9

A better diagram is something like this: Day 0. The Moon is aligned with the Sun (New Moon) and some star X behind the Sun (of course :-), as shown by the arrow at 1. (Neither the Sun nor the star X are shown in the figure.) Day 27.32. One sidereal month after figure 1. The Moon has travelled through 360 degrees orbiting around the Earth. (During that ...


5

The time difference (synodic month) - (sidereal month) will not be constant. The reason for the variation is due to the eccentricity of the Moon's orbit: the Moon moves faster at perigee (closest to the Earth) than when at apogee (farthest from the Earth). If the Moon is near perigee around the time of New Moon, it takes less time for the Moon to "catch up" ...


2

I used Skyfield to find the actual lengths of synodic and sidereal months from 2010 through 2029 according to JPL ephemeris DE430. For each synodic month, I chose the sidereal month having the same midpoint in time. Standard deviations were 0.18 day in synodic month length, 0.07 day in sidereal month length, and 0.19 day in the difference between them. The ...


1

The new moon is when the center of the Moon and the center of the Sun are at the same ecliptic longitude. The angular diameters of the Sun and Moon are not considered. Angular speeds give us another way to look at the situation. The Earth moves 360° around the Sun per sidereal year, or an average of 0.9856°/day. The Moon moves 360° around the ...


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