Fornax

Fornax is a constellation in the southern sky, partly ringed by the celestial river Eridanus. Its name is Latin for furnace. The constellation Eridanus borders Fornax to the east, north and south, while Cetus, Sculptor and Phoenix gird it to the north, west and south respectively. Covering 397.5 square degrees and 0.964% of the night sky, it ranks 41st of the 88 constellations in size. In the equatorial coordinate system, the right ascension coordinates of Fornax lie between 01h 45m 24.18s and 03h 50m 21.34s, while the declination coordinates are between -23.76° and -39.58°. The whole constellation is visible to observers south of latitude 50°N.

Fornax was portrayed under the name Apparatus Chemicus in the Uranographia of Johann Bode (1801). Bode depicted it as Antoine Lavoisier’s experiment to decompose water into hydrogen and oxygen.

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

Fornax was introduced by Nicolas Louis de Lacaille in 1756, after his trip to the Cape of Good Hope, where he observed the southern stars and constellations. Lacaille originally named the constellation Fornax Chemica, the chemical furnace, after the small fuel heater used for chemical experiments. It was the English astronomer Francis Bailey who shortened the constellation’s name to Fornax at John Herchel’s suggestion in 1845.

According to traditional Chinese uranography, the modern constellation Fornax is located within the western quadrant of the sky, The White Tiger of the West (Xī Fāng Bái Hǔ). The name of the western constellation in modern Chinese is (tiān lú zuò), meaning ‘the heaven furnace constellation.’

[https://en.wikipedia.org/wiki/Fornax_%28Chinese_astronomy%29]

[http://www.peoplesguidetothecosmos.com/constellations/fornax.htm]

The three brightest stars- Alpha, Beta and Nu Fornacis- form a flattened triangle facing south.

Alpha Fornacis is the brightest star in the constellation Fornax. It is the only star brighter than magnitude 4.0 in the constellation. It has the proper names Dalim and Fornacis. This star was originally designated 12 Eridani.

The stellar classification of Alpha Fornacis is F8IV, where the luminosity class IV indicates this is a subgiant star that has just evolved off the main sequence. It has 33% more mass than the Sun and is an estimated 2.9 billion years old. Alpha Fornacis is a binary star and has a high proper motion. This system displays an excess of infrared emission, which may indicate the presence of circumstellar material such as a debris disk.

The secondary has been identified as a blue straggler, and has either accumulated material from, or merged with, a third star in the past. It is a strong source of X-rays and is 78% as massive as the Sun.

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

Beta Fornacis is visible to the naked eye with an apparent visual magnitude of 4.46. It is located around 173 light years away from the Sun.

This is an evolved, G-type giant star with a stellar classification of G8 III. It is a red clump giant, which means it has undergone helium flash and is currently generating energy through the fusion of helium at its core. The star has an estimated 1.53 times the mass of the Sun and has expanded to 11 times the Sun’s radius. It is radiating over 55 times the solar luminosity from its outer atmosphere at an effective temperature of 4,820 K.

Beta Fornacis has a visual companion, CCDM J02491-3224B, which has an apparent visual magnitude of approximately 14.0. Located around three degrees to the southwest is the globular cluster NGC 1049.

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

Nu Fornacis is a class B9.5III (blue giant) star in the constellation Fornax. Its apparent magnitude is 4.69 and it is approximately 371 light years away. It is around 3.65 times as massive and 245 times as luminous as the Sun, with around 3.2 times its diameter. It is variable, with a period of 1.89 days- the same as its rotational period.

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

Artistic impression of HIP 13044 b

[https://fr.wikipedia.org/wiki/HIP_13044]

HIP 13044 is a red horizontal-branch star about 2,300 light years (700 pc) from Earth in the constellation Fornax. The star is part of the Helmi stream, a former dwarf galaxy that merged with the Milky Way between six and nine billion years ago. As a result, it circles the galactic center at a highly irregular orbit with respect to the galactic plane. HIP 13044 has an apparent magnitude of 9.94 and cannot be seen with the unaided eye.

This is 13044 is fairly evolved star fusing helium in its core, and has therefore already passed the red-giant phase of its evolution. Its surface temperature is about 6025 K and its radius is approximately 6.7 solar radii. HIP 13044’s mass is estimated to be 0.8 solar masses. Having a rotation period of 5-6 days, HIP 13044 is a fast-rotating star for its type. It is possible that this is because it has swallowed planets during its red-giant phase.

In 2010, it was announced that a giant planet in a 16.2-day orbit had been discovered by the radial velocity measurements. This would have had implications for planet formation in metal-poor systems and survival of planets being engulfed by expanded giant stars. Subsequent analysis of the data revealed problems with the detection. After applying the corrections, there is no evidence for a planet orbiting the star.

[https://en.wikipedia.org/wiki/HIP_13044]

HD 20782 is a 7th magnitude G-type main sequence star about 117 light-years away from Earth, in the constellation of Fornax. HD 20782 is a part of a wide binary system in which the other star is designated HD 20781, and both stars host planetary systems. Indeed, this is the first known case of a binary star system where there are planetary systems around both the primary and the secondary stars in the system. The companion star HD 20781 has a very large angular separation of 252 arcsec, corresponding to 9080 AU at the distance of HD 20782. It is estimated to be 7.1 (± 4) billion years old, with a mass close to that of our Sun. (Note that, despite the numbering, HD 20782 is the primary star of the system, and HD 20781 the secondary star.)

An extremely eccentric extrasolar planet was announced around HD 20782 in 2006. In 2009 this planet’s orbit was narrowed down, and it was found to have the highest eccentricity of all known exoplanets; this distinction has stood since 2012.

And in 2011 two also-eccentric (but less so) Neptune-mass planets were announced around the HD 20781.

[https://en.wikipedia.org/wiki/HD_20782]

Red dwarf star UDF 2457 as seen by the Hubble Ultra Deep Field (UDF)

UDF 2457 is the Hubble Ultra Deep Field (UDF) identifier for a red dwarf star calculated to be about 59,000 light-years (18 kiloparsecs) from Earth with a very dim apparent magnitude of 25.

The Milky Way galaxy is about 100,000 light-years in diameter, and the Sun is about 25,000 light-years from the galactic center. The small common star UDF 2457 may be one of the farthest known stars inside the main body of the Milky Way. Globular clusters (such as Messier 54 and NGC 2419) and stellar streams are located further out in the galactic halo.

[https://en.wikipedia.org/wiki/UDF_2457]

NGC 1049 by Hubble space telescope

NGC 1049 is a globular cluster located in the Local Group galaxy of Fornax Dwarf, visible in the constellation of Fornax. At a distance of 630,000 light years, it is visible in moderate sized telescopes, while the parent galaxy is nearly invisible.

[https://en.wikipedia.org/wiki/NGC_1049]

NGC 1360

NGC 1360, also known as the Robin’s Egg Nebula, is a planetary nebula in the constellation of Fornax. It was identified as a planetary nebula due to its strong radiation in the OIII (oxygen) bands. Reddish matter, believed to have been ejected from the original star before its final collapse, is visible in images.

[https://en.wikipedia.org/wiki/NGC_1360]

The Fornax Dwarf Spheroidal is an elliptical dwarf galaxy in the constellation. The galaxy is a satellite of the Milky Way and contains six globular clusters; the largest, NGC 1049, was discovered before the galaxy itself. The galaxy is also receding from the Milky Way at 53 km/s. It mostly contains population II stars:

Fornax dwarf galaxy

The Fornax dwarf galaxy is one of the Milky Way’s neighboring dwarf galaxies. New observations of four globular clusters- large balls of stars that orbit the centers of galaxies- found in Fornax show they are very similar to those found in our galaxy, the Milky Way. The finding is at odds with leading theories on how these clusters form — in these theories, globular clusters should be nestled among large quantities of old stars — and so the mystery of how these objects came to exist deepens.

[https://www.spacetelescope.org/images/heic1425h/]

The Fornax Cluster is a cluster of galaxies lying at a distance of 62 million light-years (19 megaparsecs). It is the second richest galaxy cluster within 100 million light-years, after the considerably larger Virgo Cluster. It lies primarily in the constellation Fornax, and may be associated with the nearby Eridanus Group. The Fornax Cluster is a valuable source of information about the evolution of such clusters, showing the effects of a merger of a subgroup with the main group, which in turn lends clues about the associated galactic superstructure.[5] At the centre of the cluster lies NGC 1399. Other cluster members include NGC 1316 (the group’s brightest galaxy), NGC 1365, NGC 1427A, and NGC 1404:

The Fornax Cluster of Galaxies

How do clusters of galaxies form and evolve? To help find out, astronomers continue to study the second closest cluster of galaxies to Earth: the Fornax cluster, named for the southern constellation toward which most of its galaxies can be found. Although almost 20 times more distant than our neighboring Andromeda galaxy, Fornax is only about 10 percent further that the better known and more populated Virgo cluster of galaxies. Fornax has a well-defined central region that contains many galaxies, but is still evolving. It has other galaxy groupings that appear distinct and have yet to merge. Seen here, almost every yellowish splotch on the image is an elliptical galaxy in the Fornax cluster. The picturesque barred spiral galaxy NGC 1365 visible on the lower right is also a prominent Fornax cluster member.

[http://apod.nasa.gov/apod/ap130111.html]

NGC 1399 is a large elliptical galaxy in the Southern constellation Fornax, the central galaxy in the Fornax cluster. It is a type-cD galaxy, with a bright center and a vast, diffuse envelope surrounding it. It is also rich in globular clusters, with a population of them that has been estimated to be between 5,700 and 6,500. A supermassive black hole with a mass of 500 million solar masses may be present in the center of this galaxy:

[https://en.wikipedia.org/wiki/NGC_1399]

NGC 1399: Massive Black Hole Implicated in Stellar Destruction

Evidence suggests that a white dwarf star has been torn apart by an intermediate-mass black hole. This object is found in a globular cluster, a very old, very crowded grouping of stars. If confirmed, this result would be the first time such a class of black hole was found in this setting. This system is found in the elliptical galaxy NGC 1399, which is in the Fornax cluster.

Evidence from NASA’s Chandra X-ray Observatory and the Magellan telescopes suggest a star has been torn apart by an intermediate-mass black hole in a globular cluster. In this image, X-rays from Chandra are shown in blue and are overlaid on an optical image from the Hubble Space Telescope. The Chandra observations show that this object is a so-called ultraluminous X-ray source (ULX). An unusual class of objects, ULXs emit more X-rays than any known stellar X-ray source, but less than the bright X-ray sources associated with supermassive black holes in the centers of galaxies. Their exact nature has remained a mystery, but one suggestion is that some ULXs are black holes with masses between about a hundred and a thousands times that of the Sun.

Data obtained in optical light with the Magellan I and II telescopes in Las Campanas, Chile, also provides intriguing information about this object, which is found in the elliptical galaxy NGC 1399 in the Fornax galaxy cluster. The spectrum reveals emission from oxygen and nitrogen but no hydrogen, a rare set of signals from within globular clusters. The physical conditions deduced from the spectra suggest that the gas is orbiting a black hole of at least 1,000 solar masses.

To explain these observations, researchers suggest that a white dwarf star strayed too close to an intermediate-mass black hole and was ripped apart by tidal forces. In this scenario the X-ray emission is produced by debris from the disrupted white dwarf star that is heated as it falls towards the black hole and the optical emission comes from debris further out that is illuminated by these X-rays.

Another interesting aspect of this object is that it is found within a globular cluster, a very old, very tight grouping of stars. Astronomers have long suspected globular clusters contained intermediate-mass black holes, but there has been no conclusive evidence of their existence there to date. If confirmed, this finding would represent the first such substantiation.

[http://chandra.harvard.edu/photo/2010/ngc1399/]

NGC 1316 (also known as Fornax A) is a lenticular radio galaxy about 60 million light-years away. The galaxy was built up through the merger of several smaller galaxies. These merger events may have fueled the central supermassive black hole, that has a mass estimated in 130-150 million of solar masses with gas, causing the galaxy to become a radio galaxy. The merger is estimated to have occurred ~3 billion years ago:

[https://en.wikipedia.org/wiki/NGC_1316]

NGC 1316: After Galaxies Collide

How did this strange-looking galaxy form? Astronomers turn detectives when trying to figure out the cause of unusual jumbles of stars, gas, and dust like NGC 1316. A preliminary inspection indicates that NGC 1316 is an enormous elliptical galaxy that includes dark dust lanes usually found in a spiral. The above image taken by the Hubble Space Telescope shows details, however, that help in reconstructing the history of this gigantic jumble. Close inspection finds fewer low mass globular clusters of stars toward NGC 1316's center. Such an effect is expected in galaxies that have undergone collisions or merging with other galaxies in the past few billion years. After such collisions, many star clusters would be destroyed in the dense galactic center. The dark knots and lanes of dust indicate that one or more of the devoured galaxies were spiral galaxies. NGC 1316 spans about 60,000 light years and lies about 75 million light years away toward the constellation of the Furnace.

[https://apod.nasa.gov/apod/ap050404.html]

NGC 1365, also known as the Great Barred Spiral Galaxy, is a barred spiral galaxy about 56 million light-years away. The core is an oval shape with an apparent size of about 50″ × 40″. The spiral arms extend in a wide curve north and south from the ends of the east-west bar and form an almost ring like Z-shaped halo. The central supermassive black hole in the active galactic nucleus, measured to be about 2 million solar masses in mass, is spinning at almost the speed of light. Supernovae 2012fr, 2001du, 1983V, and 1957C were observed in NGC 1365:

[https://en.wikipedia.org/wiki/NGC_1365]

NGC 1365: Majestic Spiral with Supernova

Barred spiral galaxy NGC 1365 is truly a majestic island universe some 200,000 light-years across. Located a mere 60 million light-years away toward the chemical constellation Fornax, NGC 1365 is a dominant member of the well-studied Fornax galaxy cluster. This sharp color image shows intense star forming regions at the ends of the bar and along the spiral arms, and details of dust lanes cutting across the galaxy’s bright core. At the core lies a supermassive black hole. Astronomers think NGC 1365’s prominent bar plays a crucial role in the galaxy’s evolution, drawing gas and dust into a star-forming maelstrom and ultimately feeding material into the central black hole. Discovered on October 27, the position of a bright supernova is indicated in NGC 1365. Cataloged as SN2012fr, the type Ia supernova is the explosion of a white dwarf star.

[http://apod.nasa.gov/apod/ap121124.html]

NGC 1097 is a barred spiral galaxy about 45 million light-travel years away in the constellation Fornax. It is a severely interacting galaxy with obvious tidal debris and distortions caused by interaction with the companion galaxy NGC 1097A. Three supernovae (SN 1992bd, SN 1999eu, and SN 2003B) have been observed in NGC 1097 since 1992:

[https://en.wikipedia.org/wiki/NGC_1097]

Hubble Eyes a Wanderer Dancing the Dance of Stars and Space

The NASA/ESA Hubble Space Telescope provides us with a spectacular image of the bright star-forming ring that surrounds the heart of the barred spiral galaxy NGC 1097. In this image, the larger-scale structure of the galaxy is barely visible: its comparatively dim spiral arms, which surround its heart in a loose embrace, reach out beyond the edges of this frame.

This face-on galaxy, lying 45 million light-years away from Earth in the southern constellation of Fornax (The Furnace), is particularly attractive for astronomers. NGC 1097 is a Seyfert galaxy. Lurking at the very center of the galaxy, a supermassive black hole 100 million times the mass of our sun is gradually sucking in the matter around it. The area immediately around the black hole shines powerfully with radiation coming from the material falling in.

The distinctive ring around the black hole is bursting with new star formation due to an inflow of material toward the central bar of the galaxy. These star-forming regions are glowing brightly thanks to emission from clouds of ionized hydrogen. The ring is around 5000 light-years across, although the spiral arms of the galaxy extend tens of thousands of light-years beyond it.

NGC 1097 is also pretty exciting for supernova hunters. The galaxy experienced three supernovae (the violent deaths of high-mass stars) in the 11-year span between 1992 and 2003. This is definitely a galaxy worth checking on a regular basis.

However, what it is really exciting about NGC 1097 is that it is not wandering alone through space. It has two small galaxy companions, which dance ‘the dance of stars and the dance of space’ like the gracious dancer of the famous poem The Dancer by Khalil Gibran.

The satellite galaxies are NGC 1097A, an elliptical galaxy orbiting 42000 light-years from the center of NGC 1097 and a small dwarf galaxy named NGC 1097B. Both galaxies are located out beyond the frames of this image and they cannot be seen. Astronomers have indications that NGC 1097 and NGC 1097A have interacted in the past.

This picture was taken with Hubble’s Advanced Camera for Surveys using visual and infrared filters.

[https://www.nasa.gov/mission_pages/hubble/science/ngc1097.html]

UDFj-39546284 is the designation given to a stellar structure reported on January 27, 2011, as light from the oldest object detected through infrared observation within the Hubble Space Telescope. The object is located in the Fornax constellation. It was initially thought (November 2012) to be at redshift z~10 using Hubble and Spitzer telescope photometric data, including Hubble Extreme Deep Field (XDF). Subsequently it was reported to possibly be at a record-breaking redshift z = 11.9 using Hubble and Spitzer telescope data, including Hubble Ultra-Deep Field (HUDF). Recent analyses have suggested this source is more likely to be a low redshift interloper, with extreme emission lines in its spectrum producing the appearance of a very high redshift source:

[https://en.wikipedia.org/wiki/UDFj-39546284]

Most Distant Galaxy Candidate Ever Seen in Universe

The farthest and one of the very earliest galaxies ever seen in the universe appears as a faint red blob in this ultra-deep–field exposure taken with NASA’s Hubble Space Telescope. This is the deepest infrared image taken of the universe. Based on the object’s color, astronomers believe it is 13.2 billion light-years away.

The most distant objects in the universe appear extremely red because their light is stretched to longer, redder wavelengths by the expansion of the universe. This object is at an extremely faint magnitude of 29, which is 500 million times fainter that the faintest stars seen by the human eye.

The dim object is a compact galaxy of blue stars that existed 480 million years after the Big Bang, only four percent of the universe’s current age. It is tiny and considered a building block of today’s giant galaxies. Over one hundred such mini-galaxies would be needed to make up our Milky Way galaxy.

The Hubble Ultra Deep Field infrared exposures were taken in 2009 and 2010, and required a total of 111 orbits or 8 days of observing. The new Wide Field Camera 3 has the sharpness and near-infrared light sensitivity that matches the Advanced Camera for Surveys’ optical images and allows for such a faint object to be selected from the thousands of other galaxies in the incredibly deep images of the Hubble Ultra Deep Field.

[http://www.nasa.gov/mission_pages/hubble/science/ancient-object-gallery.html]

GOODS-S 29323: NASA Telescopes Find Clues For How Giant Black Holes Formed So Quickly

Evidence that some early supermassive black holes formed directly from the collapse of a gas cloud has been found. These results could represent a major step in the understanding of how the Universe’s first giant black holes formed. Two candidate black hole ‘seeds’ have been identified, possibly at less than one billion years after the Big Bang.

Astronomers combined data from Chandra, Hubble, and Spitzer to make this discovery. Using data from NASA’s three Great Observatories, scientists have found the best evidence to date of a mechanism that produced supermassive black holes in the early Universe. If confirmed, this result, described in our latest press release, could lead to new insight into how black holes were formed and grew billions of years ago.

This artist’s illustration depicts a possible ‘seed’ for the formation of a supermassive black hole, that is an object that contains millions or even billions of times the mass of the Sun. In the artist’s illustration, the gas cloud is shown as the wispy blue material, while the orange and red disk is showing material being funneled toward the growing black hole through its gravitational pull.

Researchers found evidence that two objects could have formed in this way, by directly collapsing into a black hole from a large cloud of gas. These two candidates for being ‘direct collapse black holes’ are so distant that they may have formed less than one billion years after the Big Bang.

The inset boxes show data from the Hubble Space Telescope (right) and Chandra X-ray Observatory (left) of one of the objects described above. The Hubble image shows the faint, distant galaxy at the center of the image and the Chandra image shows X-ray emission from material falling onto the black hole in the same galaxy.

The researchers used computer models of black hole seeds combined with a new method to select candidates for these objects from long-exposure images from Chandra, Hubble, and Spitzer (not shown in this graphic). By analyzing the combined light from the three telescopes, the team was able to search through thousands of objects to look for any that had properties that matched those predicted by their models.

Two candidates emerged that had the expected red color, seen by Hubble and Spitzer, as well as the X-ray profile predicted from Chandra. These objects were found in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey and the Great Observatories Origins Deep Survey-South surveys. The next steps will involve getting more data on these two intriguing objects as well as extending the analysis to other surveys to look for more direct collapse black hole candidates.

Distance Estimate: About 13.2 billion light years (z=9.73)

[http://chandra.harvard.edu/photo/2016/bhseeds/index.html]

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

[Return to the 88 Modern Constellations]

Eridanus

Stars of constellations Orion and Eridanus are photographed above Sinai seashores near Dahab, northeast Egypt. At this latitude of 28 degrees north even the southern most part of the constellation Eridanus, the River, is visible. The bright star at the southern end of the river is Achernar, Alpha star in Eridanus; means the end of the river in Arabic. Achernar is the 10th brightest star in the night sky with +0.46 magnitude. Eridanus is the 6th largest constellation in the sky and its unique figure take it from the celestial equator near Orion Belt to declination -57 at Achernar (57 degrees below the celestial equator).

[http://twanight.org/newTWAN/photos.asp?ID=3003327]

Eridanus is the sixth largest constellation in the night sky, occupying an area of 1138 square degrees. It is located in the first quadrant of the southern hemisphere (SQ1) and can be seen at latitudes between +32° and -90°. The neighboring constellations are Caelum, Cetus, Fornax, Horologium, Hydrus, Lepus, Orion, Phoenix, Taurus and Tucana.

[http://www.constellation-guide.com/constellation-list/eridanus-constellation/]

Johannes Hevelius’ Eridanus from Uranographia (1690)

[http://chandra.harvard.edu/photo/constellations/eridanus.html]

The name Eridanus refers to the Po River, the main river of northern Italy. Its association with a river comes from the way its stars trace a tortuous path. In some star maps, Eridanus is depicted as a river flowing from the waters poured by Aquarius. In such maps, Aquarius is visualized as facing Eridanus, requiring a different perspective and a redesign of how the stars of Aquarius connect, so the water pours onto the same side as Eridanus.

According to one theory, the Greek constellation takes its name from the Babylonian constellation known as the Star of Eridu (MUL.NUN.KI). Eridu was an ancient city in the extreme south of Babylonia; situated in the marshy regions it was held sacred to the god Enki-Ea who ruled the cosmic domain of the Abyss- a mythical conception of the fresh-water reservoir below the Earth’s surface.

Eridanus is connected to the myth of Phaethon, who took over the reins of his father Helios’ sky chariot (i.e., the Sun), but didn’t have the strength to control it and so veered wildly in different directions, scorching both Earth and heaven. Zeus intervened by striking Phaethon dead with a thunderbolt and casting him to Earth. The constellation was supposed to be the path Phaethon drove along; in later times, it was considered a path of souls. Since Eridanos was also a Greek name for the Po (Latin Padus), in which the burning body of Phaethon is said by Ovid to have extinguished, the mythic geography of the celestial and earthly Eridanus is complex.

Another association with Eridanus is a series of rivers all around the world. First conflated with the Nile River in Egypt, the constellation was also identified with the Po River in Italy. The stars of the modern constellation Fornax were formerly a part of Eridanus.

The stars of Eridanus are also depicted as a river in Indian astronomy starting close to the head of Orion just below Auriga. Eridanus is called Srotaswini in Sanskrit, srótas meaning the course of a river or stream. Specifically, it is depicted as the Ganges on the head of Dakshinamoorthy or Nataraja, a Hindu incarnation of Shiva. Dakshinamoorthy himself is represented by the constellation Orion.

The stars that correspond to Eridanus cannot be fully seen from China. In Chinese astronomy, the northern part is located within the White Tiger of the West (Xī Fāng Bái Hǔ). The unseen southern part was classified among the Southern Asterisms (Jìnnánjíxīngōu) by Xu Guangqi, based on knowledge of western star charts.

[https://bobmoler.wordpress.com/2011/12/27/122711-ephemeris-the-constellation-of-eridanus-the-river/]

[http://www.pa.msu.edu/people/horvatin/Astronomy_Facts/constellation_pages/eridanus.htm]

The position of Achernar (lower right)

Achernar is the name of the brightest component (by visual brightness) of the binary system designated Alpha Eridani, which is the brightest ‘star’ or point of light in, and lying at the southern tip of, the constellation of Eridanus, and the tenth-brightest in the night sky. The system bears the traditional name of Achernar, derived from the Arabic ‘ākhir an-nahr,’ meaning ‘The End of the River.’ The two components are designated Alpha Eridani A and Alpha Eridani B (known informally as Achernar B). As determined by the Hipparcos astrometry satellite, it is approximately 139 light-years (43 pc) from the Sun.

Achernar is in the deep southern sky and never rises above the horizon beyond 33°N, roughly the latitude of Dallas, Texas. It is best seen from the southern hemisphere in November; it is circumpolar above (i.e. south of) 33°S, roughly the latitude of Santiago. On this latitude, e.g. the south coast of South Africa (Cape Town to Port Elizabeth) when in lower culmination it is barely visible to the naked eye as it is only 1 degree above the horizon, but still circumpolar. Further south, it is well visible at all times during night.

Achernar is a bright, blue star with about seven times the mass of the Sun. It is a main sequence star with a stellar classification of B6 Vep, but is about 3,150 times more luminous than the Sun. Infrared observations of the star using an adaptive optics system on the Very Large Telescope show that it has a companion star in a close orbit. This appears to be an A-type star in the stellar classification range A0V–A3V, which suggests a stellar mass of about double that of the Sun. The separation of the two stars is roughly 12.3 AU and their orbital period is at least 14–15 years.

As of 2003, Achernar is the least spherical star in the Milky Way studied to date. It spins so rapidly that it has assumed the shape of an oblate spheroid with an equatorial diameter 56% greater than its polar diameter. The polar axis is inclined about 65° to the line of sight from the Earth. Since it is actually a binary star, its highly distorted shape may cause non-negligible departures of the companion’s orbital trajectory with respect to a Keplerian ellipse. A similar situation occurs for the star Regulus.

Extreme rotation speed has flattened Achernar

Because of the distorted shape of this star, there is a significant temperature variation by latitude. At the pole, the temperature may be above 20,000 K, while the equator is at or below 10,000 K. The average temperature of the star is about 15,000 K. The high polar temperatures are generating a fast polar wind that is ejecting matter from the star, creating a polar envelope of hot gas and plasma. The entire star is surrounded by an extended envelope that can be detected by its excess infrared emission, or by its polarization. The presence of a circumstellar disk of ionized gas is a common feature of Be stars such as this. The disk is not stable and periodically decretes back into the star. The maximum polarization for Achernar’s disk was observed in September 2014, and it is now decreasing.

Due to precession, Achernar lay much further south in ancient times than at present, being 7.5 degrees of the south pole around 3400 BCE (decl 82º40') and still lying at declination -76 by around 1500 BCE. Hence the Ancient Egyptians could not have known it. Even in 100 CE its declination was around -67, meaning Ptolemy could not possibly have seen it from Alexandria - whereas Theta Eridani was visible as far north as Crete. So Ptolemy’s ‘end of the river’ was certainly Theta Eridani. Alpha Eridani was not visible from Alexandria until about 1600 CE.

Alpha Eridani will continue to move north in the next few millennia, rising from Crete about 500 years hence before reaching its maximum northern declination between the 8th and 11th millennia, when it will be visible as far north as Germany and southern England.

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

Beta Eridani is a giant star belonging to the spectral class A3 III. It is the second brightest star in the constellation, with an apparent magnitude of 2.796. It lies approximately 89 light years from the solar system and can be found near the border with Orion. The star has a visual companion with an apparent magnitude of 10.90, located 120 arc seconds away.

Like Achernar, Beta Eridani is a fast spinner, with a projected rotational velocity of 196 km/s. The star is classified as a variable. Its visual magnitude changes from magnitude 2.72 to 2.80.

Beta Eridani’s traditional name, Cursa, comes from the Arabic phrase Al Kursiyy al Jauzah, which means ‘the chair of the central one,’ and refers to a star association that also includes Lambda Eridani, Psi Eridani, and Tau Orionis in Orion constellation.

Acamar, Theta Eridani, is a binary star that is possibly a part of a multiple star system. The primary component in the system belongs to the spectral class A4 and has a visual magnitude of 3.2. The secondary component is a class A1 star with an apparent magnitude of 4.3. The two stars are separated by 8.3 seconds of arc. Acamar has an apparent visual magnitude of 3.2 and is about 161 light years distant from the Sun.

The star’s traditional name, Acamar, comes from the Arabic ‘Ākhir an-nahr,’ which means ‘the end of the river.’ Acamar used to represent the end of the celestial river, Eridanus. Now it is the brighter star Achernar that holds that distinction. The stars’ names share the same etymology. Since Achernar is not visible from Greece, Acamar was chosen to mark the river’s end by Hipparchus and Ptolemy.

Gamma Eridani has the stellar classification M1IIIb. It has an apparent visual magnitude of 2.95 and is approximately 150 light years distant from the solar system. The star’s proper name, Zaurak, means’the boat’ in Arabic.

Delta Eridani is a subgiant star of the spectral type K0 IV. It has a visual magnitude of 3.54 and is only 29.49 light years distant. Its traditional name, Rana, means ‘the frog’ in Latin.

[http://www.constellation-guide.com/constellation-list/eridanus-constellation/]

Artist’s impression of a Jupiter-mass planet orbiting the nearby star Epsilon Eridani

Epsilon Eridani is a star with one extrasolar planet similar to Jupiter. It is an orange-hued main-sequence star of magnitude 3.7, 10.5 light-years from Earth. Its one planet, with an approximate mass of one Jupiter mass, has a period of 7 years.

NGC 1535 using the 0.8m Schulman Telescope from the Mount Lemmon Sky Center

[https://en.wikipedia.org/wiki/NGC_1535]

NGC 1535 is a planetary nebula in the constellation of Eridanus, discovered by William Herschel on February 1, 1785. It is sometimes referred to as Cleopatra’s Eye Nebula.

[https://en.wikipedia.org/wiki/NGC_1535]

IC 2118 is a faint reflection nebula believed to be an ancient supernova remnant or gas cloud illuminated by nearby supergiant star Rigel in Orion:

IC 2118: The Witch Head Nebula

Double, double toil and trouble; Fire burn, and cauldron bubble- maybe Macbeth should have consulted the Witch Head Nebula. This suggestively shaped reflection nebula is associated with the bright star Rigel in the constellation Orion. More formally known as IC 2118, the Witch Head Nebula glows primarily by light reflected from Rigel, located just outside the top right corner of the above image. Fine dust in the nebula reflects the light. The blue color is caused not only by Rigel’s blue color but because the dust grains reflect blue light more efficiently than red. The same physical process causes Earth’s daytime sky to appear blue, although the scatterers in Earth’s atmosphere are molecules of nitrogen and oxygen. The nebula lies about 1000 light-years away.

[http://apod.nasa.gov/apod/ap051227.html]

NGC 1300 is a face-on barred spiral galaxy. The center of the bar shows an unusual structure: within the overall spiral structure, a grand design spiral exists. Its spiral arms are tightly wound:

Barred Spiral Galaxy NGC 1300

Big, beautiful, barred spiral galaxy NGC 1300 lies some 70 million light-years away on the banks of the constellation Eridanus. This Hubble Space Telescope composite view of the gorgeous island universe is one of the largest Hubble images ever made of a complete galaxy. NGC 1300 spans over 100,000 light-years and the Hubble image reveals striking details of the galaxy’s dominant central bar and majestic spiral arms. In fact, on close inspection the nucleus of this classic barred spiral itself shows a remarkable region of spiral structure about 3,000 light-years across. Like other spiral galaxies, including our own Milky Way, NGC 1300 is thought to have a supermassive central black hole.

[https://apod.nasa.gov/apod/ap160109.html]

NGC 1427A is an irregular galaxy in the constellation Eridanus. Its distance is about 52 Mly. It is the brightest dwarf irregular member of the Fornax cluster and is in the foreground of the cluster’s central galaxy NGC 1399:

[https://en.wikipedia.org/wiki/NGC_1427A]

NGC 1427A: Galaxy in Motion

In this tantalizing image, young blue star clusters and pink star-forming regions abound in NGC 1427A, a galaxy in motion. The small irregular galaxy’s swept back outline points toward the top of this picture from the Hubble Space Telescope - and that is indeed the direction NGC 1427A is moving as it travels toward the center of the Fornax cluster of galaxies, some 62 million light-years away. Over 20,000 light-years long and similar to the nearby Large Magellanic Cloud, NGC 1427A is speeding through the Fornax cluster's intergalactic gas at around 600 kilometers per second. The resulting pressure is giving the galaxy its arrowhead outline and triggering the beautiful but violent episodes of star formation. Still, it is understood that interactions with cluster gas and the other cluster galaxies during its headlong flight will ultimately disrupt galaxy NGC 1427A. Many unrelated background galaxies are visible in the sharp Hubble image, including a striking face-on spiral galaxy at the upper left.

[https://apod.nasa.gov/apod/ap050304.html]

NGC 1531 is a dwarf galaxy in the constellation Eridanus that is interacting with the larger spiral galaxy NGC 1532. Although technically classified as a peculiar lenticular galaxy, the galaxy's structure is better described as amorphous:

NGC 1531/2: Interacting Galaxies

This dramatic image of an interacting pair of galaxies was made using 8-meter Gemini South telescope at Cerro Pachon, Chile. NGC 1531 is the background galaxy with a bright core just above center and NGC 1532 is the foreground spiral galaxy laced with dust lanes. The pair is about 55 million light-years away in the southern constellation Eridanus. These galaxies lie close enough together so that each feels the influence of the other’s gravity. The gravitational tug-of-war has triggered star formation in the foreground spiral as evidenced by the young, bright blue star clusters along the upper edge of the front spiral arm. Though the spiral galaxy in this pair is viewed nearly edge-on, astronomers believe the system is similar to the face-on spiral and companion known as M51, the Whirlpool Galaxy.

[https://apod.nasa.gov/apod/ap050301.html]

MACS J0416.1-2403 is a galaxy cluster at a redshift of z=0.397 with a mass 160 trillion times the mass of the Sun inside 200 kpc (650 kly). Its mass out to a radius of 950 kpc (3,100 kly) was measured as 1.15×10^15 solar masses. The system was discovered during the Massive Cluster Survey, MACS. This cluster causes gravitational lensing of distant galaxies producing multiple images. In 2015, the galaxy cluster was announced as gravitationally lensing the most distant galaxy (z = 12). Based on the distribution of the multiple image copies, scientists have been able to deduce and map the distribution of dark matter:

[https://en.wikipedia.org/wiki/MACS_J0416.1-2403]

MACS J0416

Galaxy clusters are enormous collections of hundreds or even thousands of galaxies and vast reservoirs of hot gas embedded in massive clouds of dark matter, invisible material that does not emit or absorb light but can be detected through its gravitational effects. These cosmic giants are not merely novelties of size or girth - rather they represent pathways to understanding how our entire universe evolved in the past and where it may be heading in the future.

To learn more about clusters, including how they grow via collisions, astronomers have used some of the world’s most powerful telescopes, looking at different types of light. They have focused long observations with these telescopes on a half dozen galaxy clusters. The name for this galaxy cluster project is the ‘Frontier Fields.’

One of these Frontier Fields galaxy clusters, MACS J0416.1-2403 (abbreviated MACS J0416) is featured here in a multi-wavelength image.

Located about 4.3 billion light years from Earth, MACS J0416 is a pair of colliding galaxy clusters that will eventually combine to form an even bigger cluster.

The new images of MACS J0416 contain data from three different telescopes: NASA’s Chandra X-ray Observatory (diffuse emission in blue), Hubble Space Telescope (red, green, and blue), and the NSF’s Jansky Very Large Array (diffuse emission in pink). Where the X-ray and radio emission overlap the image appears purple. Astronomers also used data from the Giant Metrewave Radio Telescope in India in studying the properties of MACS J0416.

The Chandra data shows gas in the merging clusters with temperatures of millions of degrees. The optical data shows galaxies in the clusters and other, more distant, galaxies lying behind the clusters. Some of these background galaxies are highly distorted because of gravitational lensing, the bending of light by massive objects. This effect can also magnify the light from these objects, enabling astronomers to study background galaxies that would otherwise be too faint to detect. Finally, the structures in the radio data trace enormous shock waves and turbulence. The shocks are similar to sonic booms, generated by the mergers of the clusters.

An open question for astronomers about MACS J0416 has been: are we seeing a collision in these clusters that is about to happen or one that has already taken place? Until recently, scientists have been unable to distinguish between these two explanations. Now, the combined data from these various telescopes is providing new answers.

In MACS J0416 the dark matter (which leaves its gravitational imprint in the optical data) and the hot gas (detected by Chandra) line up well with each other. This suggests that the clusters have been caught before colliding. If the clusters were being observed after colliding the dark matter and hot gas should separate from each other, as seen in the famous colliding cluster system known as the Bullet Cluster.

The cluster in the upper left contains a compact core of hot gas, most easily seen in a specially processed image, and also shows evidence of a nearby cavity, or hole in the X-ray emitting gas. The presence of these structures also suggests that a major collision has not occurred recently, otherwise these features would likely have been disrupted. Finally, the lack of sharp structures in the radio image provides more evidence that a collision has not yet occurred.

In the cluster located in the lower right, the observers have noted a sharp change in density on the southern edge of the cluster. This change in density is most likely caused by a collision between this cluster and a less massive structure located further to the lower right.

[http://chandra.harvard.edu/photo/2016/frontier/index.html]

The Eridanus Supervoid is a large supervoid (an area of the universe devoid of galaxies) discovered as of 2007. At a diameter of about one billion light years it is the second largest known void, superseded only by the Giant Void in Canes Venatici. It was discovered by linking a ‘cold spot’ in the cosmic microwave background to an absence of radio galaxies in data of the United States National Radio Astronomy Observatory’s Very Large Array Sky Survey. There is some speculation that the void may be due to quantum entanglement between our universe and another.

The Nu Eridanids, a recently discovered meteor shower, radiate from the constellation between August 30 and September 12 every year; the shower’s parent body is an unidentified Oort cloud object. Another meteor shower in Eridanus is the Omicron Eridanids, which peak between November 1 and 10.

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

[Return to the 88 Modern Constellations]

Equuleus

Equuleus is a constellation whose name is Latin for ‘little horse,’ a foal. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy. It is the second smallest of the modern constellations (after Crux), spanning only 72 square degrees. It is also very faint, having no stars brighter than the fourth magnitude.

Equuleus, the foal, seen next to the head of Pegasus in Johann Bode’s Uranographia (1801).

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

In Greek mythology, one myth associates Equuleus with the foal Celeris (meaning ‘swiftness’ or ‘speed’), who was the offspring or brother of the winged horse Pegasus. Celeris was given to Castor by Mercury. Other myths say that Equuleus is the horse struck from Poseidon’s trident, during the contest between him and Athena when deciding which would be the superior. Because this section of stars rises before Pegasus, it is often called Equus Primus, or the First Horse. Equuleus is also linked to the story of Philyra and Saturn. Created by Hipparchus and included by Ptolemy, it abuts Pegasus; unlike the larger horse it is depicted as a horse’s head alone.

In Chinese astronomy, the stars that correspond to Equuleus are located within the Black Tortoise of the North (Běi Fāng Xuán Wǔ).

You’ll find Equuleus wedged between Pegasus’ nose, marked by the star Enif, and another small but better known constellation, Delphinus.

[https://bestdoubles.wordpress.com/2010/11/17/horsing-around-in-equuleus-delta-%CE%B4-%CF%832786-%CF%832765-%CE%B270-and-lamda-%CE%BB/]

Major stars in Equuleus include:

Kitalpha (Alpha Equulei) is a spectroscopic binary star of the spectral type G0III. It has a visual magnitude of 3.92 and is approximately 186 light years distant. It is the brightest star in Equuleus. The star’s name, Kitalpha, is derived from the Arabic phrase ‘qiṭ‘a(t) al-faras’ which means ‘a piece (or section) of the horse.’ Kitalpha is about 75 times more luminous than the Sun and has 2.72 times the mass.

Delta Equulei is another binary star in Equuleus. The components in the system belong to the spectral classes G0 and F5 and have visual magnitudes of 4.49 and 5.4. The system is approximately 60.3 light years distant from the Sun and has a combined apparent magitude of 4.47.

Gamma Equulei, or 5 Equulei, is also a double star. It belongs to the spectral class A9 Sr Eu. It has a visual magnitude of 4.7 and is 118 light years distant. Gamma Equulei is a chemically peculiar star that undergoes occasional variations in brightness and is also classified as a roAp star, or a rapidly oscillationg Ap star. (An Ap star is a peculiar star of the type A that shows an overabundance of certain metals and usually rotates much slower than regular A type stars.) The companion star has an apparent magnitude of 9.05 and is located 1.26 arc seconds away from the main component.

Beta Equulei is a main sequence star belonging to the spectral class A3V. It has four visual companions that are not physically related to the main star. The system has a combined apparent magnitude of 5.159 and is about 360 light years distant from Earth.

Epsilon Equulei is another multiple star in Equuleus. It consists of four components. It has a visual magnitude of 5.3 and is 196.4 light years distant from the Sun.

Lambda Equulei is another binary star in the constellation. The primary component in the system is a main sequence star belonging to the spectral class F6V. The system has an apparent magnitude of 6.72 and is approximately 332 light years distant from the solar system.

HD 200964 is a subgiant of the spectral type K0 IV. It has a visual magnitude of 6.64 and is some 223 light years distant. The star is notable because two large extrasolar planets were discovered in its orbit in July 2010. The planet closer to the star is almost double the mass of Jupiter, while the more distant planet is slightly less massive than Jupiter. The inner planet has an orbital period of 614 days and the outer one orbits the star every 825 days. This adds up to a 4:3 resonance: every time the bigger planet orbits the star four times, the smaller one orbits the star three times.

Deep sky objects in Equuleus include:

NGC 7015 is a galaxy with a visual magnitude of 12.4. It is 2.0′x1.8′ in size and about 212 million light years distant.

NGC 7040 is a spiral galaxy with an apparent visual magnitude of 14.0. Its coordinates are 21h 13m 16.5s (right ascension), +08°51′53.2 (declination).

NGC 7045 is a binary star in Equuleus. It was discovered by John Herschel in July 1827 and included on the list of NGC deep sky objects. It has a visual magnitude of 12.0.

NGC 7046 is a barred spiral galaxy 1.9′x1.4′ in size. It has an apparent visual magnitude of 13.10. The galaxy was discovered by William Herschel in October 1790.

[http://www.constellation-guide.com/constellation-list/equuleus-constellation/]

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

[Return to the 88 Modern Constellations]

Draco

Draco is a constellation in the far northern sky. Its name is Latin for dragon. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy and remains one of the 88 modern constellations today. The north pole of the ecliptic is in Draco. Draco is circumpolar (that is, never setting), and can be seen all year from northern latitudes. The constellation’s right ascension is 17, its declination +65, and it covers an area 1083 sq. deg., ranking 8th in size.

Draco coils around the north celestial pole, as depicted in Urania's Mirror, a set of constellation cards published in London c.1825

Dragons in Greek mythology that may have inspired the constellation’s name include Ladon, the dragon who guarded the golden apples of the Hesperides. Hercules killed Ladon during his 12 labors; he was tasked with stealing the golden apples. The constellation of Hercules is depicted near Draco. Sometimes, Draco is represented as the demon son of Gaia, Typhon.

In Greco- Roman legend, Draco was a dragon killed by the goddess Minerva and tossed into the sky upon his defeat. The dragon was one of the Gigantes, who battled the Olympic gods for ten years. As Minerva threw the dragon, it became twisted on itself and froze at the cold North Celestial Pole before it could right itself.

The most commonly accepted version of Draco’s arrival in the heavens is that Draco was the dragon killed by Cadmus. Cadmus was the brother of Europa, who was carried off to Crete by Jupiter in the form of a bull (Taurus). Cadmus was ordered by his father to go in search of his sister, and told he could not return unless he brought Europa back with him. As Ovid narrates in his Metamorphosis, “Cadmus wandered over the whole world: for who can lay hands on what Jove has stolen away? Driven to avoid his native country and his father's wrath, he made a pilgrimage to Apollo’s oracle, and begged him to say what land he should dwell in.”

Cadmus followed Apollo’s advice and found a suitable site for his new city. He sent his attendants to find fresh water to offer as a libation to Jupiter, and they wandered into a cave with springs. As they were getting water, however, they were all killed by “the serpent of Mars, a creature with a wonderful golden crest; fire flashed from its eyes, its body was all puffed up from poison, and from its mouth, set with a triple row of teeth, flickered a three-forked tongue.” After his companions did not return, Cadmus himself went into the cave and discovered the dragon. He killed it with his spear, and then (upon the order of Minerva) sowed the dragon’s teeth in the ground. From the teeth sprung warriors, who battled each other until only five were left. These five, along with Cadmus himself, were the first people of the city of Thebes.

Ovid himself does not equate the dragon of Mars with Draco. In fact he describes the dragon killed by Cadmus in terms of the constellation: “It was as huge as the Serpent that twines between the two Bears in the sky, if its full length were seen uncoiled.”

[http://www.comfychair.org/~cmbell/myth/draco.html]

Traditional Arabic astronomy does not depict a dragon in modern-day Draco, which is called the Mother Camels. Instead, two hyenas, represented by Eta Draconis and Zeta Draconis are seen attacking a baby camel (a dim star near Beta Draconis), which is protected by four female camels, represented by Beta Draconis, Gamma Draconis, Nu Draconis, and Xi Draconis. The nomads who own the camels are camped nearby, represented by a cooking tripod composed of Upsilon, Tau, and Sigma Draconis.

A Babylonian creation story tells of Tiamat, who turned herself into a dragon but was later defeated and split into two parts. One part became the heavens and the other, the Earth.

A Chinese tale sees the stars as the dragon who eats the Sun or Moon (possible represented by the north star Polaris) in an eclipse. During a real eclipse, ancient Chinese would make as much noise as possible, banging on pots and pans to try and scare away the dragon which was eating the Sun or Moon.

A Norse creation myth tells of a dragon who gnaws at the roots of Ygdrasil, the tree that covers the world.

Because Thuban was the pole star 5000 years ago the ancient Egyptians keenly observed it. Some of Draco’s stars were part of their constellation of Hippopotamus and some were of the Crocodile. They appear on the planisphere of Denderah and the walls of the Ramesseum at Thebes. Draco’s stars were also said to represent the falcon headed god Horus.

The Pharaoh Khufu ruled ancient Egypt around 2550 BCE and was buried in the largest of the Giza pyramids when he died. Khufu’s burial chamber was fashioned deep inside the Great Pyramid. Two skinny shafts bore outward from the chamber. For decades, scholars thought they were airshafts. But in the 1960s, astronomers found that they have an astronomical purpose. It was found that one of the shafts pointed directly towards Thuban. The other was aimed at the belt of Orion, which symbolized Osiris. The stars close to the pole never set. The Egyptians described these stars as ‘imperishable’ or ‘undying.’ Khufu expected that when he died, he would join not only with the Sun, but with Thuban as well, maintaining order in the celestial realm, just as he had on Earth.

Around 800 BCE, the prehistoric Adena people who lived in the Ohio area of the United States created Serpent Mound which is believed to mirror the constellation Draco. This huge mound is nearly a quarter mile long.

The Persians have regarded Draco as a man-eating serpent called Azhdeha.

In early Hindu worship, Draco is given the form of an alligator known as Shi-shu-mara.

[http://starryskies.com/The_sky/constellations/draco.html]

[https://infograph.venngage.com/p/191012/draco-constellation-ajcr11951]

[https://www.pa.msu.edu/people/horvatin/Astronomy_Facts/constellation_pages/draco.htm]

Thuban (α Draconis) was the northern pole star from 3942 BCE, when it moved farther north than Theta Boötis, until 1793 BCE. Due to the effects of precession, it will again be the pole star around the year AD 21000. It is a blue-white giant star of magnitude 3.7, 309 light-years from Earth. The traditional name of Alpha Draconis, Thuban, means ‘head of the serpent.’

There are two other stars above magnitude 3 in Draco. The brighter of the two- and the brightest star in Draco- is Gamma Draconis, traditionally called Etamin or Eltanin. It is an orange giant star of magnitude 2.2, 148 light-years from Earth. The aberration of starlight was discovered in 1728 when James Bradley observed Gamma Draconis.

Beta Draconis, traditionally called Rastaban, is a yellow giant star of magnitude 2.8, 362 light-years from Earth. Its name shares a meaning with Thuban, ‘head of the serpent.’

The four stars forming the dragons head (beta Dra, gamma Dra, xi Dra and nu Dra), build a conspicuous asterism called the Lozenge.

Epsilon Dra is a good double to be observed with scopes at a moderate magnification. Its companions are about 3 arc sec apart. The binary mu Dra is a good test for a scope with an aperture of 60mm. Good optics might split that pair consisting of two F7 main sequence stars (5.83 mag and 5.80 mag).

An outstanding binary is nu Dra. The two white stars (an A6V and an A4m) have magnitudes of 4.88 and 4.87. They are a good object for binoculars. Small scopes reveal the 8th mag blue companion of the G9IIIbCN-0.5 star omicron Dra (4.66 mag). A good binocular may be sufficient to split the pair of psi Dra. Small scopes show a 5th mag star and a 6th mag star. Another easy pair for small telescopes is 40-41 Dra. The two yellow stars are of 6th mag. Its coordinates are roughly RA=18h and DECL=+80 degrees.

A really impressive triple system is 39 Dra. Field glasses show a wide double; in larger scopes a third star close to the brighter one occurs.

Another attractive triple is 16-17. In binoculars two blue-white stars of 5th mag are revealed. Viewing with a telescope shows another star of 7th mag close to one of the first two.

[http://www.crystalinks.com/draco.html]

The constellation contains the star recently named Kepler-10 which has been confirmed to be orbited by Kepler-10b, the smallest rocky Earth-sized planet yet detected outside of the Solar System. Yet it orbits its star in less than a day, at less than a twentieth of the distance from Mercury to the Sun. Its surface temperature on the star lit side is approximately 1833 K which is as hot as a blast furnace and hot enough to melt iron.

[https://en.wikipedia.org/wiki/Kepler-10b]

One of the deep-sky objects in Draco is the Cat’s Eye Nebula (NGC 6543), a planetary nebula approximately 3,000 light-years away that was discovered by English astronomer William Herschel in 1786. It is 9th magnitude and was named for its appearance in the Hubble Space Telescope, though it appears as a fuzzy blue-green disk in an amateur telescope. NGC 6543 has a very complex shape due to gravitational interactions between the components of the multiple star at its center, the progenitor of the nebula approximately 1,000 years ago. It is located 9.6 arcminutes away from the north ecliptic pole to the west-northwest:

The Cat’s Eye Nebula

The full beauty of the Cat’s Eye Nebula (NGC 6543) is revealed in this new, detailed view from NASA’s Hubble Space Telescope. The image from Hubble’s Advanced Camera for Surveys (ACS) shows a bull’s eye pattern of eleven or even more concentric rings, or shells, around the Cat’s Eye. Each ‘ring’ is actually the edge of a spherical bubble seen projected onto the sky – that’s why it appears bright along its outer edge.

Observations suggest the star ejected its mass in a series of pulses at 1,500-year intervals. These convulsions created dust shells, each of which contain as much mass as all of the planets in our solar system combined (still only one percent of the Sun’s mass). These concentric shells make a layered, onion-skin structure around the dying star. The view from Hubble is like seeing an onion cut in half, where each skin layer is discernible.

The bull’s-eye patterns seen around planetary nebulae come as a surprise to astronomers because they had no expectation that episodes of mass loss at the end of stellar lives would repeat every 1,500 years. Several explanations have been proposed, including cycles of magnetic activity somewhat similar to our own Sun’s sunspot cycle, the action of companion stars orbiting around the dying star, and stellar pulsations. Another school of thought is that the material is ejected smoothly from the star, and the rings are created later on due to formation of waves in the outflowing material.

[https://www.nasa.gov/multimedia/imagegallery/image_feature_211.html]

Three Galaxies in Draco

This intriguing trio of galaxies is sometimes called the Draco Group, located in the northern constellation of (you guessed it) Draco. From left to right are edge-on spiral NGC 5981, elliptical galaxy NGC 5982, and face-on spiral NGC 5985- all within this single telescopic field of view spanning a little more than half the width of the full moon. While the group is far too small to be a galaxy cluster and has not been catalogued as a compact group, these galaxies all do lie roughly 100 million light-years from planet Earth. On close examination with spectrographs, the bright core of the striking face-on spiral NGC 5985 shows prominent emission in specific wavelengths of light, prompting astronomers to classify it as a Seyfert, a type of active galaxy. Not as well-known as other tight groupings of galaxies, the contrast in visual appearance makes this triplet an attractive subject for astrophotographers. This impressively deep exposure hints at faint, sharp-edged shells surrounding elliptical NGC 5982, evidence of past galactic mergers. It also reveals many even more distant background galaxies.

[https://apod.nasa.gov/apod/ap131016.html]

There are several faint galaxies in Draco, one of which is the lenticular galaxy NGC 5866 (sometimes considered to be Messier Object 102) that bears its name to a small group that also includes the spiral galaxies NGC 5879 and NGC 5907:

NGC 5866 Edge-On

This is a unique NASA Hubble Space Telescope view of the disk galaxy NGC 5866 tilted exactly edge-on to our line-of-sight. Hubble’s sharp vision reveals a crisp dust lane dividing the galaxy into two halves. The image highlights the galaxy’s structure: a subtle, reddish bulge surrounding a bright nucleus, a blue disk of stars running parallel to the dust lane, and a transparent outer halo.

Some faint, wispy trails of dust can be seen meandering away from the disk of the galaxy out into the bulge and inner halo of the galaxy. The outer halo is dotted with numerous gravitationally bound clusters of nearly a million stars each, known as globular clusters. Background galaxies that are millions to billions of light-years farther away than NGC 5866 are also seen through the halo.

NGC 5866 is a disk galaxy of type ‘S0’ (pronounced s-zero). Viewed face on, it would look like a smooth, flat disk with little spiral structure. It remains in the spiral category because of the flatness of the main disk of stars as opposed to the more spherically rotund (or ellipsoidal) class of galaxies called ‘ellipticals.’ Such S0 galaxies, with disks like spirals and large bulges like ellipticals, are called ‘lenticular’ galaxies.

The dust lane is slightly warped compared to the disk of starlight. This warp indicates that NGC 5866 may have undergone a gravitational tidal disturbance in the distant past, by a close encounter with another galaxy. This is plausible because it is the largest member of a small cluster known as the NGC 5866 group of galaxies. The starlight disk in NGC 5866 extends well beyond the dust disk. This means that dust and gas still in the galaxy and potentially available to form stars does not stretch nearly as far out in the disk as it did when most of these stars in the disk were formed.

The Hubble image shows that NGC 5866 shares another property with the more gas-rich spiral galaxies. Numerous filaments that reach out perpendicular to the disk punctuate the edges of the dust lane. These are short-lived on an astronomical scale, since clouds of dust and gas will lose energy to collisions among themselves and collapse to a thin, flat disk.

For spiral galaxies, the incidence of these fingers of dust correlates well with indicators of how many stars have been formed recently, as the input of energy from young massive stars moves gas and dust around to create these structures. The thinness of dust lanes in S0s has been discussed in ground-based galaxy atlases, but it took the resolution of Hubble to show that they can have their own smaller fingers and chimneys of dust.

NGC 5866 lies in the Northern constellation Draco, at a distance of 44 million light-years (13.5 Megaparsecs). It has a diameter of roughly 60,000 light-years (18,400 parsecs) only two-thirds the diameter of the Milky Way, although its mass is similar to our galaxy. This Hubble image of NGC 5866 is a combination of blue, green and red observations taken with the Advanced Camera for Surveys in November 2005.

[http://www.wolaver.org/Space/NGC5866.htm]

NGC 5907, located approximately 50 million light years from Earth, has long been considered a prototypical example of a warped spiral in relative isolation. In 2006 an international team of astronomers announced the presence of an extended tidal stream surrounding the galaxy that challenges this picture and suggests the gravitational perturbations induced by the stream progenitor may be the cause for the warp:

[https://en.wikipedia.org/wiki/NGC_5907]

The Star Streams of NGC 5907

Grand tidal streams of stars seem to surround galaxy NGC 5907. The arcing structures form tenuous loops extending more than 150,000 light-years from the narrow, edge-on spiral, also known as the Splinter or Knife Edge Galaxy. Recorded only in very deep exposures, the streams likely represent the ghostly trail of a dwarf galaxy- debris left along the orbit of a smaller satellite galaxy that was gradually torn apart and merged with NGC 5907 over four billion years ago. Ultimately this remarkable discovery image, from a small robotic observatory in New Mexico, supports the cosmological scenario in which large spiral galaxies, including our own Milky Way, were formed by the accretion of smaller ones. NGC 5907 lies about 40 million light-years distant in the northern constellation Draco.

[https://apod.nasa.gov/apod/ap080619.html]

A dwarf galaxy in Draco is the Draco Dwarf Galaxy, one of the least luminous galaxies with an absolute magnitude of −8.6 and a diameter of only about 3,500 light years, discovered by Albert G. Wilson of Lowell Observatory in 1954. Another one found in this constellation is PGC 39058:

Bright star - faint galaxy

Astronomers are used to encountering challenges in their work, but studying the prosaically-named galaxy PGC 39058 proves more difficult than usual. Due to a stroke of bad luck, a bright star happens to lie between the galaxy and the Earth, meaning our view is partly obscured by the glare of the star. The astounding image from the NASA/ESA Hubble Space Telescope shows the nearby star easily outshining the more distant galaxy PGC 39058. The galaxy is about 14 million light-years away and contains millions of stars- many of them not unlike the bright star in the foreground.

The bright foreground star seems to shine with incredible intensity due to the power of Hubble. Most Earth-bound observers would however consider the star to be quite faint. At magnitude 6.7, binoculars or a small telescope are needed to see it at all. That the image manages to capture both objects serves to further highlight Hubble’s excellent optics and sharp vision.

PGC 39058 is a dwarf galaxy, which explains its faintness despite its modest distance by galaxy standards. The sharp Hubble image easily resolves it completely into its component stars and also reveals many much more distant galaxies in the background.

This star and galaxy pair is located within the constellation of Draco (the Dragon). It is visible in the northern hemisphere, appearing to slither over a large portion of the sky around the north celestial pole. The ancient Greeks claimed that Draco represented Ladon, the dragon with 100 heads. One of Hercules’ twelve near-impossible tasks was to steal golden apples guarded by Ladon. The difficulty of this challenge is perhaps on a par with observing such a faint galaxy obscured by a bright star.

This picture was created from images taken using the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Images through yellow (F606W, shown as blue) and near infrared (F814W, shown as red) were combined. The exposure times were 20 minutes and 15 minutes respectively and the field of view is 2 × 1.6 arcminutes.

[https://www.spacetelescope.org/images/potw1021a/]

Draco also features several interacting galaxies and galaxy clusters. One such massive cluster is Abell 2218. It acts as a gravitational lens for even more distant background galaxies, allowing astronomers to study those galaxies as well as Abell 2218 itself; more specifically, the lensing effect allows astronomers to confirm the cluster’s mass as determined by x-ray emissions:

Abell 2218: A Galaxy Cluster Lens

Gravity can bend light, allowing huge clusters of galaxies to act as telescopes. Almost all of the bright objects in this released Hubble Space Telescope image are galaxies in the cluster known as Abell 2218. The cluster is so massive and so compact that its gravity bends and focuses the light from galaxies that lie behind it. As a result, multiple images of these background galaxies are distorted into long faint arcs- a simple lensing effect analogous to viewing distant street lamps through a glass of wine. The cluster of galaxies Abell 2218 is itself about three billion light-years away in the northern constellation Draco. The power of this massive cluster telescope has recently allowed astronomers to detect a galaxy at redshift 5.58, the most distant galaxy yet measured. This young, still-maturing galaxy is faintly visible to the lower right of the cluster core.

[http://apod.nasa.gov/apod/ap011007.html]

One of the most well-known interacting galaxies is Arp 188, also called the ‘Tadpole Galaxy.’ The tail of stars drawn off the Tadpole Galaxy appears blue because the gravitational interaction disturbed clouds of gas and sparked star formation:

Arp 188 and the Tadpole’s Tail

In this stunning vista, based on image data from the Hubble Legacy Archive, distant galaxies form a dramatic backdrop for disrupted spiral galaxy Arp 188, the Tadpole Galaxy. The cosmic tadpole is a mere 420 million light-years distant toward the northern constellation Draco. Its eye-catching tail is about 280 thousand light-years long and features massive, bright blue star clusters. One story goes that a more compact intruder galaxy crossed in front of Arp 188- from right to left in this view- and was slung around behind the Tadpole by their gravitational attraction. During the close encounter, tidal forces drew out the spiral galaxy’s stars, gas, and dust forming the spectacular tail. The intruder galaxy itself, estimated to lie about 300 thousand light-years behind the Tadpole, can be seen through foreground spiral arms at the upper right. Following its terrestrial namesake, the Tadpole Galaxy will likely lose its tail as it grows older, the tail’s star clusters forming smaller satellites of the large spiral galaxy.

[http://apod.nasa.gov/apod/ap121108.html]

Q1634+706 is a quasar that holds the distinction of being the most distant object usually visible in an amateur telescope. At magnitude 14.4, it appears star-like, though it is at a distance of 12.9 billion light-years. The light of Q1634+706 has taken 8.6 billion years to reach Earth, a discrepancy attributable to the expansion of the universe.

Draco is home to the February Eta Draconids, a meteor shower that was discovered on February 4, 2011. Observers noted six meteors with a common radiant in a short period. Its parent is a previously unknown long-period comet.

Also, the Hercules- Corona Borealis Great Wall, possibly the largest known structure in the universe, covers a part of the southern region of Draco.

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

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