Solar System

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Solar System

Event Information
Latest Appearance 2010
Forum Threads

This event rotates with Reach for the Stars.

Event Overview

This event will address the Sun, planets and their satellites, comets, asteroids, the Oort Cloud, the Kuiper Belt, meteoroids, meteorites, and meteors.

For this event be sure to acquire a glossary containing many astronomical terms, a list of famous astronomers and their accomplishments, a table of planetary facts (mass, volume, year length, etc.), detailed diagrams of the sun and solar features, and astronomy formulas.

Origins of the Solar System

The Solar system was formed about 4.57 billion years ago in a nebula, the center of which was the protosun. Surrounding it were the materials that would be the planets, planetesimals. When the Nebula was sent into a spinning motion (possibly by a large star), the heavier, rocky materials gravitated to the center, and the lighter gaseous materials fell to the outer solar system. In the inner solar system, the small planetesimals continued to gather more material becoming the 4 rocky terrestrial planets (Mercury, Venus, Earth, and Mars). In the outer solar system the rocky materials gathered to form planets, but the lighter gas materials were attracted by the gravity of the cores to form the Jovian planets(Jupiter, Saturn, Uranus, and Neptune). One group of planetesimals that never formed a planet was between Mars and Jupiter. They formed the asteroid belt. The leftover materials on the far edges of the solar system that did not form planets formed the Oort Cloud and Kuiper (kai-per) belt. These two bodies are the source of many comets, the dwarf planets Pluto, Ceres, Eris, Haumea, and Makemake, and the questionable planet Sedna.

Quick Guide to the Solar System

Planets and Basic Info
Planet Orbit Peroid Rotation Period Date Discovered Distance From Sun Radius Mass
Mercury 87.97 days 58.6 days .39 AU 2439.7 km
Venus 224.7 days 243 days .72 AU 6051.9 km
Earth 365.25 days 1 day 1 AU 6371.0 km
Mars 686.98 days 1.03 days 1.52 AU 3389.5 km
Jupiter 11.86 years 0.41 days 1610 5.2 AU 72,000 km
Saturn 29.46 years .4166667 days 9.54 AU 60,268 km
Uranus 84.01 years .7183333 days March 13, 1781 19.18 AU 25559 km
Neptune 164.9 years .67125 days September 23, 1846 30.06 24764 km

Use this chart to quickly look and compare some basic info for all the planets.

Bodies of the Solar System

(Please note that all of the largest/smallest classifications of the planets are NOT including Pluto! (Which technically isn't really a planet anymore.))

The Sun

Diameter 1,392,000 km
Mass 1.989 1030 kg
Luminosity 3.846 1033 erg/s

The Sun is the largest body in our solar system, and contains 99% of the mass. It is made up of layers, starting from the outside(with Temperatures), Corona(1,000,000 C),Photosphere(6,000 C),Convection Zone(1,000,000 C),Radiative Zone(2,000,000 C),and the Core(15,000,000 C).It produces heat from the fusion of hydrogen atoms. The heat is transferred by the process of convection, through the radiative and the convective zone, where it is radiated out through the photosphere and corona to the planets in the form of rays.This site should contain the solar features that I have not listed here: [1]


The core is the densist part of the sun, with a denistity of 160 g/cm^3. That is ten times that of lead. Although, the temperature is 15 million kelvin, or 27 millon degrees Fahrenheit, which keeps the core in a gaseous state. The core is where fusion takes place. Fusion is the proccess of small molecules combining to form larger ones, releasing energy. The force of gravity is so strong that it breaks down atoms into protons, nuetrons, and electrons. Sometimes protons will combine with nuetrons to form deuterons. If these deuterons combine with one more proton, they form a helium-3 isotope. Two of these combine to make a helium atom. The missing proton (remember that the helium-3 isotope has 1 neutron and 2 protons each) is released in the form of energy.

Raidiative Zone

Surounding the core is the raidiative zone. This area is hot and dense that energy from the core can radiate outwards through this area. Ions of helium and hydrogen emit photons, which then get obsorbed by more hydrogen and helium isotopes. Photons travel slowly this way. It can take 100,000 years for a single photon to exit the radiative zone.

Convection zone

The sun isn't hot enough in this outer layer to raidate throug here, but instead the energy moves through here through convection, or the process of hoter things rising and cooler things falling. The solar plasma here heats up as you get closer to the core, rising, lets out the energy near the top, then falls again.


The outermost part of the sun is called the photosphere. This is where the energy made in the core is finaly released into the sun's atmosphere. This is the visible part of the sun.

Inner Planets


is the smallest planet with a radius of 2439 km and the planet closest to the sun at a distance of 57.9 million kilometers. Its year is 88 earth days long, and its day is 59 earth days long. The Surface gravity of mercury is 1/3 of Earth's, so it cannot hold on to an atmosphere. Therefore its surface is scarred with the craters of meteors that would have broken up if it had an atmosphere. The surface temperatures at day and at night are very different, the day temp is 227 C and the night temp is -173 C. It's most noticeable feature is the largest impact crater on its surface, the Caloris basin.


is the 2nd smallest planet in the solar system with a radius of 6051 km, and the 2nd closest to the sun at a distance of 108.2 million kilometers. It is the only planet whose day is longer than its year. Its day is 243 Earth days, and its year is 225 Earth days. It was often called Earth's sister plane because of its close proximity to Earth, and because of its similar diameter and mass. People even thought it could hold life!, but sadly people discovered that the greenhouse effect on Venus raised the surface temp to the highest in the Solar System.


is the third planet from the Sun, and the fifth largest at a radius of 6378 km. It is the only planet in the universe known to support (supposedly) intelligent life. We use it as a basis for many measurements of planets and other things in the solar system (ex. the AU, the average distance between the Earth and the Sun, 93,000,000 miles or 149,600,000 km). The year is equal to 365.256 Earth days, and its day is 1 earth day (But you already knew that).


the fourth planet from the Sun at a distance of 227,392,000 km, is often called the Red Planet, because the large quantities of iron oxide in its soil. The Romans saw it as blood, so they named it for their god of war, Mars. It is the third smallest planet, with a radius of 3397 km. It has a day length of about 25 hours, and a year equal to 687 Earth days. It has been suggested that Mars may hold intelligent life, but it hasn't been proven.

Outer Planets


is the fifth planet from the sun at a distance of 778.3 million km, and the largest with a radius of 71,492 km. Jupiter holds most of the non-solar mass in the solar system. It gives off more energy than it receives from the sun, so it is believed that Jupiter is a failed star, that it could have formed a star, but wasn't under the right conditions. Contrary to popular belief, Jupiter has three small rings around it, made of tiny particles. Its day is the shortest in the solar system at about 10 hours, and its year is equal to 12 earth years. It has an atmosphere composed of hydrogen and helium. The outer layer is the thin visible cloud bands that we see this is also the zone that contains the circular storm known as the Great Red Spot. This is followed by a thick layer of liquid hydrogen. Beneath that is a nearly same size level of liquid hydrogen that, because of the pressure, behaves like a metal. Then beneath that is an iron-silicate core.


is the sixth planet from the sun, 1.427 billion km away. It is also the second largest at about 60,330 km radius. Its day is only 10 hrs and 40 min., and its year is about 30 Earth years. It is the least dense planet, and if placed in a large enough body of water, it would float. It has the largest and most spectacular ring system in the solar system. They have a diameter of 275,000 km, but they are only a few hundred meters thick. The rings are made up of particles that vary in size, from dust like particles, to the moons Janus and Epimetheus. Saturn, like Jupiter, is made up of only Hydrogen and Helium, and gives off more energy than it receives, but it isn’t as large as Jupiter, so it is not believed to have ever had the potential to be a star.


(pronounced your-uhn-us, not: your-anus) is the 3rd largest planet (25,560 km radius), and the seventh from the sun (2.87 billion km away). It was the first planet discovered after prehistoric times, because it is so far away from Earth. It was discovered by William Herschel. Uranus is known for having its axis of rotation parallel to its plane of orbit. Its 9-ring ring system is also parallel to its plane of orbit. These rings are different from those of Jupiter and Saturn, because they are more like hoops than rings of particles, and they have large gaps between them. Its day is about 18 hours long, and its year is 84 Earth years long. Its outer atmosphere is composed of hydrogen, helium, and methane, which gives it its blue green color. Beneath the outer layer is a layer of high pressure solid water, methane, and ammonia. Then, beneath that layer is a ball of rocky material that is very similar to Earth, but its surface is distorted by the dense inner ocean of water and methane.


the 8th planet from the sun, at a distance of 4.479 billion km, and the 4th largest at a radius of 24,765 km was discovered in 1846 after calculations in Uranus's orbit revealed that its motions were disturbed by a more distant planet. Its day is about 19 hours, and its year is 165 Earth years. The outer third of Neptune is made of hydrogen, helium, water, and methane, which, as on Uranus gives it a blue tint. The inner two thirds are made of molten rock, liquid water, liquid ammonia, and methane. Neptune's most apparent feature is a storm similar to the Great Red Spot, The Great Dark Spot.

Dwarf Planets

The definition of a Dwarf Planet is a planet with enough of a gravitional pull to keep a spherical shape, but not strong enough to "clear the nieghborhood", which means that any object that comes close to the planet, it either "pushes away" or "pulls into an orbit".


The largest object in the Asteroid Belt, containing 30% of its mass. When it was discovered in the early 1800s, Ceres was considered a planet, but was reclassified as an asteroid 50 years later. Since 2006, it has been considered a dwarf planet. Ceres orbits the Sun once every 4.6 Earth years and its day is about 9 hours.


An "egg-shaped" dwarf planet in the Kuiper belt. The odd shape is believed to come from a high rotational speed, which flattens the poles and creates a bulge around the equator. Haumea has a year of about 283 earth years. It also has two moons, Hi'iaka and Namaka.


Makemake has no moons, making it unique among the larger Kuiper Belt objects. It orbits the sun every 310 years.


To be considered a Plutoid, a dwarf planet must have a semi-major axis greater than that of Neptune. In other words, it must orbit outside of Neptune. Any Dwarf planet that orbits within Neptune is considered still considered a dwarf planet. As of right now, there are two Plutoids.


When it was still considered a planet, Pluto was the ninth planet from the Sun and the smallest planet. Very little is known about Pluto and its similarly sized moon Charon (pronounced karen). It was discovered in 1930 by Clyde Tombaugh, and is the only planet discovered in the 20th century. It is a part of the Kuiper belt, and is one of many similar Kuiper Belt objects. The only thing we know about Pluto is that it has a highly eccentric orbit, which crosses Neptune’s orbit every 200 years or so, for 20 years. It also has two smaller moons, Nix and Hydra.


Eris is in the scattered disc, a region beyond the Kuiper Belt. Since Eris is larger than Pluto, its discovery led the IAU (International Astronomical Union) to define "planet" and reclassify Pluto as a dwarf planet. Its only satellite is Dysomnia.

Small Solar System Bodies


A small solar system body orbiting the sun composed mainly of rock. They are larger than meteoroids but smaller than planets. Size ranges from 10 meters across to thousands of kilometers. The main difference between asteroids and comets is that comets have a tail of gases while asteroids do not. Comets can become asteroids if they burn off the ice on their surfaces. In fact, asteroids with eccentric orbits are most likely former comets. Most asteroids in the solar system orbit within the Asteroid Belt between Mars and Jupiter.


A "sand- to boulder-size" piece of space debris. The official definition from the IAU is "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom". Traditionally, anything smaller than 10 meters across is considered a meteoroid, while anything larger than 10 meters is an asteroid. Once a meteoroid enters the atmosphere of Earth or another planet, it is considered a meteor. If it reaches the ground and stays (more or less) intact, it's called a meteorite.


A small solar system body that has a coma (the dust particles gathered around the comet's nucleus that give it an "atmosphere") and/or a tail. The nucleus itself is made up of water ice, dust, frozen gases and small rocky particles. The nuclei range from 100 meters across to more than 40 kilometers. As the comet approaches the sun, solar radiation cause the gases inside to vaporize and carry the dust with them. The gases also become excited by sunlight and emit electromagnetic radiation. Comets leave a trail of solid particles behind them, and if a comet crosses earth's path, there will most likely be meteor showers when earth passes through the debris field. For example, Halley's Comet causes the Orionid Showers and the Swift-Tuttle Comet causes the Perseid showers.

Short-Period Comets

Comets with an orbital period of less than 200 years. Their orbits are in the same direction as the planets, close to the ecliptic, and their aphelion is generally in the area of the outer planets. They are divided into the Jupiter family (orbital period less than 20 years) and the Halley family (orbital periods between 20 and 200 years).

Long-Period Comets

Comets with orbital periods of more than 200 years, sometimes even thousands or millions of years. Their orbits are very eccentric, often don't lie near the ecliptic, and their aphelion is far beyond the outer planets. However, all long-period comets are still gravitationally bound to the sun; comets that have been ejected from the solar system by the gravity of the outer planets are no longer considered to have an orbital period.

Single-Apparition Comets

Comets that have a parabolic or hyperbolic trajectory, i.e. their trajectories only let them enter the solar system once (hence the name). Other than that, they are very similar to long-period comets.

Other Features of the Solar System

Oort Cloud

The Oort cloud is an immense cloud at the outer limits of the solar system. This is believed to be the farthest reaches of the Sun's gravitational pull that measurably affects other objects. This cloud is so vast that comets within it can be tens of millions of kilometers apart. It is believed that the cloud is denser along the elliptical plane. The estimated mass of all the bodies in the Oort cloud is about 40 times Earth's mass. These comets are easily influenced by other stars, and often a star that comes to close to another star's Oort cloud can fling these comets out into deep space or into the solar system. It is believed that this is where many of the comets and asteroids in our solar system originated from.

Oortcloud.jpgCopyright Calvin J. Hamilton

Kuiper Belt

The Kuiper belt is similar to the Asteroid belt. It lies beyond Neptune, about 30-50 AU from the Sun. It is believed that these are the remains of when the Solar System was first created. When the solar system was created, most space debris was condensed to form planets. The debris that did not form planets slowly drifted outwards to form the Kuiper Belt. No spacecraft has ever reached the Kuiper Belt, but the New Horizins spacecraft should drift past it sometime in 2015.

Moons of the Solar System

Mercury: No moons

Venus: No moons

Earth's Moons
Name Year discovered Discoverer Distance from Planet (km) Diameter (km) Orbital Period (days)
Moon prehistory prehistory 384,400 3476 27.322
Mars' Moons
Name Year discovered Discoverer Distance from Planet (km) Diameter (km) Orbital Period (days)
Deimos 1877 A. Hall 23,460 8 1.263
Phobos 1877 A. Hall 9,270 .319
Jupiter's Moons
Name Year discovered Discoverer Distance from Planet (km) Diameter (km) Orbital Period (days)
Callisto 1610 Galileo 188300 4800 16.689
Europa 1610 Galileo 670900 3126 3.551
Ganymede 1610 Galileo 1070000 5276 7.155
Io 1610 Galileo 421600 3629 1.769

There are actually 63 moons, but only the most famous ones were listed here.

Saturn's Moons
Name Year discovered Discoverer Distance from Planet (km) Diameter (km) Orbital Period (days)
Atlas 1980 R. Terrile 137640 37 0.602
Tethys 1684 G. Cassini 294660 1060 1.888
Titan 1655 C. Huygens 1221850 5150 15.945

There are 60 moons of Saturn, but I only listed the 3 most famous here.

Uranus- 27 moons

Neptune- 13 moons

Pluto's Moons
Name Year discovered Discoverer Distance from Planet (km) Diameter (km) Orbital Period (days)
Charon 1978 J. Christy 19571 1207 6.387
Nix 2005 H.A. Weaver 48675 44130 42.856
Hydra 2005 H.A. Weaver 64780 44130 38.206


Lunar Eclipses

A type of eclipse that occurs when the Earth passes directly between the moon and sun, which means that the moon is in Earth's shadow. Since Earth is in the middle of the moon and sun, it must always be a full moon for a lunar eclipse to occur. There are several types of lunar eclipses:

Penumbral Eclipse

The moon passes through Earth's penumbra, causing its surface to darken slightly.

Total Penumbral Eclipse

The moon passes "exclusively" through Earth's penumbra. The area of the moon closest to the umbra can appear darker than the rest of it.

Partial Lunar Eclipse

A portion of the moon passes through Earth's umbra.

Total Lunar Eclipse

Total Lunar Eclipse

The whole moon passes through Earth's umbra. Totality can last up to 107 minutes, depending on the distance of the moon (at apogee, the moon's speed is slower, meaning a longer eclipse).


Also known as a "horizontal eclipse", this is when the sun and the eclipsed moon can be seen at the same time. It can only occur right after sunrise or just before sunset. Technically, the moon and sun shouldn't be visible at the same time, but Earth's atmosphere refracts light and things near the horizon appear higher in the sky than they really are. The name is derived from the Greek goddess of the Moon (Selene) and their word for Sun, helios.

Total Solar Eclipse, not to scale.

Solar Eclipses

The moon passes between the Earth and sun so that the sun's light is partially or completely blocked. Solar Eclipses can only occur during a new moon, when the moon is between the earth and the sun. However, since the moon's orbit around the earth is inclined at about 5°, solar eclipses can only happen when the moon's orbit crosses the ecliptic. There are four types of solar eclipses:

Total Eclipse

The sun is completely blocked by the moon. A total eclipse often happens near perigee because the moon is closer to the earth and its apparent size is larger. When earth is close to aphelion, total eclipses are also more likely to occur. The sun's disk is obscured and its corona is visible. Total eclipses are only visible from the path of totality in the moon's umbra.

Annular Eclipse

The sun and moon are in line, but the moon's apparent size is smaller than the sun because the moon is close to apogee. Annular eclipses are more likely to occur during earth's perihelion. The sun appears as a bright ring around the moon's outline. Annular eclipses are only visible in the antumbra.

Hybrid Eclipse

A hybrid eclipse is visible as a total eclipse from some places on earth and is visible as an annular eclipse from other places. This kind of eclipse is rare compared to the other kinds.

Partial Eclipse

The moon only obscures part of the sun. Partial eclipses can be seen from "a large part of earth" (the moon's penumbra) outside the path of totality for a total or annular eclipse. Some eclipses are only visible as a partial eclipse because the umbra passes above the poles.

Newton's Laws of Motion and Gravitational Attraction

Laws of motion

1. An object at rest stays at rest unless acted on by an outside force. An object in motion stays in motion unless acted on by an outside force.

2. F=ma. Force equals mass times acceleration.

3. For every action, there is an equal and opposite reaction.

Law of Gravitational Attraction

Every object attracts every other object with a force proportional to the product of their masses and inversely proportional to the square of their distance.

F is the magnitude of the gravitational force between the two point masses,

G is the gravitational constant,

m1 is the mass of the first point mass,

m2 is the mass of the second point mass, and

r is the distance between the two point masses.

Kepler's Laws of Planetary Motion

Quick Overview

  • 1. The orbit of every planet is an ellipse with the sun at a focus.
  • 2. A line joining a planet and the sun sweeps out equal areas during equal intervals of time.
  • 3. The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.

A little more in-depth

Thanks to all the pictures I used in this section! They have a bunch of great info, and I have included a link at the bottom of this page. I would go check it out if I were you!

Law 1

The orbit of every planet is an ellipse with the sun at a focus.

To understand this law, you must first understand ellipses. You can think of an ellipse as a flatten circle, with two axises. There is the major axis, which is the longer one, and the minor axis, which is the shorter one. There are always two focuses, which are on the major axis. There is also a semimajor axis, which is half the major axis, and a semiminor axis, or half the minor axis. The sum of the distance to both of the foci is constant.


What the law states is that the sun is at one of the foci, and the planet orbits around it in an ellipse. Most of the time the ellipse is close to a circle in shape, but is never a circle.

Law 2

A line joining a planet and the sun sweeps out equal areas during equal intervals of time. This one is harder to envision. So we've established that the orbit is ellipticle, right? Two lines extending out of the sun will always have the same area, and the planet we are talking about will always travel this distance in equal time. Look at this picture:


Make sense now? The blue sections have the same area, and the Earth will travel the distance the blue area covers in the same time. So when the blue is wider, the Earth moves faster. The blue is wider closer to the sun, so the closer to the sun you are, the faster the planet will orbit around the sun.

Law 3

The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit. Ok, what does this mean? I had to do a little research, too. This is purely math. Sorry, I don't know what that little A is, or why its there.

So what this means is that these two fractions are equal. Remeber in the first law, we defined the major and minor axises? The semimajor axis is half of the major axis. (In an older version, I said the semimajor axis is the same as the minor axis which is not right. Please pay attention to this correction, and I apologize for any confuion.) So that shows that the minor axis defines the orbital period! You can use this law to find either the semimajor axis, which can then be used to find the major axis, or the orbital period. Since , we can use the formula to find the orbital period, or to find the semimajor axis.

Escape Velocity

Escape Velocity is the velocity something must reach in order to escape the gravitational pull of a planet. You can calculate the escape velocity using this formula: Where Ev is the escape velocity, M is the mass (in km) of the planet, G is the gravitational constant (equal to ), and R is equal to the radius of your planet in meters. This is a strange form of measurement for a planet, so watch out. It can change your answer dramatically.

Here is a simple, easy to use Escape Velocity calculator that I made with Microsoft Excell. To use it, you fill in each box in a row with the mass and radius of your planet, respectively. You usually use meters for the radius, but this calculator converts it for you, so fill in the radius in killometers. The first to boxes are used for the mass, so that a*10^b = mass, you would fill in "a" in the first box and "b" in the second box. Just look at the examples to figure out how to use it. Enjoy! Media:Escape_Velocity_Calculator.xls

Famous Astronomers

Tycho Brahe

Tycho Brah(1546-1601) Tycho Brahe was a Danish astronomers that was famous for creating precise measurements of the planets, and also more than 700 stars. He discovered a supernova in 1572 near Cassiopeia. The king of Denmark was so impressed with this discovery that he funded a large observatory on the island of Ven.

Galileo Galilei

Galileo Galilei (1564-1642)

Galileo Galilei was a very famous astronomer who is sometimes known as "the father of modern observational astronomy". His greatest astronomical achievements include discovering Jupiter's four largest satellites, observing and recording the phases of Venus, improving the design of the telescope, and greatly supporting the theory of a heliocentric solar system.

Galileo was born in Pisa, Italy, but moved to Florence at the age of 8. He later applied to the University of Pisa to get a medical degree, but his interests took a different course (no pun intended) and he ended up studying mathematics.

Aristotle's Universe

This upset the church, who then sentenced him to house arrest. He went blind (most likely from studying the sun), shortly before he died.

Johannes Kepler

Johannes Kepler(1571-1630) Johannes Kepler was a German astronomer most famous for developing the Kepler's Laws of Planetary Motion. He began to work on complex math formulas to explain planetary motion, which he mistakenly thought were circular in shape. Later, he became Tycho Brahe's assistant. Kepler and Tycho did not get along, however, and Tycho set Kepler to the task of understanding Mars' orbit. It was just this that allowed him to find the final piece in developing the Laws of Planetary Motion.

Clyde Thombaugh

Clyde Thombaugh (1906-1997) Clyde Thombaugh is credited for discovering Pluto. He began at home with a nine inch home-made telescope, and used this to draw pictures of Saturn and Jupiter. He sent the pictures to the Lowell Observatory, and was immediately offered a position. His goal was to discover the elusive "planet X", later to be renamed Pluto. Even after this great accomplishment, he went on to discover many more things such as comets, open clusters, globular clusters, and other things.

Nicholas Copernicus

Nicholas Copernicus (1473 -1543) Nicholas Copernicus was a Polish astronomer who was the first to develop the Copernicus theory,stating that the sun lie near the center of the Solar System, and the Earth revolve around it, not the other way around. This theory was not proven until Galileo, and not widely excepted for many more years. Later in life he went on to lecture in Rome about astronomy.

Edmond Halley

Edmond Halley (1656-1742) Edmond Halley was a British astronomer who was the first to calculate a comet's orbit. He went to the University of Oxford where he studied the theories of Sir Issac Newton. He published a book in 1705 called Astronomiae Cometicae Synopsis (Synopsis on Cometary Astronomy). Hi theories were validated when a comet appeared in 1758, just as he predicted. The comet was named after him for his remarkable accuracy, and is now known as Halley's comet.

Helpful Tips

This event often contains many questions/tasks not listed on the event sheet, so you should study anything that could be interpreted as related to our solar system. If you do this (And have a decent reference book) you should be guaranteed to get a top ten finish.


the 9 planets

the solar system

views of the solar system

soinc's solar system page

Information on famous astronomers

Kepler's Laws of Planetary Motion