1) The North Star and Constellations Employed to Find it.

Most of us are familiar with how to find Polaris (the North Star). It is useful to the hiker because it remains virtually motionless in the sky, always north. But using Polaris for navigation, if we are hiking at night, presents us with some difficulties. It may be about the 32nd brightest star visible from the Black Hills, but in its relative isolation and among the tree tops, Polaris is not always conspicuous, and it may be hidden behind clouds.

Ursa Major (the Big Dipper) as a means of identifying Polaris, will often be unavailable to us. At dusk in winter time, the Dipper is in the lower portion of its apparent route around the Pole Star. Especially in these circumstances, a view of the Dipper is prone to be obstructed by hills or trees.

When the Big Dipper is low, the constellation Cassiopia may be used to locate Polaris. Cassiopia looks like an awkward "W" on the opposite side of Polaris from the Big Dipper. The two open "V’s" on the top of the "W" embrace the general area of Polaris. Cassiopia and its orientation to Polaris is perhaps the first constellation we need to be familiar with.

In the diagram to the right, we are hiking on January 25, 2006.  The sun set at about 16:50 MST. Over an hour has passed. The moon set hours before the sun and will not rise again for many hours. The night is about as dark as it's going to get. We look for the Big Dipper, but we can't identify it because it is hidden behind a forest of tall spruce trees.

So we look for Cassiopia. We find the constellation at an altitude of about 65° to 70°. It looks like an upside-down "W." Thinking of the "W" as composed of open arms embracing the area of the North Star, we look down from the left arm at an angle perpendicular to the hypothetical line on which the "W" would be written. The distance from the "left hand" star to Polaris is an arc of about 25°.

It is important to recognize other constellations, such as Cepheus, in the vicinity of the North Star. We could even obtain data for the bearings of stars in Cepheus, but the information is unlikely to be of value in the presence of the brighter stars of Cassiopia.

2) Stars too Dim to be of Much Value

Generally speaking, dim stars have little value to us if we are moving upon a trail. If we are camping, and can identify a dim star which we know the azimuth of, that star may have value. We only need to find direction once at a campsite—if we then mark that direction upon the ground. But if, while hiking, each time we look up, it takes five minutes to positively identify the same star, we are unlikely to use it for navigation.

However, several dimmer stars grouped tightly together as in the constellation Pleiades, may be as useful as a bright star. And their arrangement makes them distinctive. So star brightness in itself is not the sole determinent of utility. Outside its limitations, which we discuss below, the Pleiades can be helpful in finding direction, as can a constellation such as Delphinus. The tight grouping of several dim stars gives these constellations a distinction which persuades us to include them with the "bright stars" we discuss below.

Also worth noting here is Pegasus. This constellation is located in an area of the sky where bright stars are scarce. The Great Square has a distinctive appearance and thus is easily identified again and again. Though the upper two stars of the Square, Alpheratz and Beta-53, reach an uncomfortably high southing altitude, they tie our vision to two lower stars, Algenib and Markab, that cross south at an altitude we find useful.

3) Bright Stars—Never High in Altitude

We can't derive direction from a bright star that is hidden behind hills, trees, or the level horizon itself. Stars with declination lower than -47° are not visible from the Black Hills. At 43.3°N latitude, at the southern end of the Mickelson Trail, Fomalhaut and Antares reach southing altitudes of 17° and 20° respectively. That is too low to be of use when hiking through valleys further inside the Hills. But these are valuable stars for those times they are available. We won't discount them, but they are at the lower margin of those stars we might regularly tabulate for navigation in the Black Hills.

4) Bright Stars—Too High at Transit

Some bright stars are too high in "southing" altitude for a hiker to drop an accurate vertical line down from them to the horizon, but these stars may be of value nearer to times of rising and setting or before their altitudes exceed 60° or so.

Deneb is an example. The term "southing" is simply not apropos for Deneb at our latitudes. At "transit," Deneb reaches an altitude almost straight up. There is no way for a hiker to transfer its azimuth to the ground at that altitude. Stars such as Vega, Castor and Pollux, Nath and Capella are also in this group.

Even the constellation Pleiades, with a southing altitude of 70°, we would include here. It is risky business to suppose in the darkness that we can derive a workable compass direction by visualizing a plumb line dropping through a 70° arc down to the horizon.

However, the Pleiades rise at 55° azimuth, that is, 35° north of east. If we find the constellation near times of rising or setting, we can take advantage of the ease with which we recognize it. In early to mid December, about the time the skies grow dark in the evening, the Pleiades reach an altitude of 25° to 30°. At that altitude, we can visualize a plumb line down to the horizon and translate azimuth into working compass direction.

5) Bright Stars—Moderate Southing Altitude.

The most useful stars for hiking navigation in the Black Hills are those with a declination between about 14° north and 16° south (+14° to -16°). At 44° north latitude, these stars will reach a southing altitude between 60° and 30°. They will rise and set within 23° azimuth of east and west respectively.

But this is an arbitrary range of figures. Both Sirius and Aldebaran slightly exceed this range—by up to 3 degrees. We don't make rules. Those two stars probably belong in this category with Altair, Spica, Regulus, Procyon, Betelgeuse, Rigel, and several others.

Selecting Stars by Time of Year

Having looked at the limitations of stars by our categories, we can sort through data on the brightest stars, remove those not visible from the Black Hills, and add distinctive constellations such as the Pleiades. Then we wish to organize these stars according to the time of year they will be useful in the evening in the first hours of darkness.

It is important that our list of stars be spread out across the sky. Depending upon the cloud cover, some may not be visible when we need them. We can include some stars which south at low altitude, but hills or trees may hide them. In such circumstances, we need alternatives. We can also list some stars which cross a north-south meridian at high altitude, but we need to keep in mind that there will be a period of time each night when they will be too high to yeild accurate directions for us.

Using the declination of each of these stars (or perhaps the declination of the center of a cluster such as the Pleides) we can tabulate some information which will not change throughout the year about each star. The arc in which each star crosses the sky from the eastward horizon to the westward horizon is consistent. The stars for our purposes are stationary. The arc in which they move is determined by the earth's rotation, which for our purposes is also consistent.

So at a central latitude of the Black Hills, such as 44°N, each star will have the same southing altitude and azimuth of rising and setting, no matter what time of night or of year that star is viewed. Also consistent will be the length of time each star is above a level horizon.

Even more data is consistent about each star. If we find a star such as Spica that consistently reaches a southing altitude of 35°, we know that Spica will have the same bearings throughout its arc as the sun does in the time of year that it crosses south at 35°. Those bearings are determined by the earth's rotation, not by the time of year or of night. The only thing that changes for the star from night to night is the exact time of southing.

We have already shown that stars with a high southing altitude are not very reliable for us in obtaining an accurate compass direction. And we have shown that stars with a low southing altitude are not likely to be seen because of hills and trees. If we include low southing stars such as Fomalhaut and higher stars such as Arcturus, there are around 50 arcs in which those stars can cross the sky. And each arc, except the very lowest, will be that of the sun on some day of the year. Of course, we are rounding off slightly to the nearest degree of southing altitude, but that will not affect our ability to apply this information on the trail.

We have already discussed how we may use the sun for navigation and how we can obtain accurate bearings for points along the arc in which the sun appears to cross the sky. On any given day, we can take with us a strip of paper (less than an inch wide) which details the arc of the sun for that day. That information is printed from spreadsheet columns. And the strip of paper can be fitted onto a wristband, easily accessible for our use.

A single line from this wristband strip of paper might read "20 WoS 13:05." That tells us the sun will be at an azimuth of 200°, that is 20° west of south, at 13:05 Sun Time. That information is from a column tabulated for the sun's position on March 1, 2006.

Since, for our purposes, there are only about 50 arcs in which the sun crosses the sky, we can fit all that information on a half dozen pages printed from a computer. On one more sheet of paper we can include all the data we need on the stars, their southing altitude, azimuth of rising and setting, and time of southing throughout the year. The southing altitude of each star will refer us to a day of the year when the sun souths at the same altitude.

So in a small booklet, we can include all the data we need to find direction by sun and stars throughout the year. That booklet is no more cumbersome than the maps we may carry. How often we refer to this information on the trail will vary. Some of us like to finish a hike in the early hours of darkness for the "poetic effect" we mentioned earlier.

In the last few miles of the trail, we are able to estimate our time of arrival at the trailhead. We notice the cloud cover and consider the chances of needing accurate direction in the last mile or two of the hike. From our topo maps we gain an idea of which portion of the skies will be open to our view.

From our review of the night skies before the hike, we know where to expect the Belt of Orion after sunset. On the trail we may short rest break and check the bearings of the star Mintaka in Orion. Descending the last hill on the way to the trailhead, we look up into the night skies to find Orion positioned as expected, and we finish the hike feeling somewhat closer to the simple decor in the great outdoor room of the universe, our home away from home.

Astronomy links:

University of Wisconsin
Nova Astronomics
My Stars Astronomy Program
Astronomy Net
Your Sky Software
Yale Bright Star Catalog
Sky Maps
Royal Astronomical Society of New Zealand
The Fifty Brightest Stars
The 300 Brightest Stars

_ENext Section: Planets