Sculptor

"...Deluded by self-love and the illusions of his senses, man long thought of himself as the centre around which the heavenly bodies moved, and his vain pride has been punished by the terrors they inspired in him. At last, several centuries of endeavour have removed from his eyes the veil that obscured the system of the universe. He now sees himself living on an almost imperceptible planet within a solar system the boundless extent of which is itself merely a faint point in the vastness of space."

~Pierre-Simon de Laplace (1749-1827)

Sculptor is a non-descript constellation formed by Abbe Nicolas de Lacaille in the 1750s from a grouping of 4th to 5th magnitude stars. For whatever reason, de Lacaille decided to honour the sculptor’s studio `L’ Atelier du Sculpteur . The brightest star is alpha Sculptoris at magnitude 4.3, a blue-white B-type giant lying 680±120 light years away. With a surface temperature of 17000ºK, alpha has a luminosity of 1700 Suns and contains 5.5 solar masses.

Delta is a triple star system, the primary component of magnitude 4.5 has a close companion of magnitude 11.5, while a further star lies 74” away at magnitude 9.3.

Sculptor lies at right angles to the plane of our Galaxy therefore we look out beyond the spiral arms into the cosmos. Unobscured by the dust and gas that pervades the spiral arms, we can delight in many faint galaxies, though of course, we lose the open clusters and nebulae that hug the spiral arm regions. All except one very large scattered open cluster, Blanco 1. Lying around 800 light years distant, these thirty B-type stars of magnitude 12 and brighter cover 1.5º of the sky and are centred on zeta Sculptoris.

Discovered by V. Blanco in 1949, he wrote:

“While counting stars of spectral type A0 in Kapteyn's Selected Areas at high galactic latitude, the writer found that Select Area number 140 had about five times the average number of A0 stars brighter than the 9th mag present in other areas at similar galactic latitudes... A definite cluster was found centred at 23:59.1 -30° 30' (1900)…”

There is one globular cluster in Sculptor, NGC 288, a loosely structured irregular group of faint stars in a 20cm telescope. The brightest stars are of the 12th magnitude so a larger aperture is a decided benefit here, pulling out some of the fainter members and filling in the gaps. Sir William Herschel first observed this object on October 27 1785 and called it:

“Considerably bright, irregularly round, 8 or 9’ diameter, a great many of the stars visible, so that there can remain no doubt but that it is a cluster of very small stars”.

Most galaxies are not alone, they huddle together in clusters. Sculptor contains the 'Sculptor Group of Galaxies', including NGC 625, NGC 253, NGC 7793, and NGC 247 in Cetus. One of the outstanding galaxies in this region is NGC 55, often quoted as being a member of the 'Sculptor Group'. Recent distance measures suggesting that NGC 55 is in fact an unassociated foreground galaxy to that group.

James Dunlop discovered NGC 55 in the 1820’s, describing it as:

“a beautiful long nebula, about 25 arcseconds in length; position N.p. and S.f., a little brighter towards the middle, but extremely faint and diluted to the extremeties. I see several minute points or stars in it, as it were through the nebula: the nebulous matter of the south extremity is extremely rare, and of a delicate bluish hue. This is a beautiful object."

Located near the southern border with Phoenix, NGC 55 is a barred spiral of around 46 billion solar masses. The estimated distance is around 7 million light years, one of the closest galaxies to our Milky Way. In terms of size, it is around 70,000 light years in extent. It lies almost edge-on, and a 25cm telescope will show a large bright glow, some mottling across the surface and a prominent dust lane east of the nucleus.

The best galaxy in Sculptor is NGC 253, sometimes called the 'Silver Coin Galaxy'. This spectacular object lies near the northern border with Cetus and is the brightest member of the Sculptor Gro up. It can be easily seen in binoculars as a hazy elongated smudge of light under a dark sky. A grouping of bright stars helps to orient the observer to its position (click on map below). Caroline Herschel first discovered this large spiral in 1783 while searching for comets. Use a low power eyepiece, especially so under light polluted skies to enhance contrast against the background sky. NGC 253 is tilted 17º from edge-on but shows a bright elongated central region and a few bright foreground stars. If we could view this galaxy face on, it would cover an area around half that of the Moon.

This galaxy is visually large and takes up the whole eyepiece field. An eyepiece giving a higher power, around 200x for a 20cm telescope will show mottling and dark dust clouds silhouetted against the background gas and unresolved stars. Sir John Herschel, observing from the Cape of Good Hope with his 18” reflector, described NGC 253 as:

“ very bright and large (24’ in length); a superb object...Its light is somewhat streaky, but I see no stars in it except 4 large and 1 very large one, and these seem not to belong to it, there being many near...” Sir William Herschel wrote “Considerably bright, much elongated,...much brighter in the middle. Above 50’ long and 7 or 8’ breadth...This nebulae was discovered Sept. 23, 1783, by my sister Caroline Herschel with an excellent small Newtonian Sweeper of 27 inches focal length, and a power of 30..”

Another galaxy worth hunting down is NGC 300, an extremely large face-on spiral galaxy with a low surface brightness, discovered by Sir John Herschel in 1834. The bright central region is easy to see but the outer glow is difficult and any skyglow will overwhelm it. Binoculars in the 11x80mm range will show this galaxy under a dark sky, the low magnification taking in the whole galaxy and its surrounds and therefore improving the contrast with the background sky. Use the lowest power available on a telescope.

NGC 613 lies near tau Sculptoris and easily seen in a small telescope from a dark site. Large telescopes show this barred spiral as having a bright and condensed nuclear region surrounded by a mottled fainter halo.

NGC 134 is also a barred spiral the same size, shape and brightness as NGC 613. It lies near eta Sculptoris, a reddish magnitude 4.8 star.

There are a number of other galaxies worth visiting in this region. NGC 24 is a bright spiral lying near the northern border with Cetus and is easily seen in finderscopes. East of beta Sculptoris is the barred spiral NGC 7713, a large and faint glow with brighter central region to larger mirrors. IC 5332 lies near a 7th magnitude double star in the southwest, appearing as a small round glow.

NGC 7755 is another barred spiral lying south of magnitude 4.5 delta. Nearby to the southeast resides NGC 7793, a large spiral appearing as an elliptical glow with a small nucleus.

Many other faint extra-galactic systems are available to the careful observer on a dark and moonless night. Clear skies and good hunting.

~CosMos