The image above – published in Science in 2008 – shows the debris ring around Fomalhaut and the location of its planet.

How to see Fomalhaut

Fomalhaut, sometimes called the Autumn Star, appears in a part of the sky that is largely empty of bright stars. For this reason, Fomalhaut is also often called the Lonely One or Solitary One.

White Fomalhaut is more or less opposite the sun in early September, and so it shines in the sky all night long during the autumn months. Finding Fomalhaut is simple. Just face south on an autumn evening and look. Fomalhaut is the brightest star in front of you, and typically less than a third of the way up in the sky (higher from far southern Texas or Florida, lower from more northerly locations). Occasionally a bright planet could be in that general location, but planets are always considerably higher and most likely brighter than Fomalhaut. This star is part of the faint constellation Piscis Austrinus the Southern Fish. It’s part of a round pattern of stars, supposedly the open mouth of the Fish. But don’t expect to see a fish in these stars.

In early September, Fomalhaut reaches its “midnight culmination,” meaning that it is highest in the sky to the south at local midnight. Finding Fomalhaut at the time it culminates is easiest, but this happens at different times on different dates. Here are just a few times and dates of culmination, but keep in mind that the times are only rough, although they are adjusted for Daylight Saving Time as needed:

July 15, 4 a.m.
August 15, 1 a.m.
September 15, midnight
October 15, 10 p.m.
November 15 , 7 p.m.
December 15, 5 p.m.

Fomalhaut is the 18th brightest star in the sky. It is probably is the most southerly bright star that many North Americans know. Granted, a few bright stars farther to the south are visible from tropical and subtropic northern latitudes, but these brighter stars lurk near or beneath the horizon as seen as from middle and far latitudes in the northern hemisphere. Fomalhaut can be seen from as far north as 60 degrees latitude (southern Alaska, central Canada, northern Europe), where it just skims the southern horizon.

History and Myth

As mentioned above, Fomalhaut is sometimes called the Solitary One. It’s sometimes called the Loneliest Star. It really does look lonely because it’s as the only bright star in a large area of sky.

Fomalhaut is Alpha Piscis Austrinus (the brightest star in the Southern Fish), and the name Fomalhaut derives from the Arabic Fum al Hut, meaning Mouth of the Fish. Strangely, another Arabic title for the star means The First Frog.

According to Richard Hinckley Allen, Fomalhaut was one of the four guardians of the heavens to the ancient Persians, and given the name of Hastorang. (The other guardians were Aldebaran in Taurus, Antares in Scorpius, and Regulus in Leo.) Allen also says that Fomalhaut was a source of worship at the temple of Demeter at Eleusis in ancient Greece. In about 2500 BC, Fomalhaut helped mark the location of the winter solstice, meaning that it helped to define the location in the sky where the sun crossed the meridian at noon on the first day of winter.

Until recently, Fomalhaut was considered the first-magnitude star farthest from other first-magnitude stars. It is just slightly more than 39 degrees from Achernar. However, proper motion of Antares, which causes a star’s position in the sky to change over long periods of time due to the star’s actual motion in the heavens, has now separated it from the nearest first magnitude star (Alpha Centauri) by a few second of arc more than the distance between Fomalhaut and Achernar.

Oddly, although Fomalhaut’s spectral type indicates a white to bluish white color, some writers have referred to it as red. There being little likelihood that this star has dramatically changed colors in historic times, the reference to a red Fomalhaut is puzzling. It may be due to a simple error, repeated unquestioning by later writers. Or it may be due to the reddening affects of Earth’s atmosphere, which filters out the bluer colors when an object is near the horizon. This causes, for example, red sunsets.

Science

Fomalhaut holds a special place in the search for planets beyond our solar system. The first extrasolar planet to be imaged at visible wavelengths – Fomalhaut b – orbits the Loneliest Star. This star was one of the first known to have a disk of dust around it, a sign that more planets might be forming there.

Artist's Conception (NASA)

The image seen at the top of this post is the actual discovery image – published in the journal Science in November 2008. The image at left is lovely as well. It’s an artists’ conception of what a planet orbiting Fomalhaut might have to endure as it plows through the dusty disk around this star.

As determined by an analysis of its light, Fomalhaut is classified as an “A3V” star, considerably hotter and heavier than our sun (as indicated by the “A3″). The “V” is called a luminosity class, and it designates the largest category of all, the “normal” stars in the mature and stable part of their life spans. The sequence, known as the Main Sequence, follows the rather odd progression of OBAFGKM, with Os being the hottest and most massive, and Ms being the coolest and least massive. In addition, there is a numerical subdivision running from 0 to 9 with each letter. Our sun is a G2V, as is Alpha Centauri. Since Fomalhaut’s designation is significantly to the left of the sun’s in this sequence, it is hotter and more massive. The other luminosity classes include I (supergiants), III (giants) and VII (white dwarfs) among others.

If it were possible to observe the sun and Fomalhaut from the same distance (astronomers like to use 10 parsecs or 32.6 light-years), Fomalhaut would outshine the sun in visible light by nearly 17 times. Its actual distance, as determined by analysis of data from the Hipparcos mission, is 25 light-years. Fomalhaut’s mass and radius are, respectively, a little more than twice and a little less than twice solar values. Being hotter than the sun (about 8500 kelvins or nearly 15,000 degrees F, compared to 10,000 degrees F for the sun), this star burns its fuel faster and has a shorter lifetime. In fact, it is estimated that Fomalhaut may have a lifespan of only about a billion years, a tenth of that of our cooler sun. Currently it is likely less than halfway through its life.

Fomalhaut appears to be a single star like the sun, but there is another faint star a couple of degrees below (south of) Fomalhaut that is at about the same distance and moving through space in the same manner. They are separated by about a light-year, although whether they are gravitationally bound as a binary star is unknown.

Fomalhaut’s position is RA: 22h 57m 39s, dec: -29° 37′ 19″.