lunar calendar accuracy for predicting new moons

I wonder, how accurate the lunar calendar is? Can we predict the new moons precisely for tens of years in future? If we know all factors that affects the movement of the moon, then why it is not possible to predict it?

• Great question! I'd love to know this. Commented Jul 6, 2016 at 12:14
• This depends on the definition of a new moon: conjunction with the sun, or the first visible crescent after that? Commented Jul 8, 2016 at 21:57
• I can give the accurate lunar calendar for next 100 years But I need a guide and some support Commented Feb 22, 2017 at 8:08

3 Answers

The motion of the moon is known with great accuracy, and so the exact moment of a new moon (the moment that the sun and moon have the same longitude in the sky) can be calculated with great accuracy for tens of thousands of years into the future. This is the astronomical meaning of New moon, and the only one which is relevant here. The uncertainty is due to effects such as the non-spherical nature of the Earth's gravity and the exact magnitude of perturbations of the orbit by other bodies.

Unless there is an eclipse, the moon is not visible at the moment of the new moon, and doesn't become visible until some time later (How Soon Could a Waxing Crescent Moon Be Seen?). The time when the moon can be seen for the first time depends on lots of factors, such as atmospheric clarity, weather and latitude, these can't be predicted from day to day.

The answer depends on what you mean with "precisely". The ELP theory seems to have an accuracy of ~10-6° in longitude over a century, which comes down to about a millisecond for phases.

• Note, they used JPL DE200 and their program's own internal precision as an accuracy comparison, not actual observations. DE200 is a numerical simulation. Historical accuracy cannot be verified, but is assumed to be very precise. In their paper, they show a disagreement with DE200 of -.00111 arcseconds over one century. The paper also contains a lot more about accuracy for those interested. articles.adsabs.harvard.edu/full/1983A%26A...124...50C Commented Feb 12, 2022 at 21:32

Moon circles around the earth in 29.5 day , if you multiply that by 24 hours then by 60 minutes and then by 60 seconds you get number of seconds in between moon cycles, this number never changes it is always the same

• The interval from New Moon to New Moon is not constant. It varies by approximately 6 hours. Commented Feb 12, 2022 at 1:14