Über die Autorin bzw. den Autor

E. C. Pielou, a former professor of mathematical ecology and Killam Professor at Dalhousie University, has been a naturalist all her life. She is the author of many books, most recently Fresh Water, A Naturalist's Guide to the Arctic, and After the Ice Age, all published by the University of Chicago Press.

Von der hinteren Coverseite

Whether planning an arctic journey, doing one, or enjoying memories of one, this book is indispensable. Designed as a compact source of information for those who must limit their load--hikers, kayakers, canoeists, rafters, photographers, and naturalists of all kinds--this guide will ensure that naturalists in the Arctic miss nothing.

Auszug. © Genehmigter Nachdruck. Alle Rechte vorbehalten.

A Naturalist's Guide to the Arctic

The University of Chicago Press

Contents

Preface......................................xiIntroduction.................................xiii1 Sky........................................12 Climate and Atmosphere.....................153 Terrain....................................274 Seas.......................................625 Plant Life.................................766 Birds......................................1917 Mammals....................................2548 Fish.......................................2999 Insects....................................307Index........................................321

Chapter One

1.1 The Land of the Midnight Sun

"The Arctic" means different things to different people. To those who pay more attention to the sky than to the ground (which includes astronomers, of course), it means all that part of the earth, centered on the North Pole, where, at least once in the year, the sun remains above the horizon for a full 24 hours without setting so that (if it isn't cloudy) the sun shines at midnight on at least one day of the year.

An understanding of why there are days in summer when the sun doesn't set (and days in winter when it doesn't rise) cannot be gained without concentrating closely on astronomical matters, specifically on the way the earth rotates around a tilted axis as it makes its yearly journey round the sun. Readers not in the mood for heavy thinking on these topics should skip to section 1.3.

The lowest latitude at which the midnight sun is ever seen is the Arctic Circle, at 66 ½° N (or at 23 ½° from the Pole; the two angles add up to a right angle). The reason for this can be understood from the diagram (fig. 1.1) showing how the axis on which the earth spins (joining the north and south poles) is tilted at an angle of 66 ½° to the earth's orbit round the sun. The day of the year on which the tilted axis points most nearly toward the sun is known as the summer solstice; it comes on June 21. On that day, as the diagram shows, every point within the Arctic Circle is in sunlight for the whole of the earth's rotation, that is, the whole day long. At the other end of the year is the winter solstice (December 22) when, at every point within the Arctic Circle, the sun is below the horizon the whole day long.

Contemplation of figure 1.1 shows that the times of sunrise and sunset must change with the seasons. The exact times, taken from the Nautical Almanac, were used to draw figure 1.2. The four diagrams show how the number of days during which the sun never sets varies from zero at 60° N (below the Arctic Circle) to over 2 months at 70° N, nearly 4 months at 80° N, and finally 6 months (half the year) at the pole itself. These periods of continuous sunlight begin and end at the dates shown, respectively, on the left and right sides of each diagram, where it is crossed by the "sunrise line" (the line separating the white part from the rest of the diagram).

The diagrams also show the duration of two kinds of twilight: Civil twilight, which begins when the sun sets and continues until it is 6° below the horizon; during this period "operations requiring daylight" can be carried on, as the legal description puts it. And nautical twilight, which begins when civil twilight ends and lasts until the sun is 12° below the horizon, by which time all the stars used for celestial navigation have "come out." In the morning, of course, the order is reversed: first comes nautical twilight and then civil twilight, which ends at sunrise.

There is a third level of twilight, so dim it is treated as darkness in the diagrams. It prevails while the sun is between 12° and 18° below the horizon, and is called astronomical twilight. During astronomical twilight, fainter stars appear, and the outlines of large objects and the horizon remain just visible. When the sun is lower than 18°, darkness is total (except for moonlight, starlight, the aurora, and nightglow, the faint radiance of the night sky itself!).

The diagrams can be used to give (roughly) the times of sunrise and sunset, and of the beginnings and ends of the two kinds of twilight, on a chosen date at each of the latitudes shown. For example, a horizontal line through April 1 on the 70° N diagram, shows that on that day, at that latitude, nautical twilight begins at about 2 A.M. and ends at about 10 P.M. Civil twilight begins at about 4 A.M. and ends at about 8 P.M. Sunrise and sunset are at 5 A.M. and 7 P.M., respectively. On the same day at 80° N, civil twilight lasts all night, even though the sun is below the northern horizon for the 3Vi hours centered on midnight. And at the pole, the sun doesn't set at all on that day.

The dates at which (at a particular latitude) the sun sets for the long winter night and rises at the end of it, can also be read, approximately, from the relevant diagram. They are the dates shown on the right and left sides of the diagram (respectively) where it is cut by a horizontal line across it, drawn so as to touch the bottom of the dip in the "sunrise line." At 70° N, for example, the sun disappears at the end of November and reappears in the middle of January. The corresponding dates at 80° N are late October and late February. The special conditions at 90° N—the Pole itself—are described later.

Note that, when the long winter night comes to an end, the sun first shows itself on the southern horizon. The first "day" lasts from a few seconds before noon to a few seconds after, when the sun is in the south. Astronomical considerations clearly show that the first sunrise of the year is never in the east even though writers accustomed to temperate latitudes sometimes forget this.

To return to the midnight sun: Even when the sun doesn't set, there is a noticeable difference in temperature between midday (when the sun is due south) and midnight (when it is due north) in all but the highest latitudes. The words "day" and "night" are often used, despite the continuous daylight, to label the warmer and cooler halves of the 24-hour day. The temperature difference is because at midday the sun is at the highest point in its path through the sky, and at midnight at its lowest point. The contrast is most marked on the Arctic Circle, where, on its single annual appearance (June 21), the midnight sun is right on the horizon. The contrast between day and night becomes less and less as the midnight sun period becomes longer and longer, that is, the farther north you go: as the latitude increases, the height of the sun above the horizon at midday becomes progressively less, and its height at midnight becomes progressively greater, until at the North Pole itself they become equal.

The course of events right at the pole deserves special attention (see fig. 1.2). After months of winter darkness (relieved only by the moon; see sec. 1.2), a day comes when a faint glow becomes just noticeable at some point on the horizon. The glow does a complete rotation, along the horizon, every 24 hours as day succeeds day (measuring days on a clock). By February 17, many of the fainter stars have become invisible in the brightening sky and the horizon can just be seen; the sun is 12° below the horizon and nautical twilight has begun. The light continues to increase gradually, as the sun slowly rises; it does not show itself, but its position below the horizon is...