Solar System

(The Water Bearer)

One of the aquatic constellations, Aquarius is a large and interesting constellation. It is southern but can be seen from northern latitudes during autumn. It contains many interesting and bizarre galaxies and also the coruscating planetary nebula known as the Helix Nebula.

The constellation also holds some unexpected relations with the Solar System. Firstly planet Neptune was discovered in this constellation in the autumn of 1846. Secondly there are many meteor showers in this constellation. Some of these include the Iota Aquarids in May and the Eta Aquarids in August.
  Helix Nebula  
    The Helix Nebula is the colourful remains of a dead star.
Image copyright R. Jay GaBany
    This is a fairly bright globular that looks spectacular in larger telescopes. It might be possible to glimpse it with the naked eye in an extremely dark sky and can be found north of the star Beta Aquarii. The stellar population is exorbitant with approximately 150 000 stars and the arrangement is slightly elliptical.
    Helix Nebula (NGC 7293):

The blazing remnants of a dead star, the Helix Nebula is a scintillating planetary nebula that is a mere 450 light years away. Because of its short distance, the apparent size is quite large. Although not very apparent when looking at it, the structure is quite chaotic and ordered. The main pink part consists of outer and inner rings.

The aquamarine part contains bizarre structures called cometary knots. Just as planetary nebulae have nothing to do with planets, cometary knots are unrelated to comets. Their name arises from their visual appearance with a head and tail morphology. They are found near the edge of the inner circle and their tails point away from the central star.

Saturn Nebula (NGC 7009):
This nebula is probably the nebula that inspired the name for the type that it is, which is planetary. Through a small telescope, it actually does look like planet Saturn with two elongated areas attached to a central sphere. These two extensions are known as ansae and are produced by the stellar winds from the central star causing nebular material to coalesce into two opposing bi-polar detachments. Telescopes with large apertures have the resolving power to reveal detail in the central sphere, what can be seen is series of overlapping shells.
NGC 7184:
114 million light years is the unbelievable distance to this fairly large tightly wound spiral galaxy. Since it is very distant, the features of the surface are less apparent but they include multiple dust lanes that require a telescope with a large aperture to be seen.
NGC 7606:
A tightly wound spiral galaxy, this one is the brightest in Aquarius. It lies at a long distance of 90 million light years and it can be found near the star Phi Aquarii.
Atoms for Peace Galaxy (NGC 7252):

The name for this galaxy comes from the shape of it, it is an elliptical galaxy with loops of gaseous material encircling it just like an atom. The structure is a result of a merger and if this sounds unbelievable, then the proof is that there are many blue globular clusters in the central part. Normally globular clusters are red with old stars but that is not the case here. The merger caused the galaxy to give birth to new clusters that were arranged in a globular shape.

A copious amount of 500 globular clusters was discovered by the HST as well as one of the most luminous globulars. This ultra luminous globular is only between 300 and 500 million years old making it very young on the galactic scale. Due to its bizarre nature, the Atoms for Peace Galaxy is also referred to as Arp 226.

R Aquarii Nebula (Ced 211):

At the heart of this celestial oddity lies a pair of stars, a hot white dwarf and a cool red giant. This type of pairing is known as a symbiotic star and they are extremely rare, only 200 reside in the Milky Way.

What is happening is that the white dwarf is sucking matter from the red giant in a vampiric fashion and some of this matter is thrown upwards to form loops of red nebulosity that enshroud the stellar pair. The nebula is extremely faint and very difficult to observe visually and is best seen by long exposure astrophotography with a large telescope. The nebula has two components, an inner rectangular shell and an outer elliptical nebula. Both are centered on the star suggesting that both parts were produced by separate outbursts, hundreds of years apart.

Historical records that date from 930 AD, Japan, indicate the star might have had a nova outburst that made the star appear brighter in the night sky. This outburst might have been responsible for the creation of the shell of nebulosity.
More recently, observations in the 1970's have proved the existence of a knotted jet that might be the result of mass being accreted from the white dwarf. As well as this optical jet, there is a second radio jet that was first detected in 1982.

The letter 'R' indicates that the star is variable. The brightness of variable stars fluctuate in regular patterns, they can become as bright as planet Mars and go down to telescope only visibility in a matter of days. The period of variability for each variable star is different and can range from a few hours to many decades. Variable stars are designated a letter and famous ones include Mira in Cetus and Eta Carinae in Carina. The period of R Aquarii's variability was first discovered in 1811 and was found to be a little over one year.

The Cederblad catalogue is comprised of 215 nebulae, mainly of the reflection type. The catalogue was compiled in 1946 by Sven Cederblad and the most prominent Cederblad nebula is Ced 214 in Cepheus and surprisingly is an obscure object as it is a difficult visual object but is popular with imagers, especially ones who specialise in h-alpha imaging.

Arp 295:

A pair of very faint galaxies that are undergoing a strong interaction phase. They are located 270 million light years away, which seems very distant as there are some galaxy clusters that are closer than this pair of galaxies. The interaction will result in both galaxies merging into one single galaxy that will be larger than either one. This is a very common part of galaxy evolution.

The effect of the gravitational influence between the two galaxies is so intense that a massive tidal bridge is currently connecting them together. The bridge is 250 000 light years long and it extends beyond the southern galaxy.

The word bridge would seemingly signify that something is transferred between the two galaxies. The truth is that nothing is transferred between galaxies that are connected by tidal bridges just as planetary nebulae are completely unrelated to planets.

The northern galaxy is a spiral that has a quite strange attribute, it is rotating in the opposite direction to the southern edge on galaxy! Another difference between the two is that the spiral has more gas as well as a more prodigious rate of star formation, this can be seen as knotty HII regions attached to the spiral arms.

Hickson 88:

A compact grouping of four spiral galaxies that are extremely faint, Hickson 88 is best suited to large apertures. Three of the galaxies, NGC 6978, NGC 6977 and
NGC 6976 are in one line with the fourth galaxy slightly separated from the triplet. This galaxy, NGC 6975 has an edge on orientation as opposed to the other three having a face on orientation, with NGC 6977 having a barred spiral structure and being the brightest at magnitude 14.

Altogether there are 100 Hickson groups of galaxies and they were compiled by the Canadian astronomer, Paul Hickson, in 1982. The criteria for inclusion was that the group had a minimum of four member galaxies. Some of the Hicksons have six or seven members! The number of galaxies in all 100 of the Hickson groups adds up to approximately 500. A common factor of many of them is a discordant redshift, one galaxy in the group isn't a physical member of the group and happens to share the line of sight with the other galaxies. Groups that consist of this include Stephan's Quintet in Pegasus and Seyfert's Sextet (Hickson 79) in Serpens.

The Hickson catalogue is ideal for advanced observers to quench their thirst of a challenge as many are on the threshold of visibility.
The most prominent are Hickson 44 in Leo, the aforementioned Stephan's Quintet (Hickson 92) and Copeland's Septet (Hickson 57) also in Leo. Other attractive groups include Hickson 87 in Capricornus and Hickson 68 in Canes Venatici.