A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding
From: Frank Reed
Date: 2017 Feb 12, 17:05 -0800
Talking about the Orion North Arrow and Mintaka reminded me of another asterism trick that I have been meaning to write about. Sometimes it's nice to be able to point out Aries, meaning that reference point in the heavens, the zero of sidereal hour angle as well as right ascension, where the ecliptic crosses the celestial equator at the equinox on or about March 21 every year. You can find it using the water jar of Aquarius. This is not a bright pattern, but it's simple and memorable once you've seen it, and you've recognized its shape as a classical amphora jar. The jar also happens to lie on its side with its axis of symmetry running right along the celestial equator. That means it's visible everywhere on Earth, just like Mintaka in Orion's belt (Mintaka is the point of the Orion North Arrow). The neck of the water jar points directly at the First Point of Aries, and if you measure off three times the length of the water jar, it takes you right to that spot, with coordinates SHA = 0° and Dec = 0°. There's nothing else there, no marker in the heavens saying "here's the prime meridian of the heavens", but with this trick, under reasonably dark skies, you can point out Aries to your friends and navigation students. Your navigation students will be amused, and your friends will be worried! But they may all get a kick out of the water jar. That's always a hit.
In the image below, I've drawn in the water jar and indicated the straight line from it that leads to Aries, marked here with a little cross. I've also dropped in an image of an actual ancient water jar that matches very nicely with the shape of this asterism in Aquarius.