1. a) An astronomical unit is described as the unit of length that is the distance between the center of the earth and the sun. It is approximated to be 149.6 kilometers though it varies.
b) A light-year is described as the distance light reflects in a vacuum in one year that is estimated to 9.5 x 10 15 kilometers.
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C) A parsec is the gap at which one astronomical unit bends an angle of one arc second which is averaged 3.26 light years.
2. One parsec is equivalent to 3.26 light years.
3. A kilo parsec is equivalent to 1000 parsecs. Light would take3262 light years to travel one-kilo parsec (Kpc).
A mega parsec is equivalent to a million parsecs. Light would take 3.26 million years to travel one mega parsec (Mpc).
4. All stars in the main sequence maintain a balance between the outward thermal pressure and the inward gravity from overlying layers otherwise known as hydrostatic equilibrium. Stars in the main sequence also known as dwarf stars all fuse hydrogen into helium in their cores. A star is in its main sequence when it is producing thermal energy in the core region through nuclear fusion of hydrogen atoms to form helium.
5. Stars with the same luminosity that is the energy emitted by the star per unit time and surface temperature which often determines the star’s color are bound to have similarities in their masses and similar color schemes examples being blue, blue to white, orange to red, red and white to yellow. It is determined by the mass where the larger stars burn brighter and hotter hence emits a certain color thus the luminosity is higher. Smaller stars on the other hand burn with cooler temperatures and dimmer hence their luminosity is low. It is, therefore, correct to say that stars with similar luminosity and surface temperature are similar in size if the distance is the same.
6. Stars in the same position in the main sequence have the same age. Though some may have formed earlier or later than others, the time difference between their formations times could be small or negligible compared to their lifetimes. The position of a star in the main sequence is determined by mass, chemical composition among other factors. The constituent materials determine chemical composition. It is, therefore, correct to say that if the stars are at the same place; their formation time is almost the same therefore their age is the same. It would also be correct to say that their components are also almost similar since the cloud of gasses from which they form the same.
7. Red dwarfs are the most common stars around the sun in the Milky Way galaxy. Proxima Centauri, the star closest to Earth, is a red dwarf. Approximately fifty of the sixty stars closest to Earth are red dwarfs. They are however not visible to the naked eye at night due to their low luminosity which is a result of their relatively low temperatures caused by their low masses, low pressure and a low rate of fusion. The helium produced from hydrogen fusion is remixed at the core the subsequent build up prolonging the period of fusion. These stars, however, have a longer lifetime as they burn out slowly.
8. There are various ways of measuring the temperatures of a star.
By viewing the color of the star, one may compare its appearance to that of the sun. Being redder than the sun means the star is less than 5200k.One may also use the fact that hot stars are blue while cool stars are red. This method is not very accurate but is used in situations lacking a good spectrum.
Using dispersion of light from a star and finding the wavelength of which you have the most radiation then applying Wien’s law to find the approximate temperatures.
The ratio of colors from two different color filters gives the temperature of objects for the Planck spectra. By using computer calibration to improve the accuracy, one is then able to get the stellar temperatures by comparing the filters with computer models of different temperatures and developing a relation. It is achieved easily using a photoelectric photometer, which involves passing light through some filters and deducing how much passes. According to the standard scales, these readings are converted to temperature readings.
Another way is by getting the total flux of light from a star, getting the distance from the parallax, getting the luminosity, measuring the radius, then using Stefan’s law to get the temperature.
One may also analyze the spectrum of the star having in mind that higher levels are found at higher temperatures. One constructs a model of the star. The outer parts absorb radiation from the inner parts, and this produces absorption lines in a sequence. The strength of an absorption line depends on the temperature of the star, chemical elements and several other variables such as gravity and atmospheric structure. Measuring lots of lines and isolating the other variables helps one come up with an almost accurate temperature.
References
1. Nola Taylor Redd (2015, May5) Main sequence stars; Definition & life cycle www.space.com?22437_main_sequence_stars.html
2. Bruce MacEvoy (2013, November 26) Spectral classification of stars. http://www.handprint.com?ASTRO/SPECCLASS.HTML
3. Bradley W. Carroll & Dale A.Ostile (2007).An introduction to modern Astrophysics. Person Education Addison Wesley San Francisco.
4. Shore, Steven N., The Tapestry of modern Astrophysics John Wiley and sons, Hoboken, 2003.
5. Bahcall, John N. Neutron Astrophysics, Cambridge University Press, Cambridge, 1989.
