logo
g Text Version
Beauty & Self
Books & Music
Career
Computers
Education
Family
Food & Wine
Health & Fitness
Hobbies & Crafts
Home & Garden
Money
News & Politics
Relationships
Religion & Spirituality
Sports
Travel & Culture
TV & Movies

dailyclick
Bored? Games!
Nutrition
Postcards
Take a Quiz
Rate My Photo

new
Houseplants
Romance Movies
Creativity
Family Travel
Southwest USA
Irish Culture
Home Finance


dailyclick
All times in EST

Full Schedule
g
g Astronomy Site

BellaOnline's Astronomy Editor

g

Constellation or Asterism


Constellations and asterisms are both patterns of stars, but the terms refer to different groupings.

One confusion between the two comes from the various ways in which we understand the word constellation. Let's start by considering the difference between traditional constellations and modern astronomical ones.

Traditional constellations
Commonly, people think of constellations as traditional patterns of stars that are often shown as “stick figures”, and may represent classical myths. There's nothing wrong with this idea, and the traditional constellations are the basis for the astronomical ones.

We have to realize that all star patterns are human inventions based on what we see from Earth. The stars in a constellation are rarely near each other in actuality. For example, of the five brightest stars in Cygnus (the swan), the nearest one to us, Epsilon Cygni, is 72 light years away. The most distant one is over twenty times farther away than that. (A light year is around ten trillion kilometers or six trillion miles.) If we were in another part of the Galaxy, the stars of Cygnus wouldn't form the pattern we're used to.

There is also a cultural basis for constellations because although astronomers use mainly the Greek and Roman constellations, other cultures have their own.

Astronomical constellations
The astronomical definition of a constellation is both broader and yet more precise than the popular one. The International Astronomical Union (IAU) agreed on a list of 88 constellations, and in 1928 also agreed on their boundaries. They cover the entire sky with no overlap.

The traditional constellations are only defined by their stars. However IAU constellations include the stars and a defined area of sky. In this sense you might think of a constellation as analogous to a country on the Earth’s surface. If we say that a comet is appearing in Leo or that Saturn is in Virgo, this means that people can see these objects within the boundaries of those constellations.

Asterisms
“Asterism” is an unfamiliar word to most people, though you’ll probably recognise the aster- part of it, which comes from the Greek for “star”. The best-known asterism is the Big Dipper (the Plough, in Britain), which is part of the constellation Ursa Major. Despite its name, the Summer Triangle can be seen for much of the year. It consists of the brightest stars of the constellations Cygnus, Lyra, and Aquila. The Great Square of Pegasus is another well known asterism.

Very simply, an asterism is a recognizable pattern of stars that isn’t a constellation, but contains a part of one or more constellations.

Click to see a summary of the differences between constellations and asterisms.

Follow Me on Pinterest
Add Constellation+or+Asterism to Twitter Add Constellation+or+Asterism to Facebook Add Constellation+or+Asterism to MySpace Add Constellation+or+Asterism to Del.icio.us Digg Constellation+or+Asterism Add Constellation+or+Asterism to Yahoo My Web Add Constellation+or+Asterism to Google Bookmarks Add Constellation+or+Asterism to Stumbleupon Add Constellation+or+Asterism to Reddit




What Are Constellations
Centaurus the Centaur
Pegasus the Winged Horse
RSS
Related Articles
Editor's Picks Articles
Top Ten Articles
Previous Features
Site Map


For FREE email updates, subscribe to the Astronomy Newsletter


Past Issues


print
Printer Friendly
bookmark
Bookmark
tell friend
Tell a Friend
forum
Forum
email
Email Editor


Content copyright © 2014 by Mona Evans. All rights reserved.
This content was written by Mona Evans. If you wish to use this content in any manner, you need written permission. Contact Mona Evans for details.

g


g features
Saturn's Moons – Facts for Kids

Celestial Sleuth – book review

Phantom Planets and Moons

Archives | Site Map

forum
Forum
email
Contact

Past Issues
memberscenter


vote
Poetry
Daily
Weekly
Monthly
Less than Monthly



BellaOnline on Facebook
g


| About BellaOnline | Privacy Policy | Advertising | Become an Editor |
Website copyright © 2014 Minerva WebWorks LLC. All rights reserved.


BellaOnline Editor