# Are the calculations of the Molad mentioned by Ramba"m based on constant or variable (seasonal) figures?

Rambam KidushHachodesh 6:3 states:

[the interval] between one conjunction of the moon and the sun and the subsequent conjunction according to their mean movement is twenty-nine full days, twelve hours of the thirtieth day, and 793 units of the thirteenth hour. This is the interval between one conjunction and the next, [and thus,] the length of a lunar month.

When referring to these terms - "day", "hours" and "chalkim" (here, translated as "units") is Ramba"m referring to 24 hour days and 60 minute hours, or sha'ot z'mani'ot - "seasonal hours" meaning that the length of the day and, thus the length of the hour varies according to the time of the year. (E.g. - during the winter the daylight hour may be < 60 minutes and in the summer, it may be > 60 minutes)?

The answer is well implied in the first 2 paragraphs of the Halachot you quote, namely that we are using 24 hour days and 60 minute hours, not sha'ot z'mani'ot.

Rambam KidushHachodesh 6:1 states:

...The first level of these calculations represent approximations of the time of the conjunction, and their accuracy is not great. This approximation of the time of the conjunction is calculated according to the mean rates of movements.[2] The time of the conjunction as calculated in this manner is referred to as the molad....

The footnote their clarifies:

[2] ... The term mean rate of movement refers to the average movement of the sun or the moon in angular degrees over a particular period. To explain: It was easy to calculate the number of conjunctions between one solar eclipse and another. Afterwards, this number would be multiplied by 360 (the number of degrees in a circle) and then divided by the number of years, months, days, or hours (depending on the mean one wanted to reach) that had passed between the two eclipses.

In fact, however, the sun - and to a much greater extent, the moon - would deviate from this mean rate of movement - i.e., the position in which they are located in the heavens differs from the position that would be reached by calculating the mean rate of progress. As is explained in the succeeding chapters, there are various ways of correcting and adjusting these mean calculations so that the actual position of these celestial bodies can be determined.

Rambam KidushHachodesh 6:2 states even clearer:

Halacha 3: According to this calculation, [the interval] between one conjunction of the moon and the sun and the subsequent conjunction according to their mean movement is twenty-nine full days, twelve hours of the thirtieth day, and 793 units of the thirteenth hour. This is the interval between one conjunction and the next, [and thus,] the length of a lunar month.