Eridanus

In Virgil (VI, 659) a river of the underworld. In Herodotus (III, 115) a river which, by some of his contemporaries, was associated with the river Po. This because the Po is situated near the end of what used to be the so-called Amber trail. According to legend, amber originated from the tears shed by the Heliades over the death of their brother Phaeton, who fell from the sky into the river Eridanus.

(Encyclopedia Mythica)

Eridanus is the river that Phaethon crashed his father's chariot into. Like every teenager before and after him, Phaethon yearned to take his father's vehicle for a spin. Helios, his father, was reluctant to allow this. After all, he needed the chariot to transport the Sun across the sky each day and he wasn't sure if his insurance covered his son's driving.

However, after much pleading, Helios relented and gave the boy charge of the chariot. Nervously, Helios explained the finer points of driving the chariot to his son but despite this, Phaethon found it very difficult to handle the four horsepower chariot. The four massive and magnificent steeds drew the chariot, Phaethon and the Sun up among the stars as the boy struggled to retain control. Scared and not knowing what to do, Phaethon panicked. Ahead of him was the giant figure of Scorpius, claws raised in ire and sting poised to strike. Phaethon let go of the reins and the chariot plunged out of control.

Diving toward the Earth, it crossed close to the ground. The tremendous heat of the Sun evaporated the seas of Africa and created vast deserts and the people of Ethiopia had their skins burnt black. Zeus, seeing the destruction that was being wrought, struck down the chariot with a thunderbolt and the chariot plunged into the river Eridanus.

Eridanus has, since classical times, been associated with many rivers, the Rhine, Po and Nile amongst them. It flows from near Rigel in Orion and, as the longest constellation in the heavens, ends at the bright star Achernar. Achernar is one of the brightest stars in the sky at magnitude 0.4. Its name comes from the Arabic Al Anir al Nahr, the ‘End of the River’. A number of the stars of northern Eridanus make up the early nomad's ‘Ostrich Nest’.

The great river starts at lambda Eridani, a magnitude 4.2 B2 sub-giant star. Look for it 1.4° southwest of the blue supergiant star Rigel in Orion. The river meanders gently northward 3.6° to magnitude 2.8 beta Eridani or Cursa. This is an A3 giant star with a magnitude 10.9 companion nearby. Look for the double star 66 Eridani in the same low power field. It lies to the northwest as a magnitude 5.1 white star though a telescope separates the components into magnitude 5.1 and 10.7 pair. The respective spectral types are a B9 dwarf and A1 dwarf.

A photographic opportunity presents itself midway west of a line joining lambda and beta. Here we have the Witch Head nebula, extremely faint visually but possibly picked up with superb seeing conditions and a nebula filter. However, film or a CCD camera will have no problem with this tenuous glow.

Our river now diverts toward the northwest, sweeps past NGC 1700 and cuts across Orion before emerging at mu Eridani. NGC 1700 lies 19'.9 to the north northeast of 62 Eridani. This elliptical galaxy is an easy object for smaller telescopes while apertures in the 30cm range show a bright halo enclosing a small bright core with a definite stellar nucleus.

Eridanus continues westward 2.3° to magnitude 3.9 nu Eridani. This magnitude 3.9 B2 giant star has a faint companion of magnitude 13.3 seen in larger apertures.

Now our river diverts towards the southwest and sweeps up omicron 1 and omicron 2 known as Beid and Keid. Beid comes from the early Arabic Al Baid, the ‘Egg’ because of its apparent white colour and its position near the ‘Ostrich's Nest’. Beid shines at an apparent magnitude of 4.0, an F2 type giant or bright giant star.

Nearby omicron 2 or Keid comes from Al Kaid, the ‘Eggshells’ which have been thrown out of the nest. Keid shines at magnitude 4.4, a light orange K-type dwarf star with two other family members. Sir William Herschel found a second star in 1783, an A2 white dwarf of magnitude 9.5 easily separated from the primary. In 1851, Otto Struve separated the secondary into a close pair, the third star an M4 red dwarf of magnitude 11.1. This is a remarkable system for the telescope, the secondary being the easiest white dwarf star available to the observer.

Plunging further southwestward, we meet the orange giant star Zaurak or gamma Eridani. The name comes from the Arabic Al Na'ir al Zaurak, the ‘Bright Star of the Boat’.

Around 4° east and slightly north lies the beautiful and bright planetary nebula NGC 1535. This small bluish disk was first seen by Sir William Herschel in 1785. Larger apertures under high power will show a magnitude 11.6 central star enclosed by a mottled disk with an outer bright ring.

Around 3.8° to the west of Zaurak lies the galaxy NGC 1421. Even small telescopes will show a needle of light while larger apertures may show some mottling but an obvious nucleus is lacking.

Once again, mighty Eridanus flows northwest, past the red giant star pi to Rana or delta Eridani. Rana presents an orange face to the telescope. Turning west, we flow past magnitude 3.7 epsilon, magnitude 4.8 zeta (Zibal) before reaching eta (Azha) at magnitude 3.9. Here the river changes course toward the south, plunging down the heavens in a great torrent of white water and rapids.

Moving 10° south and slightly west of eta we discover tau 1, a magnitude 4.5 F-type pale yellow dwarf star. Here we take a small diversion to a grouping of faint galaxies around 5.5° to the northeast. NGC 1172 is the most northerly galaxy here. Easy in a 25cm telescope, it appears as a faint round glow with a brighter middle region. Look for it west south-west of a magnitude 9.5 star.

Around 55' to the south-east lies NGC 1199, an elliptical galaxy which appears rather small with a stellar nucleus at high power. It is the brightest of a surrounding small group of even fainter galaxies which need an aperture in the 40cm range to see.

Directly east of NGC 1199 by around 35' is NGC 1209, the brightest galaxy in this immediate area. A 30cm telescope shows a double nucleus enclosed within an extended halo.

Moving back to tau 1, we seek out one of the better galaxies in Eridanus. NGC 1300 lies 8.2° east and slightly to the south. Here is a classic example of a barred spiral galaxy, the bar easily seen in a 20cm telescope as an elongated line with a slightly brighter middle. Larger telescopes in the 40cm range should show detail in the surrounding halo in the way of mottling. Also evident with larger telescopes on excellent nights are dim spiral arms. A faint companion, NGC 1297 lies close by.

Moving southeast of tau 1 by 2.8° brings us to magnitude 4.8 tau 2, a K-type orange giant called Angetenar. It comes from Al Hinayat al Nahr, the ‘Bend in the River’. Another 3.7° in a south easterly direction finds 4.1 magnitude tau 3, an A-type dwarf star near the border with Fornax. Around 47' to the north lies NGC 1187, a barred spiral galaxy which shows a little mottling with a brighter central region. This one needs larger apertures to see well.

From tau 3, the river piles up against the bank of Fornax before diverting to the north-east to magnitude 3.7 tau 4. This is a red M-type giant star with a close magnitude 9.5 companion of spectral type K0 V.

To the northwest by 2.5° brings us to the lovely face-on spiral galaxy NGC 1232. Even a telescope of 30cm aperture will start to show detail including mottling of the disk and perhaps several H II regions as well. These H II gas clouds are similar in type to the Orion Nebula, a larger aperture showing them with ease.

Eridanus flows eastward to magnitude 4.5 tau 5. Halfway along and north of a line joining tau 4 and tau 5 lies the lenticular galaxy NGC 1332. This glow is elongated east-west and has a brighter core with a tiny bright stellar nucleus. The faint galaxy NGC 1331 lies only 2.8' to the eqst-southeast. Very close to tau 5, just 9'.4 to the north is the Sc spiral galaxy IC 1953. It appears as a large and faint glow of light with a brighter middle in medium apertures. Use high power to put tau 5 out of the field as the star's light tends to overwhelm the galaxy.

Now Eridanus heads to the southeast towards tau 6, passing four galaxies aligned north-east southwest. The brightest of this gathering is NGC 1395, easily seen in a 25cm aperture. Within the halo is a brighter central region with a stellar nucleus. From here, we drop to tau 7 and tau 9 before taking a great leap southeast to the K-type orange giant star upsilon 1.

Leaving upsilon 1, we reach upsilon 2, a magnitude 3.8 G-type giant star. Also known as Theemin or Beemin, it marks the start of our rough water ride southwest to upsilon 4, a magnitude 3.5 B9 dwarf star. Just 1.5° to the north-west lie a nice pairing of galaxies, NGC 1531 and NGC 1532. Use 100x power or greater to see these two easy spiral systems. NGC 1532 is the brighter of the duo, appearing as an elongated streak with an obvious nucleus. A medium aperture, with care, will show several H II regions which trace the spiral arms. NGC 1531 is aligned more face-on but shows no detail.

The river continues on its south-westward dash, tumbling down the sky to a magnitude 4.6 orange giant star 10.4 degrees distant. Bisecting the constellations of Horologium to the east and Fornax to the west, it moves 7.4° westward to theta 1 Eridani, commonly called Acamar. Here we have a beautiful magnitude 3.4 and 4.5 pair easily resolved. Drift 3.4° further west to magnitude 4.1 iota, an orange giant.

Next lies magnitude 4.2 kappa, 8.2° to the south south-west, magnitude 3.6 phi a further 4.1°, then the river momentarily heads west to magnitude 3.7 chi. Finally, Eridanus plunges 6.2° to magnitude 0.4 Achernar, the brightest star of this constellation and the end of our journey. Achernar is derived from Al Anir al Nahr, the ‘End of the River’.

Great to see that you have arrived safe and well and time to set up camp and dwell on some of the other surrounding summer constellations nearby.

Clear skies and good hunting ~ CosMos