I divided the celestial sphere into 24 equal sectors, by dividing the octants into thirds along the perpendicular bisectors of their sides.

The octants are named by taking the direction of the vernal equinox as the positive x axis, and the north celestial pole as the positive z axis, which I presume is standard among astronomers. Then a positive component becomes 0 and a negative one becomes 1, and they’re put in order “zyx” to form a binary number, translated into a decimal from 0 to 7. (So the low numbers are in the northern hemisphere and the high numbers are in the southern hemisphere.) I would have numbered them differently, but this system is the easiest to calculate in a spreadsheet. The divisions of an octant are named after which component is largest–x, y, or z.

Alpha Antliae is in sector 5x. Therefore it’s “southwest” of the vernal equinox point.

How much further would this Antlia dwarf have to be before we lost sight of it?

There’s an interesting article here on the Starts with a Bang blog :

http://scienceblogs.com/startswithabang/2012/02/the_most_distant_dark_galaxy_e.php?utm_source=networkbanner&utm_medium=link

on an new record breakingly distant dwarf galaxy – viewed from across a whopping ten billion (yes, that’s with a ‘b’) light years of spacetime!

However, it does cheat somewhat by being gravitationally lensed!

Hope this is okay netiquette~wise, please let me know if not.

Off topic, sorry but I think this news item :

http://scienceblogs.com/gregladen/2012/02/asteroid_2011ag5_could_strike.php

is one the BA and others here may appreciate if they haven’t heard /seen it already.

Finally, on the other major bolidal threat from the skies, this item :

http://www.space.com/14704-sun-stolen-comets-oort-cloud.html

suggests some comets may be alien to solar system and have originated round other stars.

PS. BA, the “older posts” tag that lets you go back through previous days posts beyond the current main page seems to have vanished from the end of the main page here. Not sure what’s happening with that, thought I’d just let you know.

You mean this one :

http://www.youtube.com/watch?v=N9wjlpB-RrM&feature=fvst

complete with awesome astronomical space exploration videoclip?

Youtubve also has a couple of other good clips Omega Centauri~wise like this mellow & informative animation of a HST image :

http://www.youtube.com/watch?v=qRsuh2rVIHU

Plus this one :

http://www.youtube.com/watch?v=UUGdgiG-Tnk&NR=1&feature=endscreen

from the Hubblecast series- and there’s also one from the IR-relevant Astronomy series the BA has posted a few installments of before linked to my name here.

As for the galaxy/cluster question… that’s a topic of very active research! Dark matter is definitely the biggest difference, but it’s not always easy to tell for the very small galaxies because the stars are moving so slowly that the difference between how fast they would move with or without dark matter isn’t that big compared to systematics like what kinds of orbits the stars are on (radial vs. tangential).

Multiple stellar populations also isn’t distinguishing… there is actually evidence for multiple generations in a number of clusters, not all of which are so suspiciously ex-galaxies as omega Cen, and models suggest that it should be common for the most massive clusters.

So there certainly are objects that get argued about. Which leads to an interesting situation where the names of some objects don’t make sense – newly-found globular clusters are numbered (in Arabic) by the survey they come from, while newly-found dwarf galaxies are numbered (in Roman) by the constellation they appear in. But some objects that we now think are galaxies, like Segue 1 and Willman 1, were thought to be globular clusters when they were first found.