The Astral Pole is a feat of agility performed by fans as a test of merit and as an initiation rite to the Astral Leauge. Older, fatter, less fit fans reminisce about how they used to be able to do it; younger, leaner, fitter fans listen to these conversations, receive two or three minutes of instruction, and then in a significant minority of cases perform the feat without apparent difficulty.
Please read the site disclaimer before attempting this procedure!
The pole should be made of something rigid like wood, and about four to six feet long (longer is probably better). A broomstick handle is often used. It's easier to do if you're not wearing shoes or restrictive clothing.
Hold the pole out in front of you, both hands up. You can slide your hands along the pole during the manoeuvre, but not let go. Step forward over the pole one foot at a time and then bring it up and over your head. That is the easy part. The pole should now be in front of you again, but your wrists will be twisted awkwardly.
Bend down, wrap your right leg around in front of your right arm, and insert your right foot into the opening formed by the your arms and the pole. You will probably find this to be a rather uncomfortable position. Now use your left arm to move the end of the pole up and over your head, then down your back (this is the part where you may get stuck - see the photo below). Once you've done that, simply step over the pole with your left leg, lift it up, and you're back in the starting position.
For bonus points, do it again, but with left and right interchanged. Then do it backwards.
It's much easier to understand when you watch somebody else do it, so I made a video of myself riding the Astral Pole. It's in Quicktime H.263 format. The file is under the same license as the rest of the site, so feel free to share it around. Here is a still image taken from the video at the point where you're probably most likely to get stuck: