The Solar SystemSolar SystemSolar System consists of the Sun and everything that orbits around it, including planets, moons, asteroids, comets and meteoroids.

The planets in the Solar System are often considered in two groups – the Inner Solar System and the Outer Solar System.

The orbital eccentricityeccentricity eccentricity of an astronomical object is a parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values between 0 and 1 form an elliptic orbit, 1 is a parabolic orbit, and greater than 1 is a hyperbola.

The Sun is a star and the largest object of the Solar SystemSolar SystemSolar System. It contains 99,86% of the Solar System’s mass. It is the source of energy, mostly radiated in form of electromagnetic radiation. The energy emitted by the Sun is a result of nuclear fusion of hydrogen into helium, which takes place in the Sun’s core where the temperature reaches about 15000000 K.

It is the smallest of the planets and the closest to the Sun. The temperatures on the planet’s surface can reach up to 450ºC during the day and fall down to -170ºC in the night due to its extremely thin atmosphere. The planet has no natural satellites.

Venus has similar size to the Earth. The atmosphere there is ninety times denser as that on the Earth. It is the hottest of the planets - the temperatures reach up to 465ºC. Venus rotates around its axis in the opposite direction than most planets.

Earth is the largest and densest of the inner planets. It has one natural satellite, the Moon. Our planet is the only place where life is known to exist. The atmosphere is different from those of the other planets.

Mars is smaller than Earth and Venus. The atmosphere on this planet is inhospitable for human life. Its reddish colour comes from iron oxide contained in its soil. Mars has two tiny natural satellites: Deimos and Phobos.

The asteroid belt occupies the orbit between Mars and Jupiter. The asteroids are called small Solar SystemSolar SystemSolar System bodies which means that they are neither a planet, nor a dwarf planet, nor a natural satellite. The size of an asteroid ranges from a few meters to hundred kilometers. If their diameter is smaller than one meter, then they are called meteoroids. The asteroid belt contains enormous number of such objects.

Jupiter is the largest planet in the Solar System and consists of gases that transform into a liquid state in the lower atmosphere. It has four large and many smaller satellites. The confirmed number of Jupiter’s satellites is 79. Jupiter has visible colourful belts caused by strong winds in the planet's upper atmosphere.

Saturn is the second largest planet in the Solar System. It is a gas giant made up mostly of hydrogen and helium surrounded by rings made up of small rocks and ice particles. Saturn has 62 satellites.

Uranus is the lightest of the planets in the Outer System. It has 27 satellites. Uranus orbits the Sun almost on its side because its axis of its spin is very strongly tilted, over ninety degrees to the ecliptic.

Neptune is the planet whose existence has been determined using mathematical calculations. This planet was first observed in 1846. It is smaller than Uranus but has a greater mass. Neptune has 14 known satellites.

The units expressed in kilometers are useful for measuring distances on the Earth, but they are not very convenient for distances throughout the Solar SystemSolar SystemSolar System. Therefore a special unit was introduced.

The average distance between the centre of the Earth and the centre of the Sun is called Astronomical Unitastronomical unitAstronomical Unit (1 AU). This distance is about 150000000 km (exact value is 149597870700 m).

If we want to look beyond the Solar System, the larger unit is necessary. The light‑yearlight‑yearlight‑year (ly) is the distance which light can travel in one year. The nearest star (after the Sun) is Alpha Centauri, which is 4,37 light‑years away from the Earth. It means that light from this star reaching the human eye left its source 4,37 years ago.

Układ Słoneczny

galaktyka

jednostka astronomiczna

rok świetlny

ekscentryczność

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