How to use Norton's Star Atlas
A star atlas is a tool you shouldn’t be without. We reveal how to get the most out of one of the best atlases available.
Written by Will Gater.
Like the hiker’s compass, the pilot’s flight plan or the camper’s torch, a good star atlas is the one accessory that should never leave the side of an astronomer under the stars.
The Cambridge Star Atlas, Collins Atlas of the Night Sky and Uranometria 2000.0 are just three of the atlases available, but all share the aim of accurately representing the night sky. My own favourite atlas, a copy of the 19th edition of Norton’s Star Atlas, has accompanied me all around the world since I bought it many years ago; today it is dog-eared and worn from dew-soaked observing sessions and fervent flicking-through at the eyepiece.
If you’re just starting out, a star atlas should be one of your first purchases, but you might find it’s not immediately obvious how to use it. For this ‘How to…’ we’ll be looking specifically at the latest (20th) edition of Norton’s, although many of the tips we describe here are generally applicable to other atlases too.
To start, let’s jump straight in by looking at the star charts themselves. It’s very likely that these will be what you use the most in your star atlas, so it’s a good idea to get to know them well. You’ll find them starting on page 139 of Norton’s. It’s useful to have a quick glance at the index charts on pages 142 and 143, because they show you how the whole sphere of the sky has been divided up in the atlas.
As you’ll see, the night sky has been broken into 16 separate regions, each with their own charts; basically, each half or hemisphere of the celestial sphere has eight different portions. Think of these overall index charts as your first port of call when you’re searching out the detailed chart you want.
Let’s say you want to look up the lovely region around the constellations of Taurus and Perseus. The index charts tell you that you need chart 5. Turning to that chart you’ll see the barrel shape of two charts printed across two pages – the right-hand chart is chart 6, while the one you want, 5, is on the left.
Around the edges of each chart you’ll notice two main things. The first is a graduated scale. The scale running along the longest edge of the ‘barrel’ shows degrees of declination (Dec.), while the one running along the top and bottom of the ‘barrel’ shows right ascension (RA). The declination scale is broken down into increments of one degree whereas the right ascension scale has increments of five minutes.
The major grid lines running across the chart mark every 10° of declination and every hour (60 minutes) of right ascension. This scale is a useful thing to understand: if you’ve been given the RA and Dec. of an object like a comet, you can use those figures to find out where to look for it by reading the chart like a grid reference on a map.
The second thing you’ll notice at the edges of each chart are chart numbers for other charts. These tell you which chart shows the adjacent patch of sky. So if you wanted to wander from Perseus over into Andromeda, chart 5 indicates that it’s chart 3 you’ll need to turn to.
What you need to get started
If you’re using binoculars to observe then Norton’s has details of ‘Interesting Objects’ for each chart. These include their brightness, size and other features so you can see if your binoculars are up to the task.
Notebook and pencil
A pad and pencil come in handy when you want to write up an observing plan. Jot down key points you’ll need to remember later, such as pointers to faint galaxies that you’re on the trail of, or the NGC catalogue numbers of interesting objects (if you’re using Go-To). Plus, it’s handy for making notes or sketches at the eyepiece.
This is a must-have for preserving your night vision while reading a star atlas in the dark. You can easily make a regular torch astro-friendly with a transparent red sweet wrapper attached to the end of the torch with an elastic band or some sticky tape.
A star atlas is a must-have, whether you have a Go-To or manual scope. If you have a Go-To, the lists of Messier objects and chart notes provide countless suggestions for targets; while for manual telescope owners the location information and descriptions in the lists are invaluable for tracking down objects for a night’s observing.
A waterproof pouch is essential for keeping charts and sketches away from the damaging effects of dew. If you don’t, you’ll be cursing the wrinkling of pages in your beloved star atlas before long.
A key element
Delving into the detail on the charts themselves now, it’s worth familiarising yourself with the legends on each page. They’ll show you what the many and varied symbols on the charts mean. A galaxy is shown as a little ellipse for instance, while an open cluster is a dotted circle. You’ll also see that the brighter the star, the bigger the dot it gets on the chart. Norton’s plots stars down to magnitude +6.0, which is about as dim as the naked eye can see.
Translating between the dots on the chart and stars in the sky can sometimes be quite difficult. A trick that can make things easier is to first locate the brighter stars shown by the larger dots on the chart. Then use the ones you can identify as a springboard and progressively work your way towards your target by hopping to ever fainter stars.
Another invaluable addition to the charts themselves are the pages before each pair of charts. They list noteworthy objects on the two following charts in three groups: ‘double stars’, ‘variable stars’ and ‘clusters, nebulae and galaxies’ – perfect for planning
a night of observing.
As well as the star charts, you’ll find some real gems of information throughout the rest of the atlas. You’ll find maps of the Moon and Mars and guides to the various atmospheric bands of Jupiter, and Saturn’s rings. There are other useful tidbits too, such as a guide to the Antoniadi scale of seeing, lists of the annual meteor showers and plenty of practical tips on sketching, plus a table of limiting magnitudes for different telescope sizes.
So whatever your level of interest in astronomy, you can be sure that a star atlas like Norton’s will be by your side for years – if not decades – to come.
A step-by-step guide to using Norton’s Star Atlas
1. There’s a lot you can do with a star atlas, so let’s imagine a typical scenario: you’ve seen an image of the Ring Nebula (Messier 57, pictured above) on the internet and aren’t sure exactly where it is, but you’d like to observe it with your 6-inch reflector.
2. Page 132 of Norton’s has a list of the Messier objects, giving details about where and what they are, plus their location. You’ll see that M57 is in the constellation of Lyra and has a magnitude of about +9.0; perfect for your 6-inch telescope.
3. Next, you’ll need to find out which star chart M57 is on. Page 141 of Norton’s has an index of the constellations. You’ll see from the right-hand column that the constellation Lyra is on chart 13 and that it’s best visible in July and August.
4. On the pages just after chart 13 you’ll see that M57 is listed with its RA and Dec. co-ordinates. If you’re not using a Go-To scope, you can use these values to set your scope’s setting circles, which will put M57 in the eyepiece. Or simply use the chart to help you find it.
5. You’ll find Lyra on chart 13, above and to the right of centre. Use the bright star Vega to guide you in the general direction. With Altair and Deneb it makes one corner of the famous ‘Summer Triangle’ that dominates this region of the sky.
6. The chart shows that M57 lies about two-thirds of the way between Gamma and Beta Lyrae. The notes on page 171 also indicate that you’re looking for something about an arcminute across. With a bit of careful searching you should see your quarry.
This How to guide first appeared in the July 2009 issue of Sky at Night Magazine.