When to celebrate my birthday (and also yours)

If you are like most people, you celebrate your birthday on the same calendar date each year. For example, since I was born on May 4th 1973, you probably consider today, May 4th 2015, to be my birthday. But this is extremely arbitrary and culturally biased: calendars  vary from culture to culture, and change over history. Wouldn’t it be nicer–both more objective and more natural–to celebrate the anniversary of your birth in a way that was more connected to the natural movements and rhythms of the earth and the universe?

That’s the way many religions calculate the dates of their holidays. That is why they seem to “move around” on the calendar year after year. Easter, for example, is defined as the first Sunday after the first full moon after the vernal equinox. By determining Easter based on the seasons and natural cycles of the sun and the moon, it will always be possible to figure out when Easter is… even in the far far future, if we move over to a totally different calendar system that uses different months and days.

Back in 2012, I decided that I should do this with my birthday, as well. When I calculate my birthday using this type of seasonal and astronomical method, I call it my non-calendarial birthday, since it is an annual celebration that is not inherently tied to any particular culture’s calendar system. It’s more objective, more traditional, and in some small way it is more connected with the earth and the universe.

How do I define my non-calendarial birthday, then? Well, back in 1973, it just so happens that May 4th was two days after the second new moon after the vernal equinox. Instead of defining my birthday as May 4th each year, I can simply define it that way: “two days after the second new moon after the vernal equinox.”

Then, each year, to figure out what day my birthday is, I simply have to:

1) look up the vernal equinox for the year.

2) find the second new moon after that date using yearly astronomical moon tables.

3) add two days.

Using this method, I’ve calculated my birthday for the next several years. The following table is provided for your convenience.

When to celebrate your birthday, by Greg Stevens

So while I truly and sincerely thank you all of the wonderful birthday wishes you have given me today…. you’re early!  My birthday falls on May 19th this year. That’s a couple of extra weeks to plan my party.


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  1. Amanda S says:


    Just following up as I didn’t hear back from you, sorry to email you again. I noticed your page gregstevens.com/2015/05/04/celebrate-birthday-and-yours/ links to http://www.timeanddate.com/calendar. Unfortunately, that site isn’t very accessible for the sight impaired. Would you consider adding a link to a more accessible version like http://www.thetimenow.com/calendars which is WCAG 2.0 compatible?

    Also, if you ever want to see how accessible a page is, I recommend http://wave.webaim.org. It is really helpful.


    Amanda S

  2. Neil says:

    I still say this is arbitrary.

    You may as just celebrate each time Venus goes around the sun, or each time Deimos goes around Mars. Why not celebrate your birthday every time Polonium-210 decays by 50% (every 138 days)?

    • Greg Stevens says:

      That’s true…. although, in the defense of this method, we DO actually live in this planet. So basing it on stuff that has to do with this planet isn’t completely out in left field.

      I’ll be more convinced that the movement of the sun and the moon are arbitrary once we’ve migrated out into space. 🙂

  3. rocko says:

    looks like a fun game but too much work you should make some kind of app that calculates it for people.

  4. TOMG7243 says:

    Nice. It’s like when different churches can’t agree on Christmas, except with your birthday. LOL

  5. Sarah says:

    Happy birthday!

  6. MB says:

    Too confusing for me. LOL

  7. Jennifer says:

    Happy birthday, Greg!

  8. JJ says:

    Hope you had a great birthday, man!