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Constellation guide to the 88 official constellations which divide up the sky. These constellations are used to help navigate the celestial sphere. The Constellations are patterns in the sky which have been to invented and have deep mythology behind them. Constellations cover massive areas in the sky and as such are very easy to find.
Astronomical Objects Series
  1. Guide to the Constellations and Mythology
  2. What are Asteroids, Meteors and Comets?
  3. Binary Stars and Double Stars
  4. Variable Stars
  5. Supernova and Supernovae
  6. Types of Nebula and Nebulae
  7. What Is a Black Hole? Black Holes Explained - From Birth to Death
  8. Quasars
  9. Pulsars - The Universe's Gift to Physics
  10. Gamma Ray Bursts
  11. Kuiper Belt
  12. What is an Exoplanet?
  13. Galaxy Types and Galaxy Formation
  14. The Messier Catalogue
  15. The Caldwell Catalogue
  16. 25 Stunning Sights Every Astronomer Should See

Constellations are usually one of the first things new astronomers start observing, and something many professionals totally ignore in there exploration of deep space. Constellations aren't real objects, they are a figment of our creative imaginations.

Over the millennia we have grouped stars together to form imaginary outlines or meaningful patterns on the celestial sphere, typically representing animals, mythological people or gods, mythological creatures, or manufactured devices. The entire sky is divided up into 88 areas, each one a constellation. They help us navigate the night's sky, and navigate the Earth.

A constellation is a group of stars that make an imaginary shape in the night sky.

A constellation is a group of stars that make an imaginary shape in the night sky.

Constellation names, like the names of stars, come from a variety of sources and each has a different story and meaning to it. Some of the constellations have very familiar names, such as Leo, Gemini, Virgo and Aquarius. These are some of the 12 constellations which form the Zodiac. The Zodiac constellations follow the line of the ecliptic. The ecliptic is the apparent path of the Sun on the celestial sphere.

Although not an official constellation, the Plough is the most famous and easily recognised.

Although not an official constellation, the Plough is the most famous and easily recognised.

Not all of the constellations are visible from any one point on Earth. The star maps are typically divided into maps for the northern hemisphere and maps for the southern hemisphere. The season of the year can also affect what constellations are visible from where you are located on Earth.

The Big Dipper, shown above, isn't official, but one of the many unofficial constellations called Asterisms. An asterism might form part of an official constellation, like the Big Dipper, which is composed of the seven brightest stars in the constellation Ursa Major. Or the constellation might be made up of stars from different constellations. For example, the three points of the Summer Triangle asterism are Deneb, Altair, and Vega, which are the brightest stars in the constellations Cygnus, Aquila, and Lyra, respectively.

You can view more about each of the individual constellations and their mythology in the links below.

Tutorial Series

This post is part of the series Astronomical Objects. Use the links below to advance to the next tutorial in the couse, or go back and see the previous in the tutorial series.

Eridanus

The River

Location: Northern Winter - 3h RA -29° Dec

Eridanus is a mythical river associated with Phaëton, and is the sixth largest of the 88 modern constellations. It was also one of Ptolemy's 48 constellations.

At its southern end is the first magnitude star Achernar (α Eri). Achernar is a very peculiar star because it is one of the flattest stars known. Observations indicate that its radius is about 50% larger at the equator than at the poles. Responsible for this is the fact that Achernar is spinning extremely fast. Another well-known star in Eridanus is ε Eridani, which has been popular in science fiction because it is relatively close and relatively sun-like. It is now known to have at least one planet, which is thought to be a gas giant, like Jupiter.

Eridanus

Eridanus Mythology

Eridanus is associated with two Greek myths, both likely to be derived from the shape of the constellation — that of a very twisty path. Eridanus was sometimes considered to be a river which flowed from the waters of Aquarius. Eridanus was more usually connected to the myth of Phaeton, who took over the reins of Helios' sky chariot, but didn't have the strength to control it, and so veered wildly in different directions. The result was that sometimes the chariot got too close to earth, creating desert and burning people's skin (a myth they considered to explain the skin of the Ethiopians).

Eridanus Deep Space Objects

NGC 1535 is a small blue-gray planetary nebula visible in small amateur telescopes.

Constellations

Northern Circumpolar Constellations

These constellations can be viewed all year round in the Northern hemisphere as they move in a counterclockwise direction around the north celestial pole without setting or dipping below the horizon.

Northern Spring Constellations

These Northern constellations are best viewed around the spring months. The rest of the year the constellation will not rise during the night.

Northern Summer Constellations

These Northern constellations are best viewed around the summer months. The rest of the year the constellation will not rise during the night.

Northern Autumn Constellations

These Northern constellations are best viewed around the autumn months. The rest of the year the constellation will not rise during the night.

Northern Winter Constellations

These Northern constellations are best viewed around the winter months. The rest of the year the constellation will not rise during the night.