who came up with the names for every month of the year?

Answer 1

Dirk has much of the answer, but there's a bit more. The calendar we use has its origins in the "ancient Roman calendar" back around the time of the mythical Romulus & Remus, ca 750 BCE.

Rome, or more probably the ancient Etruscans, had an agricultural economy, and at the time, a 10-month calendar sufficed. Plowing and planting began around the time of the vernal equinox (first day of spring), and this is when the year began. The ten months were Martius, Aprilis, Maius, Junius, Quintilis, Sextilis, Septembris, Octobris, Novembris, and Decembris. Six of those months had 30 days, the other four had 31, so the calendar had 304 days. The 61 omitted days occurred in the dead of winter, when the harvest was completed and spring tilling and planting not yet timely.

The Latin numbers 1 through 10 are unum, duo, tres, quatoor, quinque, sex, septem, octo, novem, and decem, so the fifth through tenth months were numbered.

Mars (Martius) was the Roman god of war; Aprilis is named after Venus, the goddess of love; Maia (Maius) was a daughter of Atlas and an earth goddess; Juno (Junius) was the wife of Jupiter.

Less than 200 years later (still well before Caesar), two more months were added -- Januarius (after Janus, an ancient sky god) and Februarius (unknown origin, but probably feminine). The winter festival Saturnalia, occurring shortly after the solstice, was highlighted by an early Roman ruler who decreed that the new year should follow immediately. That's why New Years Day is now in January.

Julius Caesar reformed the calendar (the Julian calendar) and named July after himself. His successor Octavian (Augustus) did the same.

Why does February have 28 days? When January and February were added, February was the last month. The original ten months of 304 days had a 5-by-2 pattern: March through July have 31 30 31 30 31 days, and August through December have the same pattern. Following this, January holds 31 days and February could hold 30. But because the year only has 365 days, February can only have 28, with Leap Year Day added as the 29th.

I think this answers your question. Occasionally, I teach this to my students, but it doesn't quite fit into the curriculum, nor is it in the textbooks. I just squeeze it in somewhere. How else are you going to learn this interesting trivia?

Answer 2

most of the names come from the julian calender. So Julius Ceasar wouldn't be a bad answer. Yet, a false one. Julius Ceasar kept the same names:
Ianuarius, Februarius, Martius, Aprilis, Maius, Iunius, Quintilis, Sextilis, September, October, November, and December

Obviously July comes from Julius (Caesar) and August comes from Augustus (the one who ruled after julius caesar).

Answer 3

The Romans.

Answer 4

The names of the months and days are derived from Greek, Roman, and Norse mythology.

Answer 5

an old friend of mine

he made them to match my name