Overview: NGC 1360 is a planetary nebula that lies in the direction of the constellation Fornax, the furnace. Fornax is a modern constellation named by the French astronomer Nicolas Louis de Lacaille in the 18th century. Surrounding Fornax is the constellation Eridanus which in contrast is one of the original 48 constellations named by the Greco-Roman astronomer in the 2nd century AD. NGC 1360, also known contemporarily as the Robin’s Egg Nebula, has been identified as a planetary nebula due to its light emission in oxygen bands (OIII) of the visible spectrum resulting in its strong blue color.

Details: NGC 1360 was discovered in 1868 the German astronomer, Friedrich August Theodor Winnecke, who was primarily searching for comets. Comets have orbits around the sun causing them to move against the background stars, therefore, he cataloged fixed objects such as NGC 1360 to prevent mistaking them for comets.

Central Star: Clearly visible in the middle of the nebula is the blue-green central star. Since 1977, this central star has been suspected of being a binary star consisting of two stars gravitationally bound to each other and orbiting one another. Forty years later and confirmed in 2017-18, the central binary star consists of both an unsual low-mass O-type star and a white dwarf. The white dwarf is what caused the cloud of oxygen rich gas with a relatively gentle process of sluffing off its outer layers until only a dense earth-size dwarf star remains, in this case, with 0.7 times the mass of our sun. The O-type star was apparently minimally impacted by this expulsion of gas, although it is unusualy that an O-type star has such a small mass at 0.5 times the mass of our sun. Typical O-type stars are 20 times or more the mass of the sun.

Surrounding NGC 1360’s blue nebula are fragments of reddish material believe to have been ejected from the white dwarf star before it began to expel its outer shells forming the blue nebula. Of particular note are the jets of red material at either ends of the long edge of the elongated nebula. This red material is primarily ionized hydrogen emitting light in the red hydrogen-alpha (Hα) emission line. This is in contrast to the nebula’s blue light emitted in the oxygen III (O3) emission line. Note the seemingly smooth and relatively homogeneous nature of the bluish cloud of gas from its central star to the edge of the nebula. Normally, planetary nebulae have shells of gas with a central void area as is evident in M57, The Ring Nebula! The void is evidence of a stellar wind pushing the shells away from the central star. However, NGC 1360 shows no evidence of such shells. Visible in the blue cloud of the expanding nebula are darker clumps of denser, cooler gas and dust that block light from the brighter, OIII ionized gas behind them. These “knots” are referred to as low-ionization structures (LIS).

The distance to NGC 1360 is between 1200-1800 light years and with dimensions of 11 by 7.5 minutes of arc, it is about 30 by 20 light years in size. It expands at a rate of 20-40 kilometers per second and, assuming a constant expansion, originated about 300,000 years ago when the white dwarf began dissipating vast amounts of material into space!

Annotations. In the image above, hover a mouse or curser over the image to show annotations of the Robin’s Egg Nebula, with several enlarged insets identifying interesting features! Clicking on the image displays a full screen view of the nebula without animations that can be zoomed in further as desired. Starting on the far left are two enlarged insets of distant galaxies PGC 776482 and 775793, while on the far right is distant galaxy pair PGC 778645 and 778674. Upper center of the image and proceeding clockwise are the jets of hydrogen and nitrogen emitted by the central star, now and white dwarf, likely before the blue shell was formed. Likewise, ther can be seen small red knots of material all around the edges of the nebula, particularly at its visual bottom. Proceeding clockwise is an enlarged inset of the central star, noting that the bright cross-like spikes are cause by the telescope and not the object itself. Finally, is an enlarged inset of distant spiral galaxy PGC 775013. Viewing the blue nebula closely, visible through its center are more distant galaxies and stars seemingly with a blue cast due to the nebula acting as a blue filter.

Below Images: The image below is the same image as above but processed to remove all stars except for the central star that belongs to the nebula. Using a mouse to hover over the image brings all the stars back. Finally, the last image below is a zoomed in version of the nebula with and without stars!

Object Statistics: Constellation: Sculptor, Right Ascension: 03h 33m 14.6s, Declination: -25° 52' 18”, Apparent Magnitude: 9.4, Size: 11’.0 x 7’.5 (30 light-years diameter), Distance 1200-1800 light-years.