China - Wrong public holiday "Qingming Festival"

[yumi564335]

Affected country

China

Affected public holiday

清明节

Source of the information

https://www.baidu.com/s?wd=%E4%B8%87%E5%B9%B4%E5%8E%86&rsv_spt=1&rsv_iqid=0x96c009f701c58988&issp=1&f=8&rsv_bp=1&rsv_idx=2&ie=utf-8&tn=baiduhome_pg&rsv_dl=tb&rsv_enter=0&rsv_sug3=16&rsv_sug1=19&rsv_sug7=101&rsv_btype=i&prefixsug=%25E4%25B8%2587%25E5%25B9%25B4%25E5%258E%2586&rsp=5&inputT=9569&rsv_sug4=10739

More information

No response

[tinohager]

Could you perhaps provide a little more information on what exactly is wrong?

[yumi564335]

The Qingming Festival should be on April 4th, not April 5th

[tinohager]

Currently we have fixed it to April 5th.

Nager.Date/src/Nager.Date/HolidayProviders/ChinaHolidayProvider.cs

Lines 35 to 41 in 9972a95

	new HolidaySpecification
	{
	Date = new DateTime(year, 4, 5),
	EnglishName = "Qingming Festival (Tomb-Sweeping Day)",
	LocalName = "清明节",
	HolidayTypes = HolidayTypes.Public
	},

On wikipedia i found the info it moves from 4-6 April (https://en.wikipedia.org/wiki/Public_holidays_in_China)

The rule is "Occurs about 15 days after the March Equinox".

A mapping table to this must be give us the correct date.
https://www.beda.cz/~jirkaj/seasons/seasons.pdf

Could you check and confirm this for me?

2007 -> April 5th
2008-2043 -> April 4th
2044 -> April 3th
2045 -> April 4th

[yumi564335]

Why Qingming Isn't Exactly 15 Days After the March Equinox
‌Earth’s elliptical orbit‌
Earth moves slightly faster/slower around the Sun due to its non-circular orbit, causing the March Equinox-to-Qingming interval to vary by ‌±1 day‌ (14–16 days).

‌Leap year adjustments‌
Adding a day (Feb 29) in leap years shifts solar terms slightly, keeping Qingming within ‌April 4–6‌ long-term.

‌Solar-based calculation‌
Qingming is defined by the Sun’s position (15° celestial longitude), not fixed days. This position advances unevenly due to Earth’s changing orbital speed.

‌Result‌: Qingming floats by 1–2 days but stays fixed to April 4–6 through calendar adjustments.

[tinohager]

We would have to check whether we can determine the correct date values with the calculation. It would be great if we had a verified list of correct values for the years.

• https://eclipse.gsfc.nasa.gov/SEcat5/deltat.html

// 🌍 Spring Equinox 2025 in UTC (NASA)
DateTime springEquinoxUtc = new DateTime(2025, 3, 20, 08, 02, 0, DateTimeKind.Utc);

// 📈 Calculate ΔT for the year 2025
double deltaTSeconds = CalculateDeltaT(2025);

// ⏳ Convert UT to TT
DateTime springEquinoxTT = springEquinoxUtc.AddSeconds(deltaTSeconds);

// 🇨🇳 Time zone for China Standard Time (CST, UTC+8)
TimeZoneInfo chinaTimeZone = TimeZoneInfo.FindSystemTimeZoneById("China Standard Time");

// 🕒 Convert UT to CST
DateTime springEquinoxChinaTime = TimeZoneInfo.ConvertTimeFromUtc(springEquinoxTT, chinaTimeZone);

// 📌 Output the results
Console.WriteLine($"Spring Equinox 2025 UTC:  {springEquinoxUtc} UTC");
Console.WriteLine($"Spring Equinox 2025 TT:   {springEquinoxTT} TT (with ΔT)");
Console.WriteLine($"Spring Equinox 2025 in China: {springEquinoxChinaTime} CST");


// 📌 Calculate Delta T with the given formula
static double CalculateDeltaT(int year)
{
	// Calculate t
	double t = (year - 1820) / 100.0;

	// Calculate ΔT
	double deltaT = -20 + 32 * Math.Pow(t, 2);

	return deltaT;
}

[tinohager]

• Complete country China - Qingming (Tomb-Sweeping Day) #52