Lake Michigan is one of the five Great Lakes of North America and the only one located within the United States. The other four Great Lakes are shared by the U. S. and Canada. It is the second-largest of the Great Lakes by volume and the third-largest by surface area, after Lake Superior and Lake Huron. To the east, its basin is conjoined with that of Lake Huron through the wide Straits of Mackinac, giving it the same surface elevation as its easterly counterpart. Lake Michigan is shared, from west to east, by the U. S. states of Wisconsin, Illinois and Michigan. Ports along its shores include Chicago; the word "Michigan" referred to the lake itself, is believed to come from the Ojibwe word michi-gami meaning "great water". Some of the earliest human inhabitants of the Lake Michigan region were the Hopewell Indians, their culture declined after 800 AD, for the next few hundred years, the region was the home of peoples known as the Late Woodland Indians. In the early 17th century, when western European explorers made their first forays into the region, they encountered descendants of the Late Woodland Indians: the Chippewa.
The French explorer Jean Nicolet is believed to have been the first European to reach Lake Michigan in 1634 or 1638. In the earliest European maps of the region, the name of Lake Illinois has been found in addition to that of "Michigan", named for the Illinois Confederation of tribes. Lake Michigan is joined via the narrow, open-water Straits of Mackinac with Lake Huron, the combined body of water is sometimes called Michigan–Huron; the Straits of Mackinac were an important Native American and fur trade route. Located on the southern side of the Straits is the town of Mackinaw City, the site of Fort Michilimackinac, a reconstructed French fort founded in 1715, on the northern side is St. Ignace, site of a French Catholic mission to the Indians, founded in 1671. In 1673, Jacques Marquette, Louis Joliet and their crew of five Métis voyageurs followed Lake Michigan to Green Bay and up the Fox River, nearly to its headwaters, in their search for the Mississippi River, cf. Fox–Wisconsin Waterway.
The eastern end of the Straits was controlled by Fort Mackinac on Mackinac Island, a British colonial and early American military base and fur trade center, founded in 1781. With the advent of European exploration into the area in the late 17th century, Lake Michigan became part of a line of waterways leading from the Saint Lawrence River to the Mississippi River and thence to the Gulf of Mexico. French coureurs des bois and voyageurs established small ports and trading communities, such as Green Bay, on the lake during the late 17th and early 18th centuries. In the 19th century, Lake Michigan played a major role in the development of Chicago and the Midwestern United States west of the lake. For example, 90% of the grain shipped from Chicago travelled east over Lake Michigan during the antebellum years, only falling below 50% after the Civil War and the major expansion of railroad shipping; the first person to reach the deep bottom of Lake Michigan was J. Val Klump, a scientist at the University of Wisconsin–Milwaukee.
Klump reached the bottom via submersible as part of a 1985 research expedition. In 2007, a row of stones paralleling an ancient shoreline was discovered by Mark Holley, professor of underwater archeology at Northwestern Michigan College; this formation lies 40 feet below the surface of the lake. One of the stones is said to have a carving resembling a mastodon. So far the formation has not been authenticated; the warming of Lake Michigan was the subject of a report by Purdue University in 2018. In each decade since 1980, steady increases in average surface temperature have occurred; this is to lead to decreasing native habitat and to adversely affect native species survival. Lake Michigan is the sole Great Lake wholly within the borders of the United States, it lies in the region known as the American Midwest. Lake Michigan has a surface area of 22,404 sq.mi. It is the larger half of Lake Michigan–Huron, the largest body of fresh water in the world by surface area, it is 307 miles long by 118 miles wide with a shoreline 1,640 miles long.
The lake's average depth is 46 fathoms 3 feet. It contains a volume of 1,180 cubic miles of water. Green Bay in the northwest is its largest bay. Grand Traverse Bay in its northeast is another large bay. Lake Michigan's deepest region, which lies in its northern-half, is called Chippewa Basin and is separated from South Chippewa Basin, by a shallower area called the Mid Lake Plateau. Twelve million people live along Lake Michigan's shores in the Chicago and Milwaukee metropolitan areas; the economy of many communities in northern Michigan and Door County, Wisconsin is supported by tourism, with large seasonal populations attracted by Lake Michigan. Seasonal residents have summer homes along the waterfront and return home for the winter; the southern
The tz database is a collaborative compilation of information about the world's time zones intended for use with computer programs and operating systems. Paul Eggert is its current editor and maintainer, with the organizational backing of ICANN; the tz database is known as tzdata, the zoneinfo database or IANA time zone database, as the Olson database, referring to the founding contributor, Arthur David Olson. Its uniform naming convention for time zones, such as America/New_York and Europe/Paris, was designed by Paul Eggert; the database attempts to record historical time zones and all civil changes since 1970, the Unix time epoch. It includes transitions such as daylight saving time, records leap seconds; the database, as well as some reference source code, is in the public domain. New editions of the database and code are published as changes warrant several times per year; the tz database is published as a set of text files which list the rules and zone transitions in a human-readable format.
For use, these text files are compiled into a set of platform-independent binary files—one per time zone. The reference source code includes such a compiler called zic, as well as code to read those files and use them in standard application programming interfaces such as localtime and mktime. Within the tz database, a time zone is any national region where local clocks have all agreed since 1970; this definition concerns itself first with geographic areas. This is different from other definitions which concern themselves with consistent offsets from a prime meridian. Therefore, each of the time zones defined by the tz database may document multiple offsets from UTC including both standard time and daylight saving time. In the time zone text files, each time zone has one or more "zone lines" in one of the time zone text files; the first zone line for a time zone gives the name of the time zone. Each zone line for a zone specifies, for a range of date and time, the offset to UTC for standard time, the name of the set of rules that govern daylight saving time, the format for time zone abbreviations, for all but the last zone line, the date and time at which the range of date and time governed by that line ends.
The rules for daylight saving time are specified in named rule sets. Each rule set has one or more rule lines in the time zone text files. A rule line contains the name of the rule set to which it belongs, the first year in which the rule applies, the last year in which the rule applies, the type of year to which the rule applies, the month in which the rule takes effect, the day on which the rule takes effect, the time of day at which the rule takes effect, the amount of time to add to the offset to UTC when the rule is in effect, the letter or letters to use in the time zone abbreviation; the time zones have unique names in the form "Area/Location", e.g. "America/New_York". A choice was made to use English names or equivalents, to omit punctuation and common suffixes; the underscore character is used in place of spaces. Hyphens are used; the Area and Location names have a maximum length of 14 characters. Area is the name of a continent, an ocean, or "Etc"; the continents and oceans used are Africa, Antarctica, Asia, Australia, Europe and Pacific.
The oceans are included. Some are geographically connected to one continent and politically to another. See Boundaries between continents; the special area of "Etc" is used for some administrative zones for "Etc/UTC" which represents Coordinated Universal Time. In order to conform with the POSIX style, those zone names beginning with "Etc/GMT" have their sign reversed from the standard ISO 8601 convention. In the "Etc" area, zones west of GMT have a positive sign and those east have a negative sign in their name Location is the name of a specific location within the area – a city or small island. Country names are not used in this scheme because they would not be robust, owing to frequent political and boundary changes; the names of large cities tend to be more permanent. However, the database maintainers attempt to include at least one zone for every ISO 3166-1 alpha-2 country code, a number of user interfaces to the database take advantage of this. Additionally there is a desire to keep locations geographically compact so that any future time zone changes do not split locations into different time zones.
The most populous city in a region is chosen to represent the entire time zone, although other cities may be selected if they are more known or result in a less ambiguous name. In the event that the name of the location used to represent the time zone changes, the convention is to create an alias in future editions so that both the old and new names refer to the same database entry. In some cases the Location is itself represented as a compound name, for example the time zone "America/I