Quadrans Muralis
Published on Jan 3, 2007 at 8:24 pm.
1 Comment.
Filed under constellations.
Tonight is the peak of the Quandrantid Meteors. This is normally a rather nice meteor shower, but it is often not observed. For one thing, the timing is bad. It is right at the first of the year, and so many people have other holiday things going on. Secondly, the Quadrantid Meteor Shower comes in the coldest part of the winter for the northern hemisphere, and that discourages many observers. But, this is summer in the southern hemisphere, so might it not be observed there? Unfortunately, the radiant is so far to the north that it is not above the horizon at night from a bit south of the equator except during the daylight. Worse, the Quadrantids often are rather dim meteors, and so bright moonlight washes them out. The Moon this year is quite bright, being very nearly full, so the Quadrantids probably won’t be so spectacular. So, instead of talking about the Quadrantids, I thought that I’d talk about the constellation Quadrans Muralis, the Mural Quadrant.
Meteor showers get their names from the constellation that the meteors appear to radiate from. So, the Perseids shoot away from Perseus, the Geminids shoot away from Gemini, and the Leonids appear to radiate away from Leo. The Quadrantids radiate away from Quadrans Muralis. Now, serious amateur astronomers and astronomy students will go, “Huh?” That is because there is no Quadrans Muralis! What’s going on?
Well, to answer that we need to talk about constellations themselves. In the ancient world, people used to imagine pictures in the sky. Many of these pictures in the sky were characters from mythology. These became the common constellations. But, every culture saw the sky differently, and thus had different pictures in the sky. Most of the ones that we rocognize today derive from Roman adaptations of Greek constellations. But, soon the old idea of constellations being pictures in the sky didn’t work. Astronomers wanted to know where one ends and another begins. You find a new object, and you want to specify what constellation it happens to be in. Furthermore, two systems of naming stars, the Bayer Designations and the Flamsteed Numbers designate stars by their constellation. This means that every star has to be part of a constellation. So, constellations became regions of the sky. The entire sky was divided up into constellations. The problem was that the Romans only had about 66 constellations, and none of those were very far south of the celestial equator (since those stars could not be seen from Rome), and the Romans never bothered to make constellations out of the dimmest stars or in regions of the sky without any bright stars or clear patterns. So, astronomers quickly began to fill in the gaps with constellations of thier own. But, of course the French astronomers, Italian astronomers, British astronomers, etc, all had their own constelltions, and they did not agree with one another.
To alleviate confusion and to promote uniformity, the International Astronomical Union (the international body of professional astronomers, and the only ones who really can approve names, designations, etc) decided to divide the sky up into specified regions that would be the official constellations. In 1930, an official list of constellations was published.  This list comprises 88 constellations. Some three dozen constellations in occasional use failed to make the cut. Most of these were the new constellations added over the years by various astronomers, many overlapping one another. Only one constellation from antiquity got the boot: Argo Navis, the Ship Argo. This constellation was considered too big and unwieldy, so it was broken up into several smaller constellations. Gone too were Felis (the Cat), Apis (the Bee), Polophylax (the Guardian of the Pole), Solarium (the Sundial), and Quadrans Muralis (the Mural Quadrant). For the most part, nobody has noticed that these other constellations are gone. But, during the time that Quadrans Muralis was around, a meteor shower was discovered to radiate away from it, so that meteor shower became known as the Quadrantids.
Quadrans Muralis was located north of Bootes, the Herdsman, near where Bootes and Hercules come together. This constellation was created by Joseph J. de La Lande in 1795, to commemorate the quadrant used by him and his nephew, Michel Le Francais, to observe and measure stellar positions. The quadrant was an instrument very similar to today’s sextant. The constellation was first pictured in Jean Fortin’s Atlas Celeste published in that very year. The constellation was also marked in Stieler’s Planisphere and in Johann Bode’s Uranographica, as well as many other prominent star atlases, though by no means all of the major ones.
The Quadrantid Meteors were first observed in the early 1800’s, with the first recorded notation of numerous meteors on January 2, 1825, by Antonio Brucalassi, eight years before the major Leonid meteor storm that really got meteor astronomy going. By 1839, Adolphe Quetelet and Edward Herrick had both independently of one another proposed that the early January meteors were an annual event, and the meteor shower soon began to be known as the Quadrantids. The name has remained, even though Quadrans Muralis is no longer recognized as a constellation by modern astronomers. In a year or two, the Moon won’t be such a problem, and you can go look at this meteor shower from a defunct constellation.
-Astroprof
Amy Jean on May 31, 2008 at 9:01 pm: 1
Here is some more info on the Quadrantids shower, including a photo from 1995:
http://science.nasa.gov/newhome/headlines/ast28dec98_1.htm