To collide - сталкиваться
Helios heath – солнечная пустошь
stellar-windward – звездная наветренная сторона
to terminate – кончаться, ограничиваться
bluntly – прямо, резко, без острых углов
II. Read and translate the text and make 5 questions to it:
The point at which the Solar System ends and interstellar space begins is not precisely defined, since its outer boundaries are shaped by two separate forces: the solar wind and the Sun’s gravity. The solar wind is believed to surrender to the interstellar medium at roughly four times Pluto’s distance. However, the Sun’s Roche sphere, the effective range of its gravitational influence, is believed to extend up to a thousand times farther.
The Voyagers entering the heliosheath.
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Heliopause
The heliosphere is divided into two separate regions. The solar wind travels at its maximum velocity out to about 95 AU. The edge of this region is the termination shock, the point at which the solar wind collides with the opposing winds of the interstellar medium. Here the wind slows, condenses and becomes more turbulent, forming a great oval structure known as the Helios heath that looks and behaves very much like a comet’s tail, extending outward for a further 40 AU at its stellar-windward side, but tailing many times that distance in the opposite direction. The outer boundary of the heliosphere, the heliopause, is the point at which the solar wind finally terminates, and is the beginning of interstellar space.
Oort cloud
Artist’s rendering of the Kuiper Belt and hypothetical Oort cloud.
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The hypothetical Oort cloud is a great mass of up to a trillion icy objects that is believed to be the source for all long-period comets and to surround the Solar System at roughly 50,000 AU, and possibly to as far as 100,000 AU. It is believed to be composed of comets which were ejected from the inner Solar System by gravitational interactions with the outer planets. Oort cloud objects move very slowly, and can be perturbed by infrequent events such as collisions, the gravitational effects of a passing star, or the galactic tide, the tidal force exerted by the Milky Way.
Boundaries
Much of our Solar System is still unknown. The Sun’s gravitational field is estimated to dominate the gravitational forces of surrounding stars out to about two light years (125,000 AU). The outer extent of the Oort cloud, by contrast, may not extend farther than 50,000 AU. Despite discoveries such as Sedna, the region between the Kuiper belt and the Oort cloud, an area tens of thousands of AU in radius, is still virtually unmapped.
III. Explain the following terms:
Heliosphere, termination shock, intersellar medium, helios heath, heliopause, Oort cloud.
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