local interstellar cloudとは 意味・読み方・使い方

The Local Interstellar Cloud (or Local Fluff) is the interstellar cloud roughly 30 light years across through which the Earth's solar system is currently moving. The Solar System is thought to have entered the Local Interstellar Cloud at some time between 44,000 and 150,000 years ago and is expected to remain within it for another 10,000 to 20,000 years. The cloud has a temperature of about 6000 °C, about the same temperature as the surface of the Sun. It is very tenuous, with 0.1 atoms per cubic centimeter; approximately one-fifth the density of the galactic interstellar medium (0.5 atoms/cc), but twice that of the gas in the Local Bubble (0.05 atoms/cc). The Local Bubble is an area of low-density in the interstellar medium, with the Local Cloud a small, more dense area. In comparison, Earth's atmosphere at STP has 2.7 × 10¹⁹ molecules per cubic centimeter.