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Line 23: − + + + − Further evidence suggesting the star is significantly older is the slow rotation of 31 days, suggesting the star has nearly used up its [[hydrogen]] fuel for [[thermonuclear fusion]] in the core. The star's surface also appears inactive, showing a much weaker [[sunspot]] cycle then our own Sun. It is suspected that Tau Ceti is an "old dwarf" star that has migrated from the [[Milky Way|Milky Way's]] older "thick disk" based on its rather high velocity of 37 km/s and backtracked path through the galaxy.<ref>http://stars.astro.illinois.edu/sow/taucet.html</ref> −
→The Star
Most of what we learned about the physical properties of Tau Ceti has been determined through spectroscopic measurements. The star is a yellow-orange, main sequence star of spectral type G8 V<ref name="tau">http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=tau+ceti</ref>, though Tau Ceti is both smaller and less massive then our sun, with around 81 to 82 percent of the mass, and around 77 percent of the diameter of Sol (our sun)<ref>http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...406L..15P&db_key=AST&high=40d31b5ca015926</ref>. The star is also significantly dimmer with only 59 percent of the luminosity of our [[sun|star]]<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1996ApJ...460..993S</ref>.
Most of what we learned about the physical properties of Tau Ceti has been determined through spectroscopic measurements. The star is a yellow-orange, main sequence star of spectral type G8 V<ref name="tau">http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=tau+ceti</ref>, though Tau Ceti is both smaller and less massive then our sun, with around 81 to 82 percent of the mass, and around 77 percent of the diameter of Sol (our sun)<ref>http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003A%26A...406L..15P&db_key=AST&high=40d31b5ca015926</ref>. The star is also significantly dimmer with only 59 percent of the luminosity of our [[sun|star]]<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1996ApJ...460..993S</ref>.
Tau Ceti has a much lower [[metallicity]] in comparison to stars of similar age to our sun. Recent measurements show that Tau Ceti has only one-third of our sun’s abundance of iron. Past measurements have produced a [[metallicity]] of 22 to 74 percent of Sol’s<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1992A%26AS...95..273C</ref>. In all cases the [[metallicity]] is significantly lower, and using this data astronomers have estimated Tau Ceti to be around 10 billion years old<ref>http://arxiv.org/PS_cache/arxiv/pdf/0710/0710.1731v1.pdf</ref>.
Tau Ceti has a much lower [[metallicity]] in comparison to stars similar to our sun. Recent measurements show that Tau Ceti has only one-third of our sun’s abundance of iron. Past measurements have produced a [[metallicity]] of 22 to 74 percent of Sol’s<ref>http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1992A%26AS...95..273C</ref>.
The star's surface also appears inactive, showing a much weaker [[sunspot]] cycle then our own Sun.
==Dust Disk==
==Dust Disk==