How We Create the “Skygazer’s Almanac”

Sky & Telescope's year-at-a-glance guide to celestial happenings is a symphony of detailed calculations and clear, elegant design.

If you're an active backyard observer — or just celestially curious — you're always looking for quick, reliable information about "what's up" in the nighttime sky. When is the next new Moon? Can I see Saturn tonight? When will twilight end?

Creating the "Skygazer's Almanac"

Senior contributing editor Roger Sinnott (left) does the complex calculations, and illustration director Gregg Dinderman crafts the graphics, that go into each "Skygazer's Almanac".
Sky & Telescope

The editors at Sky & Telescope are no different. And while we have scores of detailed references to draw from, one of the handiest is the "Skygazer's Almanac" found in every January issue of the magazine. This single sheet represents a fruitful melding of detailed computations and graphic representation that has been perfected over the years.

A graphical sky almanac has accompanied every January issue of Sky & Telescope since 1942 — that's more than 70 years! The main purpose of this chart is to let you see, at a glance, which planets and constellations are visible, and what the Moon's phase is, on any given date and time of night throughout the year.

There have been three "epochs" of this chart since its inception. From 1942 to 1980, each January issue featured the "Graphic Timetable of the Heavens," prepared annually by the Maryland Academy of Sciences. Then for two years it was called the "Graphic Ephemeris," computed and drafted by Michael Jay Jones (who had done this work for the Maryland Academy before then).

These charts had the same basic content. They showed the hours of night increasing from left to right, while the dates of the year ran from top (January 1st) to bottom (December 31st). Smooth curves provided the times of sunrise and sunset, as well as the end of evening twilight and start of morning twilight. Additional curves gave the rise, transit, and set times of bright planets and stars. Moon symbols appeared at the times of its rising or setting each night, while other symbols indicated planetary conjunctions and oppositions.

SGA: The Next Generation

As good as they were, both of those charts suffered from the limitations of black-and-white printing. So in 1983 Sky & Telescope introduced its own computer-generated chart, the "Skygazer's Almanac." We introduced some big changes then, as well as other enhancements and improvements over the years:

  • Curves for the planets became color-coded for easy recognition.
  • Small white dots now mark 5-minute increments horizontally and each day vertically.
  • The Moon symbols actually look like its phase each night as it waxes and wanes.
  • Symbols now give the dates and best viewing times of annual meteor showers.
  • Custom visibility curves are added for predicted bright comets (Halley, Hale-Bopp).
Skygazer's Almanac for 2015

The distinctive hourglass shape of the "Skygazer's Almanac" brings together a years' worth of celestial events in a single, intuitive format.
Sky & Telescope

Two key upgrades have really improved the chart's overall utility. First, we omitted the daylight portions of what had been a rectangular graph. This gave the chart a pleasing hourglass shape and, conveniently, freed up space to list key evening and predawn events down the left and right sides, respectively.

Second, we made versions for different latitudes. The original was plotted for those living at latitude 40° north, for use throughout North America and much of Europe. But beginning in 1998, additional charts were created for latitude 50° north (handy for northern Europeans) and 30° south (for use in Australia and the southern parts of Africa and South America).

These charts aren't just used by backyard astronomers. If you visit any major observatory, don't be surprised if there's a "Skygazer's Almanac" hanging on the wall. In fact, we've always offered a 30-by-22-inch wall chart for those who wanted a more readable version than the one included with each January issue. In recent years this poster has been printed in full color, as well.

We pack a lot of information into each chart, and each is accompanied by a sheet of instructions that tell you what the symbols represent and how to "read" the events of a given night.

Detail from Skygazer's Almanac for 2015

A small portion of the "Skygazer's Almanac" wall chart, shown full size, reveals a wealth of detail about "what's up" in the evening sky during January and February.

Take a look at the section above, which is shown at roughly the full size of the wall chart. You can see how the times of sunset and the end of twilight come later and later throughout January and February. Moon symbols indicate that it's full on the evening of January 4th and again on February 3rd. An orange curve shows that Mercury made a brief evening appearance in mid-January, and the light blue one shows Venus lingering a bit higher up after sunset each week. Mars sets around 8 p.m. each night; Jupiter rises at that time on January 1st but comes up two hours earlier, around 6 p.m., by the 27th.

Other curves show when Sirius rises, the Pleiades and Orion Nebula transit the north-south meridian, and when Polaris culminates directly over the North Celestial Pole. Clearly, January and February are busy months, celestially speaking!

The more you refer to this chart, the sooner you'll get a feel for the march of planets and constellations — not just during a single night but from week to week during the year. In fact, if you compare this year's chart with those from past years, you'll discover more and more about the clockwork of the heavens. For example, on charts eight years apart, the curves for Venus match almost perfectly — a celestial cycle known to the ancient Maya. On charts 19 years apart, the Moon makes its own encore performance.

Working up the "Skygazer's Almanac" takes a lot of effort — but it's one of the most rewarding projects I do all year. If you've got one, please add a comment below to let us know how you use it and what improvements we might make.

The 2015 edition of Sky & Telescope's Skygazer's Almanac is available in double-page versions for 40°N, 50°N, and 30°S, as well as a limited-edition wall chart that measures 22 by 30 inches.

13 thoughts on “How We Create the “Skygazer’s Almanac”

  1. Anthony BarreiroAnthony Barreiro

    I read the Skygazers Almanac every week to keep track of sunrise and sunset, the planets, and the Moon. All this information is available from other sources, but the almanac puts it together in a clear and easily understood graphical format. I’ve seen similar “hourglass” charts, but the Skygazers Almanac is the most attractive and easiest to use.

  2. Faye_Kane_girl_brainFaye_Kane_girl_brain

    As always, S&T is the one-stop-shop for observing-related astro info! I’ve been looking at the SG Almanac every year since I was in high school. And in all these decades, I never knew you sold a poster-sized version. Dammit!

    Oh well. Another thing for my list of stuff to tell myself after I invent a time machine.

    One thing though: the new dotted grid adds a HELL of a lot of visual noise. You need to make the dots smaller and a different color than the data lines on top of them. The only reason Edward Tufte isn’t rolling in his grave is that he’s not dead yet.

    — faye kane ♀ girl brain

    1. Roger W. SinnottRoger W. Sinnott Post author

      Hi Faye, thanks for your comments. But when you say “the new dotted grid,” which version are you referring to? (wall chart, magazine chart, online, what year?) We’ve been doing the dotted grid since 1984. In the very earliest years we had a few problems with the dots. One year they came out a little too big, and another year they were way too small. But since 1999 or so we’ve been using exactly the same specs for the dots, and we don’t think they produce excessive visual noise. (By the way, I too am a fan of Edward Tufte!)
      — Roger

  3. Mary Barnes

    I display the chart prominently in my office, and it is recruiting new stargazers. People ask me to explain it, and later they come by to find out what that “bright star close to the moon” is. I tell them to check the chart, and they are so excited when they find it!

  4. dhstevans

    Roger W. Sinnott,
    Very helpful article. A humble suggestion: What computer program is used? Is it available for a PC, Mac or Linux OS? It would be immensely helpful for my work in paleoastronomy.

    Thanks for providing this wonderful tool for all these years.

  5. dhstevans

    Roger Sinnott,
    Your story motivated me to study the fascinating content packed into the skygazer graphic. Is the program available for PC, Mac or Linux OS. It might be extremely useful for studying some events that I’d like to investigate in paleoastronomy. How accurate would it be for years prior to 1500 CE? 1000 CE? etc. Currently, I use “Home Planet” software, but Skygazer might be much more flexible. Thanks for continuing this important and extremely useful work.

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