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Gliese 581 c
Erik Max Francis kirjutas: wrote: The Sun is a variable star - the total luminosity of the Sun changes by roughly 0,1% with 11 year period. There are slight irregularities - not all sunspot maxima are equals, and there has been a Maunder minimum with hardly any sunspots. The Sun wouldn't be classified as a variable star by astronomers by this criterion, so you seem to be playing some sort of word game. How exactly is a "variable star" defined? What is the minimum amplitude of variable stars? |
#2
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Gliese 581 c
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How exactly is a "variable star" defined? What is the minimum amplitude of variable stars? Like most terms used in astronomy, it has no official, quantitative definition by the IAU. However, it's a star that significantly changes in luminosity or spectrum over time. _No_ star has a completely constant luminosity and spectrum over its main sequence lifetime; after all, _all_ stars steadily increase in brightness on the main sequence as they consume the hydrogen in their interiors. However, natural changes of a mere 0.1% certainly wouldn't qualify. If a star with similar properties were somewhere in our skies, we wouldn't classify it as a variable star. -- Erik Max Francis && && http://www.alcyone.com/max/ San Jose, CA, USA && 37 20 N 121 53 W && AIM, Y!M erikmaxfrancis The entire Earth is but a point, and the place of our own habitation but a minute corner of it. -- Marcus Aurelius, ca. 170 |
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