the night sky
Please use these links to access the section of the guide which interests you.
The Northern Hemisphere
The Southern Hemisphere
Annual Meteor Showers
Astronomical links
Planets of the Solar System
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The twinkling stars of our night sky have fascinated generations of people for thousands and thousands of years.
Above: The Pinwheel Galaxy (M101)
in the Constellation of Ursa Minor - Picture by Lightroom Photos / NASA
This situation has changed little today and this guide aims to inform the star-gazer of the interesting bits of the various 88 constellations of our night sky in both the Northern and Southern Hemispheres.
This, I hope, will provide useful, for those who, like our ancestors for millennia, recognise the beauty and wonder of the night skies above our heads.
How to use this guide
This free, online guide to the night sky charts the 88 constellations of the entire night sky.
Each Hemisphere is allocated it's various constellations and you'll also find when annual meteor showers occur and some of the legends behind the names of these 88 constellations. Whenever possible, there are photographic illustrations from the world's observatories and links to fancy virtual ones like Google Sky and the Worldwide Telescope (which is PC only at present).
At the moment, there are no star maps to accompany the text, though these may be added at a later date. Wherever possible, a space photograph is used to illustrate this information.
What the guide consists of is the details of what is visible of each of the 88 constellations in the northern and southern celestial hemispheres, using smaller telescopes, binoculars, larger telescopes and even with the naked eye.
Each constellation has details of interesting things to look at - such as double stars, nebula galaxies and star clusters - plus interesting facts about the constellation and stars in question. Also included is advice on the best type of instrument to view these celestial objects with, be it an amateur telescope or pair of binoculars or something larger.
Most of the objects described can be viewed using “smaller telescopes” - which usually have a lens with an apeture of 50 - 60mm. Binoculars are also good for many objects and a surprising amount of astronomy can be done with a simple pair.
Telescopes comes in varying sizes and prices, generally the larger the telescope, the more expensive it is. Some can also be connected to computers and used for astro-photography or to track a star across the sky. Others are more geared up to the eye and you can build quite a large telescope a la DIY if you live in a place with fairly low light pollution (which rules out much of the UK!).
Another modern method of astronomy is to view images from large telescopes like the European Southern Observatory in Chile and the Hubble Space Telescope online or even one in your local community when they have open days. In recent years, the Worldwide Telescope on a PC (though not on a Mac!) and Google Sky (which works on both systems), also offer what are in effect digital planetariums.
Of course, to enjoy the splendor of the heavens above, you can use some very specialist, free equipment - your own eyes!
This guide can be used anywhere in the world, though of course, not all constellations will be visible depending on where you are viewing the night sky from. Constellations in the southern hemisphere, for example, will always remain over the horizon for astronomers at mid-northern latitudes and vice-versa.
It is a free guide, entirely funded by Google ads, so please support the site by clicking on the ones that interest you.
I also hope you find this guide to the night sky useful and helps aid your understanding and pleasure when viewing the beautiful heavens above our heads.
About the night sky
The night sky above our heads is simply divided into 88 costellations. These are used by astronomers to locate various objects in the night sky. Stars vary a lot in their distance from us, though appear grouped together, to some extent this liberty is taken by the astronomers who classified the 88 constellations.
Like many things, constellations come in varying sizes. One tellling statistic is that the smallest constellation Crux or the Southern Cross, occupies just 1/19 of the area of sky that is occupied by the largest constellation Hydra, the water snake.
While some constellations, such as Orion, are easy to identify, with familiar patterns of bright stars, others are more difficult to locate in the night sky.
Man began dividing the night sky into constellations thousands of years ago. Ancient astronomers being fond of naming these constellations after gods, heroes and fabled beasts of their mythology and cultures.
These connotations are more symbolic than actual, few constellations being true to their name visually-speaking. In part, this explains the muddle of mythology which makes up the 88 constellations. Figures from Greek legends are located next to more prosaic mythology such as the compass constellation, which not surprisingly, looks like a compass.
Ancient Greece recognized some 48 constellations, including the 12 signs of the zodiac - through which the Sun passes each year. This is known to astronomers as the ecliptic.
The early astronomical cartographers of the sky were free to draw up constellations as they pleased, there not being much of an International Astronomical Union at the time! Hence, there was no standardized shape and new cartographers could add, edit and remove constellations as they pleased.
Finally, in 1930, the International Astronomical Union put an end to the confusion and adopted a list of 88 constellations that are outlined in this guide. Apparently, there is no particular reason why the IAU settled on 88 constellations.
So these 88 constellations are now fixed and unlikely to change until the proper motions of stars render the whole map of the 88 constellations unrecognizable. Though this will be thousands of years from now.
The names of stars
There are several different systems for the naming of stars, hence they often have several names, especially some of the better known and easily-viewed constellations. Many of the bright stars, for example, have Arabic, Greek or Latin names. Some examples are Altair, Sirius and Regulus, respectively.
A common system is to award the bright stars in a constellation with Greek letters. This was began by the German astronomer and celestial cartographer, Johann Bayer in 1603. Due to this, these are known as “Bayer Letters”.
A good example of this is the star Sirius. This star is also known as Alpha Canis Majoris - as it is the Alpha star of the Canis Majoris constellation.
Stars not identified this way are given a number, which is called a “Flamsteed Number” (e.g. 56 Andromeda). These are named after the British Astronomer Royal, John Flamsteed (1646-1719), when he introduced them into his star catalogue. He referred to fainter stars by their numbers in several of these catalogues.
Some astronomers have also classified special types of stars, which also make up the nomenclature of the heavens.
In this online guide, “Struve Numbers” are sometimes used. These are double stars catalogued by the Russian astronomer FGW Struve.
Variable stars also have their own special names, those not named under existing systems are given one or two Roman letters, such as R Leonis. When all the combinations are exhausted, then variable stars in a constellation are sometimes given the letter V and a number, such as V 1500 Cygni.
Galaxies and star clusters also have their own nomenclature, a designation of the letters M or NGC and a number, such as M 77. The “M” numbers derive from a catalogue drawn up by the French astronomer, Charles Messier.
NGC numbers come from a Danish astronomer called JLE Dreyer, who in 1888, wrote the ‘New General Catalogue of Nebulae and Clusters of Stars’. Two supplements of the New General Catalogue (hence, NGC) were published in 1895 and 1908. Some objects in these publications were given IC numbers. Many objects have both an “M” and “NGC” classification.
Types of stars
Stars are balls of gas, with billions of nuclear reactions which produce an incandescent light and lots of heat radiation. They are usually much larger than planets like Earth. These huge stars are often very, very far away, so don’t appear as more than points of light on our night sky.
Astronomers have concluded by analyzing the light from stars that they come in a wide range of sizes, temperatures, brightnesses and colours.
The largest stars are known as giants or super-giants. These are hundreds of times the diameter of our own Sun. These stars are much older than our Sun and have swelled to a large size, all seemingly ending up as red giant stars at the twighlight of their existence.
Conversely, the smaller stars are also red, well, at least one of them, the red dwarf type stars - which are about 1/10th of the size of our Sun. More curious perhaps are white dwarf stars, which have all the mass of our Sun, though packed densely into a star the size of the Earth. Astronomers think these are perhaps the central cores of former red giant stars, whose outer layer of gas has drifted out into space.
The brightness of a star
Star brightness is called Magnitude. This is an ancient system began by the Greek astronomer, Hipparchus in the second century BCE. Hipparchus divided the stars into six magnitudes of brightness, the first being the brightest and the last being the dimmest. Hence a star of the 1st magnitude is brighter than one of the 6th magnitude. These days, photometers (like those found in most cameras) are used to work out these magnitudes to the nearest hundredth.
At this point it gets a bit complicated. A five magnitude difference is equal to a brightness difference of 100. Mathematically, this works out as each magnitude being a step equal to the 5th root of 100, which is approximately 2.5.
Those bright stars over 2.5 times than magnitude 1.0 are given minus magnitudes. Sirius, for example, the brightest star in the sky, has a magnitude of -1.46.
Fainter stars are given larger magnitudes than set out by Hipparchus all those years ago. The very faintest objects visible from Earth having magnitudes as low as 24.
Working out the magnitude of other celestial objects such as star clusters, nebulae and galaxies is more complex than a star, as this is calculated as if all the diffuse objects light were concentrated on one point. Therefore, an 8th magnitude galaxy would have the same brightness as an out-of-foucs 8th magnitude star.
The colour of stars
Many people think of stars as being white or yellow and some are, though when viewed with a telescope or binoculars will often reveal a different colour entirely, to the one seen by the naked eye. In fact stars comes in wide range of colours, with orange, red, yellow, white and blue-white, to name but a few.
A star’s colour reveals some information about it. The coolest stars are reddest in colour and the hotest are bluest. The colour reveals the surface temperature of the star in this way.
Double stars, when viewed with a smaller telescope or binoculars can reveal some great contrasts like a yellow and blue star, etc.
The positions and motions of stars
In the heavens above, latitude and longitude exist in the form of Right Ascension (RA) and Declination (Dec). This right ascension starts at the point where the Sun begins it’s yearly trip around the sky, which is known as the Ecliptic, where it moves northwards across the celestial equator. This particular point, known as the Vernal Equinox is the celestial equivalent of the Greenwich Meridian on Earth. Right ascension is measured eastwards of the vernal equinox around the sky from hours 0 to 24. Naturally, each hour of right ascension is divided into periods of 60 minutes and each minute into 60 seconds.
Declination is not measured like this, instead being measured in degrees north and south of the celestial equator, from 0 degrees at the equator to +90 degrees at the north celestial pole and -90 degrees at the south celestial pole. Celestial poles lie directly above the physical poles of the Earth. Also the celestial equator is directly overhead if you stand at the equator.
Thus, the position of a star or other celestial object can be determined precisely using right ascension and declination, similar to coordinates on Earth. Coordinate grids are often added to star charts.
However, celestial cartographers still face the dual problems of each star moving slowly, relative to it’s neighbours and also the fact that the whole celestial grid is also moving due to the Earth’s wobble in space.
The movements of stars are known as their Proper Motions, though you would need a whole lifetime and specialist instruments to measure them. One exception to this is Barnard’s Star.
This proper motion of stars renders all star maps useless over several centuries as stars drift into neighbouring constellations. Hence, astronomers need to revise our maps of the night sky every few hundred years or so.
Earth’s wobble on it’s own axis is known as procession causes the point where the ecliptic intersects the celestial equator to move once around the sky every 26,000 years. This means that the coordinates of all points of the night sky are gradually changing.
This should be noted when buying a star-map of the night sky, as it is customary to give a reference date. Hence, a map which is referenced as the year 2000, should be good for almost 100 years or so.
Star distances
The distance between stars and galaxies is usually measured in Light Years or Parsecs. In this guide, light years are used. For the uninitiated, a “light year” is the distance that a beam of light, travelling at 300,000 km/second, travels in one Earth year.
Distances of nearby stars is measured with a technique known as Parallax. This works by measuring the star’s precise position against the celestial background, as viewed from opposite sides of the Earth’s orbit, i.e. January and July observations. The change in the star’s position from these two points of the Earth orbit (which are effectively on either side of the Sun, six months apart) will reveal the star’s distance. The nearest stars to Earth show the most parallax shift.
For example, a star at a distance of 3.26 light years away, would show a one second of arc parallax shift. This is what a Parsec is (parsec being short for paralllax of one second). In reality, there is no star as close as this, that is Alpha Centauri and has a parallax of 0.76 of the arc, therefore being 4.3 light years away.
With stars further afield, over 100 light years, the parallaxes of stars are too small to be measured by ground-based telescopes. Beyond this, it is educated guesswork by astronomers as to how far away an object in the night sky actually is. Though this is a complex area of astronomy of little interest to amateurs.
Double and multiple stars
Seen through telescopes, many stars are not one star, but two or more. These are called Double Stars and Multiple Stars. Sometimes these “double stars” are very far away from each other, though lie in the same line of sight to us here on Earth. Such double stars are known as an Optical Double. These are relatively rare though and inmost cases stars are linked by gravity and orbit around each other. These are known as Binary Stars. Stars with several companions that orbit each other in this manner are known as Multiple Stars.
Separating two stars is measured in seconds of the arc. There are 60 seconds (”) in each minute (’) of the arc and 60 minutes in 1 degree of arc. This results in one second of the arc being 1/3600th of a degree. For example, the Earth Moon is about 30 minutes of the arc - or half a degree.
“Wide doubles” which have separations of several seconds of the arc or more, can be divided in smaller telescopes and binoculars. Narrower double stars need more powerful apetures of 100mm and above and often high magnification. The narrower the separation, the higher-powered the telescope needs to be to see it.
The stillness of the atmosphere, which is known in astronomy as “seeing” will also affect a telescope’s ability to separate close double stars. The constellation guide contains details on double stars which are best viewable in each of the constellations for those with smaller telescopes and binoculars, plus advice on narrower doubles for those with larger telescopes.
Variable stars
These stars vary in magnitude (brightness) over hours, days, weeks, months and even years. The brightness of variable stars can be estimated by comparing them with surrounding stars which are not variables.
Why stars pulsate like this is not always clear. Commonly it may be the star itself, being unstable, pulsates, or so think some astronomers. This may be true, though the discovery of many exoplanets has reveled that often it is the orbit of a gas giant planet (like Jupiter) around the variable in question.
One well-known class of variable is the Cepheids. These yellow super-giant stars pulsate regularly every few days or weeks. Astronomers attach importance to them, as their periods of pulsation are directly related to their luminosity. The brightest Cepheid, for example, takes the longest to pulsate.
Clever astronomers can accurately work out the luminosity of Cepheid by observing the pulsation period. By comparing this luminosity with the star’s brightness as it appears from Earth, they can work out how far away it is.
Stars like the Cepheids are relatively rare, more abundant are red giant and super-giant stars. These are more unstable due to their age and do not have the disciplined pulsations of the Cepheids. This seems to indicate that non red giant and super-giant variable stars are unstable, though other types of younger stars with variable attributes are probably home to exoplanets.
Another type of variable star is known as an Eclipsing Binary. This consists of two stars in a mutual orbit, one sometimes moving in front of the other, as seen from the Earth, hence the term eclipsing. Whenever an eclipse of these stars occurs, then the light recieved here on Earth dips. The most famous eclipsing binary is found in the constellation of Perseus, a star known as Beta Persei, also known as Algol.
The most spectacular variable stars are Eruptive Variables, which have sudden changes in light output. These are also known as Novae and Supernovae. The theory behind novae is that they are close double stars, one of which is a white dwarf. Gas from the companion spills over into this white dwarf, where it ignites and creates a surge in the light emitted by the star in question. It has been found that the star is not destroyed in a nova explosion, as some novae have been seen to light up more than once.
Some astronomers think all novae reoccur given enough time. Novae are also often first spotted by amateur astronomers in their backyards.
The most spectacular thing in our night sky in terms of variable stars is a Supernova. These, in effect, signal the cataclysmic death of a massive old star. At the end of their life, stars appear to commit suicide, blowing themselves to smitherines. The resulting light show is thought to shine as brightly as a billion stars. After the supernova has passed, a trail of debris is left to drift in space and an example of this is the Crab Nebula in the constellation of Taurus and the Veil Nebula in Cygnus. To become a supernova, a star must swell to a mass several times that of our own Sun.
The last recorded supernova in our Earth skies was back in 1604. Naturally, astronomers think we are long overdue for another.
Star clusters
Sometimes, the stars in the night sky appear to cluster together. Astronomers divide these clusters of stars into two types: open clusters and globular clusters.
Open clusters tend to be less densely packed with stars than globular ones. These open clusters usually contain younger stars, sometimes thousands of them, in irregular shapes. They are often located in the spiral arms of our Galaxy and cover 0.5 of a degree of the night sky, making them equal or greater to the space occupied by the Moon. Some famous examples of open clusters are the Pleiades and Haydes clusters Taurus.
Globular clusters often contain a dense ball of hundreds of thousands of stars, which are distributed in a sort of halo around our Galaxy. Often, globular clusters contain the oldest known stars. Famous examples of a globular clusters are Omega Centauri and M 13 in Hercules.
Nebulae
A nebula is a cloud of gas and dust in outer space. Some nebulae emit a lot of light and others very little, so they both brighten and darken parts of the night sky. Sometimes, both dark and bright nebulae can be found together in the same field of view.
Some famous nebulae, both light and dark, are the bright Orion Nebula and the Tarantula Nebula, plus the famous dark one, the Coalsack Nebula in the Crux (Southern Cross) constellation, which blots out some of the Milky Way.
Planetary nebulae
Planetary nebulae are basically also clouds of gas that have been ejected by a star like the Sun at the end of it’s lifetime. Actually, despite the name, therefore, planetary nebulae have little to do with actual planets. Often though, when observed through telescopes, these nebulae appear as round discs, so the name sticks!
The Milky Way
Almost inconcievable in itself, the Galaxy is a spiral system of over 100,000 million stars. Our Galaxy is given a capital G to distinguish it from others. The Milky Way (as the Galaxy is sometimes referred to), is technically the stars making up the spiral arm of the Galaxy in which we live. Spiral galaxies like our own rotate, so the Sun, some 30,000 light years from the Galactic Core, takes 250 million years to complete one whole orbit.
In total, astronomers say the Galaxy is some 100,000 light years across. The way to the centre of the Galaxy lies in the constellation of Sagittarius, where the Milky Way star fields are quite dense.
Galaxies
As far as the largest telescopes can see, it is galaxies like ours they see. Every galaxy is a collection of billions of stars attracted to each other by gravity. Galaxies come in two shapes, spiral and elliptical, with spiral galaxies having two further classifications as barred and normal spirals.
The Milky Way Galaxy is a normal spiral, for example. In smaller telescopes, most of the galaxies are spiral, with the familiar central bundle of stars, with the spiral arms extending far into the surrounding space.
Barred spirals have a straight bar of stars across their centre instead and the spiral arms emerge from the ends of this bar.
Planets
Our own solar system has eight planets, Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Neptune and Uranus. Pluto, long regarded as the ninth planet, was recently demoted by an international group of astronomers as being a Kuiper Belt object - of which there are several small mysterious and seemingly cold moons or larger asteroids orbiting the Sun in the same area. Hence, there is now only eight planets.
Planets can often be seen in the night sky, depending on the date and where you are observing from. Smaller telescopes often bring these out well. Usually, the monthly night sky map published in some newspapers will show any passing planets in your night sky.
Many space probes like the Cassini Huygens probe have been sent out in recent years to build on our scant knowledge of our own solar system. Cassini is looking at the moon systems of Jupiter and Saturn, plus the gas giants themselves.
These mini systems have some curious moons like Europa, which is thought to be covered in water ice and many others.
Mars has several probes on or orbiting it at the moment, with several more missions in the pipeline from both the European Space Agency and NASA. The presence of water ice is now a given for most planetary scientists and there may be more surprises yet.
NASA’s Messenger probe is orbiting Mercury, which looks a bit like the Moon, full of craters, though there may be some interesting data from certain areas of this planet, as it does not spin on it’s axis, rather remains motionless in orbit.
Venus is also being explored with the ESA’s Venus Express mission. The far flung planets like Neptune and Uranus, remain free of probes though at the moment and should offer a great chapter of discovery in the future.
Human exploration of the solar system remains limited to the famous Apollo Moon missions of the Americans. There has been recent talk of the Americans returning to the Moon and also of a manned mission to Mars (just six months of space travel away), though little in the way of concrete plans.
Meteors
Commonly known as Shooting Stars, meteors are in fact bits of dust which burn up in our atmosphere. Usually a light flares across a bit of the night sky for a second or so, seemingly leaving a trail. The spek of dust or other object is not seen, rather the trail of hot gas it produces as it disintegrates at around 100 km altitude.
Meteors can be seen almost every night if the sky is clear and these are known as Sporadic Meteors. Throughout the year, the Earth passes through a swathe of planetary dust and this creates a phenomena known as Meteor Showers, such as the Orionids, etc. The name comes from what is termed the Radiant, which is where the meteor shower appears to be coming from.
Usually, these showers peak on a particular day or two, though they can last for weeks.
Light Pollution
If you live in an industrialised country, you are probably familiar with issues surrounding air and water pollution. Light is also a polluter of a different type, bouncing around from badly-thought-out lighting and poor local planning. This light ends up lighting up the sky in a diffused way and can make things difficult for astronomers.
Some countries, like the United Kingdom, have very few places (aside from remote islands like St Kilda) where light pollution is not a problem. Governments on a local and national level have learnt more about this in recent years and some changes have been made to reduce light pollution (the modern road lights in the UK are an example), though the problem persists, largely through ignorance. Areas near cities are usually most affected and deep in the countryside, this is less of a problem. It is now rare to find a part of the populated areas of the world, where light pollution is non-existent.
Some remote parts of Asia though, like the area of the Himalayas in Nepal where Mount Everest is located, have very little light pollution and the difference compared to skies nearer cities is startling. This is also true in other continents where there is a fairly low population density (such as the Sahara Desert or central Africa). Also, the poorer the country, the less electric lighting is used, so conditions are probably better in many of these locales.
Nevertheless, you can write to your local and national government and demand something be done about it and many areas still are dark enough to see a fair bit of the night sky, so don’t let light pollution deter you from enjoying astronomy.
Note on Greek letters
The Greek alphabetical letters in this guide are spelt out, so B is Beta, A is Alpha, etc, etc. This is due to the difficulties of presenting Greek letters on many computer screens, so Alpha Centauri, etc., avoids confusion. The the full Greek alphabet can be found here.
The Greek Alphabet
Alpha
Beta
Gamma
Delta
Epsilon
Zeta
Eta
Theta
Iota
Kappa
Lambda
Mu
Nu
Xi
Omicron
Pi
Rho
Sigma
Tau
Upsilon
Phi
Chi
Psi
Omega
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