Illustration showing the core, mantle and crust of Venus. It's core consists of rock and ice composed of iron, nickel and silicates. It's mantle is equivalent to 10 to 15 Earth masses and is rich in water, ammonia and methane. The crust atmosphere consists of hydrogen, helium and methane gas.

Illustration showing the core, mantle and crust of Venus. It's core consists of rock and ice composed of iron, nickel and silicates. It's mantle is equivalent to 10 to 15 Earth masses and is rich in water, ammonia and methane. The crust atmosphere consists of hydrogen, helium and methane gas.

Illustration showing the core, mantle and crust of Pluto. Observations by the hubble space telescope suggest that the internal composition of Pluto consists of roughly 50 to 70 percent rock and 30 to 50 percent ice by mass. The diameter of the core is thought to be about 70% of Pluto's diameter. The overall color is believed to be a result of ultraviolet radiation from the distant Sun breaking up methane that is present on Pluto's surface, leaving behind a dark, molasses-colored, carbon-rich residue. Pluto is so small and distant that the task of resolving the surface is as challenging as trying to see the markings on a soccer ball 40 miles away.

Illustration showing the core, mantle and crust of Pluto. Observations by the hubble space telescope suggest that the internal composition of Pluto consists of roughly 50 to 70 percent rock and 30 to 50 percent ice by mass. The diameter of the core is thought to be about 70% of Pluto's diameter. The overall color is believed to be a result of ultraviolet radiation from the distant Sun breaking up methane that is present on Pluto's surface, leaving behind a dark, molasses-colored, carbon-rich residue. Pluto is so small and distant that the task of resolving the surface is as challenging as trying to see the markings on a soccer ball 40 miles away.

Illustration showing the core, mantle and crust of Saturn. There is no direct information about Saturn's internal structure, although, it is thought to have a similar interior to Jupiter, having a small rocky core surrounded mostly by hydrogen and helium. The rocky core is similar in composition to the Earth, but denser. Above the core there is thought to be a thicker liquid metallic hydrogen layer, with a layer of liquid hydrogen and helium above that, and a gaseous atmosphere in the outermost 1000 km.

Illustration showing the core, mantle and crust of Saturn. There is no direct information about Saturn's internal structure, although, it is thought to have a similar interior to Jupiter, having a small rocky core surrounded mostly by hydrogen and helium. The rocky core is similar in composition to the Earth, but denser. Above the core there is thought to be a thicker liquid metallic hydrogen layer, with a layer of liquid hydrogen and helium above that, and a gaseous atmosphere in the outermost 1000 km.

Illustration showing the core, mantle and crust of Uranus. The standard model of Uranus's structure is that it consists of three layers: a rocky core in the center, an icy mantle in the middle and an outer gaseous hydrogen/helium envelope. The rocky core of Uranus is relatively small, with a mass of 0.55 Earth masses and a radius less than 20 percent of Uranus's; the mantle is about 13.4 Earth masses, and comprises the bulk of the planet; the upper atmosphere weighs only that of 0.5 Earth masses and extends for the last 20 percent of Uranus's radius.

Illustration showing the core, mantle and crust of Uranus. The standard model of Uranus's structure is that it consists of three layers: a rocky core in the center, an icy mantle in the middle and an outer gaseous hydrogen/helium envelope. The rocky core of Uranus is relatively small, with a mass of 0.55 Earth masses and a radius less than 20 percent of Uranus's; the mantle is about 13.4 Earth masses, and comprises the bulk of the planet; the upper atmosphere weighs only that of 0.5 Earth masses and extends for the last 20 percent of Uranus's radius.

Illustration showing the core, mantle and crust of Venus. At the center of Venus is a primarily solid iron core, which underlies a thick mantle made mainly of silicate minerals. On top of this is a very thin crust, which is only around 30 kilometers thick (compared to a maximum of around 70 kilometers for Earth's crust). Venus also has a thick, acidic atmosphere, which traps the heat of the Sun (a runaway green house effect). This makes Venus the hottest planet in the solar system, with surface temperatures reaching over 400 degrees Celsius.

Illustration showing the core, mantle and crust of Venus. At the center of Venus is a primarily solid iron core, which underlies a thick mantle made mainly of silicate minerals. On top of this is a very thin crust, which is only around 30 kilometers thick (compared to a maximum of around 70 kilometers for Earth's crust). Venus also has a thick, acidic atmosphere, which traps the heat of the Sun (a runaway green house effect). This makes Venus the hottest planet in the solar system, with surface temperatures reaching over 400 degrees Celsius.

Artist's impression of one of the two Voyager spacecraft during its encounter with the planet Saturn. The broad white line shows the spacecraft's path through the solar system from Earth, via Jupiter, to Saturn. Also visible are (from left to right) Mars, the Sun, Mercury and Venus. Voyager 1 was launched on 5th September 1977 and flew past Saturn on 12th November 1980. Its sister spacecraft, Voyager 2, launched earlier on 20th August 1977, encountered Saturn several months after Voyager 1 in August 1981. Both spacecraft returned valuable information on Saturn and it's ring system and satellites.

Artist's impression of one of the two Voyager spacecraft during its encounter with the planet Saturn. The broad white line shows the spacecraft's path through the solar system from Earth, via Jupiter, to Saturn. Also visible are (from left to right) Mars, the Sun, Mercury and Venus. Voyager 1 was launched on 5th September 1977 and flew past Saturn on 12th November 1980. Its sister spacecraft, Voyager 2, launched earlier on 20th August 1977, encountered Saturn several months after Voyager 1 in August 1981. Both spacecraft returned valuable information on Saturn and it's ring system and satellites.

The Milky Way and Stars of constellation Sagittarius above stone formations in the heart of the African Sahara, Tassili National Park, Southern Algeria.

The familiar figure of constellation Orion stands very different in these two images. The image at right is taken from the northern hemisphere winter in Iran Alborz Mountains while the image on the left shows the coast Tasmania-Australia nearly at the same time of year.

The familiar figure of constellation Orion stands very different in these two images. The image at right is taken from the northern hemisphere winter in Iran Alborz Mountains while the image on the left shows the coast Tasmania-Australia nearly at the same time of year.

Sirius is the brightest star in night sky. It is also the alpha star of constellation Canis Major or Big Dog, a winter constellation from the Northern Hemisphere.

Sirius is the brightest star in night sky. It is also the alpha star of constellation Canis Major or Big Dog, a winter constellation from the Northern Hemisphere.

Photomontage/carte: constellation et lettres grecques. La Croix du Sud est la plus petite constellation du ciel mais c'est l'une des plus celcbres. Elle est representee sur de nombreux drapeaux nationaux et a servi de guide aux premicrs navigateurs circumterrestres. Elle n'est visible que depuis l'Hemisphcre Sud. On remarque r sa gauche le "Sac r Charbon"; un nuage de poussicres interstellaire.

Photo et carte celeste d'Orion avec denominations grecques. Situee sur l'Equateur Celeste, la constellation d'Orion est visible des deux hemisphcres. On peut l'admirer en hiver en Europe. Orion representait un chasseur chez les Anciens Grecs. On remarque sur l'image la nebuleuse d'Orion (M42), ainsi que la "Boucle de Barnard" et la minuscule "Tete de Cheval".

Carte et denominations grecques. Le Sagittaire representait un Centaure bandant un arc pour les anciens Grecs. Cette constellation est l'une des plus belle du ciel car elle est traversee par la Voie Lactee. C'est dans cette direction que se situe le centre galactique (le coeur de notre galaxie). Le Sagittaire est visible en ete en Europe , sur l'horizon sud. La carte montre les differents objets qu'elle contient (amas, nebuleuses, etc.).