Astrological Lunar Calendars: Problems and Limitations

As it often happens, this post was prompted by an email from a visitor of Lunarium. There was a number of similar questions, so I thought it will make sense to try and address them all.

A typical question goes like this: astrologers disagree with each other. One popular online lunar calendar says that on April 14th, 2017, the Moon will be in Scorpio, and it will be the 18th lunar day. The other very popular astrologer says in his calendar that the Moon will be in Sagittarius, and it will be the 19th lunar day. So who do I believe?

Here is my answer:

The easiest approach is to figure it out for yourself, if only once, and then decide which of the sources of information can be trusted. Let's start with the Moon. Yes, on April 14th the Moon will be in Scorpio. And yes, on April 14th the Moon will be in Sagittarius. My astrological lunar calendar shows the specific moment in time when the Moon will leave Scorpio and enter Sagittarius. In the time zone where I live (London, UK) it will be 11:26 am. In some other time zone, the time will be different, and my calendar will take that into account. The point is: the Moon doesn't observe the common calendar where everything begins at midnight, it can enter a sign of the zodiac at any moment during the day. So if the calendar you are using does not specify the moment of the Moon's entry into a sign, and does not specify for which time zone this time is valid, you should not trust that calendar.

Things become even more complex with the lunar days because different astrological traditions use different definitions of a lunar day. In the Western astrological tradition, however, the lunar day begins either with the New Moon (if it is the very first lunar day of the lunar month) or with the moonrise. Which means, again, that it does not coincide with the common calendar day beginning at midnight. Second, it depends on the time zone and daylight saving time. Third, as the moment of moonrise is location-specific, the current lunar day also depends on the latitude and longitude of the place of observation. So a lunar day in New York will be different from a lunar day in Philadelphia, even if they are in the same time zone.

My calendar takes all these factors into consideration, but creating such a calendar is a non-trivial technical task. Printed calendars are absolutely useless unless you use them in exactly the same location for which they were printed. And if they do not specify for which location they are valid, you simply shouldn't be using them. Most online calendars aren't much better than the printed ones because they are static. They were created once, for a specific location, and they don't change.

Lunarium takes into consideration the exact location you specify, and it tries to do its best to provide the most accurate information. This is because Lunarium is not a website but a web application, i.e. a sophisticated piece of software. Hence the difference.


  1. As someone who writes lunar horoscopes for clients based on different calendars, I found this article​ very helpful, both in terms of what I should look out for in the resources that I rely on, and how I can try to improve my own work. Keep up the good posts!


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