Star Constellations: Aquarius the Water Carrier.
Created | Updated Mar 16, 2008
| Latin: | Aquarius |
| Genitive: | Aquarii |
| Short form: | Aqr |
| Area: | 980 square degrees |
| Co-ordinates: | 22.5h, -5.00° |
| Zodiac: | Yes |
| Origin: | Ancient |
Aquarius the Water Carrier is at its most prominent during the autumn months. It can be located just south-west of the more obvious Great Square of Pegasus and lies between Pisces and Capricorn along the path of the ecliptic1 where it is the eleventh sign of the zodiac2. It shares borders with Aquila the Eagle and Capricorn the Sea Goat to its west and Cetus the Whale to its east. This is a star-poor area of the sky, but due to the predominance of these and other constellations that are associated with water, this area has in the past been referred to as 'the Sea'.
History/Mythology
Aquarius is an ancient constellation. The earliest known representation of Aquarius is on stones from the time of the Babylonians, showing a man or boy pouring water from an urn or bucket and with towel in hand. Clearly he was one of the first hitchhikers and knows where his towel is. For the Egyptians, Aquarius was associated with the all important annual flooding of the Nile and Khnum their god of water. The symbol used for Aquarius even by modern day astronomers is the Egyptian hieroglyph, a pair of parallel undulating lines signifying the waves of a river.
We now associate Aquarius with the story from classical Greek mythology of the youth Ganymede who was taken by the eagle Aquila to Mount Olympus to be the cup bearer to the gods. Aquarius was one of the 48 constellations listed in Ptolemy's Almagest. The illustration in Johannes Hevelius' 1690s star chart Uranographia shows a kneeling youth pouring water or wine from an urn, which becomes the source of the celestial river Eradanus.
Principal Stars
Aquarius is not a prominent constellation as none of its stars are brighter than magnitude 2.9 and there are only about 20 other stars brighter than fifth magnitude. Many of the Arabic names of the stars show the concept of good luck to be included in their meaning. This reflects the good fortune brought by the rainy season which accompanies the sun passing through the constellation . If you ever feel the need to wish upon a star, one of these would be a good choice.
Alpha Aquarii, Sadalmelik, meaning 'Lucky one of the King', is a magnitude 2.96 pale yellow star and is the second brightest in the constellation, where it marks the right shoulder of Ganymede.
Beta Aquarii, Sadalsuud, is the 'Luckiest of the Lucky', and is the brightest in this constellation. It is so named from its rising with the sun heralding the end of winter and the start of the long period of gentle continuous rain of the rainy season.
Gamma Aquarii, Sadachabia The name means 'Lucky Star of Hidden Things' which refers to those creatures that come out of hibernation at the end of winter.
Delta Aquarii, currently known as Skat, but formerly named as Scheat by Tycho Brahe. Probably meaning 'A Wish'. or possibly the 'Shin Bone' from its location on the body of Ganymede.
Zeta Aquarii, is a double star whose constituents are separated by about 2 arc seconds. They can be separated with a small telescope, both are white and revolve around one another in a period of some 850 years. Gamma, Pi, Zeta and Eta Aquarii form the asterism which is the water jar carried by Ganymede. All four of these stars are around fourth magnitude and are predominantly orange in colour.
R Aquarii, is a Mira-type variable star which, over the space of just over a year varies in brightness from a dim magnitude 11 to a magnitude of six. It is unusual in that it has a dwarf companion and is surrounded in nebulosity which is thought to be the result of an exchange of mass between the two.
| Star | Designation | Name | Brightness (m) | Distance (light-years) | Remarks |
|---|---|---|---|---|---|
| α Aqr | Alpha Aqu | Sadalmelik | +2.96 | 950 | Yellow supergiant |
| β Aqr | Beta Aqu | Sadalsuud | +2.91 | 980 | Yellow supergiant |
| γ Aqr | Gamma Aqu | Sadachbia | +2.91 | 180 | A Class |
| δ Aqr | Delta Aqu | Skat | +3.27 | 98 | Orange |
| ζ Aqr | Zeta Aqu | Unnamed | +4.4 | 98 | White binary |
Clusters and Nebulae
The boundaries of Aquarius contain three Messier objects. M73 is a Y-shaped group of stars and is an unusual object among those listed by Messier. In fact, as clusters of stars go it is so insignificant it is often wondered why it was included in his list at all. It is also NGC 6994 on the New General Catalogue. None of the stars are associated with any of the others, their apparent closeness is just a line of sight effect. M2 and M72 are both globular clusters. These are tight balls of stars and are some of the oldest features of the galaxy. M2 is one of the finest in the northern sky and has been described as a magnificent ball of stars which appears in binoculars as a fuzzy patch. It can be found about half way between Alpha and Beta Aquarii. M72 is much less bright and less compact. It requires a moderate telescope to be seen and is relatively unimpressive.
There are two well known planetary nebulae in Aquarius. Planetary nebulae were named by Sir William Herschel because of their disc-like appearance which can resemble planets. These are stars which are in their final stages of evolution from red giants to white dwarfs and are giving off a shell of dust and gas which is illuminated by the central star.
NGC 7009 The Saturn Nebula, when seen through a telescope appears as a small blue-green dot with an asymmetric appearance. It was discovered by Sir William Herschel in 1782 but named in 1850 by Lord Rosse who observed the extensions to either side of the disc which give the appearance of the planet Saturn when its rings are presented side-on.
NGC 7293 , the Helix Nebula is brighter overall but is spread out to about half the diameter of a full moon. It appears large because it is quite close to us, and in fact it is the closest planetary nebula to Earth. It requires a low power telescope and near perfect viewing conditions to observe. It resembles a dim smoke ring and photography reveals the helix shape to the outer ring.
| Catalogue No | Type | Brightness (m) | Distance (lightyears) | Remarks |
|---|---|---|---|---|
| M2 | Globular cluster | +6.5 | 37,000 ly | Contains apprx 100,000 stars |
| M72 | Globular cluster | +9.3 | 56,000 ly | Low luminosity |
| M73 | Cluster | +10.5 | 2,500 ly | Y shaped asterism of 4 stars |
| NGC 7009 | Planetary Nebula | +8.3 | 2,400 ly | Saturn Nebula |
| NGC 7293 | Planetary Nebula | +6.5 | 700 ly | Helix Nebula |
Meteor Shower
If the tracks of a number of meteors can be traced back to a common point of intersection, they are named from the star nearest to that point. Aquarius is host to four of these minor meteor showers through the year. The streak of light of the shooting star is caused by small specks of dust which burn up from friction with the air in the upper reaches of the Earth's atmosphere. The dust is usually from the trails of comets that have crossed the Earth's orbit leaving debris behind them.
The March Aquarids occur between 11-16 March and are predominantly hidden during daylight hours. They were originally detected in 1961 by Radar methods. Eta Aquarids are the predominant shower of the year visible between 21 April to 12 May. They reach a maximum hourly rate of around 20 in the northern hemisphere and 50 in the southern.
The Delta Aquarids can be observed between 15 July to 15 August, when they reach a maximum rate of ten per hour. They appear to be quite slow with long lasting tracks. The Iota Aquarids fall between 15 July to 25 August but are not very prominent.
Dawning Aquarius
On the 25 September, 1756 the astronomer Johann Mayer noted a fixed 'star' near Delta Aquarii. He recorded it and forgot about it. Sometime later, the first English Astronomer Royal, John Flamsteed, spotted it again in the constellation Taurus, gave it a number and recorded it in his new star catalogue as 34 Tauri. He also then presumably forgot about it. Some 25 years after Mayer's observation Sir William Herschel observed it again near H Geminorum on 13 March, 1781 and recognised it first as a comet, but later as a new planet. This was the first planet to be recognised in modern times and was eventually named Uranus.
When calculating Uranus' orbit it did not however, conform to its predicted position in the sky. Working independently, two mathematicians John Couch-Adams in England and Urbane Le Verrier in France, calculated that the reason that it wasn't quite where it was supposed to be, must be because another body was causing perturbations3 to its orbit. Working from data supplied by Le Verrier, astronomers Johanne Galle and Henrich D'Arrest of the Berlin Observatory identified another new planet even further out. The new planet, named Neptune, was discovered within the boundaries of Aquarius on 23 September, 1846. Within a space of 65 years the diameter of the solar system had effectively been more than tripled.
During the 1960s the hippy-culture, stage musical Hair made popular a song titled 'Aquarius/Let the Sun shine in' in which it was asserted that This is the dawning of the age of Aquarius. In astrological terms this was thought to be the beginning of a new age of enlightenment and understanding at the change of the millennium. In astronomical terms it is meaningless. It will be another six hundred years or so before the Earth's precession brings the Vernal Equinox, that is the point at which the Sun appears to cross from the southern to the northern hemisphere each year, within the boundaries of Aquarius, when 'the Age' can then be said to begin.
