Constellations: Aquarius 'the Water Carrier' Content from the guide to life, the universe and everything

Constellations: Aquarius 'the Water Carrier'

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The shield of the Science, Mathematics and Engineering faculty of the h2g2 University.Constellations: Overview | Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga | Boötes | Caelum
Camelopardalis | Cancer | Canes Venatici | Canis Major | Canis Minor | Capricornus | Carina | Cassiopeia | Centaurus
Cepheus | Cetus | Chamæleon | Circinus | Columba | Coma Berenices | Corona Australis | Corona Borealis | Corvus
Crater | Crux | Cygnus | Delphinus | Dorado | Draco | Equuleus | Eridanus | Fornax | Gemini | Grus | Hercules | Horologium
Hydra | Hydrus | Indus | Lacerta | Leo | Leo Minor | Lepus | Libra | Lupus | Lynx | Lyra | Mensa | Microscopium | Monoceros
Musca | Norma | Octans | Ophiuchus | Orion | Pavo | Pegasus | Perseus | Phoenix | Pictor | Pisces | Piscis Austrinus
Puppis | Pyxis | Reticulum | Sagitta | Sagittarius | Scorpius | Sculptor | Scutum | Serpens | Sextans | Taurus
Telescopium | Triangulum | Triangulum Australe | Tucana | Ursa Major | Ursa Minor | Vela | Virgo | Volans | Vulpecula
Latin:Aquarius
Genitive:Aquarii
Short form:Aqr
Area:980 sq deg
Co-ordinates1:Right Ascension 23h, Declination −15°
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 Capricornus along the path of the ecliptic2 where it is the 11th sign of the zodiac3. It shares borders with Aquila the Eagle and Capricornus 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 Ganymede4 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 Eridanus.

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 5th 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, 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 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 two 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.

Psi, phi, tau and delta Aquarii form the asterism which is the water jar carried by Ganymede, with lambda Aquarii representing the hand. All of these stars are around 4th magnitude and, except for delta Aquarii, 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 much brighter 6th magnitude. This 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 Table

StarDesignationNameBrightness (m)Distance (light years)Remarks
α Aqralpha AquSadalmelik+2.96750Yellow supergiant
β Aqrbeta AquSadalsuud+2.91680Yellow supergiant
γ Aqrgamma AquSadachbia+2.91160A Class
δ Aqrdelta AquSkat+3.27142A Class
ζ Aqrzeta AquSadaltager+3.6598Binary star system

Clusters and Nebulae

The boundaries of Aquarius contain three Messier objects. M73, also NGC 6994 on the New General Catalogue, 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. 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 the final stages of their 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 is the Saturn Nebula, when seen through a telescope it appears as a small blue-green dot with an asymmetric appearance. It was discovered by Herschel in 1782 but named in 1850 by Lord Rosse, who observed the extensions to either side of the disc which gives 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.

Clusters and Nebulae Table

Catalogue NoTypeBrightness (m)Distance (light years)Remarks
M2Globular cluster+6.537,000Contains over 100,000 stars
M72Globular cluster+9.356,000Low luminosity
M73Star cluster+10.52,500Y-shaped asterism of four stars
NGC 7009Planetary nebula+12.82,400Saturn Nebula
NGC 7293Planetary nebula+13.5700 lyHelix Nebula

Meteor Shower

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. 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 throughout the year:

  • 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 from Halley's Comet trail and 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.
  • 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.
  • Iota Aquarids fall between 15 July to 25 August but are not very prominent.

Two New Planets

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 near H Geminorum on 13 March, 1781, and at first thought it a comet, but later recognised it 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 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 perturbations5 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, now 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.

Extrasolar Planets

Several stars in Aquarius have been found to have planets in orbit, including the local star Gliese 876 which is just 15 light years away. An artist's impression of Gliese 876 d features on the Astronomy Picture of the Day website, and its discovery was given a mention on the BBC news, as it is one of the (so far) very few terrestrial planets found.

Extrasolar Planets Table

Star name or
catalogue number
Planet
catalogue number
Planet mass
(Jovian scale)
Orbital period
(Earth days)
Year of discoveryComments
Gliese 876Gliese 876 b2.2612000Hot Jupiter
Gliese 876Gliese 876 c0.7130.32000Hot gas giant
Gliese 876Gliese 876 d0.0211.942005Super Earth
Gliese 876Gliese 876 e0.0461242010Gas giant
HD 222582HD 222582 b7.75572.381999Superjovian/
eccentric orbit
HD 210277HD 210277 b1.23442.11998Gas giant/
eccentric orbit
Gliese 849Gliese 849 b0.821,8902006Gas giant/
circular orbit
psi1 Aqr91 Aqr b2.91822003Gas giant
HIP 5158HIP 5158 b1.33442009Gas giant
HD 212771HD 212771 b2.33732010Superjovian
HD 206610HD 206610 b2.26102010Superjovian
WASP-6WASP-6 b0.53.362008Hot gas giant
WASP-47WASP-47 b1.144.162011Hot gas giant
HD 215152HD 215152 b0.00877.282011Hot terrestrial
HD 215152HD 215152 c0.009710.862011Hot terrestrial
HD 220689HD 220689 b1.062,2092011Superjovian

Dawning Aquarius

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 600 years or so before the Earth's precession brings the Vernal Equinox (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 of Aquarius' can then be said to begin.

1Current IAU guidelines use a plus sign (+) for northern constellations and a minus sign (−) for southern ones.2The apparent path of the Sun on its daily journey across the sky.3The 13 constellations through which the Sun appears to travel in the course of a year. If you trace it on a star map the ecliptic actually passes through the usual 12 favoured by astrologers, plus Ophiuchus.4After whom one of the Galilean Moons of Jupiter is named.5Usually a gravitational effect by one planetary body on another that causes it to slow or speed up in its orbit, or deviate from its expected path.

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