Grus

Grus is a constellation in the southern sky. Its name is Latin for the crane, a type of bird. It is one of twelve constellations conceived by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman. Grus is bordered by Piscis Austrinus to the north, Sculptor to the northeast, Phoenix to the east, Tucana to the south, Indus to the southwest, and Microscopium to the west. The constellations Grus, Pavo, Phoenix and Tucana are collectively known as the ‘Southern Birds.’ Covering 366 square degrees, it ranks 45th of the 88 modern constellations in size and covers 0.887% of the night sky. In the equatorial coordinate system, the right ascension coordinates of the constellation lie between 21h 27.4m and 23h 27.1m, while the declination coordinates are between −36.31° and −56.39°. Grus is located too far south to be seen by observers in the British Isles and the northern United States, though it can easily be seen from Florida or California; the whole constellation is visible to observers south of latitude 33°N.

Grus cranes its neck in the Uranographia of Johann Bode (1801)

[http://www.ianridpath.com/startales/grus.htm]

The stars that form Grus were originally considered part of the neighboring constellation Piscis Austrinus (the southern fish), with Gamma Gruis seen as part of the fish’s tail. The stars were first defined as a separate constellation by the Dutch astronomer Petrus Plancius, who created twelve new constellations based on the observations of the southern sky by the Dutch explorers Pieter Dirkszoon Keyser and Frederick de Houtman, who had sailed on the first Dutch trading expedition, known as the Eerste Schipvaart, to the East Indies. Grus first appeared on a 35-cm diameter celestial globe published in 1598 in Amsterdam by Plancius with Jodocus Hondius. Its first depiction in a celestial atlas was in the German cartographer Johann Bayer’s Uranometria of 1603. De Houtman included it in his southern star catalogue the same year under the Dutch name Den Reygher, ‘The Heron,’ but Bayer followed Plancius and Hondius in using Grus.

Keyser and de Houtman assigned twelve stars to the constellation. Bayer depicted Grus on his chart, but did not assign its stars Bayer designations. French explorer and astronomer Nicolas Louis de Lacaille labelled them Alpha to Phi in 1756 with some omissions. In 1879, American astronomer Benjamin Gould added Kappa, Nu, Omicron and Xi, which had all been catalogued by Lacaille but not given Bayer designations. Lacaille considered them too faint, while Gould thought otherwise. Xi Gruis had originally been placed in Microscopium. Conversely, Gould dropped Lacaille’s Sigma as he thought it was too dim.

An alternative name for the constellation, Phoenicopterus (Latin ‘flamingo’), was used briefly during the early 17th century, seen in the 1605 work Cosmographiae Generalis by Paul Merula of Leiden University and a c. 1625 globe by Dutch globe maker Pieter van den Keere. Astronomer Ian Ridpath has reported the symbolism likely came from Plancius originally, who had worked with both of these people.

The stars that correspond to Grus were generally too far south to be seen from China. In Chinese astronomy, Gamma and Lambda Gruis may have been included in the tub-shaped asterism Bàijiù, along with stars from Piscis Austrinus.

In Central Australia, the Arrernte and Luritja people living on a mission in Hermannsburg viewed the sky as divided between them, east of the Milky Way representing Arrernte camps and west denoting Luritja camps. Alpha and Beta Gruis, along with Fomalhaut, Alpha Pavonis and the stars of Musca, were all claimed by the Arrernte.

[http://astropixels.com/constellations/charts/Gru.html]

Grus has several bright stars. Marking one wing is Alpha Gruis, a blue-white star of spectral type B6V and apparent magnitude 1.7, around 101 light-years from Earth. Its traditional name, Alnair, means ‘the bright one’ and refers to its status as the brightest star in Grus. Alnair is around 380 times as luminous and has over 3 times the diameter of the Sun.

Lying 5 degrees west of Alnair, denoting the Crane’s heart is Beta Gruis, a red giant of spectral type M5III. It has a diameter of 0.8 AU (if placed in the Solar System it would extend to the orbit of Venus) located around 170 light-years from Earth. It is a variable star with a minimum magnitude of 2.3 and a maximum magnitude of 2.0.

Lying in the northwest corner of the constellation and marking the crane’s eye is Gamma Gruis, a blue-white subgiant of spectral type B8III and magnitude 3.0 lying around 211 light-years from Earth. Also known as Al Dhanab, it has finished fusing its core hydrogen and has begun cooling and expanding, which will see it transform into a red giant.

There are several naked-eye double stars in Grus. Forming a triangle with Alnair and Beta, Delta Gruis is an optical double whose components- Delta1 and Delta2- are separated by 45 arcseconds. Delta1 is a yellow giant of spectral type G7III and magnitude 4.0, 309 light-years from Earth, and may have its own magnitude 12 orange dwarf companion. Delta2 is a red giant of spectral type M4.5III and semiregular variable that ranges between magnitudes 3.99 and 4.2, located 325 light-years from Earth. It has around 3 times the mass and 135 times the diameter of our sun.

Marking the other wing is Theta Gruis, yet another double star, lying 5 degrees east of Delta1 and Delta2.

[https://ross-harrison.com/tag/gliese/]

Six star systems are thought to have planetary systems. One of them, Gliese 832, was announced in 2014 to be hosting the closest potentially habitable Earth-mass-range exoplanet to the Solar System. This is a red dwarf of spectral type M2V. The apparent visual magnitude of 8.66 means that it is too faint to be seen with the naked eye. It is located relatively close to the Sun, at a distance of 16.1 light years and has a high proper motion of 818.93 mas per year. This star achieved perihelion some 52,920 years ago when it came within an estimated 15.71 ly (4.817 pc) of the Sun. Gliese 832 has just under half the mass and radius of the Sun. Its estimated rotation period is a relatively leisurely 46 days. The star is roughly 9.5 billion years old.

Gliese 832 hosts two known planets. In September 2008, it was announced that a Jupiter-like planet, now designated as Gliese 832 b, had been detected in a long-period, near-circular orbit around this star. Despite its relatively large angular distance, direct imaging is problematic due to the star–planet contrast.

In 2014, a second planet was discovered by astronomers at the University of New South Wales. This one is believed to be of super-Earth mass and has since been given the scientific name Gliese 832 c. It was announced to orbit in the optimistic habitable zone but outside the conservative habitable zone of its parent star. The planet is believed to be in, or very close to, the right distance from its sun to allow liquid water to exist on its surface.

[https://en.wikipedia.org/wiki/Gliese_832]

C 5148, nicknamed the Spare Tyre Nebula, taken by the ESO Faint Object Spectrograph and Camera (EFOSC2) on the New Technology Telescope.

IC 5148 is a planetary nebula located around 1 degree west of Lambda Gruis in the constellation of Grus. Around 3000 light-years distant, it is expanding at a rate of 50 kilometers a second, one of the fastest of all planetary nebulae.

[https://en.wikipedia.org/wiki/IC_5148]

Northeast of Theta Gruis are four interacting galaxies known as the ‘Grus Quartet.’ These galaxies are NGC 7552, NGC 7590, NGC 7599, and NGC 7582. The latter three galaxies occupy an area of sky only 10 arcminutes across and are sometimes referred to as the ‘Grus Triplet,’ although all four are part of a larger loose group of galaxies called the IC 1459 Grus Group. NGC 7552 and 7582 are exhibiting high starburst activity; this is thought to have arisen because of the tidal forces from interacting:

The Grus Quartet, NGC 7552, 7582, 7590, 7599

Here we are looking well away from the plane of our Milky Way Galaxy into a realm many, many millions of light years away. In the midst of a field containing thinly dispersed stars of our own Galaxy are countless galaxies, the four of the Quartet appear the largest and are closest to us at distances estimated at 55-70 Mly. They are beautiful spiral galaxies presented to us in a range of orientations: NGC 7552, at the top right, is a lovely face-on barred spiral; NGC 7582, in the middle, is a loosely wound spiral, whilst the pair at the bottom, NGC 7590 and NGC 7599, are more tightly wound. Note the compact cores, red star-forming regions and dusty structures visible.

Close inspection of this deep exposure reveals that there are many hundreds of deep yellow and red objects with fuzzy outlines; these are in fact distant galaxies hundreds of millions of light years away! To the left of NGC 7590 and NGC 7599 is what appears to be a substantial galaxy cluster dominated by two giant elliptical galaxies. There are several such collections in the field in addition to several very distant edge-on spirals.

[http://www.russellsastronomy.com/sky/Narrow%20Field/Hi-res/Grus%20quartet.htm]

NGC 7424 is a barred spiral galaxy with an apparent magnitude of 10.4 located around 4 degrees west of the Grus Triplet:

Grand Spiral Galaxy NGC 7424

The grand, winding arms are almost mesmerizing in this face-on view of NGC 7424, a spiral galaxy with a prominent central bar. About 40 million light-years distant in the headlong constellation Grus, 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 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 well before the above image was recorded.

[http://apod.nasa.gov/apod/ap130108.html]

GRB 050709: 35-Year-Old Cosmic Mystery Solved in a Flash

An artist’s rendering (left) of GRB 050709 depicts a gamma-ray burst that was discovered on 9 July, 2005 by NASA’s High-Energy Transient Explorer. The burst radiated an enormous amount of energy in gamma-rays for half a second, then faded away. Three days later, Chandra’s detection of the X-ray afterglow (inset) established its position with high accuracy.

A Hubble Space Telescope image showed that the burst occurred in the outskirts of a spiral galaxy about 2 billion light years from Earth. This location is outside the star-forming regions of the galaxy and evidence that the burst was not produced by the explosion of an extremely massive star.

The most likely explanation for GRB 050709 is that it was produced by a collision of two neutron stars, or a neutron star and a black hole. Such a collision would result in the formation of a black hole (or a larger black hole), and could generate a beam of high-energy particles that could account for the powerful gamma-ray pulse as well as observed radio, optical and X-ray afterglows.

This gamma-ray burst is one of a class of short-duration bursts that now appear to have a different origin from the more powerful, long-duration gamma-ray bursts that last more than two seconds. Long-duration bursts have been connected to black holes formed in the explosion of extremely massive stars, or hypernovas.

[http://chandra.harvard.edu/photo/2005/grb050709/]

OCO-2 Night Launch

In this alluring time exposure, star trails arc across the night sky above foggy Monterey Bay and the lights of Santa Cruz, California in the United States of America. Since the exposure began around 2:56am PDT on July 2 2014 it also records the trail of a Delta II rocket lofting NASA’s OCO-2 spacecraft into orbit. Seen from a vantage point 200 miles north of the Vandenberg Air Force Base launch site, the trail represents the first five minutes of the rocket's flight along a trajectory south and west over the Pacific to join the A-Train in polar orbit around planet Earth. The entire trail through main engine cut-off is captured, with a very faint puff at the end marking the nose fairing separation. Under the rocket's path, the two brightest trails are the alpha and beta stars of the constellation Grus, flying high in southern skies. The OCO-2 mission goal is a study of atmospheric carbon dioxide, watching from space as planet Earth breathes.

[https://apod.nasa.gov/apod/ap140704.html]

[https://en.wikipedia.org/wiki/Grus_%28constellation%29]

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