The Vernal (Spring) Equinox this year was on March 20^th.

The first Full Moon following the Vernal Equinox of this year was on April 17^th.

That means that day-after-tomorrow, Sunday April 24^th, is the first Sunday following the first Full Moon following the Vernal Equinox.

That means that Sunday, April 24^th is Easter Sunday for most of the world’s Christians. 

Generally speaking, this is how you calculate Easter Sunday:  

Vernal Equinox + the following Full Moon + the following Sunday = Easter Sunday.

Given the range of possible dates on which the Full Moon can occur following the Vernal Equinox, this means that the earliest possible Easter Sunday could be March 22^nd, and the latest possible date for Easter is April 25^th.

 If you want to really geek-out about this subject and explore the “generally speaking” qualifier that I mentioned above, and if learning the difference between an “Astronomical Full Moon” and an “Ecclesiastical Full Moon” sounds interesting to you, then go here. 

Happy Easter!

Astronomically speaking, how long is a month? It is the length of time that it takes for the Moon to orbit around Earth once. While that definition may seem simple, that length differs depending on how an orbit is defined. While astronomers define five different “months,” most of the confusion that I run into arises from the two are most commonly used.

The Moon completes one (360 degree) orbit of Earth in about 27.3 days. This is called a sidereal month (meaning in relation to the stars or constellations). After one sidereal month, the Moon has completed one orbit of Earth relative to the stars. So, about every 27 days, we see it near the same stars. Even though it has returned to the same place among the stars is not at the same phase. This is NOT how long it takes the Moon to complete one cycle of phases. That takes about 29.5 days. Because Earth is also moving around the Sun, the Moon must travel more than 360 degrees to bring Earth, Moon and Sun back into the same relative positions or alignment (as they were in the previous month). This is called a synodic month.

Here is an animation that demonstrates this.

Full moon image courtesy NASA

As sidereal and synodic are unfamiliar words to most people, when I speak of the Moon’s orbital period, I usually say, “the Moon takes about 29.5 days to go around Earth relative to the Sun” or “27.3 days to go around Earth relative to the stars.” This clarifies which orbital period I am using.

Here is an example. On November 21, 2010, the full moon was seen near the Pleiades, a star cluster in the constellation of Taurus. On December 18, (27 days later), the Moon will again appear near the Pleiades. However, the Moon will not be full but will be at a gibbous phase because it is not opposite the Sun in the sky. It will be full on December 21, having moved eastward relative to the stars over the additional 2.2 days, into the constellation Gemini.

I have occasionally seen 28 days given as the Moon’s orbital period (especially in elementary schools). I guess that this is sort of an average between the sidereal and synodic months, but this is not astronomically accurate and should not be used.

Anyway, I was noticing  that the Full Moon for April, 2010 occurs on the 28th and is known as the ‘Pink Moon.’ I thought to myself, “Pink Moon? Where’d that name come from?”

I know that all Full Moons have names, and these names are most commonly associated with the Old Farmer’s Almanac, which takes the full moon names from the cultural histories of native american tribes of the  northeastern parts of the United States. The Cold Moon in December, the Snow Moon in February, the Harvest Moon in September/October all kind of make sense as to their name and origin. But the Pink Moon in April I had to look up. I doubt it had anything to do with the pastels of Easter or little girls’ new spring dresses to wear for Sunday church, because I’m sure native american tribes didn’t know much about either one at the time.

The Pink Moon refers to “the herb moss pink, or wild ground phlox, which is one of the earliest widespread flowers of the spring (citation).” Other full moons have different names, which kind of make sense if you think about them long enough…

The Full Moon names are:
January–Wolf Moon
February–Snow Moon
March–Worm Moon
April–Pink Moon
May–Flower Moon
June–Strawberry Moon
July–Buck Moon
August–Sturgeon Moon
September–Corn Moon
October–Harvest Moon
November–Beaver Moon
December–Cold Moon

The moon won’t look any pinker this week, certainly, wild flowers or not. Sometimes the moon looks red, however. But that’s only during a total lunar eclipse, which can only happen during Full Moon, and will happen later this year, on the night of December 2oth/21st.

Any takers?

The “2012″ disaster-pic opens Friday, and some folks are actually asking, “Is the world really going to end in 2012? Will the Earth’s magnetic field really reverse?  Is there really a planet Nibiru headed toward us? Is it all tied to the Mayan calendar?”

The short answer to all these questions is “no.”

Here’s how sure I am of that. If Earth’s magnetic field reverses and compass arrows begin pointing south instead of north by December 21, 2012 then I’ll buy you a dozen really good doughnuts  - provided that there are any bakeries still open in the post-apocalyptic  world envisioned by the folks claiming that life as we know it comes to an end on December 21^st, 2012.

If Earth’s magnetic polarity reverses in 2012 then the doughnuts are on me.

Here at Clark Planetarium we settle differences of opinion with a three-step, tried-and-true problem-solving process:

First, competing opinions are required to make falsifiable predictions.   An example of a falsifiable prediction is, “Earth’s magnetic field will reverse polarity in 2012.”  An example of a non-falsifiable prediction is, “Something unusual will happen in the world in 2012.”  Get the difference? One prediction is specific and you can test it, the other is vague and impossible to test.

Next, we find a way to test the prediction.  In this case it’ll involve watching compass needles in 2012.

Finally, if the prediction is proven wrong then the person who made that prediction brings doughnuts to the next staff meeting.

Why am I willing to bet doughnuts on this?

Because while it is true that Earth’s magnetic poles have reversed polarity many times in Earth’s past, and doubtless will again many times in Earth’s future, it takes a minimum of several thousand years to accomplish a polarity reversal.

If you take this wager and the magnetic poles don’t reverse in 2012 then you owe me a dozen really good doughnuts.

I’m not only willing to wager fresh doughnuts against Earth’s magnetic field reversing in 2012, I’m also extending a “doughnut bet” challenge for all the other “the world ends in 2012!” predictions.

Specifically, I’m betting a dozen fresh, frosting-with-sprinkles doughnuts that in 2012:

#1.  No Center-of-the Galaxy Alignment. The Sun is no better-aligned with the center of the galaxy on December 21st than it has been at any time in the past several hundred years or will be any time in the next several hundred years.  On 12/21/12 the Sun will be more than six degrees (twelve times the diameter of the full moon) from the galactic center. That’s not much of an alignment.

The Sun will not align between us and the Galactic Center in 2012. Even if it did, nothing would happen.

More to the point, the center of our galaxy is two billion times farther from the Sun than the Sun is from Earth.

This is exactly like worrying about whether these two asterisks ** here in Salt Lake City ever “align” with Sydney, Australia when I move my computer monitor around. If there is anything the center of the galaxy can do to our solar system, it’s already doing it, whether it’s December 12st or the 4th of July. Galactic “alignments” are irrelevant.

#2. No mystery planet, whether it’s called “Nibiru” or by any other name, wanders through our solar system disrupting orbits and generally wreaking havoc in 2012.  How do we know this?  Because if such a large planet or Brown Dwarf star really did orbit our Sun every 3,600 years, as some imaginative folks are claiming,  then 3,600 years ago the passage of this object through the inner solar system would have been devastating and tremendously noteworthy.  There was plenty of history being recorded in 1,600 B.C.E., and the complete absence of records describing something as phenomenal as Nibiru is compelling evidence that Nibiru exists solely in the imagination. Plus, so large a planet or Brown Dwarf star would have been the #1 target of thousands of professional astronomers worldwide for the past 50 years, and the #1 target of millions of amateur astronomers for at least the past decade.

The only way to see “Nibiru” is with your imagination (and maybe Photoshop).

#3.  The Mayan Calendar is interesting, but not a big deal. The resetting of the Mayan “Long Count” (144,000 days) calendar on 12/21/2012 will have the exact same impact on human behavior that the calendar that we use has when it “resets” to January 1^st every year.  There will be parties, and then we’ll go on with their lives.

The Mayan “Long Count” Calendar resets every 144,000 days, just as our calendar “resets” every 365 days.

Any takers on the doughnut bet?

Mmmmm… science.  It not only works, it’s also delicious with a fresh cup of coffee.

And, yes, I’m planning to see the movie.  I love a good disaster flick.