Almanacs in Astronomy Classes

In memory of my maternal grandmother

Dorothy Marie Blalock Clark

(1912-1997)

TL;DR: Ubiquitous farmers’ almanacs are an inexpensive printed source of accurate astronomical information despite being mostly advertising vehicles. This information can be used in the classroom to generate questions and learning about not only astronomy, but also history, mathematics, and computation.

Thanks to my maternal grandmother, I grew up with farmers’ almanacs around the house. I was never interested in the ads, tall tales, weather predictions, astrology, or funny stories. I was interested in their astronomical content. I would look at the neatly arranged columns of information and wonder how planetary alignments, times of moonrise and moonset, times of sunrise and sunset, could be predicted and tabulated. I saw strange new terms like lunar nodes, equation of time, ember day, southing, and trine and wonder what they meant. As I grew and learned more about astronomy, I realized that these almanacs were an inexpensive source of reliable astronomical information provided one overlooks the other somewhat questionable content. As a teacher, I think they are perhaps the very best quick source, even in these digital times, for certain information and I use them every semester in my astronomy classes. In this article, I present an exhaustive, but not necessarily complete, list of $\approx 10^2$ questions that can be addressed by researching the history of farmers’ almanacs and by studying their astronomical content. I have not addressed all of these questions in my classes, but I have indeed addressed many of them. Many of these questions provide an excellent introduction to applied mathematics. Many involve making graphs or charts.

Some of these questions take the reader into the world of astrology and perhaps other pseudosciences, but that is okay with me because at one time astrology was widely practiced as science and most astronomical terminology originated there. Some of these questions may seem deceptively trivial. If you see one like that, I challenge you to research it closely. Some questions are more about almanacs themselves than the information they contain. Yes, some of these questions invite rote use of search engines. Keep in mind these didn’t exist when I was a child; books in libraries were all I had. Also keep in mind that not all almanacs tabulate the exact same information so some of these questions may not make sense with certain almanacs.

What roles did almanacs play in colonial America?
What roles did almanacs play in the rest of the world?
Who was Benjamin Banneker and what was his connection to almanacs?
What is the Julian calendar?
What is the Gregorian calendar?
What is the proleptic calendar?
What is the ecclesiastical calendar?
Why do we have leap years (also called bissextile years)?
What is the metonic cycle?
What is the golden number?
What is the epact?
What is the dominical letter?
What is the solar cycle? (hint: It has nothing to do with sunspots.)
What is the Roman indiction?
What is the Julian day number?
What is the Julian period?
What are Ember Days?
Refer to almanacs for several consecutive years (the more the better). For each year, look at the date of Easter, the date of the March equinox, and the date of each month’s full Moon. What do you conclude?
How is the date of Easter determined?
What does conjunction mean?
What does inferior conjunction mean?
What does superior conjunction mean?
What does opposition mean?
What does elongation mean?
What does greatest elongation mean?
What is retrograde motion?
What is prograde motion?
What is eastern quadrature?
What is western quadrature?
What is trine?
What is sextile?
What is greatest brilliance? (hint: It has nothing to do with gemology.)
What is the zodiac?
In what sense are there really not twelve zodiacal constellations?
In what sense are there really only twelve zodiacal constellations?
What is your astrological sign?
What is your astronomical sign?
What is the celestial meridian?
Why is Moon not always in the same constellation at the same time on consecutive days?
What is upper culmination?
What is lower culmination?
Why do full (or new, first quarter, last quarter, or any other specific phase) Moons appear in different constellations in consecutive months?
Refer to two almanacs for years exactly nineteen years apart. Compare the dates of the cardinal lunar phases. What do you conclude?
Based only on information tabulated in the almanac, what must Earth’s shape be?
When is noon on any artibrarily chosen date? (hint: Noon doesn’t always mean 12:00.)
What is the equation of time?
How are the times of sunrise and sunset determined?
How are the times of moonrise and moonset determined?
Why is there no moonrise or moonset on certain dates?
What would you say to someone who says Moon is only visible during nighttime and never during daytime?
How does lunar visibility correlate with lunar phase?
Why do solar and lunar rise and set times vary with geographic location?
Why do solar and lunar rise and set times vary with date?
What is meant by southing?
Refer to two almanacs for years exactly eighteen years apart. Compare the dates of eclipses in those years. What do you conclude?
Refer to two almanacs for years exactly thirty-six years apart. Compare the dates of eclipses in those years. What do you conclude?
Refer to two almancs for years exactly fifty-four years apart. Compare the dates of eclipses in those years. What do you conclude?
Refer to almanacs for several consecutive years (the more the better). Make a graph showing which constellations the lunar nodes are in from year to year. What do you conclude?
Refer to as many almanacs as you can find. Count the number of each type of solar and lunar eclipses in each year. What type of eclipse is the most frequent? What type of eclipse is the least frequent?
Refer to two almancs exactly twenty-eight years apart. Compare the days of the week on which the dates fall. What do you conclude?
Refer to three almanacs, with eighteen years separating consecutive almanacs. Pick one eclipse in the earliest almanac. Can you find it in the other two almanacs?
Refer to almanacs for several consecutive years (the more the better). Make a graph showing the dates on which eclipses occur from year to year. What do you conclude?
When do the Dog Days begin? When do they end? What is their significance?
What is a heliacal rising? What is a heliacal setting?
Refer to an almanac for any arbitrary year. Make a graph of the duration of daylight as a function of date for the entire year. What do you conclude?
Refer to an almanac for any arbitrary year. On what date is the duration of daylight a maximum?
Refer to an almanac for any arbitrary year. On what date is the duration of daylight a minimum?
Refer to an almanac for any arbitrary year. Make a graph of the time of sunrise (or sunset) as a function of date for the entire year. What do you conclude?
Refer to an almanac for any arbitrary year. Make a graph of the time of moonrise (or moonset) as a function of date for the entire year. What do you conclude?
Refer to an almanac for the same year as in the previous question. Make a graph of the lunar phase as a function of date for the entire year. What do you conclude?
Is there a correlation between lunar phase and the time of moonrise or moonset?
On what date does the year’s midpoint fall?
On what date is Earth closest to Sun?
On what date is Earth farthest from Sun?
Based on information in the almanac, why do we have seasons?
Many almanacs tabulate Moon’s location along the zodiac for 7:00 am local time. Why do you think this time was chosen?
Refer to an almanac for any arbitrary year. On what date does the earliest sunrise occur? Is this what you expect?
Refer to an almanac for any arbitrary year. On what date does the latest sunrise occur? Is this what you expect?
Refer to an almanac for any arbitrary year. On what date does the earliest sunset occur? Is this what you expect?
Refer to an almanac for any arbitrary year. On what date does the latest sunset occur? Is this what you expect?
Refer to an almanac for any arbitrary year. Compare the dates of earliest sunrise and latest sunset to the date of maximum duration of daylight. What do you conclude?
Refer to an almanac for any arbitrary year. Compare the dates of latest sunrise and earliest sunset to the date of minimum duration of daylight. What do you conclude?
Refer to an almanac for any arbitrary year. Compare the dates of the equinoxes and solstices to the duration of daylight, perhaps in graphical form, during the year. What do you conclude?
Do the equinoxes and solstices mark the beginning, middle, or end of each season?
If possible with your almanac, find the same astronomical event (such as a particular or constellation rising, setting or crossing the celestial meridian) on as many dates as possible during the year. Does it occur at the same time on these dates?
What is a blue moon? Can you find examples for a given year?
Refer to as many almanacs as you can find. For each year, look for the date of the harvest moon. Can you devise a general rule for predicting its occurrence?
Refer to as many almanacs as you can find. For each year, look for the dates of the equinoxes and solstices. What do you conclude?
Refer to as many almanacs as you can find. For each year, count the number of occurrences of each of the four cardinal lunar phases. What do you conclude?
Refer to an almanac for any arbitrary year. Pick a random date and determine the lunar phase for that date. Find the date of the next occurrence of that exact same lunar phase. What do you conclude?
What role do time zones play in using an almanac?
In how many different constellations does Moon appear throughout the year? List them.
How many lunar perigees are there in a given year?
How many lunar apogees are there in a given year?
How many calendrical intervals can you find that relate to astronomical objects?
Can you find a month in which any given lunar phase does not occur?
Can you find a month in which any given lunar phase occurs twice?
Most almanacs tabulate sunrise/sunset and moonrise/moonset times for at least two different geographical locations. What effect does location have on these times throughout the year?
Given the time of sunrise and time of sunset, can you devise a method for calculating the time at which noon occurs?
Find a date on which Mercury is at inferior conjunction. Find the next date on which Mercury is at inferior conjunction. What can you conclude?
How would information in an almanac change, if at all, if you were on the hemisphere opposite your present location?

So which almanacs can I recommend? Fortunately, I have a good list of them and I will describe each one here. First, the traditional farmers’ almanacs.

Blum’s Farmer’s and Planter’s Almanac

This is the one I remember from childhood, and I still refer to it as “the orange almanac” becuase of its distinctive color that makes it stick out in stores. Santa left one in my stocking every Christmas well into young adulthood. This is the almanac my grandmother steadfastly followed for knowing when to make homemade mints and homemade sauerkraut and planning for the winter. I have to admit the mints and sauerkraut were always good so there may have been something to that, but it was the astronomical information that hooked me on this almanac. Blum’s almanac is also near and dear to me because it is published just up Interstate 40 from me in Winston-Salem. Unlike other almanac publishers, Blum’s has kept the astronomical information intact over the decades with only a few changes. One of those changes is that information about the equation of time has been removed for several years. There has always been a page near the beginning (page 10 of the 2018 edition to be precise) tabulating all kinds of calendrical information and it was here that I first became interested in calendars, their history, and their computational underpinnings. I did much research on calendars in the 1990s with an emphasis on the ecclesiastical calendar and the reforms involved in the transition from the Julian calender to the Gregorian calendar.

This almanac has always contained a glaring nonsensical error that annoyed me so much that I once called the publisher to discuss it. Still, the error remains. It’s not so much as an error as an unnecessary detail. On the page I mentioned in the previous paragraph, there is a listing of the dates and times of the equinoxes and solstices for the year, along with a statement that reads, “Calculated at 7:00 a.m. EST converted to EDT March 11 to November4.” Now, I understand the reasoning for expressing the times in EDT for events occurring while daylight saving time is in effect, but I never have understood the point of disclaiming the time at which the calculations were made. The times of celestial events do not depend on when we make the computational predictions.

Allow me to digress a bit and explain that the astronomical information in these almanacs (to my knowledge, all of them) is computed by someone else and provided to the almanac’s publisher. This information may then be sold to anyone willing to pay for it. At one time, well known broadcast meteorologist and amateur astronomer Joe Rao told me via email that he did the claculuations for one popular almanac (I forget which one) and how he provides it in a spreadsheet to the publisher, who then edits it into the almanac for the next year. I want to emphasize that the astronomical information is indeed accurate and can be trusted. It should also be reproducible using existing computational algorithms.

With that said, I have no idea why the publisher insists on stating that the times of the equinoxes and solstices are “Calculated at 7:00 a.m. EST” and when asked, the publisher himself had no idea either. This is something most people probably wouldn’t catch, but it annoys me and, I think, sticks out in an otherwise most excellent general compilation of astronomical information. Ah well…can’t win ’em all.

I should point out that Blum’s Almanac may not be well known outside of the southeastern United State, but like all of these almanacs it can be purchased through the mail via the publisher’s website.

The Old Farmer’s Almanac

This almanac is the one most people probably know about because it has distribution far and wide across the country and is frequently cited for its weather forecasts. It comes in both U.S. and Canadian editions, and there is usuall a Southern Edition too (although I have not yet seen it for 2019). The Old Farmer’s Almanac is rich with astronomical information and even includes tide predictions for notable coastal locations (e.g. Boston and Charleston). No other farmer’s almanac I know of provides tide predictions. You can’t go wrong with The Old Farmer’s Almanac.

Farmer’s Almanac

Don’t confuse Farmer’s Almanac with the other one above with a very similar name. It too comes in U.S. and Canadian editions and even a digital edition (others offer a digital edition too). This was my “new favorite” almanac for a while but the 2019 edition is very disappointing becuase nearly all of the astronomical information in the monthly calendar pages has been replaced with other trivia, such as the birthdates of celebrities. If this persists in future editions, I will have to stop recommending this almanac.

Harris Farmer’s Almanac

I had never knowingly noticed this almanac until the 1990s when I began adding it to my collection every year. It contains a lot of astronomical information and its monthly calendar pages are formatted quite to look very much like those from Blum’s. While this almanac doesn’t really stand out in my opinion, it is quite useful and you can’t go wrong with it.

Hagers-Town Town and Country Almanack

I first saw this almanac in stores about a decade ago but it mysteriously disappeared from this region. I really liked it becuase it seemed to contain the most astronomical content of all the almanacs. I contacted the publisher and was able to purchase a nice quantity of almancs for classroom use and a very nice discount once I explained to the publisher I was a teacher and I planned to use the almanac to teach astronomy. He was delighted to hear this! It’s been a number of years since I’ve seen a copy of this almanac but I will purchase a copy of the 2019 edition for my collection. Needless to say, unless there have been drastic changes to the 2019 edition (I will soon see) I fully recommend this almanac for classroom use.

Grier’s Almanac

As you can see from its website, this almanac is also more or less known only in the southeastern states, but it has one distinct advantage over all the rest: it is free! That’s right, free. It is distributed mainly through local independent drugstores and pharmacies, like the one I have frequented for two decades (Bowman Drug Co. in Conover), and in feed stores and general stores common in this region of the country. Even better, I once requested multiple copies from the publisher, again explaining that I wanted to use them in my classes, and received a box of about two hundred as I recall. How can I not recommend this almanac given the publisher’s generosity? This almanac is also printed in black and white “newsprint” style and has the look and feel of a small, handheld newspaper. The astronomical content is definitely on par with the other almanacs but not quite as extensive. Still, it would be a useful (and free!) almanac to start with.

All of these almanacs are definitely for nonprofessionals. Those of us obsessed with the almanac concept, which I think is mostly astronomers, have more grown up almanacs to use.

The Astronomical Almanac (published jointly by the U.S. Naval Observatory‘s Nautical Almanac Office and Her Majesty’s Nautical Almanac Office in the UK) is the professional gold standard for astronomical information of the “almanac type.” Indeed, it was the hundreds and hundreds of references to this book in the books I began reading in high school that caused me to nearly lose my breath when I first found a copy in a college library near my childhood home and opened it for the first time. From that second, I knew I wanted to learn how all those numbers are computed and I can honestly say I fulfilled that dream and even wrote a book about it. This almanac is definitely not for classroom use (although that depends on the nature of the class of course) and it is expensive. I do not have copies for every year, but I will get a 2019 edition. For less exacting use, The Astromical Almanac has a related publication, Astronomical Phenomena, and despite its name, it is not as comprehensive as the better farmer’s almanacs described above. It is more or less a subset of information from The Astronomical Almanac published years in advance for planning purposes. Incidentally, the official documentation for how the contents of The Astronomical Almanac and Astronomical Phenomena, outside of journal publications, is the Explanatory Supplement to the Astronomical Almanac and every computational astronomer probably has a copy of this. It is in its third edition and is truly a canonical work in my field. The U.S. Naval Observatory and Her Majesty’s Nautical Almanac Office also jointly publish The Nautical Almanac and The Air Almanac. These are highly specialized almanacs and not within the scope of introductory astronomy classes.

I offer yet another tidbit of personal history. The U.S. Naval Observatory published the Almanac for Computers from the late 1970s into the early 1990s. I still have my 1984 edition. It was specifically this almanac that introduced me to serious computation and I will forever treasure its brief presence and its nearly infinite influence on me. I now have a goal of acquring one copy of every edition ever published. It is no longer even mentioned anywhere on the Observatory’s website so I imagine few if any copies survive. If you know of any, please let me know.

Finally, I offer my personal favorite for actual use outside: the Observer’s Handbook published by the Royal Astronomical Society of Canada. I began collecting this handbook (it goes far beyond a simple almanac) in 1985 when I started as a freshman at UNC-CH. I saw it in the Morehead Planetarium giftshop and I purchased it every year since. It is THE handbook I take to the observatory and THE one I use to look up things when asked and I don’t already know the answer (e.g. Neptune’s average distance from Sun). It’s about as comprehensive as it can get. If you don’t order in advance it can sometimes be difficult to get in the States.

So, as usual I have a secret motive here. Using almanacs in introductory astronomy is a pretty radical thing from what I can tell becuase I don’t know of anyone else doing it. If you’re doing it, then by all means let’s compare notes. However, I contend that doing so may be a good way to introduce students to computation. The tabulated numbers must come from somewhere; they don’t just materialize out of nothingness. With Python more or less ubiquitous these days, why not take the plunge and show students how almanacs are compiled.

For a long time, I contemplated creating an Almanac for Astronomy Students or something similar, and I still may give that a shot.

This was a long post and I thank you for reading it. I am preparing a condensed version to submit to AstroNotes in The Physics Teacher.

As always, feedback is welcome.

In memory of my maternal grandmother

Dorothy Marie Blalock Clark

(1912-1997)

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