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Throughout the waterfalls of time, mankind has invented many myths and legends. The purpose of them was to entertain each other but more importantly it was an attempt to explain the natural processes and phenomena that surrounded them.

Many of these mythological characters were projected on to the night sky.

They were basically patterns that resembled the corresponding person or object. Some of these myth based constellations include Perseus and Hercules.

In other words, constellations are patterns of stars in the night sky that resemble a wide variety of people, mythological beasts, animals and man made objects.

 
  Historical starchart
  An old star chart showing the constellations as the objects that they represent.
             

Altogether there are 88 constellations and their boundaries were decided by the International Astronomical Union in 1930. This means that there are no spaces between constellations and they also don’t spill over into another constellation’s boundary.

Each constellation is part of an imaginary shell called the ‘celestial sphere’. This surrounds Earth and as time progresses in the space of a year, the Earth faces a different part of the celestial sphere and different constellations are visible in the sky in each season. Also there are constellations that can only be seen in either the northern or southern hemisphere and there are also constellations that are visible in more than one season. These are known as circumpolar constellations because they appear to rotate around the ‘north celestial pole’ and the ‘south celestial pole’.

             
Celestial sphere   The pattern of stars in a constellation isn’t physically fixed in one location, each star in a constellation is at different distances. These distances are measured in a type of measurement called a light year. The distance of other objects in the Universe such as galaxies and nebulae are also measured using this type of measurement. The reason that a group of stars of differing distances appear together is because of line of sight. This means that they appear towards the same direction but each star is at a different distance. Other things that also share the line of sight of a constellation are galaxies, nebulae, star clusters and double stars. The objects belong to a category called ‘deep sky objects’.
The celestial sphere is an imaginary sphere around planet Earth used to explain the emergence of different constellations at different times of the year.
 
Image copyright Lunar and Planetary Institute
   

The reason for this name is that they are much further away than the stars. The deep sky objects that share the line of sight are said to be ‘in the constellation’. This basically means that the objects are within the boundaries of that constellation. The number of stars and deep sky objects within the boundary of each constellation is different, some constellations have many objects and some have relatively few.

The constellations can be glimpsed with the naked eye during the night. Different constellations can be seen depending on the season. For example during spring, Ursa Major the great bear can be seen and is also home to many galaxies. Summer heralds the Milky Way to light up the night sky. Autumn has many constellations that resemble aquatic objects, Aquarius the water bearer and Pisces the fish to name a few. Winter has constellations with bright stars and this is probably the best time for a novice skywatcher to start their search for the constellations for the very first time.

Some constellations contain a part that is more recognisable than the whole constellation. These are known as asterisms and they are not official constellations. Examples are the Big Dipper part of Ursa Major, the Orion’s Belt part of Orion the hunter and the Winter Triangle made out of three stars, Procyon in Canis Minor, Sirius in Canis Major and Betelgeuse in Orion.
   
   

All 88 constellations are covered in this section. Each page will contain information about the constellation in general and a selection of interesting deep sky objects.

Underneath the name of each constellation will be text that tells what the constellation is supposed to be. To the right, there will be two icons. One will tell you whether it is in the north or south celestial hemisphere and the other icon will tell you the season that the constellation is visible in. Some of the constellations in the northern celestial hemisphere can be seen from southern countries and also the other way around. Also seasons are reversed in the southern hemisphere of Earth, so when it is winter in the north, it will be summer in the south.

There will be descriptions of some of the deep sky objects in the constellations. Next to each deep sky object that is described will be an icon that represents either an eye, pair of binoculars or a telescope. This is the minimum equipment required to see the object. A better instrument than the one shown in the icon will show the object in more detail.

The ordering of the deep sky objects on each page is from popular to obscure with bright well known objects at the top and faint obscure objects at the bottom. Also some deep sky objects have an informal popular name such as NGC 2024 in Orion also being referred to as the Flame Nebula. Popular names are given to some objects because they resemble certain objects or they were discovered by famous individuals. An object isn't necessarily well known if it has a popular name such as the obscure nebula DWB-111 also having the name of the Propeller Nebula. Some objects might not resemble the object referred to in their popular name in images as they only have the resemblance visually through a telescope as photographs can show the fainter parts. Also some deep sky objects have more than one popular name, for example the emission nebula known as M17 is also called the Swan Nebula and Omega Nebula.

Most pages will have some images illustrating both popular and obscure objects and every single image is true colour. The colours seen in the images will look a lot more dim with the eye through a telescope. There are many reasons for this such as receptors in the eyes shutting down at night. The primary reason is the vast distances the light from deep sky objects has to travel to reach the eyepiece. Another reason is that eyes are more sensitive to green light, most deep sky objects that show any colour through a telescope are green or blue planetary nebulae. Even with huge professional observatories, virtually no colour can be seen. Colours of star clusters can also be seen, this is more apparent with star clusters that have different coloured stars such as the Jewel Box Cluster. This is because the colours seem enhanced by a contrast effect. The colours of stars will look different to everybody, what looks like a red star to one person might look orange coloured to another.

Colour is not the only thing that is barely visible through a telescope, many details and structures of galaxies and nebulae seen in photographs are not seen through a telescope. The reason they are visible in photographs is the more efficient light gathering capabilities of high resolution cameras, they are vastly more sensitive than our eyes. Another reason is that most images are the result of being exposed for many hours over multiple nights. Most images have exposure times of tens of hours as the longer the exposure time is, the more brighter, colourful and detailed an object will appear.

In the photography of nebulae, details can be accentuated or new details revealed if they are imaged with specialised filters. The most common one of these is an 'hydrogen alpha' filter as it specifically isolates the light emitted by hydrogen molecules. This works best with emission and planetary nebulae as well as certain reflection nebulae. Another one is 'OIII' and isolates light from oxygen atoms, this can be used when imaging planetary nebulae and supernova remnants. When certain planetary nebulae are imaged with OIII or Ha filters, a halo can be seen surrounding them. Examples include the Ring Nebula and the Dumbbell Nebula. These filters aren't specifically for astrophotography, they are also used by visual observers to observe deep sky objects and to aid in finding them although a 'H-beta' filter rather than Ha is used for observing emission nebulae.

Many images of nebulae taken with professional observatories and the Hubble Space Telescope are usually false colour. The reason is to uncover parts that aren't visible normally as well as revealing the distribution of gases. These images are taken with Ha, OIII and SII filters and are also commercailly available to amateur astronomers. Even though they are false colour, they are still considered to be in the optical wavelength. None of the images on the constellation pages are false colour but some of them link to one as they are quite dramatic and beautiful.

Images can be taken in different wavelengths such as infrared and ultraviolet. These make a dramatic difference in revealing details. For example infrared images can reveal star clusters in star forming regions that are invisible to the human eye. This can apply to objects other than nebulae, an image of a star taken in 2007 with an ultraviolet observatory revealed a huge pluming tail, this would also be invisible optically. Images of galaxies taken in different wavelengths can reveal more information than true colour optical images such as how active a galaxy is and massive radio jets that aren't visible optically such as the ones in the peculiar galaxy, Centaurus A.

Deep sky objects have been catalogued following the invention of the telescope.
The most well known catalogues are the Messier and the New General Catalogue. This can also be abbreviated to ‘NGC’ and Messier is commonly referred to as ‘M’. There are other catalogues and these are referred to by their abbreviations. On the constellation pages, when there is a description of an object belonging to a catalogue that hasn't been previously mentioned, an explanation of the catalogue and what the abbreviation stands for is provided.

Some catalogues are dedicated specifically to a certain type of object, such as the Sharpless catalogue of nebulae and the Abell galaxy cluster catalogue. There are very few that encapsulate various different types but include the aforementioned NGC and Messier catalogue that are the staples of telescopic observations as well as less common ones such as the 'IC', the Index Catalogue, which is a subset of the New General Catalogue.

Many objects tend to be in more than one catalogue. For example the Pinwheel Galaxy in Ursa Major is commonly referred to as M101 but is also known as
NGC 5427. It also happens to be the 26th entry in the Arp atlas of peculiar galaxies. Another example is the famous Orion Nebula, M42 is the instantly recognisable designation but it is also NGC 1976 as well as Sharpless 281.

   

The Constellations

A

Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga

B

Bo÷tes

C

Caelum | Camelopardalis | Cancer | Canes Venatici | Canis Major | Canis Minor

Capricornus | Carina | Cassiopeia | Centaurus | Cepheus | Cetus | Chamaeleon

Circinus | Columba | Coma Berenices | Corona Australis | Corona Borealis | Corvus

Crater | Crux | Cygnus

D

Delphinus | Dorado | Draco

E

Equuleus | Eridanus

F

Fornax

G

Gemini | Grus

H

Hercules | Horologium | Hydra | Hydrus

I

Indus

L

Lacerta | Leo | Leo Minor | Lepus | Libra | Lupus | Lynx | Lyra

 

   
The rest of the constellation pages are unavailable as they haven't been completed yet. This section is scheduled for completion in 2021.