Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site utastro.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!ut-sally!utastro!ethan From: ethan@utastro.UUCP (Ethan Vishniac) Newsgroups: net.astro.expert Subject: Re: Where's the center of the universe? Message-ID: <163@utastro.UUCP> Date: Fri, 31-May-85 10:31:16 EDT Article-I.D.: utastro.163 Posted: Fri May 31 10:31:16 1985 Date-Received: Sat, 1-Jun-85 13:31:40 EDT References: <1544@amdahl.UUCP> <5869@duke.UUCP> <514@x.UUCP> <5879@duke.UUCP> Distribution: net Organization: U. Texas, Astronomy, Austin, TX Lines: 68 > In article <514@x.UUCP> john@x.UUCP (John Woods) writes: > >> > >Well, not quite. It is, in fact, a tad warmer in the rough direction of > >Saggitarius, which is therefore the center. The difference is extremely > >small, so it took some time to detect it. > > Well, Saggitarius is the direction of the centre of the Milky Way > galaxy; I`m just a poor innocent philosopher, but that seems like quite > a coincidence to me (i.e. that we just happen to be at the point in our > orbit around galactic downtown at which the centre and the Universe's > own central point are in the same direction. > > On the other hand, that it is a big coincidence doesn't mean it can`t be > a coincidence. But doesn't the universe having an observable centre > screw up some cosmological stuff that works well otherwise? > > Charlie Martin OK folks. Allow me summarize the current state of affairs. The blackbody background of the universe, which is detectable in the microwave region, is isotropic to a high degree of accuracy. The only exception to this is a weak dipole moment (of order 10^-3). All higher order anisotropies are down from this by *at least* an order of magnitude. This dipole moment has a straightforward interpretation. It is exactly what one would expect if the observer (that's us) were moving at a few hundred kilometers a second with respect to the microwave background. The direction of motion of the sun is toward RA 11.4, dec 5 degrees. The velocity is about 400 km/sec. The galactic center is at RA 12.8, dec 27.5 degrees. In other words, they are not in the same direction. The motion of the sun is presumed to have the following components motion with respect to the local standard of rest [ This is approximately our motion with respect to the motion of stars at the same distance from the galactic center and orbiting in perfect circles.] rotation of the galaxy motion of our galaxy within the local group motion of the local group within the Virgo Supercluster motion of the supercluster due to nearby superclusters If we correct for the motion of the sun relative to the local group of galaxies we find a residual motion of about 550 km/sec toward galactic coordinates longitude = 265 degrees, b=35 degrees. Although our motion within the local supercluster is not entirely certain there is evidence that our average motion with respect to galaxies at a distance of 50 Mpc h^-1 is the same as that observed in the microwave background. In other words, the frame of reference in which the galaxies are, on the average, motionless is the same as the one in which the microwave background is isotropic. This is taken as evidence that the universe is homogeneous and isotropic, which is to say that it has no center. Of course, this is science. I have been privately assured that the center of the universe is well known to be in Texas somewhere. "Don't argue with a fool. Ethan Vishniac Borrow his money." {charm,ut-sally,ut-ngp,noao}!utastro!ethan Department of Astronomy University of Texas -- "Don't argue with a fool. Ethan Vishniac Borrow his money." {charm,ut-sally,ut-ngp,noao}!utastro!ethan Department of Astronomy University of Texas