The Solar System; planetary orbits
The orbits of the 8 planets in our Solar System are elliptical.
planet, Solar System, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, planetary orbit, gas giant, rocky planet, dwarf planet, asteroid, asteroid belt, Sun, star, astronomical object, moon, Milky Way, circulatory system, rotation, spiral galaxy, astronomy, geography
Mercury is one of the planets of the Solar System, an inner planet closest to the Sun. The smallest planet of the Solar System; 2 of the moons are larger than Mercury: Ganymedes (orbiting Jupiter) and Titan (orbiting Saturn). It is a rocky planet (terrestrial planet), the second most dense in the Solar System (5.43 g/cm³ or 0.196 lb/in³), due to its iron core. When observed from the Earth, it is always close to the Sun, never moving further away than 22 degrees from it, and it has phases, similarly to the Moon.
Venus is one of the planets of the Solar System, the second closest inner planet to the Sun. It is a rocky (terrestrial) planet, with great density (5.25 g/cm³ or 0.196 lb/in³). It is very similar to the Earth, in size and mass, and it is often called the sister of Earth.
Jupiter is the fifth planet from the Sun, second from the Earth, the closest of the outer planets. It is the largest planet in the solar System, its diameter is 142,984 km (88,846.14 mi), with two and half times the mass of all the other planets combined.
Saturn is the second largest planet in the Solar System, a spectacular outer planet. It is a gas giant, or Jupiter-like (Jovian) planet.
Saturn is the most oblate planet, because of its high speed of rotation and low density. It is the least dense planet in the Solar System, the only one with a density less than that of water (0.69 g/cm³ or 0.025 lb/in³).
The Sun is one of the billions of stars in the Milky Way, located in the plane of our barred spiral galaxy, in the Orion spiral arm. The Sun, and the whole solar system orbit around 27,000 to 28,000 light years away from the center of the disk, which measures 50,000 light years in radius. It takes roughly 240 million years for the Sun to complete one orbit. The environment of the solar system is sparse, the nearest stars – Proxima Centauri and the double system of Alpha Centauri – are 4.2–4.4 light years away from us, and there are only 11 stars within 10 light years.
By solar system we mean the Sun and all the variously sized celestial bodies orbiting it. The solar system is the area where the gravitation of the Sun is dominant. This is a sphere of about 2 light years in radius; on its border the gravity of the Sun is equal to the gravity of the nearest stars. The solar system is completely filled with solar wind, a continuous flow of electrically charged particles emitted by the Sun.
The solar system consists of the Sun, the planets, the moons of the planets, asteroids and comets, meteoroids and interplanetary matter i.e. dust and gas. Eight planets orbit the Sun; six of these have moons, the exceptions being Mercury and Venus.
In the order of their distance from the Sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Planets can be divided into two separate groups: four terrestrial or Earth-type planets and four gas giants, also called Jovian planets. Terrestrial planets are closer to the Sun. They are smaller and denser, rotate more slowly, and have thinner atmospheres and weaker magnetic fields.
All of the planets orbit the Sun on nearly the same plane, in the same direction, their motion is direct, which means they move in an anticlockwise direction, as seen from the North Pole of the Earth. Except for Venus and Uranus, their rotation is direct too. The Sun also rotates in this direction.
Planets are kept in orbit by the gravity of the Sun. The mass of the Sun is 750 times larger than the total mass of the planets. There is also gravitational force between the planets; therefore, they influence each other’s motion. As a result, their orbits might undergo slow, minor changes.
Besides planets, there are billions of small objects in the solar system. Asteroids can be found just about everywhere. Many of them have orbits that cross that of the Earth. Most of the asteroids are located in two zones. The inner asteroid belt is between Mars and Jupiter (where there are at least 1 billion asteroids larger than 1 km or 0.62 mi in diameter); the outer belt, i.e. the Kuiper belt – is located beyond the orbit of Neptune (where several thousand Pluto-like, icy asteroids have been discovered).
Since 2006, Pluto has no longer been considered a planet. Pluto and a few other large asteroids are called dwarf planets. The orbits of the majority of the comets are entirely different from that of other objects: they have elongated elliptical orbits with different orbital planes. As the 5–20 km (3.1–12.4 mi) large icy core evaporates near the Sun, a rare, spectacular tail is formed. Due to solar wind, this tail points away from the Sun. Billions of comets orbit in the Oort cloud, the outer region of the Solar system, 0.5–2 light years from the Sun.
Since 1995, numerous exoplanets have been discovered around hundreds of stars. In many of these systems, giant planets orbit the stars, therefore we can safely assume they are not similar to our solar system.
The three important laws describing planetary motion were formulated by Johannes Kepler.
The diameter of our galaxy is about 100,000 light years; it contains more than 100 billion stars, one of which is our Sun.
A demonstration of nearby planets, stars and galaxies.
The inner planets of the Solar System are terrestrial planets while the outer planets are gas giants.
This animation introduces the studies of astronomers and physicists whose works fundamentally changed our view of the universe.
The diameter of the Sun is about 109 times that of the Earth. Most of its mass consists of hydrogen.
Uranus is the 7th planet from the Sun, a gas giant.
The animation shows the two-seater Lunar Rover used in the Apollo 15 mission
Comets are spectacular celestial bodies orbiting the Sun.
The Earth is a rocky planet with a solid crust and oxygen in its atmosphere.
Galileo Galilei's scientific achievements contributed greatly to the advancement of physics and astronomy.
This animation presents some interesting facts in the field of astronomy.
Jupiter is the largest planet of the Solar System, it has two and a half times the mass of all the other planets combined.
Possible traces of water and life are sought on Mars.
The first calendars and time-measuring instruments were already used by ancient Eastern civilizations.
Mercury is innermost and smallest planet of the Solar System.
Neptune is the outermost planet of the Solar System, the smallest of the giant planets
The largest satellite of Pluto is Charon.
Saturn is the second largest planet in the Solar System, easily recognisable by its rings.
The formation of the Sun and the planets started with the contraction of a dust cloud about 4.5 billion years ago.
Venus is the 2nd planet from the Sun, the brightest object on the night sky (after the Moon).
The Voyager space probes were the first man-made objects to leave the Solar System. They gather data about outer space and carry information about humanity.
A spacecraft on its path is in a constant state of free fall.
The Hubble Space Telescope orbits outside the distorting influence of Earth´s atmosphere.
Neil Armstrong, one of the crew members of Apollo 11 was the first man to set foot on the Moon.
This animation demonstrates Sir Isaac Newton's three laws of motion that laid the foundation for classical mechanics.
During its orbit around the Earth, the visibility of the Moon's illuminated part constantly changes.
Satellites orbiting the Earth can be used for civilian or military purposes.
Studying Ceres and Vesta will help us learn more about the early history of the Solar System and how rocky planets are formed.
The Moon is the Earth's only natural satellite
The apparent movement of the Sun is caused by the Earth's rotation around its axis.
The animation shows the way forces act on wheeled vehicles and vehicles with runners.
The International Space Station is a habitable satellite built with the cooperation of 16 countries.
Space probes and Mars rovers examine the structure of Mars and possible traces of life.
The Earth is composed of several spherical layers.
The Cassini spacecraft was exploring Saturn and its moons for nearly 20 years.
The New Horizons space probe was launched in 2006, with the objective to study Pluto and the Kuiper Belt.
Yuri Gagarin became the first human in space on April 12, 1961.