《宋书·志·卷十三》
就以月份与四仲相联系，这样位置在中央的星宿是不变地位于面腥处，董、扣用它来定季节是根据其永远不变的特点。
直以月推四仲，则中宿常在卫阳，羲、和所以正时，取其万代不易也。
The time when the location of the central constellation in the middle of the month coincided with the four seasons, that is, when the constellation was fixed, the observation of the time of the four seasons was based on the constant nature of the constellation.
<s>[INST] Identify the key themes in this Classical Chinese text and explain them in English: 直以月推四仲，则中宿常在卫阳，羲、和所以正时，取其万代不易也。 [/INST] The time when the location of the central constellation in the middle of the month coincided with the four seasons, that is, when the constellation was fixed, the observation of the time of the four seasons was based on the constant nature of the constellation.</s>
Identify the key themes in this Classical Chinese text and explain them in English: 直以月推四仲，则中宿常在卫阳，羲、和所以正时，取其万代不易也。
user
The time when the location of the central constellation in the middle of the month coincided with the four seasons, that is, when the constellation was fixed, the observation of the time of the four seasons was based on the constant nature of the constellation.
assistant