# translation of kstars_colorandtemp.po to 
# translation of kstars_colorandtemp.po to
# translation of kstars_colorandtemp.po to
# Copyright (C) 2002 Free Software Foundation, Inc.
# Lwandle Mgidlana <lwandle@translate.org.za>, 2002
#
msgid ""
msgstr ""
"Project-Id-Version: kstars_colorandtemp\n"
"POT-Creation-Date: 2001-02-09 01:25+0100\n"
"PO-Revision-Date: 2002-09-26 12:32+0200\n"
"Last-Translator: Lwandle Mgidlana <lwandle@translate.org.za>\n"
"Language-Team:  <xh@li.org>\n"
"MIME-Version: 1.0\n"
"Content-Type: application/x-xml2pot; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"X-Generator: KBabel 1.0beta2\n"

#: index.docbook:5
#, no-c-format
msgid ""
"<firstname>Jasem</firstname> <surname>Mutlaq</surname> "
"<affiliation><address> <email>mutlaqja@ku.edu</email> "
"</address></affiliation>"
msgstr ""

#: index.docbook:14
#, no-c-format
msgid "Star Colors and Temperatures"
msgstr ""

#: index.docbook:16
#, no-c-format
msgid ""
"Stars appear to be exclusively white at first glance. But if we look "
"carefully, we can notice a range of colors: blue, white, red, and even gold. "
"In the winter constellation of Orion, a beautiful contrast is seen between "
"the red Betelgeuse at Orion's \"armpit\" and the blue Bellatrix at the "
"shoulder. What causes stars to exhibit different color remained a mystery "
"until two centuries ago, when Physicists gained enough understanding of the "
"nature of light and the properties of matter at immensely high temperatures."
msgstr ""

#: index.docbook:27
#, no-c-format
msgid ""
"Specifically, it was the physics of <link linkend=\"ai-blackbody\">"
"blackbody radiation</link> that enabled us to understand the variation of "
"stellar colors. Shortly after blackbody radiation was understood, it was "
"noticed that the spectra of stars look extremely similar to blackbody "
"radiation curves of various temperatures, ranging from a few thousand Kelvin "
"to ~50,000 Kelvin. The obvious conclusion is that stars are similar to "
"blackbodies, and that the color variation of stars is a direct consequence "
"of their surface temperatures."
msgstr ""

#: index.docbook:39
#, no-c-format
msgid ""
"Cool stars (i.e., Spectral Type K and M) radiate most of their energy in the "
"red and infrared region of the electromagnetic spectrum and thus appear red, "
"while hot stars (i.e., Spectral Type O and B) emit mostly at blue and "
"ultra-violet wavelengths, making them appear blue or white."
msgstr ""

#: index.docbook:47
#, no-c-format
msgid ""
"To estimate the surface temperature of a star, we can use the known "
"relationship between the temperature of a blackbody, and the wavelength of "
"light where its spectrum peaks. That is, as you increase the temperature of "
"a blackbody, the peak of its spectrum moves to shorter (bluer) wavelengths "
"of light. This is illustrated in Figure 1 where the intensity of three "
"hypothetical stars is plotted against wavelength. The \"rainbow\" indicates "
"the range of wavelengths that are visible to the human eye."
msgstr ""

#: index.docbook:58
#, no-c-format
msgid "Figure 1"
msgstr ""

#: index.docbook:58
#, no-c-format
msgid "The spectra of three hypothetical stars of different temperatures"
msgstr ""

#: index.docbook:66
#, no-c-format
msgid ""
"This simple method is conceptually correct, but it cannot be used to obtain "
"stellar temperatures accurately, because stars are <emphasis>not</emphasis> "
"perfect blackbodies. The presence of various elements in the star's "
"atmosphere will cause certain wavelengths of light to be absorbed. Because "
"these <firstterm>absorption lines</firstterm> are not uniformly distributed "
"over the spectrum, they can skew the position of the spectral peak. "
"Moreover, obtaining a usable spectrum of a star is a time-intensive process "
"and is prohibitively difficult for large samples of stars."
msgstr ""

#: index.docbook:78
#, no-c-format
msgid ""
"An alternative method utilizes <firstterm>photometry</firstterm> to measure "
"the intensity of light passing through different filters. Each filter allows "
"<emphasis>only</emphasis> a specific part of the spectrum of light to pass "
"through while rejecting all others. A widely used photometric system is "
"called the <firstterm>Johnson UBV system</firstterm>. It employs three "
"bandpass filters: U (\"Ultra-violet\"), B (\"Blue\"), and V (\"Visible\") "
"regions of the electromagnatic spectrum."
msgstr ""

#: index.docbook:90
#, no-c-format
msgid ""
"The process of UBV photometry involves using light sensitive devices (such "
"as film or CCD cameras) and aiming a telescope at a star to measure the "
"intensity of light that passes through each of the filters individually. "
"This procedure gives three apparent brightnesses or "
"<firstterm>fluxes</firstterm> (amount of energy per cm^2 per second) "
"designated by Fu, Fb, and Fv. The ratio of fluxes Fu/Fb and Fb/Fv is a "
"quantitative measure of the star's \"color\", and these ratios can be used "
"to establish a temperature scale for stars. Generally speakiing, the larger "
"the Fu/Fb and Fb/Fv ratios of a star, the hotter is its surface temperature."
msgstr ""

#: index.docbook:103
#, no-c-format
msgid ""
"For example, the star Bellatrix in Orion has Fb/Fv = 1.22, indicating that "
"it is brighter through the B filter than through the V filter. furthermore, "
"its Fu/Fb ratio is 2.22, so it is brighest through the U filter. This "
"indicates that the star must be very hot indeed, since the position of its "
"spectral peak must be somewhere in the range of the U filter, or at an even "
"shorter wavelength. The surface temperature of Bellatrix (as determined from "
"comparing its spectrum to detailed models that account for its absorption "
"lines) is about 25,000 Kelvin."
msgstr ""

#: index.docbook:115
#, no-c-format
msgid ""
"We can repeat this analysis for the star Betelgeuse. Its Fb/Fv and Fu/Fb "
"ratios are 0.15 and 0.18, respectively, so it is brightest in V and dimmest "
"in U. So, the spectral peak of Betelgeuse must be somewhere in the range of "
"the V filter, or at an even longer wavelength. The surface temperature of "
"Betelgeuse is only 2,400 Kelvin."
msgstr ""

#: index.docbook:124
#, no-c-format
msgid ""
"Astronomers prefer to express star colors in terms of a difference in <link "
"linkend=\"ai-magnitude\">magnitudes</link>, rather than a ratio of fluxes. "
"Therefore, going back to blue Bellatrix we have a color index equal to"
msgstr ""

#: index.docbook:131
#, no-c-format
msgid "B - V = -2.5 log (Fb/Fv) = -2.5 log (1.22) = -0.22,"
msgstr ""

#: index.docbook:135
#, no-c-format
msgid "Similarly, the color index for red Betelgeuse is"
msgstr ""

#: index.docbook:139
#, no-c-format
msgid "B - V = -2.5 log (Fb/Fv) = -2.5 log (0.18) = 1.85"
msgstr ""

#: index.docbook:143
#, no-c-format
msgid ""
"The color indices, like the <link linkend=\"ai-magnitude\">magnitude "
"scale</link>, run backward. <emphasis>Hot and blue</emphasis> stars have "
"<emphasis>smaller and negative</emphasis> values of B-V than the cooler and "
"redder stars as illustrated below."
msgstr ""

#: index.docbook:151
#, no-c-format
msgid ""
"An Astronomer can then use the color indices for a star, after correcting "
"for <firstterm>reddening and interstellar extinction</firstterm>, to obtain "
"an accurate temperature of that star. The relationship between B-V and "
"temperature is illustrated in Figure 2."
msgstr ""

#: index.docbook:159
#, no-c-format
msgid "Figure 2"
msgstr ""

#: index.docbook:159
#, no-c-format
msgid "The relationship between a stars's B-V color index and its temperature."
msgstr ""

#: index.docbook:167
#, no-c-format
msgid "The Sun with surface temperature of 5,800 K has a B-V index of 0.62."
msgstr ""
