Solar System

(The River)

The source of this galactic river lies adjacent to the star Rigel in Orion and its meandering form is concluded by the bright star Achernar. Quite aptly, Achernar is the Arabic word for 'end of river'.

The whole constellation is the sixth largest in the sky with Hydra being the largest. Despite its considerable size, there seems to be a lack of bright stars but it is still easily located in a dark sky as the river lies between the two bright stars, Rigel and Achernar.

Deep sky objects in Eridanus consist mainly of spiral galaxies but there are some examples of stellar death such as NGC 1535 and the reflection nebula, the Witch Head Nebula.

  NGC 1300:   Barred spiral NGC 1300

Probably the most spectacular barred spiral galaxy in the sky, NGC 1300 joins many other southern barred spirals as vying for the place of the greatest barred spiral. It is curious that many of the most exquisite barred spirals are found in the southern sky.

It is a massive galaxy and even at its 75 million light year distance, it is still quite large through amateur scopes. The dimensions of the galaxy even exceed our home galaxy, the central bar is longer than the Milky Way at an incredible length of 150 000 light years!

Dark brown rivers of dust flow through the centre of the two spiral arms. Many star clusters are found at the parts where the arms originate from the bar, it is likely that some are super star clusters.


Quite possibly the greatest barred spiral galaxy in the sky, NGC 1300 is a truly magnificent example of its type. The majestic blue spiral arms wrap enigmatically around a golden summery bar of ancient stars where the dark morass of a supermassive black hole churns violently.
Once you have sampled the insouciant delights of NGC 1300, you will never forget why you fell in love with the night sky in the first place!

Image copyright R. Jay GaBany
    Witch Head Nebula (IC 2118):

Casting her venomous gaze at the heroic Rigel, it almost seems as if this stellar witch is concealing herself with an invisibility cloak as it is difficult to see the silhouette of the witch against the dark blue nebula. The witch's head is more easily seen in images that are rotated 180 degrees.

The silhouette of the witch head is caused by stellar winds that might emanate from the nearby Orion OB association. In fact a star of Orion, Rigel, is responsible for illuminating the gas and dust. The blue colour is a direct influence of Rigel's intense colour and another contributor is that the dust reflects blue light more efficiently than any other colour.

NGC 1535:
NGC 1535 is an aquamarine planetary nebula floating amongst the majestic galaxies that dwell within the gushing river that is Eridanus. It has a highly luminous blue dwarf at the centre and an outer halo that tends to be a characteristic of many other planetary nebulae. The glowing shell is punctured by multiple voids, these are illusions caused by the gas being thinner in some areas. This very popular planetary is nicknamed 'Cleopatra's Eye' and is a firm favourite of many astronomers including Adam Block.
NGC 1232:
With many spiral arms streaming from the core, NGC 1232 is a magnificent grand design spiral galaxy that is only 5 million light years closer than NGC 1300. Instead of curving gracefully around the core, the spiral arms are slightly bent due to a small companion galaxy that is gravitationally interacting with NGC 1232. Because of this peculiar behaviour, NGC 1232 is also Arp 41.
NGC 1531-2:
These two galaxies are currently engaged in a ferocious game of gravitational tug of war. NGC 1531 is a small dwarf galaxy that is promoting a high unusual rate of star formation in the adjacent edge on spiral galaxy, NGC 1532. If this pair could be viewed face on, it might resemble the more familiar Whirlpool Galaxy.
Lo 1:

A planetary nebula that is more obscure, larger and fainter than the classic
NGC 1535. An OIII filter greatly increases visibility but astrophotography is the best way to see the green disk. Near the top, the gas is interacting with the interstellar medium and a bright shock front is apparent. This is reminiscent of limb brightening found in other planetaries.

The central star is bright blue and the thinning of the gas allows background galaxies to be visible through it, this is a trait shared with other obscure little known planetary nebulae such as PK164+31.1 in Lynx and Abell 36 in Virgo.

This object is found near the border with Horologium towards the middle of the vast river that is Eridanus. Fortunately there are no bright stars in the vicinity to overwhelm it with unwanted glare but as a downside, the faint stars might be challenging to use as stepping stones to find it. This planetary nebula was discovered in 1971 by Lubos Kohoutek.

Witch Head Nebula    

The Witch Head Nebula is an ominously shaped reflection nebula. Using your imagination, the gruesome visage of a witch can be seen!

The nebula shines by reflecting the light of the blue supergiant star Rigel in the neighbouring constellation of Orion. In addition to the dust reflecting starlight, towards the south are opaque patches of brown dust.

Looking more closely, very faint red emission nebulosity can be seen surrounding the nebula, this is revealed due to the image containing exposures taken through a hydrogen-alpha filter.

Image copyright G. Ratto