Months

Etymology

There were originally only ten months in the Roman calendar; January and February were added in about 150 BC. Before this, apparently, the days of what we know as January and February didn't belong to any month.

	January	Named after the god of beginnings and transitions (Janus) – whose name in turn is derived from the word for a door (ianua)
	February	Named after Februa, the festivals of purification celebrated in Rome during this month
	March	Named after the Roman god of war (Mars)
	April	Uncertain – possibly from the Latin verb meaning "to open" (aperire), in allusion to its being the season when trees and flowers begin to open
	May	Named either after the eldest of the Pleiades (Maia – the mother, by Zeus, of the Greek god Hermes), or after the Roman goddess of honor and reverence and the wife of the god Vulcan (Maiesta – who may in fact be the same being)
	June	Named after the wife of Jupiter and the queen of the Roman gods (Juno)
	July	Named in honor of Julius Caesar in 44 BC, the year of his assassination; it was the month in which he was born. Previously known as Quintilis (the fifth month)
	August	Named after the first Roman emperor (Augustus – because several fortunate events of his life occurred during this month). Previously known as Sextilis (the sixth month)
	September	The seventh month of the ancient Roman calendar
	October	The eighth month of the ancient Roman calendar
	November	The ninth month of the ancient Roman calendar
	December	The tenth month of the ancient Roman calendar

Birthstones

In the following table, the first column of answers (headed 'UK NAG') lists the birthstones published by the UK's National Association of Goldsmiths (now archived on the Wayback Machine). This list also includes several alternatives, which are listed in the second column.

Wikipedia also gives a "traditional" list of birthstones (from a book entitled The Curious Lure of Precious Stones – George F. Kunz, 1913) and an equivalent (modern) list for the USA (from the Gemological Institute of America). These are listed in the third and fourth columns. (I haven't bothered to hide these 'alternative' answers as I don't really see anyone wanting to test themselves on them).

The above references (National Association of Goldsmiths, Gemological Institute of America, and The Curious Lure of Precious Stones) are all cited by Wikipedia.

	UK NAG	UK NAG Alt	Kunz	GIA
January	Garnet
February	Amethyst		Hyacinth, pearl
March	Aquamarine	Bloodstone	Jasper
April	Diamond	Rock crystal	Sapphire
May	Emerald	Chrysoprase	Agate
June	Pearl	Moonstone	Cat's eye, turquoise, agate	Alexandrite
July	Ruby	Carnelian	Turquoise, onyx
August	Peridot	Sardonyx	Carnelian, moonstone, topaz	Spinel
September	Sapphire	Lapis lazuli	Chrysolite
October	Opal		Aquamarine	Tourmaline
November	Topaz	Citrine	Pearl
December	Tanzanite	Turquoise	Bloodstone, ruby, lapis lazuli (US)	Zircon

According to Wikipedia, the American Gem Trade Association changed December's birthstone in 2002 – the first change to any birthstone list since 1912. The gemstone they chose is known scientifically as blue–violet zoisite, but the marketing department of the New York luxury goods retailer Tiffany & Co. decided that this was not "consumer friendly" enough. They renamed it after the country it comes from – the only place where it's found, and that only in a very small area of about five square miles. It's known for its trichroism – having three different colors, according to the angle from which it's observed – especially in polarised light.

The UK NAG clearly decided to follow suit, as its archived website names the same gemstone as its birthstone for December.

Zodiac Signs, French Revolutionary Months, and Moons

The table below lists the Zodiac signs, the months of the French revolutionary calendar, and the names for the full moons alongside the months in which they begin or occur.

The Sun enters each Zodiac sign on either the 20th, 21st, 22nd or 23rd day of the calendar month.

In the French revolutionary calendar, each month had 30 days. The year began after the Autumn equinox; so the first month, Vendémiere, began on either the 22nd, 23rd or 24th of September. The day of the "standard" calendar month on which each French month began then moved progressively backwards through the year, until Fructidor began on the 18th or 19th of August. The five or six "complementary days" began after the 30th day of Fructidor – i.e. on the 17th or 18th of September.

The French revolutionary calendar was used for about twelve years, from late 1793 until 1805, and again for 18 days by the Paris Commune in 1871.

The Full Moons are listed in The Old Farmer's Almanac, and also on timeanddate.com.

Timeanddate.com claims to be "the world's number one website on time". It's run by an independent company based in Stavanger, Norway; it has English, German and Norwegian language versions. Its contributors come from four continents. In the context of Full Moon names, it specifically refers to the Old Farmer's Almanac, which is of American origin and states that its Full Moon names "come from a number of sources, including Native American groups, Colonial Americans, or other traditional North American names passed down through generations." It adds that "each full Moon name was applied to the entire lunar month in which it occurred."

Note also that all of these New Moons have several different names, only one of which is listed here.

Month	Zodiac sign	French Republican	Full Moon
January	Aquarius – the water carrier	Pluviose (Rainy)	Wolf
February	Pisces – the fish	Ventose (Windy)	Snow
March	Aries – the ram	Germinal (Seedy)	Worm
April	Taurus – the bull	Floreal (Flowery)	Pink
May	Gemini – the twins	Prairial (Grassy)	Flower
June	Cancer – the crab	Messidor (Wheaty)	Strawberry
July	Leo – the lion	Thermidor (Hot)	Buck
August	Virgo – the virgin	Fructidor (Fruit–bearing)	Sturgeon
September	Libra – the scales or balance	Vendémiaire (Wine–harvest)	Harvest (Corn)
October	Scorpio – the scorpion	Brumaire (Foggy)	Harvest (Hunter's)
November	Sagittarius – the archer	Frimaire (Frosty)	Beaver
December	Capricorn – the goat	Nivose (Snowy)	Cold

In Western astrology, each sign of the Zodiac is associated with one of of the four classical elements (air, water, fire or earth). You might occasionally be asked about these:

Air	Aquarius	Gemini	Libra
Water	Pisces	Cancer	Scorpio
Fire	Aries	Leo	Saggitarius
Earth	Taurus	Virgo	Capricorn

Specifics

First day in the astrological calendar		21 March
First sign of the Zodiac		Aries
Twelfth and last sign of the Zodiac		Pisces
Only sign of the Zodiac that isn't a living (or mythical) creature		Libra
Month that's traditionally known or described as 'filldyke'		February
Month that (proverbially) "comes in like a lion and goes out like a lamb"		March
Month that's mentioned in the first lines of Chaucer's Canterbury Tales and Eliot's The Waste Land		April
Longest month of the year in Britain (because the clocks go back!)		October

The Hebrew Calendar

I don't think I've ever been asked anything about the Hebrew calendar, except to be given a list of words (for example, "Kislev, Iyar and Tammuz") and asked what they are – the answer being "Months of the Hebrew (or Jewish) calendar". (A particularly inventive one would be "Which Japanese car manufacturer has the same name as a month in the Hebrew calendar?")

The Hebrew calendar is based strictly on the lunar cycle, which means that each month lasts 29 or 30 days. Every few years (about every three, if my calculations are right) there's an intercalary month – an extra month, a bit like the extra day in a leap year.

As you can imagine, this means that there is no exact correlation between the months of the Hebrew calendar and those of the Gregorian one that we're all familiar with. The following table lists the months, and the approximate months in the Gregorian calendar that they correspond to – just to put them in context.

Because it's the way we do things round here, I've hidden the names of the Hebrew months. This doesn't mean that I expect anybody to learn them – I only expect you to see what they are, so that you'll recognise them if you get asked a question of the sort I've described above.

Mar–Apr	Nissan	Apr–May	Iyar	May–Jun	Sivan	Jun–Jul	Tammuz
July–Aug	Av	Aug–Sep	Elul	Sep–Oct	Tishrei	Oct–Nov	Marcheshvan
Nov–Dec	Kislev	Dec–Jan	Tevet	Jan–Feb	Shevat	Feb–Mar	Adar

Av is sometimes referred to as Menachem Av (literally Father Comfort), but "mostly only in the sanctification of the month recited on the Shabbat before Rosh Chodesh and following Tisha B'Av". (Sorry, I have no idea what this means; for more details, please refer to Wikipedia …)

Marcheshvan is sometimes known as Cheshvan for short.