Abbreviation: Gru

Genitive: Gruis

English: The Crane

Size Ranking: 45th

Area: 366 square degrees.

It is that time of the year when the Southern constellations, invented in the late 16th century by the Dutch navigators, Keyser and de Houtman, are high in the sky. Grus like Pavo and Tucana represents one of several celestial birds. In this case – the crane, the long necked wading bird of the family Gruidae; it has also been depicted as a flamingo. Grus is considered to be the most distinctive of the ‘Southern Birds’, with the contrast in colour between αGru and βGru being quite marked. It is fully visible below 33°N.

To locate Grus, I suggest that a line be drawn, starting at αCen, the brightest of the two Pointers, and extended through αTrA, the star at the apex of Triangulum Australe, to the next brightest star, αGru, such that the distance αCen to αGru, is approximately 3.7 times the distance αCen to αTrA.

Features of Interest:

α(alpha)Gru, named ‘Alnair’, ‘the bright one’, at magnitude 1.7, is the brightest star in this constellation. It is a blue-white star, 101ly distant.

β(beta)Gru, named ‘Al Dhanab’, is a variable red giant 170ly away, and varies between about 2.0 and 2.3 magnitude with no set period.

γ(gamma)Gru, at magnitude 3.0, is a blue giant 203ly away.

δ(delta)Gru, is a naked eye pairing of two unrelated stars, δ1 and δ2, which are , respectively, a magnitude

4.0 yellow giant, 296ly away, and a red giant, magnitude 4.1, 325ly distant.

μ(mu)Gru, is another naked-eye double of unrelated yellow giants that appear, by chance, on the same line of sight. μ1 is magnitude 4.8 and 262ly distant, while μ2 is magnitude 5.1 and 240ly away.

π(pi)Gru, is a duo of unrelated stars, visable using suitable binoculars, consisting of π1, a deep-red semi-regular variable star that ranges between magnitudes 5.4 and 6.7, every 150 days approximately, and lies 500ly away, and π2, a white giant of magnitude 5.6 and 132ly distant.

NGC 7424, a spiral galaxy with a prominent central bar is  about 40 million light-years distant from earth. This island universe is also about 100,000 light-years across making it remarkably similar to our own Milky Way. Following along the winding arms, many bright bluish clusters of massive young stars can be found. The star clusters themselves are several hundred light-years in diameter. And while massive stars are born in the arms of NGC 7424, they also die there. Notably, this galaxy was home to a powerful stellar explosion, supernova SN 2001ig, which faded before this deep European Southern Observatory image was recorded.

 

References:

1. Redshift 2 – Maris Multimedia

2. The Guiness Book of Astronomy – Patrick Moore

3. Stars and Planets – Ian Ridpath and Wil Tirion

4. Where the Stars Are – Orion.

5. http://apod.nasa.gov/apod/ap041216.html

IC5148-planetary nebula

IC5148 (Grus) was first discovered by the Sydney amateur Walter Gale in 1894, near the ‘neck’ of Grus the Crane. For some reason it is not marked in Sky Atlas 2000.0 but does appear in the Sky Catalogue 2000.0! The planetary itself is found in a rather desolate field some 1.3O West of Lambda ( ) Gruis. It takes at least a 15cm. to see the nebulosity, as the total visual magnitude is given as 13.0 while the photographic magnitude is a near equal 12.9. Unlike the majority of planetaries, this one is large c.120″sec.arc, as most of the literature states. Observationally, little difference is observed in the apparent size from the CCD or photographic images. A 20cm. clearly reveals its colourless annular structure, including a smallish 25″ to 30″sec.arc. hole, and consequently, IC5148/IC5150 is classified as planetary Type IV. A 30cm or 40cm. starts to reveal some of the internal diamond-shaped ‘braded structure’, as seen in the images, with the eastern side appearing broader and brighter. Contrary to this, AOST1&2 obscurely states; “…and a considerable area looks paler (grey), but still luminous.” This central hole is much smaller than most of the annular type planetaries. In theory, the appearance of a central hole is thought to be due to the radiation pressure pushing the surrounding gas away from the white dwarf core, leaving a ‘vacant’ space. It is likely that the development of annular structures is the last stage of planetary nebulae formation – before the object transforms into its solitary white dwarf phase. The planetary in three-dimensions is probably one, if not, two shells, that we are looking directly down the ‘poles’. Visually, the PNN is at magnitude 16.5 and can possibly be seen in a 40cm. or 50cm. telescope, though I have to admit that I have never seen it. (http://www.blackskies.org/nsp06.htm)