Chinese Festival dates are sometimes based on the Chinese Lunar Calendar. This page provides functions for calculating the Gregorian dates of various lunar festivals. Converting lunar dates to Gregorian could involve complex mathematics, this can be avoided by using calender conversion routines buit into the .NET framework. (They are part of all recent releases of VB.Net and will not need any external packages or additional references.)
 
The following comments indicate some potential problems linked to lunar-Gregorian date conversions

• The number of days in a Lunar year can vary between 353 and 385 days. (The Gregorian Calendar only varies between 365 and 366 days.)
• The first day of the lunar calendar can fall anywhere in the Gregorian period of 21 January to 20 February
• Normally, a gregorian year will have a single date matching a chinese festival.
• Occassionally, a single Gregorian Year will contain the same festival from 2 successive Lunar years (when festival lands each side of 1 Jan). You can also get Gregorian years where a specified festival does not occur.
• The Lunar calendar uses "Leap Months" to remain "approximately" aligned with a solar year. Any of the 12 "normal" lunar months can be repeated before starting the next lunar month
• The "Leap Month" will only occur in Lunar leap years. The repeated month could be any of the 12 normal months and will create a 13 month year.
• Converting dates within the original and repeated month of a leap year may require additional knowledge. (Do you use original month or the repeated leap-month?)
• The Lunar .NET calendar conversion feature is only valid for the lunar years 1901 to 2100.
• Geographic location, local time and cultural differences affect Calendrical Calculations. These functions are based on Beijing time/location.

Private Function ChineseEventDate_To_GregorianDate(yyyy_Chin As Integer, mm_Chin As Integer, dd_Chin As Integer) As Date
' When a lunar event falls in the repeated month of a leap year, we normally celebrate in 1st occurence of month
 Dim chinese As New Globalization.ChineseLunisolarCalendar
 Dim gregorian As New Globalization.GregorianCalendar
 Dim leapMonth As Integer
 Dim LeapAdjustedMonth As Integer
 Dim dat_Chin, dat_Greg As Date
 leapMonth = chinese.GetLeapMonth(yyyy_Chin)
 If leapMonth > 0 AndAlso leapMonth <= mm_Chin Then
  LeapAdjustedMonth = mm_Chin + 1
 Else
  LeapAdjustedMonth = mm_Chin
 End If
 dat_Chin = chinese.ToDateTime(yyyy_Chin, LeapAdjustedMonth, dd_Chin, 12, 0, 0, 0)
 ' using midday to avoid risk of clock adjustmenst etc. changing dates
 dat_Greg = New Date(gregorian.GetYear(dat_Chin), gregorian.GetMonth(dat_Chin), gregorian.GetDayOfMonth(dat_Chin), 12, 0, 0, 0)
 Return dat_Greg
End Function
  

 

Dim yyyy_Chin as integer
' yyyy_Chin should be year in the Chinese calendar. Typucally either year_Gregoraian or (year_Gregorian - 1)
Dim ChineseNewYear As Date = ChineseEventDate_To_GregorianDate(yyyy_Chin As Integer, 1, 1)
Dim LanternFestival As Date = ChineseEventDate_To_GregorianDate(yyyy_Chin As Integer, 1, 15)
Dim Zhonghe Festival As Date = ChineseEventDate_To_GregorianDate(yyyy_Chin As Integer, 2, 2)
Dim ShangsiFestival As Date = ChineseEventDate_To_GregorianDate(yyyy_Chin As Integer, 3, 3)
Dim DuanwuFestival As Date = ChineseEventDate_To_GregorianDate(yyyy_Chin As Integer, 5, 5)
Dim QixiFestival As Date = ChineseEventDate_To_GregorianDate(yyyy_Chin As Integer, 7, 7)
Dim GhostFestival As Date = ChineseEventDate_To_GregorianDate(yyyy_Chin As Integer, 7, 15)
Dim MidAutumnFestival As Date = ChineseEventDate_To_GregorianDate(yyyy_Chin As Integer, 8, 15)
Dim DoubleNinthFestival As Date = ChineseEventDate_To_GregorianDate(yyyy_Chin As Integer, 9, 9)
Dim SpringFestival As Date = ChineseEventDate_To_GregorianDate(yyyy_Chin As Integer, 10, 15)
Dim LabasFestival As Date = ChineseEventDate_To_GregorianDate(yyyy_Chin As Integer, 12, 8)
  

 

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