right of way, in land and air traffic and in sea navigation, rules that determine precedence in the use of traffic lanes. The rules are framed in the simplest possible terms and with nearly absolute uniformity in order to minimize the possibility of collisions. In land traffic, railroad trains, military vehicles in convoy, government vehicles (e.g., mail trucks), and emergency vehicles have the right of way over ordinary private vehicles. Rules of sea and air navigation are largely governed by international conventions and law. The term "right of way" is also applied to an easement in gross (e.g., that of a railroad). See air, law of the; maritime law.

Valerian Way: see Roman roads.

United Way of America: see community chest.

Praenestine Way: see Roman roads.

Pilgrims' Way, ancient English road that ran from Hampshire to Kent, over the Sussex Downs. It is so called because it may have been used during the Middle Ages by pilgrims who came to Canterbury to the shrine of Thomas à Becket from the southwest, via Winchester.

Milky Way, the galaxy of which the sun and solar system are a part, seen as a broad band of light arching across the night sky from horizon to horizon; if not blocked by the horizon, it would be seen as a circle around the entire sky. Although its motion is not readily apparent, the entire galaxy is rotating about the Milky Way's center. Relative to the universe, the galaxy is moving at a speed of c.370 mi per sec (c.590 km per sec) in the same direction that the constellation Leo lies relative to the earth; it is also moving at c.60 mi per sec (c.100 km per sec) relative to the center of mass of the Local Group of galaxies. The sun, traveling at a speed of c.150 mi per sec (c.240 km per sec) in a nearly circular orbit, takes 200-230 million years to complete one revolution.

Visual Characteristics of the Milky Way

Among the constellations the Milky Way passes through are Carina, Crux (the Southern Cross), Sagittarius (where it is brightest), Scorpius, Aquila, Cygnus, Perseus, Cassiopeia, Auriga, and Gemini. In the direction of Cygnus is the Great Rift, a band of dark matter that lies along the Milky Way, dividing it into two forks. Another dark region is the Coalsack, in Crux. Once believed to be vast empty regions in space, these dark areas are now known to be clouds of dark matter blotting out the light behind them. Such nonluminous clouds of dust and gas, called dark nebulae, obscure many parts of the sky from sight; in the direction of the galactic center, the view is almost entirely obscured.

Size and Shape of the Milky Way

The Milky Way is a large galaxy comprising an estimated 200 billion stars (some estimates range as high as 400 billion) arrayed in the form of a disk, with a central elliptical bulge (some 12,000 light-years in diameter) of closely packed stars lying in the direction of Sagittarius. It is surrounded by a flat disk marked by six spiral arms—four major and two minor—which wind out from the nucleus like a giant pinwheel. Because of these arms, the Milky Way was classified as a spiral galaxy. However, increasing evidence indicates that the Milky Way probably has a bar or barlike structure of new, bright stars in its central region. This would modify its classification to a barred spiral or an intermediate type between barred and "normal" spiral. Our sun is situated in one of the smaller arms, called the Local or Orion Arm, that connect the more substantial next inner arm and the next outer arm. The sun lies roughly two thirds of the way from the center of the disk, which is some 28,000 light-years distant, and in the galactic plane. When we look in the plane of the disk we see the combined light of its stars as the Milky Way. The diameter of the disk is c.100,000 light-years; its average thickness is 10,000 light-years, increasing to 30,000 light-years at the nucleus.

Certain features of the region near the sun suggested that our galaxy resembles the Andromeda Galaxy. In 1951 a group led by William Morgan detected evidence of spiral arms in Orion and Perseus. Another bright arm stretches from Sagittarius to Carina in the southern sky. With the development of radio astronomy, scientists have extended a nearly complete map of the spiral structure of the galaxy by tracing regions of hydrogen that dominate the spiral arms.

Surrounding the galaxy is a large spherical halo of globular star clusters that extends to a diameter of about 130,000 light-years; this is called the stellar halo. The galaxy also has a vast outer spherical region called the corona, or dark halo, which is as much as 600,000 light years in diameter and, in addition to dark matter which accounts for most of the Milky Way's mass, includes some distant globular clusters, the two nearby galaxies called the Magellanic clouds, and four smaller galaxies.

Stellar Populations and Galactic Evolution

The stars, gas, and dust that make up the Milky Way can be grouped into two broad stellar populations that suggest how the galaxy evolved. The spiral arms and central plane of the Milky Way contain the interstellar gas, cosmic dust, and bright young stars categorized as Population I. The halo, spaces between the spiral arms, and central core of the galaxy contain the older, less spectacular stars that are categorized as Population II. This distribution can be explained by an evolutionary model in which an enormous cloud of gas and dust began to condense to form what are now Population II stars. The remaining gas and dust then collapsed, either suddenly or in stages, into the relatively thin disk in which Population I stars were (and still are being) formed.

Like other galaxies, the Milky Way is growing by absorbing small satellite galaxies. It is currently merging with the Large and Small Magellanic Clouds, a process that will be completed in about 100 million years. In 2003 a previously unknown galaxy was found to be colliding with the Milky Way. Its distinctive red stars are slowly being pulled into the Milky Way, and the dwarf will soon lose all its structure. Called the Canis Major dwarf galaxy after the constellation in which it lies, it is about 25,000 light years away from the solar system and 42,000 light years from the center of the Milky Way. This is closer than the Sagittarius dwarf galaxy, discovered in 1994, which is also colliding with the Milky Way. Several other galaxies are also, apparently, on a collision course with the Milky Way. The biggest and most spectacular collision will be with the Andromeda Galaxy. In about 2 billion years, massive tidal gravitational effects will tear spiral arms apart and start to shred the pinwheels from the outside in. The result will be an elliptical rather than a spiral Milky Way.

Latin Way: see Roman roads.

Kendall, Henry Way, 1926-99, American physicist. A professor at the Massachusetts Institute of Technology, Kendall won the 1990 Nobel Prize in Physics with Jerome Friedman and Richard Taylor for a series of experiments (1967-73) that showed that the fundamental particles of matter are not protons and neutrons, but smaller particles known as quarks (see elementary particles). As the founder and chair of the Union of Concerned Scientists, Kendall was openly critical in the 1980s of the Strategic Defense Initiative, or "Star Wars," antimissile project.

Half-Way Covenant, a doctrinal decision of the Congregational churches in New England. The first generation of Congregationalists had decided that only adults with personal experience of conversion were eligible to full membership but that children shared in the covenant of their parents and therefore should be admitted to all the privileges of the church except the Lord's Supper. The question arose (c.1650) whether this privilege should be extended to the children of these children, even though the parents of the second generation may have confessed no experience that brought them into full communion. It was proposed (1657) and adopted (1662) by a church synod that the privileges should be extended. The measure, to which the nickname Half-Way Covenant became attached, provoked much controversy and was never adopted by all the churches. Portions of many congregations seceded to form new settlements, among them Newark, N.J.

Fosse Way, Roman road in England. It apparently ran from Exeter (Isca Dumnoniorum) NE past Bath (Aquae Sulis), Cirencester (Corinium Dobunnorum), and Leicester (Ratae Coritanorum) to Lincoln (Lindum). It intersected Watling Street.

Flaminian Way, one of the principal Roman roads, the greatest artery from Rome to Cisalpine Gaul. Construction was begun (220 B.C.) by Caius Flaminius. The road ran N from Rome to Narnia (modern Narni), to Mevania (Bevagna), NE to Nuceria (Nocera Umbria), thence N to the Burano River at Cales (Cagli), thence to the Metauro River, thence NE to Fanum Fortunae (Fano) on the Adriatic, thence along the coast NW to Ariminum (Rimini).

Appian Way, Lat. Via Appia, most famous of the Roman roads, built (312 B.C.) under Appius Claudius Caecus. It connected Rome with Capua and was later extended to Beneventum (now Benevento), Tarentum (Taranto), and Brundisium (Brindisi). It was the chief highway to Greece and the East. Its total length was more than 350 mi (563 km). The substantial construction of cemented stone blocks has preserved it to the present. Branch roads led to Neapolis (Naples), Barium (Bari), and other ports. On the first stretch of road out of Rome are interesting tombs and the Church of St. Sebastian with its catacombs. In 1784, Pope Pius VI built the new Appian Way from Rome to Albano, parallel with the old.

Aemilian Way: see Roman roads.

Latin Via Appia.

First and most famous of the ancient Roman roads, running from Rome to Campania and southern Italy. Begun in 312 BC by the censor Appius Claudius Caecus, the road originally ran 132 mi (212 km) to ancient Capua; by 244 BC it extended 230 mi (370 km) to the port of Brundisium (Brindisi) in Italy's heel. Built of smoothly fitted blocks of lava on a heavy stone foundation, the road provided a long-lasting surface for transporting merchandise to these seaports (and thence by ship to Greece and the eastern Mediterranean). Remains can be seen today outside Rome.

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