Please follow us on a travel throughout the Universe and among the galaxies. This web site does not require any scentific knowledge, and is accessible to everyone, adults and children.
We wish to draw your attention to the beauty of our Universe. To show you that it gathers extraordinarily diverse types of galaxies, arranged in a astounding way.
To make you apprehend dimensions with no comparison to what we are familiar to on Earth, or in the solar system. To recount what the astrophysicists have presently deciphered on the nature of galaxies.
Your delight will be our reward.
Please do not forget to deliver your impressions
into the Guest Book...
Galaxies: their nature
Galaxies are huge swarms of stars similar to our Sun, held together by the force of gravity.
They have different forms, colours, and sizes which characterize them.
Large galaxies can contain 100 billion stars, the smallest galaxies less than a million.
Les galaxies : leurs formes
La majorité des grandes galaxies sont appelées des spirales. Elles tournent sur elles-mêmes a la manière de roues majestueuses.
Les autres grandes galaxies sont appelées elliptiques. Elles ont la forme d'un ballon plus ou moins ovale.
Les galaxies irrégulières sont plus petites et sans forme particulière.
Sous l'effet de l'attraction gravitationnelle des galaxies environnantes, certaines galaxies sont déformées. Parfois, elle vont jusqu'a fusionner avec une galaxie voisine.
Tentez de les identifier dans le diaporama !
Galaxies: their forms
The majority of large galaxies are called spirals. They turn around themselves like majestic wheels.
The other large galaxies are called ellipticals. They are globes shaped in a more or less oval way.
Irregular galaxies are smaller and without any particular shape.
Some galaxies are distorted by the gravitational attraction of nearby galaxies. Sometimes, two neighbouring galaxies merge.
Try to identify them in the slide show.
A spiral galaxy: the Milky Way
The Milky Way, this swarm of stars running across the entire sky, is the spiral galaxy within which lies our Sun and its procession of planets, among them the Earth.
It is composed of a thin disk containing spiral arms, and it hosts in its center a bulge through which goes a bar. The density of stars is very high in the bulge.
Because we are inside the Milky Way, it is not possible to take a photograph of it. Astronomers draw outlines of it using their various observations.
Les couleurs des galaxies
Les couleurs des galaxies indiquent l'âge et la température des étoiles qu'elles contiennent.
Les disques bleus des spirales et les galaxies irrégulières contiennent des étoiles jeunes et très chaudes.
Les bulbes jaunes des spirales et les galaxies elliptiques des étoiles vielles et moins chaudes.
Galaxies: their colours
The colours of galaxies indicate the age and temperature of the stars they contain.
The blue spiral arms of spiral and irregular galaxies are composed of young and hot stars.
The yellow or white bulges of spiral galaxies, and the elliptical and lenticular galaxies contain old and warmless stars.
Spirale Elliptique Lenticulaire Spirale
Spirale Irrégulière Spirale Spirale
Galaxies: their sizes
Galaxies follow a large range in size, from 1000 to more than 100 000 light-years in diameter, like our Milky Way.
In each image, observe smaller neighbouring galaxies around the large central galaxy.
The light-year for measuring distances
The huge distances and sizes in the Universe require an adapted unit: the light-year.
It is the distance travelled by light in one year, at the speed of 300 000 kilometers per second.
At this breathtaking velocity, light goes 7 times around the Earth in one second. It also runs in one second from the Moon to Earth.
And it requires no less than 8 minutes for light to cover the 150 million kilometers which separate the Sun from our planet Earth.
Distances to galaxies
It is the expansion of the Univers resulting from the Big Bang, the explosion within which our Universe supposedly formed, which allows one to measure distances to galaxies. The more distant they are, the faster they move away from us.
The closest galaxies to the Milky Way are at millions of light-years in distance.
The more distant are galaxies, the smaller they appear on the sky, and the harder it is to make out their shape.
In the sky
Galaxies in the sky
The deep images presented in background are obtained using the large telescopes which observe the sky from Earth. One may see in them millions of galaxies similar to those observed in the nearby Universe.
The large galaxies in these images are hundreds of millions of light-years away from the Milky Way.
The most distant galaxies, which appear like small colour spots, are billions of light-years away.
Take a walk across the skies and gaze at the diversity of galaxies in these images: look at their shapes, colours, sizes, distances, and their grouping together.
Continue the walk
For an interactive walk: "Astromatic.net/gallery"
Galaxy grouping together
Under the force of gravity, galaxies tend to group themselves together, constituing pairs, groups and clusters of galaxies.
As galaxies draw closer to each other, they sometimes merge, creating a new and larger galaxy.
The spatial arrangement of galaxies
Seen altogether, the distribution of galaxies in the Universe is not uniform.
Another web site will unveil the mysteries of their spatial arrangement.
Mapping the Universe
Images of elliptical galaxies
Elliptical galaxies are globes called bulge. They are composed of old stars, which are grouped together with high concentration in the central part of the bulge, and more diffusely in the surrounding parts. The bulge is more or less oval.
Images of lenticular galaxies
Lenticular galaxies are composed of a bulge similar to those of elliptical galaxies, placed at the center of a disk. The bulge and the disk are composed of old stars.
The disks of lenticulars do not contain any spiral arms, contrary to spiral galaxies. Depending on their orientation on the sky, we see them face-on, inclined or edge-on.
Inclined of face-on lenticulars
Images of spiral galaxies
Spiral galaxies are composed of a blue disk containing in its center a yellow and more or less significant bulge, similarly to our Milky Way.
The disks of spiral galaxies are adorned with spiral arms: they are waves of matter which evolve with time.
Depending on the orientation of spiral galaxies on the sky, we see their disk face-on, inclined or edge-on.
Bars and rings
Galaxies with bars
Galaxies with rings
Bars and rings in the disks of galaxies
The disks of lenticular and spiral galaxies often host a bar, and sometimes one or more rings.
Like spiral arms, the bars and rings are waves of matter, caused by the movement of gas and stars within the disk of a galaxy.
Bars and rings are sporadic in the history of a galaxy, and modify its appearance with the passing of the billion years.
Irregulars and dwarves
Images of irregular galaxies
Irregular galaxies are smaller than elllipticals and spirals. They have neither a bulge nor a disk, and tend to be blue.
Images of dwarf galaxies
Dwarf galaxies are as small as irregular galaxies. They look like a diffuse halo with either the round shape of an elliptical, or the flat shape of the disk of a lenticular. They are white in colour, with sometimes a very dense nucleus of stars in their center.
Pairs and mergers
Images of galaxy pairs
Despite the millions of light-years separating neighbouring galaxies, the force of gravitation exerts on these huge and massive systems. Pairs get formed by breaking away from the surrounding expansion.
Images of interacting and merging galaxies
Galaxies in pairs are to collide and merge. This may take billions of years, and leads to the formation of a more massive galaxy. Like beacons, luminous bursts of star formation light up the new galaxy.
Gallery of deformations
Galaxies deformed by the gravitational attraction of their neighbours display vast feathers and loops of stars.
Gallery of unusual galaxies
The transformations undergone by galaxies produce sometimes objects with unusual shapes !
Look how the floor of heaven
Is thick inlaid with paterns of bright gold.
There's not the smallest orb which thou behold'st
But in his motion like an angel sings,
Still choiring to young-eyed cherubins.
Such harmony is in immortal souls,
But whilst this muddy vesture of decay
Doth grossly close it in, we cannot hear it.
"The merchant of Venice"
Read the Guest Book
Write into the Guest Book
Please send us your impressions on this web site.
Does it make you dream ? Become aware of our place in the Universe ?
Do you have any comments ? Difficulties in loading specific pages of the site ?
Would you be interested if other subjects related to galaxies were developped ?
A very pedagogical and clear website which allows
me to explore the subject, at last. Irene, France 07/09/2009
A very beautiful site to marvel at. It reminds me
of how infinitely small we are. Muriel, France 17/09/2009
Many thanks ! It is handsome, magical, and rich in
material. Michel, France 23/09/2009
Congratulations for this very pedagogical site.
When will there be a national portal to direct young
people towards sites working for scientific culture
as this one... Please continue to make us dream. Philippe, France 21/03/2010
Public and school conferences
For requesting a public conference in english at any level (amateur astronomers, children, teenagers, mixed audience, associations), or to school or university students, please send a message.
You organize a training workshop for your collaborators, or a meeting with your clients, and you wish to offer them a cultural event, a trip to millions of light-years, at the frontier of present scientific knowledge.
For requesting a private conference, please send a message.
* Société Astronomique de France . . . . . . . . . . . . . Paris, February 14, 2008
* Grand Palais (Exposition "Paris Ville Européenne
des Sciences) . . . . . . . . . . . . . . . . . . . . . . . . . . Paris, November 16, 2008
* Classes CM1-CM2 (La Science en Fête) . . . . . . . . . Paris, November 17-18, 2008
* Terminale S (Lycée Saint Nicolas) . . . . . . . . . . . . .Paris, April 2, 2009
* Société des Sciences . . . . . . . . . . . . . . . . . . . . . Châtellerault, April 15, 2009
* Société d'Astronomie de Nantes . . . . . . . . . . . . . . Nantes, December 12, 2008
* International Year of Astronomy . . . . . . . . . . . . . . Caen, May 13, 2009
* Institut d'Astrophysique de Paris . . . . . . . . . . . . . Paris, September 8, 2009
* 2nde et Terminale S (Lycée André Maurois) . . . . . . Deauville, October 9, 2009
* Classes CM1-CM2 (La Science en Fête) . . . . . . . . . Paris, November 16-17, 2009
* Classes préparatoires MPSI, MP (Lycée Malherbe) . . Caen, December 4, 2009
* Société Française de Physique . . . . . . . . . . . . . . . Strasbourg, December 16, 2009
Send us a message
Please feel free to contact us if you wish :
- to ask a question about galaxies in the Universe
- to make a comment about this website
- to request a public, school or private conference
Links of interest
- Free Encyclopedia "Wikipedia"
- "Astronomy" magazine
- Astronomy news "Universe Today"
- The human language of colour "Testcolor"
Designed and produced by Valérie de Lapparent, astrophysicist at CNRS in France. She studies galaxies and the structure of the Universe at large scales. She shares with you her knowledge and the results of her research.
A simple and fun tool for creating oneself
ultra designed web sites.
Logo : Thomas Gurriet
Chosen pieces by Frédéric Verger, professor of Litterature and columnist in "Revue des deux Mondes".
- Legacy Survey of the Canada-France-Hawaï Telescope (CFHTLS)
- TERAPIX Data Processing Center Centre (CNRS/INSU - IAP - CEA)
- Image processing software : "Astromatic.net" (E. Bertin)
- EFIGI Catalogue (A. Baillard, E. Bertin, V. de Lapparent)
- "Sloan Digital Sky Survey" :
- Panomara : Lund Observatory (K. Lundmark, 1955)
- Sketch : NASA , Jet Propulsion Lab-Caltech, Spitzer Science Center-Caltech (R. Hurt)
Le financement pour le relevé "Sloan Digital Sky Survey" provient de la Fondation Alfred P. Sloan, les Instituts participants, la "National Science Foundation", le Département pour l'Energie des Etats-Unis, la NASA, la Monbukagakusho Japonaise, la Société Max Planck, et le Conseil de Financement de l'Education Supérieure pour l'Angleterre. Le relevé "Sloan Digital Sky Survey" est géré par le Consortium de Recherche en Astrophysique (ARC) pour les Instituts participants. Les Instituts participants sont le Musée Américain d'Histoire Naturelle, l'Institut d'Astrophysique de Potsdam, l'Université de Bâle, l'Université de Cambridge, l'Université Case Western Reserve, l'Université de Chicago, l'Université de Drexel, Fermilab, l'Institut d'Etudes Avancées de Princeton, le Groupe Japonais Participant, l'Université Johns Hopkins, l'Institut Conjoint d'Astrophysique Nucléaire, l'Institut Kavli pour l'Astrophysique des Particules et la Cosmologie, le Groupe Scientifique Coréen, l'Académie des Sciences Chinoise (LAMOST), le Laboratoire National de Los Alamos, l'Institut Max-Planck pour l'Astronomie (MPIA), l'Institut Max-Planck pour l'Astrophysique (MPA), l'Université du Nouveau Mexique, l'Université de Pittsburgh, l'Université de Portsmouth, l'Université de Princeton, l'Observatoire Naval des Etats-Unis, et l'Université de Washington.
Funding for the "Sloan Digital Sky Survey" has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.