Tuesday, September 18, 2012

Finding Fomalhaut

As the earth continues its progress around the sun into the fall months (for the northern hemisphere), the time is propitious for finding the brilliant 1st-magnitude star Fomalhaut (its name taken from Arabic and meaning "Mouth of the Fish").

Fomalhaut is located well south of the celestial equator, about thirty degrees to the south in fact, making it difficult to see for the northern hemisphere for much of the year.  However, it is now reaching its zenith during the prime viewing hours after about 9 pm, and reaching it slightly earlier each night, meaning that the next several weeks are some of the best times to go out looking for it.

To locate Fomalhaut, first find the constellation Aquarius.  This previous post tells you how to find him.  Aquarius is pouring two streams from his water vessel towards the Southern Fish (Piscis Austrinis), and Fomalhaut is by far the brightest star in the Southern Fish.   That previous post depicted the stars of the Southern Fish but did not identify them -- they are circled in the version below so you can find them, just beneath the streams from the vessel of the Water Bearer, Aquarius.  For most viewers in the northern hemisphere, only bright Fomalhaut will be visible -- the rest are too dim to be seen so low in the sky.

As explained in that previous post, Aquarius is located between the Great Square of Pegasus (seen to his left in the above diagram) and Capricorn the Goat (seen to his right in the above diagram, with his horn pointing to Aquarius' lower foot).

The diagram below, from Sky & Telescope by way of Wikimedia commons, shows the stars of Piscis Austrinus with their celestial coordinates.

The diagram above actually outlines the constellation in the same manner as does H.A. Rey in his essential and revolutionary The Stars: A New Way to See Them.  In his discussion of the Southern Fish and Fomalhaut on page 56 of that book, Mr. Rey writes:
The faint stars which make up most of this constellation cannot be seen in our latitudes.  They are above the horizon at times but too low to penetrate the ground haze.  The constellation's main star, however, is all the more conspicuous: blue-white FOMALHAUT, one of the 20 brightest stars.  You can hardly fail to see it when it is up; a line through the two bright stars on the Pegasus side of the Great Square and far downward points straight to brilliant Fomalhaut, solitary in a very dull region.  In case you find another bright star halfway between the Great Square and Fomalhaut, it's not a star but a planet passing through the Water Carrier. 

FOMALHAUT is one of our closer neighbors, about 22 light-years away and 13 times as luminous as the sun.  It announces the coming of fall: the leaves begin to turn when you see it for the first time at nightfall, in mid or late September.
Perhaps Mr. Rey had a special affinity for this star, as it became visible right around his birthday (September 16).

The ancient Egyptians depicted the Southern Fish in the Round Zodiac of the Temple of Dendera.  In the close-up below, you can find Aquarius just as you do in the night sky, by finding the Great Square first (in this case, the square is not very big but easily located between the two fish of Pisces, which are tied together by a string -- for the worldwide span of art depicting a square flanked by two water-creatures, see this previous post).  

Then look to the right and find the image of a Water Bearer pouring two streams of water, in this case from two vessels rather than from one as we usually think of him (the Egyptians usually depicted the constellation we know of as Aquarius this way, and associated him with the Nile River god Hapi).  Below the streams issuing from these vessels you will clearly see the Southern Fish (note that Hapi is depicted as wearing the white crown of the South, which is significant):

Below is an image of the "big picture" of the Dendera Round Zodiac, with a box showing the location of the detail depicted above:

Below is one more image of the detailed area containing Aquarius and the Southern Fish, with arrows clearly identifying them.  The larger fish-tail leading out of the frame below belongs to Capricorn (as you can see if you look closely in the image of the entire Round Zodiac above).

If you look closely enough, you will also see that Hapi was usually depicted by the Egyptians as having pendulous female breasts, symbolic of the fact that the fertile Nile nourished all of Egyptian civilization.  There may also be some connection here to the Greek myth regarding Hermaphroditos, discussed at the end of this previous post.

The Bighorn Sacred Circle in Wyoming contains an alignment from Cairn F to Cairn D indicating the rising point of Fomalhaut (see this page for detail).

Finally, Fomalhaut is famous for its amazing elliptical "debris ring," the sharpness of the edges of which led scientists to hypothesize are caused by planets orbiting on either edge of this ring.  In 2008, scientists found evidence in images taken within the visible light spectrum indicating a planet along the inner edge, dubbed "Fomalhaut b."  Later imagery taken during the months September through October of last year appear to have found evidence for a second planet along the outer edge, as suspected.

Take advantage of this time of year to go out on your own mission of observation to admire this mysterious star in the Southern Fish.