Which is the longest month of the year?

Option 1:

This is *usually* asked as a trick question. The answer to that trick question is September. "September" has 9 letters, all the others have between 3 and 8. That makes it the "longest" month. There are a number of months that have 31 days, as you likely know, so you need a semantic trick to answer this question.

Option 2:

If you are looking for a very technical, scientific answer ... it depends on where you live in the world. The longest month depends on where you live and in some places it's 31 days. In the western hemisphere a leap second is added at the end of December and in the eastern hemisphere in January making both months 31 days and 1 second long when they are added.

The actual world's longest month clocks in at 31 days 1 hour due to reverting from daylight saving time. In most of Europe this occurs in September and since September has only 30 days they do not experience the longest month. In America (except for a few states), Britain, Canada and other countries DST ends in October making October the world's longest month, but not the only one. In Australia DST ends in March giving it an extra hour and a tie for the world's longest month. In 2007 many countries, including America, will be extending DST till November, which has only 30 days, so the longest month will not apply.

According to this page from Wiki, 2 of the months of the Javanese calendar have 43 days. Mangsa Kanem & Mangsa Kapitu.
https://en.wikipedia.org/wiki/Javanese_calendar

January, March, May, July, August, October, and December all have 31 days in the Gregorian.
https://en.wikipedia.org/wiki/Gregorian_calendar

Daylight savings time in the USA which would add an hour to the length of a month in the turn back month and subtract an hour in the turn ahead month, adds an hour to November and subtracts an hour from March leaving only January, May, June, August, October and December as months with 31 full days in them. The change of adding an hout to November still leaves it short of 31 days while March only comes out to having 30 days 23 hours.

https://en.wikipedia.org/wiki/Daylight_savings_time_(united_states)

But that is longest month time wise. The longest month of the year spelling/letter-wise is September.

During Jewish leap years, Adar is expanded from 30 to 60 days (though the new moon in the middle denotes another month on the calendar). The longest time most Jews go without celebrating the start of a month is from the first day of Elul to the 29th of Tishrei. While Rosh Hashannah (the new year) occurs on the first day of the month of Tishrei, the end of the month of Elul is announced earlier to prepare for the special festival, and the holiday is not celebrated as the beginning of a new month. Thus there is a 58-day "month-season" celebrated by Jews around the world. The current one started on the 30th of August and will end on the 27th of October.