Q 01/05

How many days does a leap year contain in the Gregorian calendar?

A) 360

B) 364

C) 365

D) 366

Answer · why

D) 366

The extra day keeps the calendar year lined up with the seasons, which is why some lunisolar calendars add a whole month instead.

Q 02/05

Under the Gregorian rule, a year divisible by 100 is a leap year only if it is also divisible by what?

A) 400

B) 800

C) 1000

D) 4000

Answer · why

A) 400

That is why 2000 was a leap year but 1900 was not and 2100 will not be; the rule removes three leap days every 400 years.

Q 03/05

Which of these years was NOT a leap year?

A) 1600

B) 2000

C) 2400

D) 2100

Answer · why

D) 2100

The February 2100 calendar will go straight from the 28th to March 1, just as 1900's did; 1900's missing day famously breaks Microsoft Excel, which st...

Q 04/05

Roughly how far does the Julian calendar, with its 365.25-day year, drift from the true seasons?

A) About 1 day every 400 years

B) About 3 days every 100 years

C) About 1 day every 40 years

D) About 3 days every 400 years

Answer · why

D) About 3 days every 400 years

By 1582 that slow slip had pushed the spring equinox ten days early, which is what prompted the Gregorian reform.

Q 05/05

The average Gregorian calendar year works out to how many days?

A) 365.2425

B) 365.2475

C) 365.25

D) 365.2525

Answer · why

A) 365.2425

The mean tropical year is about 365.2422 days, so the Gregorian calendar still gains roughly a day every 3,000 years or so.