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?
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).
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.
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.