夏至 Summer solstice interesting facts

2023年6月21日

Parowan gap, Utah

日影最短，白晝最長Longest day

- Almost.

Eg Netherlands happens on 20 June in 2023

Maplog , solartopo

Timing（香港時間）：

氣象台

-都採用地心視黃經 geocentric apparent ecliptic longitude 等於90度為標準。right ascension 6 hours and a northern declination equal to the obliquity of the ecliptic (23.44°)

USNO: 22:58

HKO: 22:58

PMO紫金山: 22:57:48

- 节气时间的计算转换为两部分：建立太阳位置随时间变化的计算模型，和根据太阳位置函数反求时间引数的数值方法。其中太阳位置计算模型涉及基本天文学的重要研究工作，包括太阳系基本历表的研制，时间系统的定义和转换，参考系的定义和转换，天文常数系统的建立等。可以说，节气的计算模型和精度能够反映基本天文学的发展成就。

目前，紫金山天文台建立的节气计算模型遵循国际天文学联合会IAU、地球自转和参考系服务关于基本天文学的决议和规范。介紹

IMCCE: 22:57:50

USNO： 22：58

NAOJ： 22：58

其他組織：

HKAS: 22:57:51.018

- HKAS 以往跟氣象台的計算往往有1至3數分鐘不等的偏差。但計算夏至節氣反而比較接近

Astropy: 22:57:48.087

- stackexchange

通勝，農曆算命網站，利用eg 許劍偉壽星天文曆 github in JavaScript, github.io，精度表

因再加上 based on 身處地理位置(topocentric)的真太陽時 , so do not match 氣象台.

壽星天文曆sxtwl 基於 VSOP87, IAU2000, ELP github

Nongli, bmcx: 22:57:37

- bbs

Xmizi, sheup: 22:53:37

命理網: 22:57:43.48

- based on JPL DE

元谷海棠萬年曆用c++ github， gitee， pypi install ，snyk 改良自壽星天文曆 . 772BC to 9999AD, 精度與壽星天文曆相同， multi platform , but google playstore app is broken

吹泡泡的小猫 oRbIt

sunhou

Kowala

Kumkee by JPL Horizons query

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