Star is a brilliantly glowing sphere of hot gas whose energyis produced by an internalnuclear fusion process. Stars are contained in galaxies. A galaxy contains not only stars, but clouds of gas and dust. These clouds are callednebulae, and it is in a nebula where stars are born. In the nebula is hydrogen gas which is pulled together by gravityand starts to spin faster. Over millions of years, more hydrogen gas is pulled into the spinning cloud. The collisions which occur between the hydrogen atoms starts to heat the gas in the cloud. Once the temperature reaches 15,000,000 degrees Celsius, nuclear fusion takes place in the center, or core, of the cloud. The tremendous heat given off by the nuclear fusion process causes the gas to glow creating a protostar. This is the first step in the evolution of a star. The glowing protostar continues to accumulate mass. The amount of mass it can accumulate is determined by the amount ofmatter available in the nebula. Once its mass is stabilized, the star is known as a main sequence star. The new star will continue to glow for millions or even billions of years. As it glows, hydrogen is converted into helium in the core by nuclear fusion. The core starts to become unstable and it starts to contract. The outer shell of the star, which is still mostly hydrogen, starts to expand. As it expands, it cools and starts to glow red. The star has now reached the red giant phase. It is red because it is cooler than the protostar phase and it is a giant because the outer shell has expanded outward. All stars evolve the same way up to the red giant phase. The amount of mass a star has determines which of the following life cycle paths the star will take.
<span>A. Keynote address
In the Keynote address is most likely a world-famous surgeon would give his/her speech in order to motivate, inspire and challenge pursing scientists and medical professionals in their pursuit of their successful career and the like endeavors. </span>
Motor neurons conduct nerve impulses from the central nervous system (brain and spinal cord) to an effector. A single motor neuron carries messages from the spinal cord to an effector. One or more interneurons in the spinal cord carry messages from a sensory neuron to a motor neuron.
Henry observed the aquatic life in the pond, but also the
trees, vegetation, and animal’s species on land. The diversity observed by
henry is ecological diversity. Ecological diversity is the variation in the
ecosystems found in a region or the variation in ecosystems over the whole
planet. Ecological diversity includes the variation in both terrestrial and
aquatic ecosystems.
