General Astronomy Questions - Assignment Example

Describe the three main layers of the solar atmosphere and how you would best observe them. Staring from the inner side of the Sun it consists from photosphere, chromosphere and corona. Photosphere is not transparent for visible light, because of high gas density at this layer. The photosphere can be observed directly by looking at Sun with strong filters, because two layers above chromosphere and corona are transparent. The unique property of the chromosphere is the hydrogen alpha emission that gives the red color. It can be directly observed by using very spectrometers tuned on the hydrogen alpha emission length. The last outer layer corona is very large compared to previous two, has considerable smaller gas density, but much higher temperature. Corona is observed with a coronagraph, which blocks the central part of the Sun, therefore providing more contrast to the outer layer of corona. How do astronomers detect the presence of a magnetic field in hot gases, such as the field in the solar photosphere? The magnitude of magnetic field can be measured indirectly through the gyro resonance emission. Free electrons gyrate in the presence of a magnetic field due to the Lorenz force and emit radiation in radio spectrum. This spectrum can be measured directly and used to calculate back the original magnetic field present in the solar gas. Why do thermonuclear reactions in the Sun take place only in its core? Thermonuclear reaction requires both high temperature and high pressure to overcome Coulomb barrier and fuse atoms together. The high pressure is achieved in the core of the Sun due to the gravitational collapse that formed the start in the first place. With increased density comes the high temperature, because the volume of the gas is decreasing. At some point there is enough energy to produce sustainable thermonuclear reaction and the energy dissipation counteracts with continuing collapse. Measurements of a binary star system are required to determine what property of stars? a. Luminosity, b. Apparent magnitude, c. distance, d. mass e. temperature Binary starts are two start that rotate around their common center of gravity. Through the observation we can determine the period of rotation, i.e. time of one full turn of one start around another. This is enough information to calculate the stellar mass, therefore the answer is d. What is the difference between apparent magnitude and absolute magnitude? Both measurements are designed to provide information about brightness of a star. Apparent magnitude introduces a measure of how bright is a start when observed directly from Earth. Originally it concerned only the visible spectrum, but later the scale was increased to accommodate stars that emit mostly in invisible spectrum. Brighter starts have smaller apparent magnitude. An absolute magnitude is equal to the apparent magnitude of a star as if it were put 10 parsecs away from Earth. Therefore, the apparent magnitude depends on the distance to the star and the absolute magnitude does not. Draw an H-R diagram and sketch the regions occupied by main-sequence stars, giants, supergiants, and white dwarfs. Briefly discuss the different ways you could have labeled the axes of your graph. The Hertzsprung–Russell diagram differentiates star by two main properties: luminosity and effective temperature. Luminosity can be replaced with absolute magnitude as they are can be calculated one from another. The same goes for the effective temperature that can be replaces with a spectral type or classification. For example, supergiants are not hot, but bright stars. Main sequence represents almost 90% of all know stars and refers to stars with healthy thermonuclear fusion reaction in their cores. Main sequence represents a diagonal on H-R diagram and is a starting place for a star evolution. What is the source of energy that enables a main- sequence star to shine? a. Friction between its atoms, b. Fusion of hydrogen in a shell that surrounds the Core c. Fusion of helium in its core d. Fusion of hydrogen in its core e. Burning on its surface d. The main source of energy for main sequence start, as for the Sun as well, is the fusion reaction in the core that fuses hydrogen into helium. After that the energy is transmitted up to the surface and released further in radiation of different wavelength, including the visible part of the spectrum, which can be observed by a naked eye and attributed to shining. Why do thermonuclear reactions not occur on the surface of a main-sequence star? The surface of main sequence starts does not provide conditions that are enough to start a thermonuclear reaction. Even if the temperature condition can be satisfied in some regions, for example corona, the pressure is far from high enough to bring atoms close enough to start nuclear fusion. What does it mean when an astronomer says that a star "moves" from one place to another on an H-R Diagram? All processes that are happening in a star, such as thermonuclear fusion reaction, change the properties of the star, such as mass, stored energy etc. As a result with time the amount of fuels decreases and the star transforms and together with the transformation it changes its spectral class and in some cases absolute magnitude. There are several known evolution tracks on the H-R diagram that depend on the initial mass of the start. In most cases a star moves from the left to right, which means changing its temperature and the absolute magnitude also changes, but in different proportions. What prevents a neutron star from collapsing? a. Hydrogen fusion b. friction c. electron degeneracy pressure d. neutron degeneracy pressure e. helium fusion d.Neutron degeneracy pressure prevents a neutron star to succumb to the gravitational pull. This counter effect is possible, because neutrons are fermions and according to the Pauli exclusion principle two identical fermions cannot occupy the same quantum state. This quantum effect counteracts the gravitational pull that targets to collapse the star. What is a planetary nebula, and how does it form? Planetary nebula is a specific form of nebula that contains expanding ionized gas that was ejected at the late stage of life of red giants. During the evolution of a red giant on H-R diagram before a transformation into a white dwarf it releases its outer region of gas that forms a planetary nebula. What is the Oppenheimer-Volkov limit? The Oppenheimer-Volkov limit defines a limit for the mass of a star after which it succumbs to the gravitational collapse and becomes a black hole. It can be turned around from another side and defined as a lower limit for the mass for black hole. Which feature is found with Kerr black holes but not Schwarzschild black holes? a. a singularity b. an event horizon c. gravitational redshift of photons outside of the black hole d. an ergo region e. warping of nearby space time d. Ergo region or ergo sphere is a region of space that is found just outside of a rotating black hole. A unique property of this region is that it is possible to extract matter and energy from the black hole into this region. It is also possible to escape from the ergo sphere, therefore, it plays a role of a buffer for matter and energy between the black hole and surrounding space. If light cannot escape from a black hole, how can we detect X rays from such an object? Indeed there is no light coming out of a black hole, however, there are particles that are on their way to collapse into the black hole. These particles form a structure called an accretion disk around the black hole. The gravitational pull is so strong from the black hole that particles from the accretion disk emit radiation in X-ray part of spectrum. Therefore, this observation of the black hole is indirect. Read More