IYA Live Telescope Today: Fomalhaut – Alpha Piscis Austrini

by Tammy Plotner on July 23, 2009

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UTsidebaraddLocated just south of the ecliptic plane, Piscis Austrinus was one of the original 48 constellations charted by Ptolemy, and it remains one of the 88 modern constellations adopted by the IAU. Spanning 245 square degrees of sky, it ranks 60th in size. Piscis Austrinus contains 7 mains stars in its asterism and has 21 Bayer Flamsteed designated stars within its confines. It is bordered by the constellations of Capricornus, Microscopium, Grus, Sculptor and Aquarius. Piscis Austrinus can be seen by all observers located at latitudes between +55° and -90° and is best seen at culmination during the month of October. Today the IYA “Live” Telescope was aimed at its brightest star… Wanna’ see?

Piscis Austrinus is also known as Piscis Australis – Latin for the “Southern Fish”. Prior to the 20th century, it was also known as Piscis Notius. In mythology it is said to represent the parent of Pisces. Perhaps the legend came from the Syrians who did not eat fish, but worshipped them as gods. The Greeks also kept fish ponds at their temples and one legend tells of woman who was turned into a mermaid when she threw herself into a pond in a suicide attempt. There are those who believe Pisces Austrinus is associated with the Assyrian fish god Dagon and the Babylonian god Oannes, but at least all accounts give a rather “fishy” tale!

Let’s take a look at Piscis Austrinus’ brightest star – Alpha – the “a” symbol on a star chart. Alpha Piscis Austrini is best known as Fomalhaut – the “Mouth of the Whale”. This class-A main sequence star is about 25 light years from Earth, and like Vega, has an excess of infra-red radiation which indicated a circumstellar disk. Not only does it have a disk, but it has an extrasolar planet, too… One that was photographed by the Hubble Space Telescope between 2004 and 2006 and confirmed in 2008! The Jupiter-sized planet orbits about 11 billion miles away from the parent star and takes about 872 years to make the full trip – and may very well have a ring system which dwarf’s that of Saturn’s.

As stars go, Fomalhaut is quite interesting enough on its own. In ancient times it was considered one of the four “royal” stars that marked the cardinal directions and Ptolemy gave it astrological significance as well. It is a young star, maybe around 100 to 300 million years old and part of the Castor Group of Moving Stars. The stellar association in the Castor group include stars of similar age, origin and similar velocity and include Castor, Fomalhaut, Vega, Alpha Cephei and Alphae Librae. All of these stars may have originated from the same location at some point in time which may have made them part of star cluster. In binoculars you will also notice another nearby star – TW Piscis Austrini – it is also a member of this group and may actually be a physical companion of Fomalhaut. Keep a watch on TW, though! Because as its two letter designation indicates, it is a variable star… But not just any variable. TW Piscis Austrini is a flare star! While flares can erupt periodically within a matter of hours or days with no predictable timetable, TW is also a prime candidate for harboring an Earth-like habitable zone, too!

About 

Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.

andyf July 24, 2009 at 4:03 AM

It’s Fomalhaut, not Formalhaut.

With luck I could just see it from my old house in Glasgow, UK., but not from my current location at 57 27N. Have to make do with reading about it.

Tammy Plotner July 24, 2009 at 5:53 AM

thanks, andy! i’ve corrected my error and i appreciate the heads up.

i wish you could have been watching it live yesterday. while it’s not quite the same as being at the eyepiece, it is just a shade better than reading!

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