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Dr.Astros response to "2012 A-Z" pin!!
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Original Message
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Dr. Astro, if you care to reply, what do you think of that video going around glp titles "2012 A-Z" ? If you watched it?
Quoting: Albanian 12582427
It's crap. Earth does NOT orbit Alcyone. Our sun does NOT orbit Alcyone. Our solar system does NOT orbit Alcyone. Let alone in 25,627 years. Nor do we orbit Sirius.
Let's look at the numbers for Alcyone just to show you how ridiculous this is. Alcyone is of course part of the Pleiades, so let's use the total mass of the Pleiades cluster to see if we're orbiting it. Alcyone has a parallax of about 8.09 milliarcseconds, which corresponds to a distance of about 402 light years.
[link to simbad.u-strasbg.fr]
It also has a proper motion of about 19.34 milliarcseconds in right ascension and -43.67 milliarcseconds in declination per year. Now at a distance of 402 light years, those 43.67 milliarcseconds/year in declination translate to 805,195,033 kilometers per year or about 25.515 km/second. Now the Pleiades cluster has a total mass of about 740 sun masses ( [link to arxiv.org] ), so at a distance of 400 light years, the escape velocity for the entire Pleiades cluster is about 0.227861 km/second (that velocity will not get you around the 2,500 light year circumference of the orbit in 25,627 years either; just look at it, a roughly circular orbit would have to be about a tenth the speed of light!). In other words, even just taking into account our proper motion in declination, to say nothing of our total motion relative to Alcyone including in right ascension and radial velocity, we're traveling over 100 times too fast to be orbiting the Pleiades! We are not orbiting the Pleiades, let alone Alcyone, not even close.
As for Sirius, it has a proper motion of 1.2 arcseconds/year in declination and .546 arcseconds per year in right ascension ( [link to simbad.u-strasbg.fr] ) (15 km/sec and 6.8 km/sec velocity relative to our solar system respectively). Since we're about 8.6 light years from the Sirius system, and since Sirius A and B have a combined mass of nearly 3 times the sun's mass, the escape velocity from the Sirius system at the distance of our sun is about 0.1 km/sec. In other words, our solar system is traveling many times too fast relative to Sirius to be able to orbit it or be in a trinary configuration with it.
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