We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

What is a Lunar Month?

Mary McMahon
Updated: May 21, 2024

A lunar month or synodic month is a period of time measured in relationship to the movement of the moon. There are actually several different ways to calculate a lunar month, which means that it can vary in length depending on which system is used. Several religions use these months to establish their calendars, and the lunar month is also sometimes seen used to mark time in a pregnancy.

One common method used to determine a lunar month is to look at the period between syzygy, when the moon and sun are lined up to make a new moon or a full moon. In this case, the synodic month as it is also known runs from new moon to new moon or from full moon to full moon. This lunar month lasts about 29 days, 12 hours, and 44 minutes. Other modes of calculation use the moon's orbital period, in a type of lunar month sometimes called a sidereal month.

Lunar months can also be measured by tracking the moon as it moves from perigee to perigee, when it is closest to the Earth, or when the moon returns to one of the two nodes in its orbit which intersect with Earth's orbit. These different calculation techniques used to determine the lunar month can yield months which last between 27 and 29 days.

The problem with the lunar month is that if lunar months are used to calculate time, over an extended period of time, the calendar will start to be off. Eventually, the lunar calendar won't actually map up with the phases of the moon. As a result, lunar calendars must be periodically adjusted to bring them back up to speed and to keep them on track with the actual movements of the moon. Among faiths which use lunar months to mark time, special calendars are issued annually so that people can keep up with the lunar months.

As it is, the Gregorian calendar used internationally is also off a bit, which is why leap years must be inserted to keep pace. Periodically, leap seconds are also added. This is because orbits are not perfectly precise, and small variations can translate into huge calendar miscalculations over the course of time. In nations where numerous people use the lunar calendar, dates are sometimes given in both calendar systems for convenience, and converters are also readily available.

All The Science is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a All The Science researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By Denha — On Jan 04, 2011

Like pregnancy, many women also find that their menstrual cycles end up flowing on a lunar month calendar rather than on a more Gregorian one. While my own has always been more irregular, I do have a who swears that she is part werewolf- she always menstruates during the the full lunar phase, and stops shortly after the moon starts waning.

By helene55 — On Jan 03, 2011

When looking at how different the lunar calendar and other calendars, such as the Gregorian, can vary, just imagine the concept of a Blue Moon. Usually only once a year or less, a Blue Moon is a calendar month in which there are two separate full moon periods- somehow, the lunar cycle both ended and then went through an entire cycle in the same 30- or 31- day period.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

Learn more
All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.

All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.