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Chinese New Year (Posted on 2015-01-16) Difficulty: 3 of 5

Chinese New Year (CNY) falls on 19th February this year. That's an unusually late date; CNY generally falls around the beginning of February.

CNY can also fall on 20th February, though that's only happened once in my lifetime.

a. When will CNY next fall on 20th February?
b. Can CNY ever fall on 21st February? If so, when will that happen next?

See The Solution Submitted by broll    
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Solution computer solution | Comment 2 of 8 |
Verizon (my ISP) removed all personal websites, including mine, which included a Chinese New Year calculator, but it's available at

If you look at the source code of the page you can see the calculations in javascript. To run it, you'll probably need to ok the running of the script.

I modified the source code portion that gives a series of years to report only those years where the date was February 20 or 21, and ran with an initial year of 1900 and entered a request to run for 2000 years. The results are:

February 20 1920 Monkey 
February 20 1985 Ox 
February 20 2148 Monkey 
February 20 2167 Rabbit(Hare) 
February 20 2205 Snake 
February 20 2224 Rat 
February 20 2243 Sheep(Goat) 
February 21 2319 Boar(Pig) 
February 20 2615 Sheep(Goat) 
February 20 2729 Ox 
February 20 2911 Rabbit(Hare) 
February 20 2930 Dog 
February 20 3063 Boar(Pig) 
February 20 3082 Horse 
February 20 3112 Rat 
February 20 3131 Sheep(Goat) 
February 20 3264 Monkey 
February 20 3302 Dog 
February 20 3340 Rat 
February 21 3416 Dragon 
February 20 3454 Horse 
February 20 3503 Sheep(Goat) 
February 20 3522 Tiger 
February 20 3636 Monkey 
February 20 3712 Rat 
February 20 3731 Sheep(Goat) 
February 20 3788 Dragon 
February 20 3807 Boar(Pig) 
February 20 3826 Horse 

Answers to:

a. 2148

b. Yes, 2319

Verify at

More information is at:

The farther into the future one goes, the more dependent on the accuracy of estimates of the rate of slowing down of the earth's rotation, which determines, in close cases, which side of a midnight instant a given moon phase or transition of the sun from one segment of the zodiac to another takes place. I didn't trace or manually step through the code to see whether the 2319 case depends on a transition near midnight.

Also, in 1928, the longitude for which time calculations are used, was switched from 116° 25' East to 120° East, moving it to Peking standard time rather than a time zone about a quarter hour off from any standard one.  If the time zone is changed in the future, that would affect the astronomical details.

  Posted by Charlie on 2015-01-16 20:30:14
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