Understanding How to Navigate Under the Night Sky: Basic Principles
To gain a basic understanding of the movement of the stars, an introductory course in astronomy would be very valuable. However, here is a very simple explanation of the stars and their apparent movement.
Go outside on a clear night and observe whatever stars you can see. You may or may not know the constellations, so just observe what you see and take note of the various patterns or shapes that you see formed by the stars and where they are relative to your position.
Focus on one section of the sky so that you’ll start to see some patterns. Then, take a break. Go back inside, have a coffee, and then go back outside in an hour and look again at the same stars. Hey! Those stars are not in the same location as an hour ago! What happened? Initially, you will think, well, the stars all moved, and yes, from your Earth perspective, they did “move.”
You observed the apparent motion of the stars, due to the fact that Earth is constantly revolving. Earth is moving, rotating around and around, just like the model Earth that sits in every school classroom.
Once you spend enough time outdoors observing the stars, you’ll notice that all the stars are rotating, and if you detect the point of rotation, you’ll have found the North Star. [Note: This article focuses on observations from the Northern Hemisphere.]
The North Star (Polaris) is coincidentally located in space about 1 degree from true north. It appears to be static in the sky, with all the other stars rotating around it because it is directly overhead from the North Pole, and the movement of the other stars is what we observe from Earth.LET’S GET TO KNOW THE NORTH STAR
The North Star is NOT the brightest star in the sky. However, it is highly significant for finding directions. If you follow it with time-lapse photography, the North Star will appear to be stationary, and all the other stars will appear to rotate counter-clockwise around it. If you were standing on the North Pole, the North Star would be directly overhead.
To find the North Star, begin by locating the Big Dipper. The North Star is in a direct line with the two stars that define the far side of the bowl of the Big Dipper (see the drawing below). If you’re just starting out, you should determine where the northern part of the sky is located in your area so you’re not looking in the wrong place.
If you don’t already know where north is in your area, refer to a local map — all standard maps have north located at the top — or use a navigation app or compass on your smartphone.
On a clear night, go outside to your viewing spot and face the north. If you live in a rural area with minimal light pollution, there may be so many visible stars that it could be hard to make out distinct constellations. You might even see the Milky Way. If you live near or in an urban area, you’re going to see only the brightest stars because the light from the city obscures the less bright stars.
Are you able to discern the Big Dipper? In this combination of stars, ancient people saw a large water dipper, as if it were scooping water.
Locate the two stars that comprise the far wall of the bowl of the “dipper.” We call the space between those two stars “distance x.” They are in a direct line to the North Star. If you continue along a line for a distance of five times “distance x” in the direction that the dipper would be pouring, you find the North Star! Wow, people who are seeing it for the first time often say, “That’s the North Star? It’s not all that bright.”
Now that you’ve located the Big Dipper and the North Star, take a note of their locations. Come back in an hour and note the Big Dipper’s location. What happened? Earth rotated and, although the North Star appears to be in pretty much the same location, the Big Dipper has now rotated counter-clockwise by about 15 degrees in the sky. Come back in another hour, and the Big Dipper will have rotated another 15 degrees in the sky. You’re witnessing the great clockface of the sky, with the North Star smack in the middle.
Now you know how to find north at night, assuming it’s a cloudless night.SIMPLEST CALCULATION
If you know north, you obviously know south, and perpendicular to your imaginary north-south line is the east-west line. If you can find the North Star in the Northern Hemisphere, you now know all your cardinal points!THE SIDEREAL DAY
What we call the Big Dipper is actually part of the larger constellation known as the Great Bear, or Ursa Major. The handle of the dipper is the tail of the Great Bear. Ursa Major is probably the most widely known constellation, going back to ancient times. Ancient people saw this big bear in the sky, rotating forever around the middle of the sky, and they told countless stories and myths about it.
IF YOU’RE LOST AND YOU CAN SEE ORION, YOU MIGHT BE ABLE TO RE-ORIENT YOURSELF, IN THE SAME WAY AS YOU SHOULD BE ABLE TO RE-ORIENT YOURSELF IF YOU SAW THE SUN, WHICH RISES IN THE EAST, AND SETS IN THE WEST.
Now, because you’re viewing the North Star from a particular location in the Northern Hemisphere, it will always appear in the sky as high above the horizon as your latitude. That means, for example, since I live at 34 degrees above the equator, I can measure 34 degrees above the horizon with a protractor in order to locate the North Star.
How do I know I live 34 degrees above the equator? I read it on a map. But if I didn’t know that, I could use a protractor to see how high the North Star is above the horizon where I live, and that angle equals my latitude. (It would be useful to know this if you’re at sea with no instruments, or if you were kidnapped by terrorists and they dumped you in some unknown area.)
As the North Star/Big Dipper rotates counter-clockwise around the North Star, it will sometimes be below your visible horizon. Now it’s time to get familiar with another grouping of stars called Cassiopeia.GETTING TO KNOW CASSIOPEIA
Cassiopeia is on the opposite side of the North Star from the Big Dipper. Cassiopeia means The Queen, and ancient people saw a seated lady in their imaginations when they looked at this cluster of stars.
When I saw Cassiopeia for the first time, when the Big Dipper was below the horizon, I thought, “That sorta looks like the Big Dipper, but it’s like a sloppy Big Dipper with a few stars missing.” Some people call this constellation the big M or big W, which more accurately describes the shape of the brightest stars of the constellation.
If you spot Cassiopeia, you can spot the North Star. Cassiopeia is found roughly the same distance away from the North Star as the Big Dipper, and roughly speaking, at the opposite side of the North Star. So, Cassiopeia rotates counter-clockwise around the North Star at roughly 180 degrees from the Big Dipper. This means you can use Cassiopeia in the same manner as the Big Dipper to locate the North Star.
To reiterate, once you’ve found the North Star, you know the whole range of directions. Turn your back to the North Star and you are facing south, and to your right is the west, and to your left is the east.A SEMI-CLOUDY NIGHT
You’re now aware that all stars appear to rotate counter-clockwise around the North Star. But the night is a bit cloudy, with just a few stars visible here and there. How can you determine directions?
From a fixed location, begin to observe the stars you can see. This could be a bit challenging, because the clouds will continue to move. Still, if you can see certain stars, watch them to see the direction in which they are moving. If the stars appear to be rising, you are facing east.
If the stars appear to be dropping in the sky, you’re facing west. If you can mentally visualize all the stars, slowly rotating counterclockwise around the North Star, this makes perfect sense.
If you’re looking in the southern sky, the stars will appear to be moving flatly to your right. Looking to the north can be a little challenging. If you’re sighting above the North Star, the stars will appear to be moving flatly to your left. However, if the patch of stars you’re viewing lie under the North Star, their movement will be a somewhat flat swing to your right.
As long as you grasp the fact that all the stars appear to rotate counterclockwise around the North Star, you’ll be able to look at the movement of stars over the course of an hour or so and determine your cardinal directions. It’s not particularly complex, but it works, and it might really help you if you’re confused.GETTING TO KNOW ORION
Orion is an easy-to-recognize constellation, probably the most widely known constellation after the Big Dipper.
Orion is said to resemble a hunter with a shield and a raised club. Four conspicuous stars provide a general outline for his body, and three stars in a line define his belt. From his belt hangs his sword. Below him is his dog, in the Big Dog constellation (Canis Major) with the brightest star in the sky, Sirius, or the Dog Star, being the brightest in the sky.
Orion is easily noted, and the constellation travels across the sky just to the south of the ecliptic. This means that, roughly speaking, Orion rises in the east and sets in the west, just like the sun and moon.
If you’re lost and you can see Orion, you might be able to re-orient yourself, in the same way as you should be able to re-orient yourself if you saw the sun, which rises in the east, and sets in the west. This is not perfect, of course, because when Orion rises you’re facing east, and then when it is at its highest point, you’re facing south, and you’re facing the west when it sets.
With practice, you should be able to use these constellations to determine directions. There are others, as well, that are very useful for navigation, which you can read about in the references listed.WHAT IS THE ZODIAC?
Though you don’t have to be a professional astronomer, or astrologer, to enjoy the sky, it does help to know some of the terminology used to describe the sky and the activities we see up there.
For example, we all hear the word “zodiac,” and somehow, we’re pretty certain that it has something to do with astrology and the horoscopes that you read in the comics section of the newspaper.
From our observation on Earth, the path that the sun and moon follow in the sky, as well as the path of the principal planets, is known as the ecliptic. This imaginary band in the sky is 15 degrees high, and astronomers have divided it into divisions, each 30 degrees wide. [30 degrees x the 12 signs of the Zodiac = 360 degrees, the complete circle.]
The center of this band is called the ecliptic by astronomers. It is in this path that ancient people have noted and charted constellations. Each of these divisions of the sky, each 30-degree-wide division, is named for a constellation, many of which are named for animals. Zodiac means “circle of animals.”
If you were to extend an imaginary plane out into space from the Earth’s equator, you have the celestial equator. The ecliptic is not the same as the celestial equator. The path of the ecliptic, the zodiacal belt, moves across the celestial equator at an angle of 23.5 degrees.
Once you get to know the observed path of the sun and the observed path of the moon in the area where you live, you’ll have grasped a greater understanding of the night sky. If you get to know the constellations along the ecliptic – which rise in the east and set in the west – you will be able to tell directions from those constellations.
“Constellations of the Northern Sky,” Mechler and Chartrand,
National Audubon Society Pocket Guide, Knopf, 1998. This field guide fits in your pocket and includes color photos.
“The Natural Navigator: The Rediscovered Art of Letting Nature be Your Guide,” by Tristan Gooley, The Experiment, 2010. If you enjoy learning how to navigate by commonsense observational skills, you must read this book!
“The Stars: A New Way to See Them,” by H.A. Rey,
Houghton Mifflin Co., Boston, 1976. (Originally published 1952). This is the best way to learn to recognize the constellations and understand the night sky that I’ve ever seen in print.
Editor’s note: A version of this article first appeared in the January, 2020 print issue of American Survival Guide.