Unlike planets, comets move on highly elongated orbits, and therefore are visible only at short periods close to the Sun.
The main part of any comet is its nucleus .
According to the hypothesis of the famous American researcher of comets Fred Lawrence Whipple, cometary nucleus is an ice consisting of a mixture of frozen water and frozen gases interspersed with refractory rocky and metallic particles . Figuratively speaking, it looks like a “dirty iceberg”.
Let us imagine that we see the newly opened the comet, which is somewhere in the vicinity of Jupiter’s orbit. Seeing through the telescope hazy pale speck, like a spherical nebula (such unattractive are presented to the observer of a distant comet), we may be disappointed at first. With the approach of the comet to the Sun the solar flux increases. Comet “ice” begin to evaporate rapidly. Around the nucleus formed a vast glowing gas shell – coma. Together with the core of it is the head of the comet. Continue reading
Radiation risk for astronauts (radiobiological rationale)
The book covers a fairly wide range of materials concerning the sources of cosmic rays affecting astronauts in the implementation of interplanetary and orbital space flight, the quantities of the doses, the reactions of individual systems and the whole organism of animals and humans, and changes its stability when the complex character of radiation exposure in space.
The results of a 14-year experiment on a large lot dogs with simulation values of the doses and nature of dose distribution in time, which will affect astronauts during the flight to Mars. The considered models of formation of radiation damage in the hematopoietic system and the level of the organism during long exposures with varying dose rate, and the model of radiation mortality rate of mammals, describing accelerated aging and the changing age-specific mortality rates in a dose-and dose rate radiation exposure.
The book presents the algorithms and results of calculations of the radiation risk in the process of interplanetary and orbital missions throughout the life of astronauts, as well as data on possible sacramentoa life expectancy. The new approaches to the regulation of radiation exposure and justifies the new lower acceptable dose to astronauts during flights and during the whole professional activity. Continue reading
Of course, the oceans are huge and mountains impress with their value. And seven billion people is a lot, but still. Since we all live on planet Earth (whose diameter is 12 742 km), it is easy to forget how insignificant we really are small. All we need to do is look up at night, the sky, and realize that we are just a bunch of dust in the immeasurable vast Universe.
10. Jupiter. The largest planet (142 984 kilometres in diameter)
Jupiter – the largest planet of our Solar System. Ancient astronomers named Jupiter after the main Roman God. Jupiter is the fifth most close planet to the Sun. The atmosphere of Jupiter consists of about 84 percent hydrogen and about 15 percent helium, with small amounts of acetylene, ammonia, ethane, methane, phosphine, hydrogen and water vapor. Jupiter has a mass 318 times the mass of Earth and a diameter 11 times larger than the diameter of the Earth. The mass of Jupiter is 70% of the total mass of all other planets of our Solar System. The volume of Jupiter is large enough that it could fit 1300 planets the size of Earth. The planet has 63 known satellites (moons) but most of them have very small sizes, and disappear. Continue reading