Solar System

(The Twins)

Gemini is a very well known constellation due to being one of the signs of the zodiac. It represents the two twins Castor and Pollux, these are also the names of the two brightest stars. The stars of Gemini are fairly bright so the constellation is easy to find in the sky near Orion and Taurus.

In Greek mythology, Castor and Pollux were the children of Zeus and Leda. Throughout their remarkable lives they had many adventures including riding along on the Argo Navis with Jason. They once saved the Argo Navis from sinking during a strom, because of this sailors found Gemini to be a good omen if it was in the sky.

Gemini is similar to another sign of the zodiac, Aquarius, as not one but two of the planets were discovered while they were in this constellation. Uranus was discovered by William Herschel in 1781 and Clyde Tombaugh found Pluto in 1930.

The constellation is home to numerous planetary nebulae as well as a supernova remnant.


Glittering like a swarm of fireflies in the fading embers of the summer sun, M35 is an incredibly populous open cluster of 700 blazing furnaces with more than a hundred stars being brighter than magnitude 13. In fact the cluster is so bright it can be glimpsed with the naked eye as a misty patch in a dark winter sky.

Complementing the blue glow of M35 is the golden cluster of stars, NGC 2158. This requires a telescope to be seen as it is considerably fainter and is also five times more distant than M35’s distance of 2800 light years. Besides being more distant than M35, it also contains more stars than M35 and was once mistaken for a globular cluster.

As well as major differences in distance and stellar populations, another difference between both clusters is their ages. M35 is relatively young at 100 million years but is slowly on its eventual decline into old age as there are a few red giants in the cluster. In utter contrast, NGC 2158 has existed for a billion years, the golden brown light of its stars is testament to this.
Eskimo Nebula (NGC 2392):

There are two conventions for naming astronomical objects. One is to name something after its resemblance to something. The second one is naming an object after its discoverer.

This popular planetary nebula gets its name from having a resemblance to an Eskimo! It arises from the double shell structure which consists of a small inner shell that represents the face and a thick outer shell that represents the fur parka hood.

The outer shell is rife with bizarre comet shaped structures, these are cometary knots that are also found in other planetary nebulae such as the Helix Nebula in Aquarius. The inner shell appears to be incredibly strange with a structure that can only be described as multiple bubbles overlapping. The theory is that they were formed by the collision of gases from two separate fronts that were moving at different speeds. Also it is likely that the pole of the planetary nebula is the part that faces us.

Although it can be seen in small telescopes, larger apertures are necessary to do this amazing nebula justice. The angular size is fairly small because the nebula lies at a distance of 3000 light years. It is also known as the Clownface Nebula for obvious reasons and was discovered in 1787 by William Herschel who also discovered Uranus six years earlier.

Jellyfish Nebula (IC 443):

Twisting its tendrils into the darkness of space, the Jellyfish Nebula is a supernova remnant that was formed by the shock front of a supernova that exploded 30 000 years ago. The shock front collided with a molecular cloud causing the molecular gas to be ionized and glow with HII emission. This HII gives it the deep red colour seen in photographs.

Because of the dynamical nature surrounding its formation, the remnant blazes in the x-ray and infrared wavelengths. This suggests it is incredibly energetic and might induce star formation in the molecular cloud.

The Jellyfish Nebula is the third brightest supernova remnant after the Crab Nebula in Taurus and the Veil Nebula in Cygnus. Even though it is fairly bright, it is still difficult to see and it was discovered photographically.

To the left of the Jellyfish Nebula is the almost equally sized emission nebula,
IC 444. This nebula has a few elongated dark patches that are probably closer than the nebula. Above and between IC 444 and the Jellyfish Nebula, sparkles a small blue reflection nebula called vdB75.

Jellyfish Nebula

A cosmic creature or a supernova? The Jellyfish Nebula shares more than a resemblance with its namesake, it is also deadly to any intergalactic explorers as it emits a wide multitude of radiation that would vaporise your body!

Near the centre lies the mysterious form of a pulsar, a type of star that spins at a dizzying rate of 30 000 times a minute! Pulsars are an evolved form of neutron stars, a type of star that crams the mass of a normal star into the space of a mountain! They are exotic objects that are incredibly dense, a piece the size of a rock would weigh as much as a mountain range! The pulsar isn't visible in this picture.

Click the image for a psychedelic false colour version by
Russell Croman

Image copyright D. Salman
NGC 2266:

Old is an underestimation when describing the age of this open cluster, it is positively ancient at an impressive billion years. Even though it is as old as
NGC 2158, it contains a surprising number of blue stars that accentuate the redness of the old red giant stars.

Overall, the shape of the cluster is triangular with many of the stars forming various interlocking patterns. A fun way of observing this cluster is trying to make as many different chains as possible with your mind, there are dozens of variations and each observer would see different patterns as each person's mind perceives what they see differently to others.

Medusa Nebula (Abell 21):

Looking at this planetary nebula will not turn you to stone, but you might feel as if you have when you find yourself enraptured by the wispy tendrils that gives the object its name. Despite being the brightest Abell planetary nebula, it still glows at an elusive magnitude of 10.3 that contributes to its dimness. Finding it isn't too much of a chore, it lies near the bright open cluster NGC 2395.

Initially thought of as being a supernova remnant, it was found to be a planetary nebula due to the lack of a neutron star that usually lies in the middle of supernovae. One trait it shares with other Abell planetaries besides the faintness is a thin shell that allows background galaxies to be visible. Suffice to say, they can only be seen in photographs taken with large telescopes. The alternative designation of PK 205+14.1 is usually the label for the Medusa Nebula in star charts.

NGC 2371-2:

A ghostly planetary nebula, it is fitting that NGC 2371-2 is found in Gemini as it consists of two lobes around a 14th magnitude central star. Because of this unreal structure, some observers call this the Gemini Nebula or Twin Nebula.

It is one magnitude fainter than the Medusa Nebula yet it is easier to see due to it being smaller and the light being more concentrated as opposed to being spread out across a large area. Some observers have even seen it in small telescopes!