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Where does space begin? How big is the universe? Constituents of Universe 
Constituents of Universe The limitless expanse of space around us consisting of the solar system, stars, galaxies etc., is called the universe. Important constituents of the universe as given below- 1. Solar system. It is the name given to the family of the sun and is part of the universe in which we live. The sun is the centre of the solar system around which nine heavenly bodies (called planets) revolve in elliptical orbits. The velocity of the planets and their distances from the sun keep on changing during rotation. The speed is the highest when they are closest to the sun and slowest when farthest away. The gravitational pull of the sun on the planets controls their motion. These planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto* in the order of their increasing distance from the sun. There are many other heavenly bodies, which revolve around the planets called satellites (or moons) of the planets. The moon, which we seen at night is the satellite of the earth. The solar system also includes asteroids, comets and meteors. Solar System 2. Stars. A star is a fiery luminous heavenly body. The temperature of the star is very high and it emits light of its own. Our sun is one of the nearest stars that we can see. Its light reaches the earth in 8-3 minutes. Some of the stars are extremely large that they are equivalent to many suns put together. On a clear night, we can see about 2500 stars at the time through the total number is much more. These stars may occur as single star, in pairs or in clusters. After the sun, the nearest star is Alpha Centauri. It is at a distance 4-3 light years from the earth. 3. Galaxies. A galaxy is a large group of stars, dust and gas held together by mutual gravitational forces. Milky way or Akashganga is one such galaxy in which we live. It can be seen on a clear night as a hazy band of white light stretching across the sky. Our sun and other stars, which can be seen by naked eye, belong to this Milky Way, which contains more than a hundred billon stars. There are million of such galaxies in the universe which can be seen through large telescope. We will now see each constituent of universe in detail starting with the solar system. Basic Conditions for existence of Life on a planet The following basic conditions are required for the life to exist on a planet. (i) There should be a suitable temperature range as required for life to exist on a planet. (ii) There must be proper atmosphere free from poisonous gases. (iii) There should be plenty of water. Space Medicine Space medicine is a branch of science that deals with the effects of space flights on human beings. Space medicine is a very important factor in manned missions. If the mission is long-term space mission then this poses serious health threat for the human body. Several dangers await the space traveler. All celestial bodies are sources of radiation, and missions to planets like mars often imply dangerous passages close to the Sun. Sun is the most important source of radiation in the solar system. The spacecraft has to provide protection against background radiation and also from extraordinary solar activity. Astronauts returning from prolonged stays aboard space stations have clearly shown that the human body severely deconditions when exposed to micro gravity conditions. On average, 1% of bone marrow is lost per month, which makes it practically unacceptable to consider a several years long mission without providing for artificial gravity by means of rotating the spacecraft. Space medicine combines many types of medical specialties to examine the effects of space flight on humans and prevent problems associated with living in this unique, isolated, and extreme environment. Medical, scientific, and engineering teams work together to maintain the physical, mental, and social well being of humans in space and upon return to Earth. The space medicine group performs three functions: Medical operations- provides medical support to astronauts during all phases of training and missions. Projects- development of medical technologies and procedures for enhancing performance and for the prevention, diagnosis, and treatment of illness and injury. Aerospace medicine training- provides aerospace medicine training opportunities to medical students, medical residents, and physicians Explorations Propellants Propulsion Propulsion Spaceshuttle Spaceshuttle Space TravelS Space Stations Other |
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