Exhibition of astronomical images promoted by the International Astronomical Union and by the Andalusian Network for Technical and Scientific Public Outreach (RECTA) to commemorate the International year of the Astronomy.

If you look at the Universe it appears full of galaxies to our eyes. The cluster of galaxies in Hercules contains 100 members of all kinds: elliptical, spiral and irregular galaxies.

The smallest groups of galaxies would have only two members. The pair known as “The Eyes” offers one example. Another group of galaxies is “Stephan´s Quintet”, containing only four members. The name is due to the presence of a fifth galaxy not belonging to the group, but interposed in the line of sight.

Apart from groups of galaxies such as the Hickson Compact Group 44 (made up of four galaxies), the so-called clusters of galaxies contain thousand of members. The combined gravitational attraction of such clusters is capable of bending the light coming from objects situated behind them. These further galaxies appear as light arclets. This phenomenon is known as gravitational lens.

The Universe harbours an astounding variety of galaxies with elliptical, spiral and irregular shapes. NGC 5128 is a peculiar elliptical system with a dusty lane across its centre caused by a collision with another galaxy. Common elliptical galaxies contain no dust. If you look at galaxy M106 you will see that it is a spiral system with a prominent nucleus surrounded by a disc containing several spiral arms.

Our Galaxy belongs to the spiral type, like NGC 7331. Spiral galaxies have a central bulge surrounded by a plane disc containing several spiral arms. You can see this shape clearly defined in the image of the Whirlpool Galaxy.

The Magellanic Clouds (Large and Small) are two galaxies orbiting around our own. The are the closest stellar systems to us.

The largest member in the Local Group is the spiral in Andromeda. This galaxy has a central bulge made up from older and cooler stars, yellow in color, while the spiral arms inside the disc contain younger and hotter stars that shine with bluish hue.

If you look at the centre of our Galaxy, you will perceive the huge quantity of stars that it contains. This area of the sky is situated towards the constellation of Sagittarius, in the southern celestial hemisphere. This part of the sky can be seen from almost any place in the world.

When you look at the sky, beside Sagittarius, you can see the constellation of Scorpius with the reddish star Antares, one of the most luminous known. The river of light of the Milky Way shines at the left in this image, where stellar clouds intermix with clumps of gas and dust.

If you look at the sky on a dark night, you will see the Milky Way as a luminous band: it is made from accumulations of stars and nébulas in the plane of the disc of our Galaxy. This image displays the whole of the Milky Way, and is made up from photographs obtained in Germany and Namibia.

In this image you can see several astronomical objects in the northern constellation of Cygnus. The brightest star is Deneb and to the left of it you have the North-America and Pelican nebulas: dust and gas clouds. Further down, to the right, beside the star Sadr, you can find the Buttterfly Nebula, one of the brightest regions in the Cygnus nebular complex.

Other interesting nebulas are the Horsehead and other nebulosities in the Orion constellation, all of them composed mainly from hydrogen gas.

These dust and gas clouds known as nebulas get condensed and stars are born inside them. You can see this process running in the Cone Nebula: in the upper part there is a very bright star, 5 Monocerotis, beside other recently formed objects. The Rossete Nebula shows a set of newly born stars at the very centre of the rose window.

The Eta Carinae Nebula lies in the constellation of Carina. Stars of all sizes are being born from these clouds. Especially outstanding among them is the star Eta Carinae, one of the most luminous yet known in the Galaxy.

Stars are born in groups. You can see an example of these groups insde the Lagoon Nebula, a region of intense star-forming activity. The group of stars recently formed from these nebulosities bears the name NGC 6530. The energy from these stars lights up nebular hydrogen and makes it shine with reddish hues. One more star-forming region is the neightborhood of star cluster NGC 3603. This area contains one of the most outstanding groups of young stars in the Galaxy.

Star formation starts when a gas and dust cloud gets condensed. Stars originate in groups, the so-called star clusters, like NGC 650. NGC 6250 was born 200 million years ago from the dark nebula Barnard 86.

The Universe offers to your sight young star clusters, like the Pleiades, or The Seven Sisters. This cluster is made up of young and hot stars. Greek mythology identifies its seven brightest members with the seven daughters of Atlas and Pleione.

Young clusters contain up to several thousands of stars. This is the case of the Double Cluster in Perseus. These two clusters count among the most luminous, dense and closer star groups. It is believed that both were born from the same interstellar nebula some 13 million years ago. Young star clusters are also known as open clusters, of galactic clusters.

The universe contains old star clusters too. NGC 6752 belongs to the group of old star clusters, in the southern constellation of Pavo. So does the Globular Cluster in Hercules, whose age exceeds ten billion years. Globular clusters are the oldest structures known to our Galaxy.

Stars have the same chemical composition as the nebulas from wich they were born: mainly hydrogen and helium. At stellar core, hydrogen is transformed into heavier elements through nuclear fusion reactions. The energy unleashed in the process comes out to the stellar surface and atmosphere. This ultraviolet image of the Sun shows the outermost layers of our star: the solar corona.

The Sun is an ordinary star. It is situated at a distance of 8.3 light-minutes from our planet. In this image, obtained with the light emitted by hydrogen atoms, yo can perceive the details of the solar surface, also known as photoshphere.

If you pay a closer look at the Sun, you will see sunspots. There are surface areas that become cooler tan their surroundings because the solar magnetic fields block the flux of energy coming from lower layers. Sunspots are the most conspicuous manifestation of solar activity. You can better appreciate the details of the solar chromosphere in images taken with ultraviolet light. The chromosphere is a solar layer placed between the visible photosphere and the corona. In the image you can witness a huge solar flare ejecting matter towards the outer atmosphere. This notwithstanding, the Sun is a rather quite star that displays a very constant enerby output.

Coronal loops count among many different phenomena related to solar activity. These curved structures are bridges of solar matter at extremely hight temperature and electrically charged, that rise from the chromosphere and deepen into the solar corona. This material falls again, which causes an explosive solar flare known as coronal rain. Other manifestation of solar activity are ordinary solar flares, violent eruptions that appear around sunspots.

Our star is surrunded by planets, ours among them. The largest planet in the Solar System is Jupiter. Observed with visible light, Jupiter shows brown and yellowish tones. But this image was obtained with infrared light and shows the height of different cloud formations: highest in white, médium in blue and lowest in red.

In Jupiter you can see a Great Red Spot. It is a storm the size of the Earth, found in the southern hemisphere of that planet. Another giant planet is Uranus, third in size and seventh in distnce from the Sun. Giant planets consist mainly of gas. The green-bluish hue of Uranus is due to the absorption of red light by methane gas.

Another giant planet you can see in the sky is Saturn, the most beautiful gaseous world in the Solar System. This image was taken by the space probe Cassini. In it you can see the shadows projected by the rings onto the northern hemisphere of the planet. Also, some stormy formations can be appreciated in the southern hemisphere.

Looking at the sky under the right circumstances, you will see the planet Mars, a rocky workd smaller than Earth. This image, taken by the space probe Mars Global Surveyor, shows clouds made of water ice crystals. Lower left there are clouds over the three volcanoes in Tharsis. The upper part shows the icy cover of the northern polar cap.

Another rocky planet is the Earth. This image displays the view over the Northern Atlantic. The view was generated with the software “Blue Marble” by NASA, a system that relays on images taken by several artificial satellites. Our planet has one natural satellite, the Moon, found at a distance of 1.25 light-seconds. The lunar landscapes show clear highlands and darker plains full of solidified magma known as the seas of the Moon (lunar maria). The lunar surface is covered by the scars left by meteoritic impacts: the lunar craters.

Comets moving inside the Solar System are small icy blocks with sizes ranging from a few hundred metres (yards) to several kilometres (miles). When the solar radiation heats them up, the icy materials sublimate, and gases and dust are emitted, forming the cometary hair and tail. Examples of such objets are comet Machholz, C/2001 Q4, and comet Hale-Bopp.

Nebulas containing larger quantities of dust are prone to the birth of stars with planets around them. This is the case of those nebulas in the Corona Australis constellation, that appear as a large tail of shining interestelar dust lit up by nearby young stars. Aproximately one third fo the stars are surrounded by planets.

Helix nebula displays the shining envelope expelled by Sun-likes stars at the end of their existence. Sun-like stars die in a peaceful process that gives back to the interestelar médium part of the material that had been retained within the stellar interior.

The Sun will have a quite ending, but other stars die in cataclysmic supernova explosions. Some supernovas leave behind compact objets called neutron stars. The energy emitted bu the neutron star found at the centre of the Crab Nebula makes the gas emit light and radio waves. Supernova explosions disperse into the interstellar médium huge quatities of heavy chemical elements produced from hydrogen inside the star throughout its stellar life.

Supernova explosions are the only means by which the Universe is able to produce many of the chemical elements required for life. Nebula G292.0+1.8 was formed by a nearby supernova explosion some thousands of year ago. Tycho´s supernova remmant shows how the exploding material is expanding and becoming mixed with the interstellar medium. This matter gets incorporated into other nebulas.

The material expelled by the stars at the end of their lives is incorporated into interstellar nebulae and feeds the formation of new generations of stars and planets. Stars contribute the elmenets needed for life to the Cosmos. New stellar generations are born from material enriched with heavy chemical elements produced by stars that existed and disappeared a long time ago. The bright dot inside the darkest part of the Elephant Trunk Nebula is a newly-born star.

Star formation is a current process in our Galaxy and in others. The Triangulum Galaxy shows signs of this. This galaxy is a spiral system whose arms appear sprinkled with pinkish nebulas that glow with the cahracteristic color of ionized hydrogen, the most outstanding tell-tale of current star formation. This galaxy is the third in size within our Local Group of galaxies.

When galaxies collide, intense star-forming processes are induced. You can see this clearly in the pair of colliding galaxies called The Antennae. The violent impact of gaseous masses compresses gas and causes intense starbursts. In the far fuure our Galaxy will collide with the Adromeda Galaxy.

This image shows the centre of our Galaxy, seen in infrared light. More tan one million stars are registered inside this frame. The total number of stars in our Galaxy is around several hundred billion.

The Hubble Space Telescope captures objects hundreds of millions of times fainter tan the dimmest star visible with the naked eye. This image contains more tan 10.000 objects, wich gives you an idea of the hundreds of billions of galaxies existing in our Universe.