The International Astronomical Union (IAU) divides the sky into 88 constellations with clear boundaries, mapping every part of the sky to one of these. Each constellation is grouped within one of eighty-eight constellation families (bordered in orange). In three-dimensional space, the stars in the constellations have little or no relation to each other but, as viewed from Earth, appear grouped together against the night sky. Other patterns of stars are well known but are not constellations, an example of which is The Plough – a pattern formed from the seven brightest stars within the constellation of Ursa Major. Such patterns of stars are called asterisms and may contain stars from one or more constellations. The constellations not only help to identify and locate stars and planets travelling through them, but also other objects of interest such as Deep Sky Objects.
Providing a way to segment the sky, the constellations are used to describe and find the location of objects. One of the first tasks for an observer is to learn the constellations, at what time of year they are visible and in which constellations interesting objects are found. To begin recognising constellations it is useful to take well-known reference points. The Plough is probably the best-known reference point in the northern hemisphere where it is visible all year round. Within The Plough, Mizar is a double star, with a companion called Alcor, sometimes visible to the naked eye. There are numerous galaxies lying within the constellation of Ursa Major, plus other deep sky objects, to be explored by telescope.
Interesting objects that can be Seen
Here are a few lists of interesting objects that can be easily seen with the naked eye, binoculars and/or telescopes.
CIRCUMPOLAR CONSTELLATIONS – The 6 constellations visible throughout the year in the northern hemisphere:
Camelopardalis / Cassiopeia / Cepheus Draco / Ursa Major / Ursa Minor
SPRING CONSTELLATIONS – The 16 spring constellations in the northern hemisphere:
Antlia Bootes / Cancer / Canes Venatici / Centaurus / Coma Berenices / Corvus / Crater / Hydra / Leo / Leo Minor / Lupus / Lynx / Pyxis / Sextans / Virgo
SUMMER CONSTELLATIONS – The 21 summer constellations in the northern hemisphere:
Aquila Ara / Capricorn / Corona Australis / Corona Borealis Cygnus / Delphinus / Equuleus / Hercules / Indus / Libra / Lyra / Microscopium / Ophiuchus / Scorpio Scutum / Serpens / Sagitta / Sagittarius / Telescopium / Vulpecula
AUTUMN CONSTELLATIONS – The 13 autumn constellations in the northern hemisphere:
Andromeda / Aquarius / Aries / Cetus / Grus / Lacerta Pegasus Perseus / Phoenix Pisces Austrinus / Pisces / Sculptor / Triangulum
WINTER CONSTELLATIONS – The 18 winter constellations in the northern hemisphere:
Auriga Caelum / Canis Major / Canis Minor / Carina / Columba Eridanus / Fornax / Gemini / Horologium / Lepus / Monoceros / Orion / Pictor / Puppis / Reticulum / Taurus / Vela
SOUTHERN HEMISPHERE CONSTELLATIONS – The 14 constellations visible throughout the year in the southern hemisphere:
Apus / Chamaeleon / Circinus / Crux / Dorado / Hydrus / Mensa / Musca / Norma / Octans / Pavo / Triangulum Australe / Tucana / Volans
Looking at Constellation Map 1, a straight line drawn from The Plough`s two pointer stars Merak and Dubne extended five times as far again, finds Polaris, the north star, within the constellation of Ursa Minor. If an arc is followed through the Plough`s handle stars of Megrez, Mizar and Alkaid the bright star of Arcturus in the constellation of Bootes is found. Dropping through the ´pan` of The Plough, between Phecda and Merak, will bring you to the constellation of Leo, within the Zodiacal family of constellations. Within Leo the Leonids meteor shower can be seen radiating out during November (at their best from the 16th to 18th).
Andromeda is another highlight of the winter sky in the northern hemisphere. When you have found it look through binoculars at the huge Andromeda Galaxy which is our nearest large galaxy. It is visible to the naked eye and through binoculars will look like a small ball although it is 250,000 light years across, more than twice the size of the Milky Way. The spiral Andromeda Galaxy has two companion galaxies known as M32 and M110, which are bright dwarf elliptical galaxies.
Another well-known reference point is the constellation of Orion, with three prominent and evenly spaced stars making up his belt. During winter, Orion is clearly visible and is one of the brightest constellations.
Orion is home to one of the most beautiful sights in the sky, the Orion Nebula. With a magnitude of 4 it is one of the brightest deep sky objects. It is situated below Orion´s belt as the middle of three stars that form Orion´s sword. If you look at this area through a pair of binoculars, you can see not one, but many stars. Through a telescope, you can see some of the giant gas clouds. The Hubble telescope has discovered that at least half of the young stars have proto-planetary discs, which are considered to be the formation of solar systems. The high numbers are used as strong evidence that solar systems are common in the Milky Way. This nebula is part of the huge Orion Molecular Cloud, composed of gas and dust, which extends throughout the constellation of Orion and includes other nebulae.