Glenn Chaple’s observing basics: How to navigate the heavens

“In each issue of Astronomy, you’ll find an all-sky map — a circular chart that shows the appearance of the sky after sunset this month. The all-sky map — found on page 63 of this issue — can help beginners locate and identify major stars and constellations. As the directions note, you hold the all-sky map overhead and orient it so a direction label matches the direction you’re facing. Do your arms tire easily? You also can hold the map in front of you, as if it were a car’s steering wheel. Turn it so the direction label corresponding to whichever horizon you’re facing is at the bottom.

But, perhaps you want to go outside before sunrise tomorrow, when the stars and constellations will be totally different from what’s portrayed on the all-sky map. What then? You need a planisphere!

Like our all-sky chart, a planisphere portrays a full view of the night sky. It adjusts for any time and date of the year. It has two rotating parts — a star wheel and a horizon mask with an oval window. Align the date with the time you’re observing, and the visible stars and constellations appear in the window. Now use it the same way you’d use our all-sky map.

A planisphere isn’t just a beginner’s toy. For more than 30 years, a planisphere has been my go-to tool for planning evening skygazing sessions. Early last April, I participated in a Messier marathon star party sponsored by the Amateur Telescope Makers of Boston. Early in the day, I consulted a planisphere to determine which constellations — and, therefore, Messier objects — would have set in the west by the time I planned to begin observing. This planning resulted in a more efficient marathon.

Where can you get a planisphere? Try the gift shop of your local planetarium or science museum, the science section of a bookstore, or any specialty shop that sells telescopes and binoculars.

You also can purchase one by mail or online through major suppliers of astronomical goods, like the companies that advertise in this magazine. Expect to pay between $10 and $15. One word of caution — be sure the planisphere you select is designed for your latitude.

Enjoy a more detailed look
As useful as it is, a planisphere can’t do it all. It can show you where to find Aquarius in tonight’s sky, but not the location of the globular cluster Messier 2 in that constellation. Here’s where a star atlas comes in.

A star atlas is a road map of the night sky. For the novice skygazer, I recommend the following atlases:

Norton’s Star Atlas and Reference Handbook, 20th edition by Ian Ridpath. This classic star atlas, recently revised, has been around for nearly a century.

The Cambridge Star Atlas, 3rd edition by Wil Tirion. This atlas contains excellent sky charts, and lists of interesting sky objects.

The Edmund Mag 6 Star Atlas by Terence Dickinson et al. Astronomy writer Terence Dickinson wrote the handbook portion of the Mag 6 Star Atlas, artist Victor Costanzo drew up the sky charts, and I supplied data tables on noteworthy objects plotted on each chart. Alright, so maybe I’m a bit prejudiced on this one.

Don’t forget your magazine
Planispheres and star atlases have a common limitation — neither can portray the continually changing positions of solar system objects. Your monthly issue of Astronomy takes care of that!

Our “Sky this month” (page 60) provides easy-to-understand tips on what to see and where to see it in the night sky — from the Moon to deep-sky wonders. With your current issue of Astronomy, a planisphere, and a star atlas, you have the night sky covered!

Next month: Observing Mars with small telescopes, plus a return to the “Great Square.” Clear skies.