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On Sunspot and Starspot Lifetimes - Patrick M. Hartigan
On Sunspot and Starspot Lifetimes - Patrick M. Hartigan

... brightness contrast between spot regions and the surrounding photosphere on hotter stars, which suggests that the temperature difference between them increases with stellar temperature. The temperature difference is about 2000 K in stars of spectral type G0 and only 200 K in stars of type M4. This p ...
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fundamental concepts of physics
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... It is likely that the problem of explaining the motion of planets in the night sky is one of the oldest to which humanity gave any attention. Ancient civilizations gave much thought to the problem of the objects wandering through the heavens and arrived at a wide variety of explanations for the obse ...
Preview Sample 3 - Test Bank, Manual Solution, Solution Manual
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Entering the Universe of Vedic Astrology

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The Emerald Tablet of Hermes
The Emerald Tablet of Hermes

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pdf - at www.arxiv.org.
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... 4. The local sky looks like a dome because we see half of the full celestial sphere at any one time. Horizon—The boundary line dividing the ground and the sky. Zenith—The highest point in the sky, directly overhead. Meridian—The semicircle extending from the horizon due north to the zenith to the ho ...
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Tropical year

A tropical year (also known as a solar year), for general purposes, is the time that the Sun takes to return to the same position in the cycle of seasons, as seen from Earth; for example, the time from vernal equinox to vernal equinox, or from summer solstice to summer solstice. Because of the precession of the equinoxes, the seasonal cycle does not remain exactly synchronized with the position of the Earth in its orbit around the Sun. As a consequence, the tropical year is about 20 minutes shorter than the time it takes Earth to complete one full orbit around the Sun as measured with respect to the fixed stars (the sidereal year).Since antiquity, astronomers have progressively refined the definition of the tropical year. The Astronomical Almanac Online Glossary 2015 states:year, tropical:the period of time for the ecliptic longitude of the Sun to increase 360 degrees. Since the Sun's ecliptic longitude is measured with respect to the equinox, the tropical year comprises a complete cycle of seasons, and its length is approximated in the long term by the civil (Gregorian) calendar. The mean tropical year is approximately 365 days, 5 hours, 48 minutes, 45 seconds.An equivalent, more descriptive, definition is ""The natural basis for computing passing tropical years is the mean longitude of the Sun reckoned from the precessionally moving equinox (the dynamical equinox or equinox of date). Whenever the longitude reaches a multiple of 360 degrees the mean Sun crosses the vernal equinox and a new tropical year begins"". (Borkowski 1991, p. 122)The mean tropical year on January 1, 2000, was about 365.2421897 ephemeris days according to the calculation of Laskar (1986); each ephemeris day lasting 86,400 SI seconds. By 2010 this had decreased to 365.2421891 (365 ephemeris days, 5 hours, 48 minutes and 45.14 seconds). This is about 365.242181 mean solar days, though the length of a mean solar day is constantly changing.
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