees, and two more days, before reaching the next new moon.

A year being 365 1/4 days, there is not an even number of synodic or sidereal months in a year. This was not a problem for cultures who referred to these intervals by the names they gave full moons, such as Harvest, Hunter’s and Long Night Moon.

But when our ancestors devised formal calendars, adjustments were required, such as adding or subtracting days and even ignoring periods of time.

These months approximate but no longer exactly correspond with the lunar cycles. The names we use for our months derive from the Romans and their Latin language.

Originally, the Roman year had 10 months that began with March, named for Mars, the god of war. The second month, April, was named for Aphrodite (Venus), the goddess of love and beauty. May is the month of Maia, goddess of spring. June honors Juno, goddess of women, childbirth and marriage.

July was originally called Quintilis (quintus being Latin for fifth) as the fifth month; it was renamed by Julius Caesar in 46 BCE to honor himself. Similarly, August, first known as Sextilis (sex = six) as the sixth month, was changed by Augustus Caesar.

The next four retained their Latin numeric names: September (septem = seven) as the seventh month, October (octo = eight) as the eighth month, November (novem = nine) as the ninth month, and December (decem = ten) as the tenth month.

The winter months apparently went unnamed until about 700 BCE when the 11th and 12th months were added. January was named for Janus, the double-faced god of beginnings and endings who could see the past and the future. February came from Februa, the festival of purification.

So like the names we use for many constellations, as well as the days of the week, the names of our months were invented by our ancient ancestors.

* Next two weeks: Average sunrise: 6:58 a.m.; average sunset: 6:24 p.m. The moon is at first quarter tomorrow. Thursday evening (and all night), Mars is to the left of the bright gibbous moon.

The Feb. 28 full moon is called Wolf Moon, Snow Moon and Hunger Moon. The evening of March 1, the moon is to the right of Saturn as they rise around 8 p.m. and accompany each other across the sky all night; by morning the moon is to Saturn’s lower left.

* Naked-eye planets: (The sun, moon and planets rise in the east and set in the west because of Earth’s west-to-east rotation on its axis.) Evening: Mars is prominent high in the east as Saturn rises some two hours after sunset. Morning: Saturn is in the west southwest.

Stargazer appears every other Saturday. Paul Derrick is an amateur astronomer who lives in Waco. Contact him at 918 N. 30th St., Waco 76707, (254) 753-6920 or paulderrickwaco@aol.com. See the Stargazer Web site at stargazerpaul.com.