Andromeda Galaxy and Milky Way

The virial mass of the Andromeda Galaxy is of the same order of magnitude as that of the Milky Way, at a trillion solar masses (1012M☉). The mass of either galaxy is difficult to estimate with any accuracy, but it was long thought that the Andromeda Galaxy is more massive than the Milky Way by a margin of some 25% to 50%. This has been called into question by a 2018 study which cited a lower estimate on the mass of the Andromeda Galaxy,
combined with preliminary reports on a 2019 study estimating a higher mass of the Milky Way. The Andromeda Galaxy has a diameter of about 220,000 light-years, making it the largest member of the Local Group at least in terms of extension, if not mass.



Full moons make for a wonderful setting for criminal activity, as we find in detective novels. It's that night when the gruesome murderer commits the ghastly crime and is seen by a non-descript, aged neighbor. The neighbor's claim to credibility in the witness box is the fact that there was a full moon on the night in question and everything was there for all to see; it was only a matter of chance that he or she was the only one to spot it! Full moon nights also offer the perfect cover for the snooping detective to hide behind the bush with his dim-witted assistant in tow. We earthlings love to look up at the moon. So much does the moon enamor us; we write movies, songs and poems by the droves that contain the name of the earth's super satellite. A case in point is the fact that one of the biggest selling record albums of all time is Pink Floyd's "Dark Side of the Moon." Furthermore, the icy stuff that collected on Methone's surface could even be more lightweight than that which lies beneath. It is possible that such fluffy, snowy, stuff can actually flow--at least over long periods of thousands to millions of years--thus filling in the tell-tale scars of impact craters.