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The Solar System Our solar system is a part of the Milky Way, one of a billion other galaxies, and came into existence 4 to 5 billion years ago. Our sun is in one of the spiral arms of the milky way about 27,000 light-years from its center and moves every 240 million years around its middle point. 1 light-year (Lj) is the distance that light travels in the course of a year. 1 Lj corresponds to 9.5 trillion km. The speed of light, c = 300,000 km/s ( ~ 1,000,000 000 km/h). Besides the sun, planets with their moons, planetoids, comets, and meteorites belong to our solar system, as well as interplanetary material like gas and dust. The sun itself contains over 99.9% of the entire solar system. The order of the planets starting closest to the sun is the following: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto. The planets revolve around the sun in the same direction on similar semicircular, elliptical orbits. All planetary orbits (with the exception of Pluto’s) proceed with small deviations in a single ecliptic plane. The solar system is a construct of a large flat disc with the sun in its center. The earth is closest to the sun at the beginning of the year in January with a distance of 147.1 million km and is furthest from the sun in July with a distance of 152.1 million km. In its orbit around the sun, the earth reaches its quickest speed when it is closest to the sun and slowest speed at the furthest distance. The average speed in its orbit around the sun is just barely 30 km/s (~ 100 000 km/h). The Marburg Planetary Learning Path has a scale of 1 to 1 billion for our solar system, meaning that 1 m in the model corresponds to 1 million km in reality. In Marburg’s Planetary Learning Path, the distances of the celestial bodies as well as their size were designed to correspond to this scale. The almost 6 billion kilometers from the sun that are between the sun and Pluto’s orbital become thereby about 6 km, and the diameter of the earth shrinks from 12,756 km to 1.3 cm. Due to this scale, the distance from Frankfurt to Rome (1,000 km) becomes just a “length of 1 mm (!). The light would thus have a speed of only a little more than 1 km/h in this scale. In the model, a pedestrian would thus move about 4 times as quickly as the speed of light, and whoever is riding a bike would move at more than 10 times the model’s speed of light.
Sun Our central star is 4 to 5 billion years old and belongs to the relatively small stars of the universe. Betelgeuse, the eastern shoulder star of the well-known constellation Orion, for example, has a diameter about 700 times that of our sun. The next-closest visible star in the northern hemisphere is Sirius, the brightest star in the sky, at a distance of circa 80 trillion km (that is an 8 with 16 zeros). Light, i.e. radio, signals would require 8.7 years to travel this distance. At a speed of 100,000 km/h, a space ship would take 90,000 years to travel this distance. The sun shines a mostly in a yellow color due to its surface temperature of about 5,500 °C and contains over 99% of the mass of the solar system. The sun creates its energy in its most interior area through unimaginable high pressures and temperatures via the fusion of hydrogen nuclei into helium (nuclear fusion). A part of the matter is transformed to radiation, part of which is light and warmth. To create the same amount of energy as the sun does in a second, a modern atomic power plant would have to be at full power for 10,000 years. The sun thus loses about 4 million tons of its mass per second, but its hydrogen reserves will be sufficient for quite a few billion years. After depleting its reserves, the sun will expand like a balloon to become a so-call Red Giant, the external edge of which will reach as far as Venus’ orbit. Due to the strong radiation and the high temperatures, there will be no form of life on Earth that will be able to exist, since all water will have evaporated and even the earth’s crust will be molten. The sun will then blast a large portion of its matter into space in something similar to an explosion and will then become a White Dwarf, then being about the size of the earth. The matter in it will be so densely packed that a thimble-full would weigh multiple tons on the earth’s surface. The sun, or what remains of it, from this stage onward will no longer produce any energy but will slowly glow out of energy over billions of years. Did you know that the sun (thus also we) are whirling around the center of Sun in Numbers
Mercury Mercury, named for the Roman messenger-god (Greek: Hermes) and god of merchants and thieves is the quickest runner of the planets, spinning around the sun at almost 50 km/s or 180,000 km/h. Mercury is, when viewed from Earth, only a stone’s throw from the sun and can thus only be seen shortly before sunrise in the East or shortly after sunset in the West. In our region, searching for it is pretty much futile due to the constant layer of condensed water and the strong illumination of the sky from artificial lights. Its surface is not notably protected by any atmosphere and is covered with craters, similar to that of the moon. On the day side of Mercury, the sun heats the surface to enormous temperatures, and on the opposite side, the temperatures fall to far below freezing. Due to its low rotational speed, Mercury only turns three times in two Mercury-years (two of its orbits around the sun). Seen from the earth, the second smallest planet often only seems to be a small sickle like the view of the moon and Venus from Earth. In 1975, the space probe, Mariner 10, flew only 300 km away from Mercury. Mercury in Numbers:
Venus Although named for the Roman godess of love and beauty (Greek: Aphrodite), Venus is a truly hellish planet. Venus is only a little smaller than the earth and its closest neighbor (the least distance between the two being 40,000 km) but, in contrast, is constantly surrounded by light-impermeable clouds of carbon dioxide in its atmosphere. Water is not present and only occasionally does it rain sulfuric acid droplets, which evaporate before they reach the ground. Through the concurrent greenhouse effect, the surface of the planet is very hot. For this reason, it is the hottest planet in the solar system. Water would immediately start to boil and even lead and zinc would melt. The Space probes have identified mountains, canyons, and high, inactive volcanic cones on the surface of the desert-like planet. A large portion of any light shone in the direction of Venus cannot permeate the thick cloud cover and are reflected, such that Venus is the brightest object in the firmament next to the sun and moon. Appropriately called the morning or evening star, it shimmers softly and without twinkling in the sky. Depending on its orbit, Venus is visible in telescopes as a large or small sickle, thus the fluctuations in its brightness. Our neighbor-planet requires more time for a single rotation on its axis than for an orbit around the sun, thus one day on Venus requires more time than a year on Venus. Seven Soviet Verera-type space probes landed softly on the surface of Venus between Venus in Numbers:
Earth The Earth, the blue planet, belongs to the small companions of the sun and is the only planet in our solar system on which higher life forms have come into existence. It is also the only planet with a significant amount of oxygen in its atmosphere and has fluid water on its surface. The comparatively thin layer of air, which would be less than a millimeter thick on a model Earth, protects life from destructive UV radiation and X-rays on the one hand and on the hand lets as much light and warmth through, such that the optimal requirements for the emergence of life are present. The rotational axis of the earth is at a 24.5° tilt in comparison to its path of orbit, such that, according to the position in its revolution around the sun, it alternates the heavier distribution of sunlight to the northern and southern hemispheres. This is the cause for the seasons on Earth and not, as is often falsely assumed, that the changing distance to the sun from its path of orbit. In order to visualize the construct of the earth, it is often compared to a raw egg. In this model, the thickness of the eggshell would be the solid crust of the earth, the egg white would be the fluid mantel of the earth, and the egg yolk would be the solid core of the earth, which consists mainly of nickel and iron. The earth is, as most other planets, not an ideal sphere but is instead a little flat at its poles. The circumference of the earth around the equator is about 40,070 km and around the poles about 40,030 km. The earth is accompanied by a moon, which is the only celestial body that has heretofore been reached by mankind. Thus, no man has been further away from the earth than the moon (384,000 km; in the model: 38.4 cm). In comparison to the other distances in the solar system, this was just a small hop; Mars alone is 200 times as far away when Earth is at the closest orbit to it. Do you know that the gravitational pull resulting from the moon also raises and sinks the solid ground on Earth by about 30 cm twice a day? Earth in Numbers
Mars Because of its red color, Mars was named for the Roman god of war (Greek: Ares); its moons are called Phobos (Greek for fear) and Daimos (Greek for to strike fear). Mars has only a very thin atmosphere, consisting mostly of carbon dioxide and a sandy, stony surface that contributes to the red color via the high content of iron oxide. The canals formerly sighted have been proven to be faked, but notwithstanding there are geological formations which must have be formed by fluid water. With a height of over 25 km and a crater diameter of 500 km, Olympus Mons is the highest and largest volcano in the solar system. On its poles, large tracts of ice can be recognized, which change there size with amount of sunshine, e.g. Martian seasons. These seasons are created on Earth by its tilted rotational axis, in comparison to its orbital vector. Mars is definitely the best researched planet. Over 20 Soviet and U.S.-American space probes have researched it. The first live television pictures reached the earth from the Pathfinder Mission in 1997. Although unlikely, it is still impossible to definitely rule out whether there are or were simple forms of life on Mars, despite the fact that no sign of living Martian life form has yet been discovered. Mars may be the first (and probably the only) planet that mankind will make a landing on in the foreseeable future. Did you know that in the past, you could see more than 3,000 stars on a clear night and today at best only a few hundred? Mars in Numbers:
Planetoids or Asteroids Between Mars and Jupiter, multiple small and large celestial bodies were discovered: the planetoids and asteroids. Today, the orbits of more than 5,000 planetoids are known. The largest planetoid, Ceres, has a diameter of about 900 km. It is thought that the so-called Planetoid Belt consists of more than 50,000 objects with more than 1 km diameter. A few planetoids deviate strongly from the orbit of the Planetoid Belt and cross even into Earth’s orbit.
Jupiter The source of the name for this planet, Jupiter (Greek: Zeus), toppled his father Kronos and became therewith the highest god on Olympia, the god of Earth and Heaven. The moons of Jupiter were all named for Zeus’ lovers. Jupiter is the largest planet in the solar system; it alone has almost as much mass as all of the other planets combined. It is justifiably regarded as a gas planet, because its largest part (> 70 %) consists of gaseous hydrogen and probably only has a small core, being about 20,000 km in diameter. In only 10 hours, the giant planet makes one complete rotation on its axis, such that speeds of up to over 40,000 km/h arise at its equator. On the surface of its atmosphere, there are immense storms with up to 1,500 km/h, the best known of which, the Red Eye, has been determined to be the eye of the storm. It has already been observed for almost 400 years and has a longitudinal diameter of over 40,000 km, making it 3 times the diameter of Earth. Of the many moons with accompany Jupiter, the four largest were already discovered by Galileo Galilei in 1610. These Galileic moons, Io, Europa, Ganymede and Kallisto, are identifiable from the earth with binoculars. The remaining moons were first discovered only upon the application of a strong telescopes or space probes, as are the rings of all four large gaseous planets. All of the Galileic moons are as large as the planet Pluto and consist of solid material, just like the small planet. The largest moon of Jupiter and of the whole solar system is Ganymede, which, with a diameter of 5,260 km, is larger than Mercury and almost the size of Mars. On the moon Io, there has been active volcanic activity observed. Even a thin atmosphere has been discovered on both of these moons. These moons are therefore more interesting to us than Jupiter itself. Both the Pioneer and Voyager space probes delivered important data about Jupiter and its moons in the 70’s. Did you know that there are stars, which are 1,000 times the size of our sun? Jupiter in Numbers:
The second largest planet is named for Saturn (Greek: Cronos), who was Zeus’ father and the first ruler of Olympia until he was toppled by Zeus. Saturn is a gas planet like Jupiter and Uranus and is especially noteworthy due to its extensive rings, which are identifiable even with small telescopes. It is the furthest visible planet, which can be seen with the naked eye. Saturn has the lowest density of all planets and is even lighter than water. Its rings consist of thousands of different rings, as small as microscopic particles of ice and dust and as large as immense boulders, many meters in diameter. The rings have a diameter of almost 300,000 km and are almost half as wide but only about 1 km thick. The number of Saturn’s moons cannot presently be exactly determined. The space probe, Pioneer 10, discovered multiple new moons, such that it is now said that Saturn has at least 20 moons, thus being the planet with the most natural satellites. The Voyager missions in 1980 and 1981 sent especially clear and detailed photographs of the planet, its rings, and its moons back to earth. Saturn in Numbers:
Uranus Uranus was named for the first ruler of the world, a.k.a. god of the world, god of the heavens, and father of Cronos. The Planet was unintentionally discovered by Friedrich Wilhelm Herschel in Berlin in 1781. With some certainty, it can be said that astronomers had already observed Uranus but had not thought it was a planet due to its relatively low-speed orbit, as viewed from Earth, which makes it seem practically immobile in the sky. Its thick atmosphere is 80% hydrogen, which does not permit a further look at its interior layers. The rotational axis of Uranus is at a 90° tilt, compaired to its orbit, such that the gaseous planet waltzes on its orbital path. Voyager 2 delivered the first pictures of its rings in 1986, and in the beginning of 1998, Uranus in Numbers:
Neptune This planet, discovered in 1846 by Johann G. Galle in Berlin, was named for the Roman god of the sea (Greek: Poseidon, Brother of Zeus) and was discovered by predicting its position from irregularities in the orbit of Uranus. Neptune has characteristics similar to those of Uranus; particular features still have not been clarified. Besides hydrogen and helium, the atmosphere of the blue-shining planet was determined to also contain ammonium and methane. A giant dark blob in the upper atmosphere of the planet may be a large circular storm, such as the one on Jupiter. From the movements of the cloud bands, very high wind speeds (above 1,000 km/h) in Neptune’s atmosphere could be interpolated. Voyager 2 discovered a system of rings and six smaller moons around the planet in 1989; the probe left our solar system and has been traveling since then via its inertia into interstellar space. Neptune is the furthest planet from the sun, from which the probe delivered information about. All data that reached us from Voyager 2 traveled 4 hours until it arrived on Earth. Due the very elliptical orbit of Pluto, Neptune was the furthest planet from the sun from 1979 until 1999; Pluto, however will, however, be the furthest planet from the sun for the next 230 years. Neptune in Numbers:
Pluto The smallest and most distant planet was discovered in 1930 and named for the god of the underworld (Greek: Hades) and his accompanying moon Charon for the ferryman that takes the dead across the river Styx, which constituted the border to the underworld. Both celestial bodies rotate around one another like two spheres on a rod in a bound system, in which Pluto and Charon always have the same side facing each other. Charon was first discovered in 1948 in an orbit only 20,000 km from Pluto, and since it is more than half the size of Pluto, Pluto and Charon must actually be described as a double planet. During newer research, more and more smaller planetoids beyond Neptune’s orbit were found. The case is such that Pluto and Charon can now be assumed not to really be “real” planets, instead belonging to a second planetoid belt (Kuiper Belt), accordingly named the Plutinos. Pluto’s path of orbit is very strongly elliptical; its shortest distance from the sun is 4.4 billion km, and its longest distance is 7.3 billion km. Thus, in the course of every orbit, it is closer to the sun than Neptune for a short while (the last time being from January 1979 until 1999.) Furthermore, its orbit is strongly tilted, in comparison to the (ecliptic) orbits of the earth and all other planets. A space probe has not been able to make it as far as Pluto yet. Pluto in Numbers:
At the End of the Road... At the Pluto Station, you have reached the end of Marburg’s Planetary Learning Path and the model solar system. The sun shines from here only like a bright little radiant disc that looks about as big as a penny that is 50 m away. The light of the sun takes 6 hours to reach this distance in the solar system. The sun’s influence still reaches this far into interstellar space, however. A cloud of material (Oort Cloud) exists at about 1,000 times the distance of Pluto’s orbit from the sun. It is estimated that it consists of billions of single objects, made from ejected particles of comets. It is about 4.3 light years (or 40,000 km in the scale of the Planetary Learning Path) to the next star, Toliman or Alpha Centauri, with its still a little closer little accompanying star, Proxima Centauri. Thus, there is not even enough room on the face of the earth to designate a position for the next-closest star in the scale of Marburg’s Planetary Learning Path. A hundred times larger scale must be used in order to display the distance from the solar system to the next star; the sun in the field in Cappel would then only be 1.4 cm big and would be circled by a 0.1 mm large Earth at a distance of 1.5 m, and Pluto could be found around where Mercury is presently located on the Planetary Learning Path. The model of Alpha Centauri would have to be pretty close to the Genf Sea in Switzerland, and a Sirius model would be best placed on the island of Elba in Italy. A model of the North Star would have to be placed at a distance of 100,000 km and our globe would again be inadequate for such a stellar model. A rocket-propelled space ship in a modern technological design would require a speed of 100,000 km/h for over 400,000 years to reach Alpha Centauri. At the beginning of 1972, the US space probe, Pioneer 10, was sent into space and has since then left our solar system and is already about 10 billion km far away; it has however only managed to make 0.2 thousandths of the journey from the sun to Alpha Centauri. There is pretty much empty space between the stars, because the interstellar material of the galaxy only has a density of a million times less than that of a man-made terrestrial vacuum. It takes over 2 million years for the light from next closest galaxy to reach the naked eye on a good night as a tiny, blurry speck in the Andromeda constellation. With modern technology, signals from object are received from distances of even billions of light-years away. These few examples of the unimaginable dimensions of the universe may give a small insight into the distant fathoms and may make the following clear: “We live on a small planet, orbiting a very average star on the edge of a common galaxy, which is only one of a hundred billion others.” (Stephen Hawking). The text was taken from the brochure for the Schwarzbach-Planetary Way
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