Science Of Stars
...o a single beam that is then split into its spectrum by a prism; the spectrum is then measured and compared against the spectra of known elements to help determine the composition of the Sun. The corona of the Sun is typically visible only during an eclipse. A coronograph mimics an eclipse and allows the corona to be observed and studied at any time. A spectroheliograph splits a thin beam of light into a prism and filters out all but one wavelength of light. This wavelength of light is then exposed to photographic media, allowing the Sun to be photographed in more detail. A bolometer is a device used to measure temperature and a pyrheliometer is a device used to measure solar heat and energy (Columbia, 2005). The Energy Output of the Sun The energy output of the Sun is typically measured by the heat and radiation that the Sun produces this is called the Sun’s luminosity. The luminosity of the Sun affects the Earth’s climate and makes it a place with the right conditions to support life. The energy output from the Sun varies with the solar cycle. The solar cycle lasts about 11 years. When the least amount of Sunspot activity occurs, the amount of energy released decreases and the luminosity remains constant. This state is called the solar minimum. In contrast, during the solar maximum, Sunspot activity is at its peak. The sudden bursts of radiation from solar flares may even disrupt communications here on Earth due to the large amount of energy released from the Sun’s magnetic field (Bennett, pp. 512-513, 2004). How the Sun Produces Energy The Sun produces energy by nuclear fusion caused by the extreme pressure in the Sun’s core. When the nucleus of atoms split to smaller nuclei it is known as nuclear fission; however on the Sun the nuclei’s are joining or fusing together creating more protons and neutrons than the original atomic mass. The intense heat and pressure allows for the positively charged protons to stick together to over come the electromagnetic repulsion. When this happens the atomic mass is increased and helium is created. The three steps needed to create a proton-proton chain include two protons fusing to form a nucleus of one proton and one neutron creating deuterium. The second step is to have the deuterium nuclei collide with another proton creating helium-3. The helium-3 nucleus adds another neutron to create helium-4. Kinetic energy results as the radioactive gamma rays created by helium-4 are released (Bennett, pp. 502-503, 2004). The Sun in Equilibrium Equilibrium is a balance between two forces. When the nuclear fusion forces the competition of gravity pulling inward and the pressure pushing outward the Sun is in gravitational equilibrium status. Points within the Sun are part of equilibrium when the weight of overlying material is supported by underlying pressure (Bennett, p. 497, 2004). The Sun was born from a collapsing cloud of interstellar gas. Contractions of clouds released an energy that raised the interior temperature of the Sun higher and higher, but not enough to halt the contraction. As the central temperature and density of the Sun eventually reached the values required to sustain the nuclear fusion, the Sun’s interior energy generation matched the energy lost from the surface by forms of radiation. The long lasting state of gravitational equilibrium of the Sun, by the onset of fusion, has persisted for 4.6 billion years. As the Sun ages it will exhaust the nuclear fuel and the internal pressure will drop. Gravitational contraction will begin once again. The gravitational contraction is what makes the Sun hot enough to sustain nuclear fusion in its core (Bennett, p. 498, 2004). The Evolution of a Star Stars have a life cycle that can be compared to that of a human life cycle. How long of a life cycle has is dependent on a star’s mass. A star has five stages of life. Stars are born in nebulae which are huge clouds of dust and gas in the spiral arms of galaxies. These clouds collapse under gravitational forces and a protostar emerges. The rising pressure created from the collapse pushes back against gravity and the cloud becomes a protostar. During this stage of evolution, a protostar’s mass continues to increase. A protostar may look star-like but it is not hot enough for fusion to occur. A protostar beco...