Find Fomalhaut in the Celestial Sea

The celestial sea covers over a quarter of the horizon, from southeast to southwest. Shown is the evening sky from mid-northern latitudes for this time of year. CREDIT:

At dusk this week, we can see the Great Square of Pegasus standing on one corner in the east while the brilliant orange star Arcturus – a souvenir of warmer nights – glimmers very low in the northwest. 

We come to realize now that our night sky is in a transition phase.  Yet, many of the striking star groups and the beautiful Milky Way of balmy summer evenings still remain with us high overhead and down toward the western part of the sky.  Summer nights are typically hazy, but now, at this time of the year, football weather brings the promise of many clear, dry nights with far better observing conditions.

Just a couple of hours after sunset, the stars of the autumn season cover much of the eastern and southern parts of the sky.  There are very few bright stars in these areas, but during this week as the bright Moon moves out of the way you'll find some interesting constellations in this part of the sky.  There is Capricornus, the Sea-Goat; Aquarius, the Water Bearer; Piscis Austrinus, the Southern Fish; Pisces, the Fishes; Cetus, the Whale; and Eridanus, the River.

Watery fraternity

In fact, this whole area has been called the "Wet Region" or the "Celestial Sea," probably because it is rather vague and dim like some dark pool.  All these constellations have a rich body of lore and mythology associated with them.  They have been associated with the rainy season of Mideast lands.  This attribution actually refers not to the constellations' visibility in the night sky, but to the Sun's location in front of their stars (Capricornus, Aquarius and Pisces belong to the zodiac).  There is also a mythological connection between these dim star pictures and an ancient flood in the Tigris-Euphrates basin, which has sometimes been linked to the Deluge in Genesis.

The star pattern that contains the brightest star of this watery fraternity is found in Piscis Austrinus, the Southern Fish.  It is here that we find the most southerly of all the first magnitude stars visible from mid-northern latitudes and the one that is usually associated with these chilly autumn evenings is the bluish-white star Fomalhaut. 

This week, at around 7 p.m. local daylight time, you'll see Fomalhaut shining sedately, low almost due south above horizon.  And just before midnight, it's dropping out of sight below the southwest horizon.

Its name is derived from the Arabic Fum al Hut, the "Mouth of the Fish."  An alternate name was Al Difdi al Awwal, "The First Frog." In ancient legend, as recorded by the poet Aratos, the fish was on its back. The Stregheria religion from Italy, portrays Fomalhaut as a fallen angel and quarter guardian of the northern gate.  A relatively modern legend suggests that Fomalhaut symbolizes the New Testament story of St. Peter and the coin found in the mouth of the fish.

All alone

Fomalhaut, ranked 18th brightest star in the sky is also the only first magnitude star in the whole collection of watery constellations.  Indeed, Fomalhaut is the only true first magnitude star of autumn.  Though Vega, Altair and Deneb are still very much present high in the west, they form the Summer Triangle. 

Fomalhaut was also known to the stargazers of ancient Persia as the star announcing the arrival of autumn weather. But unless you live in the southern states or points south, you can forget about seeing the faint stars that compose the rest of this constellation. Although now at their highest point above the southern horizon, more often than not they're too dim to penetrate the haze, which often lies near the horizon.

Fomalhaut usually appears as the one lone star in this very dull and unexciting region of the sky. In fact, it is sometime referred to as "The Solitary One," because it lies in a rather empty region of the southern autumn sky.  Yet it was also an important star to the ancients being one of the four "Royal Stars" of Persia, along with Aldebaran of the wintertime sky, Regulus of spring and Antares of summer.

In her book "The Friendly Stars," Martha Evans Martin wrote:

". . . the loneliness of this star, added to the somber signs of approaching autumn and sometimes gives one a touch of melancholy.  In November and December, when the winter stillness has fallen upon us, a glance toward the southwest will discover Fomalhaut, still placid and alone" 

It's often described in various observing books as "reddish," though it is probable that the effects of our atmosphere are responsible for this impression, as this star is always seen at a low altitude for northern observers. 

Draw an imaginary line southward along the western (right) side of the Square of Pegasus and three times as far again beyond will bring you to Fomalhaut. It's believed to be a young star, only about 200 million years old, with a potential lifespan of only a billion years.. Compared to the Sun, it's more than twice as massive, about 16 times more luminous, and more than one and a half times larger.  It's one of our closer neighbors in space, at 25 light years away.

And now, a new planet!

Fomalhaut is now making headlines because of a recently announced discovery: A new planet has been photographed circling around it.

Back in 2005, a photograph taken by the Hubble Space Telescope provided a detailed visible-light image of a narrow, dusty doughnut-shaped ring around Fomalhaut about 23 billion miles wide. The geometric center of the disk is offset nearly 14 billion miles from Fomalhaut, and offered strong evidence that an unseen planet might be gravitationally tugging on the ring. 

And last May, University of California, Berkeley, astronomer Paul Kalas was finally able to confirm the existence of that planet in the first ever visible-light snapshot of a world outside of our solar system, a feat announced yesterday.

The planet, now known as Fomalhaut b, orbits its parent star once in 872-years at a distance of 11 billion miles.  And Kalas thinks there might yet be other planets in orbits between Fomalhaut b and the star; possibly even a planet that could host liquid water on the surface.  The James Webb Space Telescope, a large, infrared-optimized space telescope, scheduled for launch in 2013, might just be able to bring such a planet (or planets) into view.

So it seems that Fomalhaut is not so solitary after all!

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Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.