This creative science project in Sweden allows you to climb the sun, moon and stars

Take a cosmic journey with the world's largest model of the solar system.

Written by | Fan Ming

The solar system is a system of planets, asteroids and comets that are bound together by the sun's gravity, including the sun (Sun ☉) and celestial bodies that move directly or indirectly around the sun. The five planets visible to the naked eye in the solar system - Mercury, Venus, Mars, Jupiter and Saturn - were discovered by humans as early as prehistoric times. The ancient Greek philosopher Aristotle and others proposed the "geocentric theory" based on the astronomical observations at the time, and the Greek scholar Ptolemy (Claudius Ptolemaeus) further developed and perfected it. He envisioned that all celestial bodies revolve around the earth in circular orbits or a combination of circular orbits. In the second century AD, the "geocentric theory" was systematized and later became the official cosmology of medieval Europe.

In the 16th century, the Polish astronomer Nicolaus Copernicus tried to replace the geocentric theory with the heliocentric theory, although he still used and believed in Ptolemy's circular orbit theory. The Danish astronomer Tycho Brahe was a legendary figure who observed planets and other celestial phenomena with the naked eye before the invention of the (optical) telescope. The young German astronomer Johannes Kepler summarized the famous "Kepler's Three Laws" from Tycho's planetary observation data, which undoubtedly supported Copernicus's heliocentric theory. More importantly, he deeply realized that the movement of several known planets around the sun should be described by elliptical orbits rather than circular orbits, so that humans knew that the earth itself is also a planet moving in an elliptical orbit around the sun.

In 1687, the first Latin edition of Sir Isaac Newton's famous book "Mathematical Principles of Natural Philosophy" (abbreviated as "Principia") was published. Based on Kepler's three laws, Newton proposed the famous law of universal gravitation in a beautiful mathematical form in the book, and successfully applied it to the observational data of several known planets. He pointed out that all members of the solar system revolve around the common center of gravity of the entire system in elliptical orbits, and this center of gravity must be near the sun with the largest mass. Therefore, for the first time in physics, the theoretical sublimation of the "heliocentric theory" was completed. Later, based on Newton's theory of universal gravitation and the inexplicable deviations in the observational data of the orbital motion of known planets, humans successively searched for and discovered Uranus, Neptune, Pluto and other celestial bodies. This is a great monument in the history of the development of natural sciences, and at the same time established a paradigm for human understanding of natural laws.

Swedish solar system model | imgur.com (left), SSS official website (right)

The Swedish Solar System (SSS) is the world's largest permanent solar system model. This refreshing and unique concept was proposed by Nils Brenning, a plasma physicist at Stockholm University, and Gösta Gahm, an astronomer, at a seminar in the 1990s and began to be created in 1998. In this model, the sizes of the main celestial bodies in the solar system and the distances between them are distributed over a 1,400-kilometer-long Swedish territory from south to north at a ratio of 1:20 million. So far, the model has included more than 20 planets, satellites, asteroids, dwarf planets, comets and other solar system bodies. Each celestial body model has a hosting organization, and it continues to increase and expand.

The Swedish solar system model vividly shows the size and distance ratio of the celestial bodies in the system to the sun, and closely links art, mythology, science, and architectural and cultural activities across Sweden. The model representing the sun is the largest hemispherical building in the world today, the Globen Arena in the south of Stockholm, the capital of Sweden. It was built in 1989, with a diameter of 110 meters and a total volume of 605,000 cubic meters. On May 19, 2021, the arena was officially named Avicii Arena after the stage name of Tim Bergling, a famous Swedish electronic musician who passed away in 2018. The above picture below is a light and shadow show on the exterior of the arena during the United Nations International Year of Astronomy in 2009, commemorating the 400th anniversary of the first use of a telescope by Italian astronomer Galileo Galilei for astronomical observations.

Avicii Arena and sunrise over the Baltic Sea | SSS official website (above), pictures provided by the author (below three pictures)

In the Stockholm area, there are four old and new planetariums that are closely related to this solar system model. The Stockholm Old Observatory is located on a hilltop in the city center. It is the first observatory building of the Royal Swedish Academy of Sciences (KVA). It was built in the mid-18th century and the observatory dome was built in 1875. It used to be Sweden's national zero meridian, and now it is 18 degrees 3 minutes 29.8 seconds east of Greenwich. In the 1930s, the observatory moved to a new site in Saltsjöbaden, a peninsula southeast of Stockholm. Saltsjöbaden Observatory ordered a large number of optical telescopes from famous manufacturers in Germany and other countries, such as the world's largest 40-inch astronomical reflecting telescope at the time. Therefore, its position in Northern Europe is unique, and the seminar that proposed the solar system model was also held at this observatory.

In 1991, the Saltsjöbaden Observatory moved back to the city, settling in Albanova, the Stockholm Center for Physics, Astronomy and Biotechnology in the north of the city. It houses the largest optical telescope in Sweden, with a mirror diameter of 1 meter and a focal length of 11 meters. Cosmonova, an annex of the Natural History Museum (NRM) in Stockholm, is an IMAX 3D cinema located in the dome of NRM and one of the major planetariums in Europe. Both Albanova and Cosmonova end with Nova, which means "nova", specifically referring to the phenomenon that hydrogen accreted on the surface of a white dwarf is heated by the high temperature of the white dwarf to cause a violent nuclear explosion. Almost all nova explosions occur in binary star systems containing white dwarfs. In 1572, Tycho Brahe discovered the supernova SN 1572 (Note: SN is the abbreviation of Supernova in English) and first used this name in his book De nova stella. (Note: Nova and supernova are actually two completely different phenomena.)

Top left: Stockholm Old Observatory, Top right: Saltsjöbaden Observatory

Lower left: Albanova, lower right: Cosmonova | Photo courtesy of the author

The word "planet" in English comes from the ancient Greek word πλανήτης, which means "wanderer", corresponding to Roman or Greek gods. In ancient China, the five classical planets were named after the Five Elements theory: "wood is green, gold is white, fire is red, water is black, and earth is yellow". In 1859, Alexander Wylie, a British sinologist and missionary of the London Missionary Society, and Li Shanlan, a Chinese mathematician, jointly translated the popular masterpiece "Outlines of Astronomy" by the famous British astronomer Sir John Frederick William Herschel. This was the first introduction of the heliocentric theory in Chinese literature, and it was also the first appearance of the Chinese word "planet". (Note: The European Space Agency launched a space astronomical satellite in the far-infrared and submillimeter bands in 2009, named after Herschel.)

In 2006, at the 26th IAU (International Astronomical Union) held in Prague, Czech Republic, astronomers accurately defined three conditions for a planet: orbiting directly around a star, having a mass large enough to be spherical, and being able to clear small bodies in nearby orbits. It was also at this IAU conference that astronomers voted to reject Pluto in the solar system as a planet. From this historical moment, the solar system went from nine planets to eight planets. This was mainly because humans discovered Kuiper Belt objects farther from the sun in the solar system, many of which were larger than Pluto, so Pluto was unfortunately excluded from the ranks of planets.

According to the rocky surface of the planets, the eight planets in the solar system can be divided into "terrestrial planets" with rocky solid surfaces, namely Mercury, Venus, Earth and Mars; "gas giant planets" with hydrogen and helium as the main components, namely Jupiter and Saturn; "ice giant planets" with icy surfaces under a thick atmosphere, namely Uranus and Neptune. Among them, Mercury and Venus are closer to the sun than the earth, and will not appear around midnight. They will show a complete series of phase changes relative to the earth, so they are also called "inner planets", and the other five planets are called "outer planets".

The terrestrial planets have dense rocky components, with impact craters and geological features of varying sizes formed by meteorite impacts. They do not have external ring systems orbiting the planets. Mercury and Venus have no satellites, while Earth has one, the Moon, and Mars has two. Except for Mercury, all terrestrial planets have atmospheres that produce substantial weather changes. The remaining four giant planets have no clearly defined solid surfaces, contain 99% of the mass of the known orbiting bodies around the Sun, and have their own ring systems orbiting their respective planets. The objects representing the four terrestrial planets are all located in or near Stockholm, while the four giant planets are located in different cities north of Stockholm on the Baltic Sea.

Solar System | es.blastingnews.com

Terrestrial planets

Mercury is the smallest and closest planet to the Sun, with an orbital period of 87.969 Earth days. It has the largest eccentricity among the eight planets (between 0 and 1, the larger the eccentricity, the flatter the ellipse), and its orbital speed far exceeds that of other planets in the solar system. Mercury's rapid movement gave it the name Mercury, the fast-flying messenger who delivered messages to the gods in Roman mythology, corresponding to Hermes in Greek mythology. The symbol for Mercury ☿ represents Mercury's helmet with wings and his staff. In the Five Elements, black is used to match Mercury, and in ancient China, Mercury was also called "Chenxing". The model of Mercury is located in the City Museum in Slussen, south of Stockholm. It has a diameter of 25 cm and is 2.9 km away from the solar model. The model depicts Mercury's craters and symbols such as orbital drift, the latter of which is an important confirmation of Einstein's theory of relativity.

Model of Mercury | Image provided by the author

Venus is the second planet from the inner to the outer solar system. Its orbital period is 224.7 days. It is second only to the moon in brightness in the night sky. Venus is named after the goddess of love and beauty in Roman mythology, Venus, which corresponds to Aphrodite in Greek mythology. The symbol of Venus, ♀, represents the dressing mirror in Venus's hand, which is also a symbol of women. In the five elements, white is matched with Venus. It was called "Taibai" in ancient times. It was called "Qiming" when it appeared in the east in the morning and "Changgeng" when it appeared in the west in the evening. The size, mass, volume and distance of Venus from the sun are similar to those of the Earth, so it is often called the sister planet of the Earth. However, Venus is completely different from the Earth in other aspects. Although Venus has the thickest atmosphere among the terrestrial planets, its main component is carbon dioxide.

More than four hundred years ago, Galileo was also the first person to use a telescope to discover the details of the movement of many celestial bodies in the solar system. In 1610, he observed that Venus would show phase changes like the moon. Under the framework of the geocentric theory, Venus should always show a single phase, which became a strong evidence to prove Copernicus' heliocentric theory. On December 4, 1639, two British astronomers, Jeremiah Horrocks and William Crabtree, independently observed and recorded the transit of Venus for the first time in history, and discovered its cyclical pattern, which was later recognized as the beginning of modern British astronomy. On September 15, 2020, astronomers detected phosphine in the atmosphere of Venus, which may be a sign of extraterrestrial life. The model of Venus is located outside the aforementioned AlbaNova center, with a diameter of 62 cm and a distance of 5.5 kilometers from the solar model in Stockholm.

Model of Venus | Image provided by the author

The Earth is the third planet from the inside to the outside of the solar system. It is the largest terrestrial planet in terms of mass and density. The Earth is the only celestial body in the universe known to mankind where life exists. It is the home of mankind. The Earth rotates and revolves simultaneously (the rotation axis and the revolution axis have an angle of 23.5 degrees), which results in the alternation of day and night and the four seasons. The English name of the Earth, Earth, comes from Middle English. In many cultures, the Earth is the earth mother goddess in charge of fertility. The symbol of the Earth ⊕ represents a sphere with an equator and a meridian. The Chinese word "Earth" first appeared in the period of Western learning in the Wanli period of the Ming Dynasty. The Italian Jesuit missionary Matteo Ricci first used the word in the longitude and latitude world map "Kunyu Wanguo Quantu" compiled and published when he was preaching in China. He and Xu Guangqi translated the first six volumes of Euclid's "Elements of Geometry".

The original Earth was formed about 4.54 billion years ago, the biosphere began to evolve 3.5 billion years ago, and photosynthesis began to produce oxygen 2.7 billion years ago, thus forming an atmosphere containing 21% free oxygen. The Earth has a unique hydrosphere among terrestrial planets, 71% of its surface area is covered by oceans, and it appears blue from a distance, so it is also known as the "Blue Planet". The Earth has only one natural satellite, the Moon, which is 380,000 kilometers away from the Earth. It is also the only large satellite owned by terrestrial planets in the solar system. The origin of the Moon remains a mystery. The Earth model is located at the entrance of the aforementioned Cosmonova, with a diameter of 65 cm. The Moon model is fixed on a pillar 20 meters away, with a diameter of 18 cm. The Earth model is 7.5 kilometers away from the Sun model. The actual average distance between the Earth and the Sun is about 150 million kilometers, which is defined as an astronomical unit (Astronomic Unit, abbreviated AU), which is often used as a distance unit between celestial bodies in the solar system.

Models of the Earth and the Moon | Image provided by the author

Mars is the fourth planet from the inside to the outside in the solar system and the second smallest planet after Mercury. It has two natural satellites, Phobos and Deimos. Mars is named after the Roman god of war Mars, and its two satellites are named after Phoebus and Deimos, the sons of Ares, the Greek god of war. The symbol of Mars ♂ represents the shield and spear of Mars, and is also a symbol of male. Because the soil of Mars contains iron oxide (Fe₂O₃), the surface is orange or dark red, and it is often called the "Red Planet". In the Five Elements, red is matched with Mars. In ancient China, it was called "Yinghuoxing" because it glows like fire and its position and brightness often change, making it unpredictable. About 4 billion years ago, Mars had a climate similar to that of the Earth, with rivers, lakes and even oceans. Mars had a thin atmosphere composed mainly of carbon dioxide, and its surface had a large number of craters, volcanoes, peaks and rift valleys.

Mars was once considered the most likely planet in the solar system to have extraterrestrial life, and one of the closest planets that humans can explore. So far, it has been explored by dozens of unmanned spacecraft from different countries. On July 23, 2020, China launched its first Mars probe, Tianwen-1, from the Wenchang Launch Center in Hainan, with the goal of orbiting, landing, and patrolling, opening up China's deep space exploration program. A few days before and after this launch, the United Arab Emirates and the United States also launched Mars probes. On May 15, 2021, Tianwen-1 and Zhurong Mars Rover successfully landed in the southern part of Utopia Planitia on Mars. The Mars model is located in the Mörby Shopping Center in the Danderyd district in the northeastern suburbs of Stockholm. It has a diameter of 35 cm and is 11.6 kilometers away from the solar model. The model is connected to a steel base with an image of the Earth through an "umbilical cord", symbolizing the close connection between humans and Mars through the frequent visits of probes. The main chemical elements and their contents found on Mars are also marked on the surface of the model.

Mars model | Photo provided by the author

Giant planets

Jupiter is the fifth planet from the inside to the outside in the solar system. It is the largest of the eight planets and has the fastest rotation speed (a period of about 10 hours). It has a huge magnetosphere and extremely strong radiation belts, and can be called the "giant" in the solar system. Jupiter's mass is about one thousandth of the sun, but it is 2.5 times the total mass of other planets in the solar system. Its main component is hydrogen (the central core may even have metallic hydrogen formed under high pressure), while helium, which accounts for only one-tenth of the number of atoms, accounts for a quarter of the total mass. Jupiter is the third brightest celestial body in the night sky after the moon and Venus. Jupiter is named after Jupiter, the main god in Roman mythology, corresponding to Zeus in Greek mythology. The Jupiter symbol ♃ represents Jupiter's lightning or eagle. In the five elements, Jupiter is matched with blue. Ancient China called it "Sui Xing" because it takes 12 years to orbit the celestial sphere, which is the same as the earthly branches.

Jupiter is the planet with the largest satellite system in the solar system, with 79 known satellites. It has a dim planetary ring system composed of a lot of dust and black debris. Galileo was the first person to discover Jupiter's satellites. He discovered the four largest ones with an optical telescope in 1610 and named them "Galilean satellites", providing important evidence to overturn the geocentric theory that all celestial bodies revolve around the earth. Jupiter's most famous feature, the Great Red Spot, is a persistent anticyclonic storm larger than the Earth (it has existed for more than 400 years since its discovery). The Jupiter model is located in the lobby of the Clarion Hotel at Stockholm's Arlanda Airport. It is a glowing ring with a diameter of 7.1 meters and is 40 kilometers away from the solar model. The hotel corridor also displays pictures of the Galilean satellites.

Model of Jupiter (left) and image of Galileo satellites (right) | SSS official website, astb.se

Saturn is the sixth planet from the inside to the outside of the solar system. It is mainly composed of hydrogen, with a small amount of helium and other elements. It is second only to Jupiter in volume and is the only planet in the solar system with a density lower than Mercury. The intensity of Saturn's planetary magnetic field is between that of Earth and the stronger Jupiter, and there are auroral rings at the north and south magnetic poles. Saturn is named after Saturn, the god of agriculture in Roman mythology, and its symbol ♄ represents Saturn's sickle. In the five elements, yellow is used to match Saturn, and ancient China called it "Zhenxing". The biggest feature of Saturn is its wide ring system composed of small ice and rock particles, so it is the "Lord of the Rings" of the solar system. In the 17th century, Dutch physicist Christian Huygens discovered Saturn's second largest satellite, Titan, using a telescope he developed. It is the first satellite discovered in the solar system with a thick atmosphere. Later, Italian astronomer Giovanni D. Cassini discovered four more Saturn satellites and the Cassini Gap in Saturn's rings.

Anders Celsius, a famous Swedish physicist and astronomer, founded Sweden's first astronomical observatory in 1741 and proposed the Celsius scale to measure temperature in 1742. The Celsius Observatory in the center of the historical and cultural city of Uppsala is one of the oldest buildings in the city. The Saturn model is located in the observatory, with a diameter of 6.1 meters and a distance of 73 kilometers from the sun model. The small ball in the left picture is the Huygens satellite, and the picture on the right is the Celsius astronomical sculpture near the observatory. When two celestial bodies have the same ecliptic longitude on the celestial sphere, it is called "conjunction". At the end of 2020, the astronomical wonder of "Saturn-Jupiter conjunction" appeared, which is said to be the closest distance between the two planets since 1623.

Celesius Observatory (left) and sculpture (right) | Photo provided by the author

Uranus is the seventh planet from the inside to the outside of the solar system, 18.37-20.08 AU from the sun. It was discovered by Herschel in 1781 and was the first planet discovered using a telescope. Uranus is named after Uranus, the god of the sky in ancient Greek mythology and grandfather of Zeus. It is the only planet in the solar system named after a Greek god. It is written as "Tianyuxing" in Chinese character cultural circles such as China, Japan, and South Korea. The symbol of Uranus is ♅ or ⛢, the latter is a combination of the symbols of Mars and the sun, because Uranus is believed to be controlled by the combined power of the two. Uranus is the planet with the coldest atmosphere in the solar system, with a minimum temperature of only 49K (-224℃), and its outer atmosphere has a complex cloud structure.

Neptune is the farthest from the sun among the eight planets, about 30 AU, with an orbital period of about 165 years, a mass of 17 times that of the Earth, and a radius of 3.86 times that of the Earth. It was discovered in 1846. Neptune is named after Neptune, the god of the sea in Roman mythology and Jupiter's brother, corresponding to Poseidon in Greek mythology. Therefore, the Chinese character is "海王星", and its symbol ♆ represents Neptune's trident. Around New Year's Day in 1613, Galileo observed and depicted Neptune twice, but he mistakenly thought it was a star. More than two hundred years later, French astronomy teacher Urbain Le Verrier predicted Neptune using physical models and mathematical calculations when studying the perturbation problem of Uranus' orbit, and it was discovered by telescope observation in 1846. This is the most successful application case of Newton's theory of universal gravitation. Shortly before Le Verrier's prediction, British astronomer John Couch Adams also calculated the existence of Neptune when solving the problem of Uranus' orbit, but the position error was large and did not attract the attention of the observatory that received his prediction.

Neptune and Uranus are a pair of sister planets. Their atmospheres are basically composed of hydrogen, helium and a small amount of methane. Therefore, both appear beautiful blue in space, but the former is deep blue and the latter is azure blue. Uranus ranks third in volume and fourth in mass in the solar system, with 27 satellites; Neptune ranks fourth in volume and third in mass, with only 14 satellites. The Uranus model (left) is located in the industrial town of Lövstabruk in the north of the Uppland Plain. It has a diameter of 2.6 meters and is 146 kilometers away from the solar model. The Neptune model (right) is located in the small town of Söderhamn on the Baltic Sea. It is an acrylic sphere with a diameter of 2.5 meters. It emits blue light at night and is 229 kilometers away from the solar model.

Uranus model and Neptune model | flickr.com, SSS official website

Asteroids and dwarf planets

Asteroids are celestial bodies in the solar system that are similar to planets and orbit the sun, but are much smaller in size and mass than planets. They are the remnants of the early solar system. There are millions of asteroids with a diameter of more than one kilometer. The main asteroid belt is distributed between the orbits of Mars and Jupiter. There are four asteroid models in the Stockholm and Uppland regions. Eros is the first asteroid landed by a space probe. Before Valentine's Day in 2001, a space probe of NASA landed on its surface, so it was named after Eros, the god of love in Greek mythology. There are also two craters on Eros, named after Jia Baoyu and Lin Daiyu, a pair of lovers in the Chinese classical novel "Dream of Red Mansions". Vesta is the largest asteroid in the solar system and the brightest asteroid visible from the earth. It is named after Vesta, the goddess of protection of the hearth and family in Roman mythology, which is equivalent to Hestia in Greek mythology.

Saltis is an asteroid discovered in 2000 at the aforementioned Saltsjöbaden Observatory in Stockholm. It is named after the nickname of the place. Its diameter is about 2 to 4 kilometers, and its surface area is slightly larger than that of the Saltsjöbaden area. Palomar-Leiden (5025 PL) was once a lost asteroid. It was named after the Palomar Observatory in Los Angeles, USA and the Leiden Observatory in the Netherlands. Except for the ellipsoidal Vesta model with a diameter of 3 cm, the sizes of the other three asteroid models are no more than millimeter level. They are 11, 17 (north), 17 (east), and 60 kilometers away from the solar model respectively. The following pictures show the models of Eros, Vesta, and Saltis, respectively. The first two are located on the campuses of two secondary schools in the northeastern suburbs of Stockholm. Palomar-Leiden is a small dot on the left relief in the first picture of this article. It is located in a park in Knivsta, a small town south of Uppsala.

Model of Eros (upper left), model of Vesta (upper right), model of Celtis (lower) | imgur.com, SSS official website

Dwarf planets, also known as intermediate planets, quasi-planets, and dwarf planets, are celestial bodies with planetary mass but are neither planets nor satellites. Similar to planets, dwarf planets orbit directly around stars and are large enough to make themselves spherical in shape, but are unable to clear small bodies in neighboring orbits. There are currently five dwarf planets recognized by the IAU. The largest known dwarf planet in the solar system and the second largest in mass is Pluto. Pluto was discovered by American astronomer Clyde Tombaugh in 1930 and is named after Pluto, the god of the underworld in Roman mythology. Its astronomical symbol ♇ is a monogram composed of PL. Unlike the orbits of other planets in the solar system, which are close to circles and close to the ecliptic plane, Pluto's orbit is a highly inclined and highly eccentric ellipse.

Pluto was considered the ninth planet in the solar system for 76 years after its discovery. It was not until 2006 that the IAU officially defined the concept of planet and classified Pluto as a dwarf planet. Although Pluto is no longer considered the ninth planet in the solar system, its discovery was based on astronomers' observations of Neptune, which led to the speculation that Uranus' orbit might be disturbed by another planet other than Neptune, which is also the legend of Newton's theory of universal gravitation. The model of Pluto is located on the shore of Dellensjöarna Lake in northern Sweden. This group of lakes was formed by a large meteorite impact 90 million years ago. The model has a diameter of 12 cm and is 300 kilometers away from the solar model. Its base has the appearance of a tomb in the kingdom of the dead, which shows the mythological significance of Pluto. The meteorite impact would definitely destroy all life in the area.

Pluto model | flickr.com

Haumea is the third largest known dwarf planet in the solar system. It was discovered in 2004 and is named after Haumea, the goddess of conservation and mother earth in Hawaiian mythology. Haumea is ellipsoidal in shape and has a rare high-speed rotation, high density and high albedo. Its model was set up in Borlänge, a city in central Sweden, on September 27, 2019, 200 kilometers away from the solar model, and is the latest member to join so far. Makemake is the fourth largest known dwarf planet in the solar system. It was discovered shortly after Easter in 2005 and is named after Makemake, the god of creation and fertility in the mythology of the indigenous people of Easter Island. The Makemake model is located in Göteborg, a city on the west coast of Sweden, 400 kilometers away from the solar model. Pluto, Haumea and Makemake are all objects in the Kuiper belt, a dense disk-shaped area of ​​celestial bodies near the ecliptic plane outside the orbit of Neptune.

Eris, the largest known dwarf planet in the solar system, was discovered in 2005. Initially, Eris was considered the tenth planet in the solar system, but due to the discovery of other similar-sized celestial bodies, the number of solar system celestial bodies that met the original definition of a planet increased sharply, prompting the International Astronomical Union to redefine it the following year. This dwarf planet is therefore named after Eris, the goddess of discord in Greek mythology. The Chinese name comes from the "Book of Songs·Xiaoya·Changdi": "Brothers quarrel over the wall, and defend against external forces (insult)". The model of Eris is located in the northern city of Umeå, with a diameter of 13 cm and a distance of 510 kilometers from the solar model. The following pictures show the models of Haumea, Makemake and Eris. Another dwarf planet is Ceres, but for some reason there is no model of it.

Models of Haumea (left), Makemake (center), and Eris (right) | SSS official website

There are dozens or even hundreds of dwarf planets in the solar system that are almost certain or candidates, and models of four of them are scattered around Sweden. Quaoar was discovered in 2002 at the Palomar Mountain Observatory and is named after the creator god Quaar in the mythology of the local indigenous Tongva people. Its model is located in Gislaved, a small town in southern Sweden, 340 kilometers from the solar model. Ixion is located at the edge of the solar system. It was discovered in 2001 and is one of the largest asteroids discovered by researchers at Uppsala University. Ixion is an arrogant Lapith king in Greek mythology who was punished by Zeus with a wheel of fire. Its model is located in Härnösand, a small town in northern Sweden, 360 kilometers from the solar model.

2007 OR10 was the largest unnamed object in the solar system, slightly larger than Makemake and Haumea. In February 2020, it was officially named after the water god Gonggong in ancient Chinese mythology. According to the Classic of Mountains and Seas, Gonggong was the descendant of Emperor Yan and the son of Zhurong. The model of Gonggong is located in Malmö, a city in southern Sweden, 500 kilometers away from the solar model. When Sedna was discovered in 2003, it was the most distant and coldest object in the solar system. Legend has it that it lives in the depths of the Arctic Ocean, so it was named after Sedna, the frozen sea goddess in Inuit mythology. The Sedna model is located in Luleå, a city within the Arctic Circle, 912 kilometers away from the solar model.

Model of the planet Creator (upper left), model of Ixion (upper right), model of Gonggong (lower left), model of Sedna (lower right) | SSS official website

Other celestial bodies

A comet is a small solar system body whose brightness and shape change with the distance from the sun. It is divided into three parts: the nucleus, the coma, and the tail. The astronomical symbol is ☄. The nucleus of a comet is composed of ice. When a comet approaches the sun, a hazy coma forms around the nucleus, and a tail composed of gas and dust forms in the direction away from the sun. This phenomenon is caused by the solar wind. There are records of comets in ancient Eastern and Western cultures. The original meaning of comet in Chinese is "broom", and the ancients called comets "stars". There are 29 comet pictures on the Mawangdui Han Tomb Silk Book unearthed in Changsha, depicting a total of 19 types of comets. The word "comet" in the Western context comes from the Greek word "long-haired star", which was first used by Aristotle.

Newton made a detailed analysis of the observation records of the great comet of 1680 and personally observed the comet of 1681. In his masterpiece "Principia", he pointed out that "comets are a type of planets that orbit the sun in an orbit with great eccentricity", and used the law of universal gravitation to prove that the orbit of a comet is a conic section. Comets with elliptical orbits can return to the sun regularly, which is called a periodic comet. Halley's Comet is the only periodic comet that can be seen directly from the earth with the naked eye, and it is also the first recurring celestial body in history. In 1705, British astronomer Edmond Halley used Newton's law of universal gravitation to calculate the orbit and period of this comet, and successfully predicted its return in 1758, so it was named "Halley's Comet". The period of Halley's Comet is between 75-76 years. The last return was in 1986, and the next one will be in 2061.

There are two comet models in Sweden, one is Halley's Comet (1P/Halley) and the other is Swift-Tuttle's Comet (109P/Swift-Tuttle). Discovered in 1862, Comet Swift-Tuttle is named after two independent discoverers and is the parent comet of the Perseids, one of the three major meteor showers in the Northern Hemisphere. The model of Halley's Comet is located in Skövde, a city in southwestern Sweden. The image is three reliefs made from drawings by sixth-grade students (upper left) and a comet tail formed by lasers (upper right). It is 260 kilometers away from the solar model. The model of Swift-Tuttle's Comet is located in Karlshamn, a port city in southern Sweden. It has a diameter of less than 1 cm and is 390 kilometers away from the solar model. It is the scaled aphelion of Swift-Tuttle's Comet. The purple oval on the left side of the picture below is its orbit.

Model of Halley's Comet and its orbit diagram | SSS official website (two pictures above), The Sky Live (below)

Periodic comets can be divided into two categories based on their orbital periods: short-period comets and long-period comets. Most short-period comets revolve around the sun, with an orbit size of no more than 10 astronomical units and a period of no more than 200 years. They are in the same plane as the ecliptic plane, and short-period comets are believed to originate from the Kuiper belt. Halley's Comet and Swift-Tuttle's Comet are both short-period comets, the latter of which has a period of 133 years. The orbits of long-period comets are very large, exceeding the order of thousands of astronomical units, and are not limited to the ecliptic plane. In 1950, the famous Dutch astronomer Jan Hendrik Oort speculated that long-period comets with orbits that deviate from the ecliptic plane at a large angle originated from a cloud or cloud cluster at the outermost end of the solar system that envelops the solar system. Later, scientists called it the Oort Cloud. The Oort Cloud is theoretically a spherical cloud cluster surrounding the sun, mainly composed of icy microplanets, but it is still a hypothesis.

Oumuamua is the first extrasolar object discovered by humans in the solar system. It means "scout" or "pathfinder" in Hawaiian. It was discovered by NASA's Panoramic Survey Telescope and Rapid Response System (PANSTARRS) in Hawaii on October 19, 2017. At first it was mistaken for a comet, but after a long period of observation and research, astronomers speculated that this uninvited guest may have come from a star cluster near the solar system and was thrown out by a planet 40 million years ago. On its way through the Milky Way at an extremely high eccentricity, Oumuamua happened to hit the solar system and is moving away from us, never to return. The Oumuamua model is located in Halland, on the southwest coast of Sweden. It has a diameter of 0.3 mm and is 440 kilometers away from the solar model.

The heliosphere, also known as the heliosphere, is a plasma bubble created by the continuous solar wind in the space of interstellar matter. There is a termination shock in the heliosphere, where particles in the solar wind collide with the interstellar medium composed of hydrogen and helium infiltrated from the Milky Way, and the speed rapidly decreases from 0.33 kilometers per second to below subsonic speed. This is the final end of the solar wind and the starting point of interstellar space, which can be said to be "the sun ends here and the stars begin here". The termination shock model is located at the National Institute of Space Physics in Kiruna, the northernmost city in Sweden, 950 kilometers away from the solar model, while the actual distance is about 126.7 astronomical units.

Oumuamua model (left), terminal shock wave model (right) | SSS official website

There are at least trillions of galaxies in the vast universe, each of which contains hundreds of billions of stars and trillions of planets. The 2019 Nobel Prize in Physics recognized two studies, one for the new understanding of the structure and history of the universe, and the other for the first discovery of a planet orbiting a sun-like star outside the solar system. For their "contributions to advancing our understanding of the evolution of the universe and the place of the Earth in the universe", the 84-year-old Canadian-American cosmologist James Peebles, the 77-year-old Swiss astrophysicist Michel Mayor, and the 52-year-old Swiss astronomer Didier Queloz jointly won the Nobel Prize in Physics. Their discoveries have forever changed our understanding of the universe.

Over the past 50 years, Peebles' insights into physical cosmology have enriched the entire research field. His theoretical framework has become the foundation of contemporary cosmology and laid the foundation for the transformation of cosmology from conjecture to empirical science. Using his theory and many observations, it can be inferred that the universe is composed of 68% dark energy, 27% dark matter and 5% matter. In October 1995, Mayor and Queloz discovered for the first time a planet orbiting a sun-like star outside the solar system based on the Doppler effect of stellar spectra using a telescope at the Haute-Provence Observatory in southern France. This is a gaseous sphere comparable to Jupiter, the largest planet in the solar system. This discovery started a revolution in astronomy. Since then, astronomers have discovered more than 4,000 exoplanets in the Milky Way, forcing scientists to revise their theories about the physical processes of planetary origin.

More than 900 years ago, when Su Dongpo, a great writer in the Northern Song Dynasty, climbed the Pingdu Mountain in Sichuan, he left a famous quote that has been passed down through the ages: "Looking up and looking around, the universe is vast, and the sun, moon and stars are at my disposal." In today's highly developed science and technology, reaching for the stars is no longer a poetic imagination of the ancients. 2019 is also the 50th anniversary of NASA's Apollo 11 spacecraft landing on the moon. On July 20, 1969, astronaut Neil Armstrong and lunar module pilot Buzz Aldrin became the first humans to set foot on a planet other than Earth, which can be described as "a small step for a man, a big step for mankind." So far, humans have successfully sent 66 spacecraft to the moon. The picture below shows the annual Christmas window light show at NK Department Store in downtown Stockholm in 2019, with the theme of "50 Years of Mankind's Moon Landing."

"50 Years of Moon Landing" window light show | Photo provided by the author

Acknowledgements: We would like to thank Professor Lou Yuqing from the Department of Physics at Tsinghua University for reading this paper in advance and providing detailed revision comments.

References

Swedish Solar System Model Official Website

http://www.swedensolarsystem.se/en/

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