A Brief History of Rocketry

The earliest solid rocket fuel was a form of gunpowder, and the earliest recorded mention of gunpowder comes from China late in the third century before Christ. Bamboo tubes filled with saltpeter, sulphur and charcoal were tossed into ceremonial fires during religious festivals in hopes the noise of the explosion would frighten evil spirits.

It's probable that more than a few of these bamboo tubes were imperfectly sealed and, instead of bursting with an explosion, simply went skittering out of the fire, propelled by the rapidly burning gunpowder. Some clever observer whose name is lost to history may have then begun experiments to deliberately produce the same effect as the bamboo tubes which leaked fire.

Certainly by the year 1045 A.D.--21 years before William the Conqueror would land on the shores of England--the use of gunpowder and rockets formed an integral aspect of Chinese military tactics.

A point of confusion arises tracing the history of rocketry back before 1045. Chinese documents record the use of "fire arrows," a term which can mean either rockets or an arrow carrying a flammable substance.

By the beginning of the 13th Century, the Chinese Sung Dynasty, under pressure from growing Mongolian hordes, found itself forced to rely more and more on technology to counter the threat. Chinese ordnance experts introduced and perfected many types of projectiles, including explosive grenades and cannon.

Rocket fire-arrows were certainly used to repel Mongol invaders at the battle of Kai-fung-fu in 1232 A.D.

The rockets were huge and apparently quite powerful. According to a report: "When the rocket was lit, it made a noise that resembled thunder that could be heard for five leagues -- about 15 miles. When it fell to Earth, the point of impact was devastated for 2,000 feet in all directions." Apparently these large military rockets carried incendiary material and iron shrapnel. These rockets may have included the first combustion chamber, for sources describe the design as incorporating an "iron pot" to contain and direct the thrust of the gunpowder propellant.

The rocket seems to have arrived in Europe around 1241 A.D. Contemporary accounts describe rocket-like weapons being used by the Mongols against Magyar forces at the battle of Sejo which preceded their capture of Buda (now known as Budapest) December 25, 1241.

Accounts also describe Mongol's use of a noxious smoke screen--possibly the first instance of chemical warfare.Rockets appear in Arab literature in 1258 A.D., describing Mongol invaders' use of them on February 15 to capture the city of Baghdad.

Quick to learn, the Arabs adopted the rocket into their own arms inventory and, during the Seventh Crusade, used them against the French Army of King Louis IX in 1268.

It is certain that, not later than the year 1300, rockets had found their way into European arsenals, reaching Italy by the year 1500, Germany shortly afterwards, and later, England. A 1647 study of the "Art of Gunnery" published in London contains a 43-page segment on rockets. The Italians are credited, by the way, with adopting military rockets for use as fireworks -- completing the circle, so to speak, of the bursting bamboo used at the Chinese festivals 1,700 years earlier.

The French Army traditionally has been among the largest, if not THE largest, army in Europe and was quick to adopt rockets to military operations. Records from 1429 show rockets in use at the siege of Orleans during the Hundred Years War against the English.

Dutch military rockets appear by 1650 and the Germans' first military rocket experiments began in 1668. By 1730, a German field artillery colonel, Christoph Fredrich von Geissler, was manufacturing rockets weighing 25 to 54 kilograms (55 to 120 pounds).

As the 18th Century dawned, European military experts began to take a serious interest in rockets -- if only because they, like the Magyars 500 years earlier, found themselves on the receiving end of rocket warfare.

Both the French and the British, during the Eighteenth Century, began wrestling for control of the riches of India. In addition to fighting one another, they also found themselves frequently engaged against the Mogol forces of Tippoo Sultan of Mysore. During the two battles of Seringapatam in 1792 and 1799, rockets were used against the British. One of Tippoo Sultan's rockets is now displayed in the Royal Ordnance Museum at Woolwich Arsenal, near London.

Tippoo Sultan's father, Hyder Ally, had incorporated a 1,200 man contingent of rocketeers into his army in the year 1788. Tippoo Sultan increased this force to about 5,000 men, about a seventh of his total Army's strength.

Profiting from their Indian experience, the British, led by Sir William Congrieve (KON-greeve), began development of a series of barrage rockets ranging in weight from 8 to 136 kilograms (18 to 300 pounds). Congrieve-design rockets were used against Napoleon.

It is surprising that Napoleon seems to have made no use of rockets in the French Army but it must be remembered Napoleon was an artillery officer and may have simply been too hide-bound a traditionalist to favor new-fangled rockets over more familiar cannons.

The scope of the British use of the Congrieve rocket can be ascertained from the the 1807 attack on Copenhagen. The Danes were subjected to a barrage of 25,000 rockets which burnt many houses and warehouses.

An official rocket brigade was created in the British Army in 1818.

Rockets came to the New World during the War of 1812.

During the Battle of Bladensburg, August 24, 1814, the British 85th Light Infantry used rockets against an American rifle battalion commanded by U.S. Attorney General William Pickney. British Lieutenant George R. Gleig witnessed the Americans' response to the new threat. "Never did men with arms in their hands make better use of their legs," he wrote.

On December 4, 1846, a brigade of rocketeers was authorized to accompany Maj. Gen. Winfield Scott's expedition against Mexico. The Army's first battalion of rocketeers -- consisting of about 150 men and armed with about 50 rockets -- was placed under the command of First Lieutenant George H. Talcott.

The rocket battery was used March 24, 1847, against Mexican forces at the siege of Veracruz.

On April 8 the rocketeers moved inland, being placed in their firing position by Captain Robert E. Lee (later to command the Confederate Army of Northern Virginia in the War Between the States). About 30 rockets were fired during the battle for Telegraph Hill. Later, the rockets were used in the capture of the fortress of Chapultepec, which forced the surrender of Mexico City.

With typical foresight, as soon as the fighting in Mexico was over, the rocketeer battalion was disbanded and the remaining rockets were placed in storage.

They remained in mothballs for about 13 years -- until 1861 when they were hauled out for use in the Civil War. The rockets were found to have deteriorated, however, so new ones were made.

The first recorded use of rockets in the Civil War came on July 3, 1862, when Maj. Gen. J.E.B. Stuart's Confederate cavalry fired rockets at Maj. Gen. George B. McClellan's Union troops at Harrison's Landing, Va. No record exists of the Northerners' opinion of this premature "Fourth of July" fireworks demonstration.

Later in 1862, an attempt was made by the Union Army's New York Rocket Battalion -- 160 men under the command of British-born Major Thomas W. Lion -- to use rockets against Confederates defending Richmond and Yorktown, Virginia. It wasn't an overwhelming success. When ignited, the rockets skittered wildly across the ground, passing between the legs of a number of mules. One detonated harmlessly under a mule, lifting the animal several feet off the ground and precipitating its immediate desertion to the Confederate Army.

The only other documented use of rockets is at Charleston, S.C., in 1864. Union troops under Maj. Gen. Alexander Schimmelfennig found rockets "especially practical in driving off Confederate picket boats, especially at night."

As an interesting sidelight, the author Burke Davis, in his book "Our Incredible Civil War," tells a tale of a Confederate attempt to fire a ballistic missile at Washington, D.C., from a point outside Richmond, Va.

According to the author, Confederate President Jefferson Davis witnessed the event at which a 3.7 meter (12 foot) solid-fueled rocket, carrying a 4.5 kilogram (10 pound) gunpowder warhead in a brass case engraved with the letters C.S.A., was ignited and seen to roar rapidly up and out of sight. No one ever saw the rocket land. It's interesting to speculate whether, almost 100 years before Sputnik, a satellite marked with the initials of the Confederate States of America might have been launched into orbit.

The military appears to have remained underwhelmed with the potential of rockets. They were employed in fits and starts in many of the brushfire wars which punctuated the otherwise calm closing days of the late Victorian Era. If the military was lukewarm to rockets, another profession welcomed them with open arms.

The international whaling industry developed rocket-powered, explosive-tipped harpoons which were most effective against the ocean-going leviathans.

During the First World War, rockets were first fired from aircraft attempting to shoot down enemy hydrogen gas-filled observation balloons. Successes were rare and pilots resisted being asked to fire rockets from the highly flammable, cloth and varnish covered wings of their biplanes. The French were the principal users of aerial rockets, using a model developed by a Naval lieutenant, Y.P.G. LePrieur.

The principal drawback to rockets throughout this period of development was the type of fuel. Both here and abroad, experiments were under way to develop a more powerful, liquid-propelled rocket. Two young men stand out in this effort -- one an American, Robert H. Goddard -- the other a German, Wernher von Braun.

Radio commentator Paul Harvey tells a story of how young von Braun's interest in rocketry almost got him labeled as a juvenile delinquent. At the age of 13, von Braun exhibited an interest in explosives and fireworks. His father could not understand his son's consuming interest in so dangerous a hobby. He feared his son would become safecracker. One day the young teenager obtained six skyrockets, strapped them to a toy red wagon and set them off. Streaming flames and a long trail of smoke, the wagon roared five blocks into the center of the von Braun family's hometown, where the rockets finally exploded.

As the smoke cleared, the toy wagon emerged as a charred wreck. Young von Braun emerged in the firm grasp of a policeman. Despite being severely reprimanded by his father, the youngster's interest would not be denied. By the age of 22 he had earned his doctorate in physics. Two years later he was directing Germany's military rocket development program.

Von Braun and his colleagues produced a number of experimental designs, the most famous of which was the A-4 rocket, which has gained distinction in history under another name -- the vengeance weapon number two -- V-2 for short. The V-2 was the first successful, long range ballistic missile, and von Braun is credited as its principal developer.

As World War II drew to a close, von Braun led his contingent of several hundred rocket scientists and engineers -- all marked for death by the Nazis to prevent their capture by the Allies -- into American lines.

In 1946, von Braun and his team arrived at White Sands, N.M., where, for the first time, von Braun learned of work done by the American rocket pioneer Robert Goddard.

Goddard's interest in rockets began in 1898 when, as a 16-year-old, he read the latest publication of that early science fiction writer, English novelist H.G. Wells. The book which so excited Goddard was later made into a 1938 radio program that nearly panicked our entire nation when it was broadcast. Orson Well's too realistic rendition of the "War of the Worlds" still causes many to shudder.

As the 20th Century began, Wilbur and Orville Wright were preparing to become the first men to fly. Goddard, however, was already designing rockets to probe the upper atmosphere and delve into space. Half a world away -- and unknown to Goddard -- a Russian school teacher, Konstantin Tsiolkovsky, was thinking along much the same lines. Both came to the conclusion independently that, if a rocket was going to do the things they dreamed of, it would have to be powered by liquid fuels. Solid fuels of the time simply didn't have sufficient power. Tsiolkovsky lacked Goddard's practicality. While Tsiolkovsky worked out many principles of astronautics and designed suitable rockets, he never built any. By contrast, Goddard was a technical man. He could and did build rockets. By the time he died in 1945, Goddard held 214 patents in rocketry -- patents which still produce royalties for his estate.

Goddard began his experiments in rocketry while studying for his doctorate at Clark University in Worcester, Mass.

He first attracted attention in 1919 when he published a paper titled, "A Method of Reaching Extreme Altitudes." In his paper he outlined his ideas on rocketry and suggested, none too seriously, that a demonstration rocket should be flown to the Moon.

The general public ignored the scientific merit of the paper -- latching instead onto Goddard's Moon rocket proposal. At the time, such an endeavor was absurd and most dismissed Goddard as a "crank."

The experience taught Goddard a hard lesson -- one which caused him to shy away from future opportunities to publicize his work. Publicity was far from Goddard's mind on the morning of March 16, 1926. On that day, barely a year after Wernher von Braun's rocket wagon fiasco, Goddard launched a liquid-powered rocket he had designed and built from a snow-covered field at his Aunt Effie Goddard's farm in Auburn, Mass. The rocket flew only 46 meters (152 feet) -- about the same distance as the Wright Brothers' first manned flight -- but it did fly! It was the first flight of a liquid-fueled rocket in history.

When Goddard was later approached by the American Interplanetary Society in 1930 to publicize his work, Goddard refused. The society, rebuffed and learning that no one in the United States aside from Goddard was working with rockets, turned its attention to rocket research under way in Europe, where rocketry was beginning to develop a following.

In the spring of 1931, two founder-members of the American society, husband and wife Edward and Lee Pendray, travelled on vacation to Germany where they made contact with the German Rocket Society, which had been formed in 1927. The visiting Americans were given a preview of the future when a member of the German Rocket Society -- Prof. Willy Ley -- took the pair to the Germans' rocket flying test ground in the suburbs of Berlin.

Returning home, the Pendrays filed an enthusiastic report of their visit, prompting the American society to build its first rocket. The attempted test flight in November 1932 ended with the American design firmly on the ground. It's unfortunate the Pendrays didn't meet another future rocketry hall-of-famer who also was a member of the German society. Rumanian-born Hermann Oberth wrote, in 1923, a highly prophetic book: "The Rocket into Interplanetary Space." The book enthralled many with dreams of space flight, including that precocious German teenager, Wernher von Braun, who read the book in 1925. Five years later, von Braun had joined Oberth and was assisting with rocket experiments.

By 1932, the German Army was beginning to show an interest in the German Rocket Society's efforts, and in July of that year, a "Mirak" rocket was launched as a demonstration for the head of the newly created German Army rocket research group, Captain (later Major General) Walter Dornberger.

Mirak didn't impress Dornberger.

Von Braun did.

Three months after the demonstration flight, von Braun was engaged to work on liquid propelled rockets for the Army. Most of the German Rocket Society followed von Braun into national service and the society disbanded.

By December 1934, von Braun scored his first successes with an A2 rocket powered by ethanol and liquid oxygen. Two years later, as plans for the follow-on A3 rocket were being finalized, initial planning began for the A4 rocket -- a rocket that was to be, in Dornberger's words, a practical weapon, not a research tool. As noted earlier, most know the A4 by another name -- the V-2.

The rocket researchers quickly outgrew their facilities at Kummersdorf on the outskirts of Berlin and, in 1936, operations were transferred to a remote island on Germany's Baltic coast -- Peenemuende.

Between 1937 and 1941, von Braun's group launched some 70 A3 and A5 rockets, each testing components for use in the proposed A4 rocket.

The first A4 rocket flew in March 1942. The rocket barely cleared some low clouds before crashing into the sea a half mile from the launch site.

The second launch in August 1942 saw the A4 rise to an altitude of 11 kilometers (7 miles) before exploding.

The third try was the charm. On October 3, 1942, another A4 roared aloft from Peenemuende, followed its programmed trajectory perfectly, and landed on target 193 kilometers (120 miles) away. This launch can fairly be said to mark the beginning of the space age. The A4, the first successful ballistic rocket, is the ancestor of practically every rocket flown in the world today.

Production of the A4 began in 1943 and the first A4s, now renamed V2s, were launched against London in September 1944.

The V-2 offensive came too late to affect the course of the war. By April 1945, the German Army was in full retreat everywhere and Hitler had committed suicide in his bunker in Berlin.

At an inn near Oberjoch, the Haus Ingeburg, von Braun and over 100 of his rocket experts waited for the end. The entire team had been ordered executed by Hitler to prevent their capture. Wernher von Braun's brother, Magnus, however, managed to contact nearby American forces before Hitler's SS henchmen could reach the rocket team. On May 2, the same day Berlin fell to the Soviet Army, von Braun and his rocket team entered American lines and safety.

With the fighting over, von Braun and his team were heavily interrogated and jealously protected from Russian agents. V2s and V2 components were assembled. German rocket technicians were rounded up. In June, General Eisenhower sanctioned the final series of V2 launches in Europe. Watching each of the three V2s which rose from a launch site at Cuxhaven was a Russian Army colonel, Sergei Korolev. Ten years later, Korolev would be hailed as the Soviet Union's chief designer of spacecraft and the individual responsible for building the Vostok, Voshkod and Soyuz spacecraft which, since 1961, have carried all Soviet cosmonauts into orbit.

Few members of von Braun's team participated in the Cuxhaven launches. Most had already begun setting up shop at Fort Bliss, near El Paso, Texas. Piled up in the desert near Las Cruces, New Mexico, were enough parts to build 100 V2s. Von Braun and his team soon moved to nearby White Sands Proving Ground where work began assembling and launching V2s. By February 1946, von Braun's entire Peenemuende team had been reunited at White Sands and, on April 16, the first V2 was launched in the United States. The U.S. space program was under way!

Up to 1952, 64 V2s were launched at White Sands. Instruments, not explosives, packed the missiles' nosecones. A V2 variant saw the missile become the first stage of a two stage rocket named Bumper. The top half was a WAC Corporal rocket. The need for more room to fire the rockets quickly became evident and, in 1949, the Joint Long Range Proving Ground was established at remote, deserted Cape Canaveral, Fla. On July 24, 1950, a two-stage Bumper rocket became the first of hundreds to be launched from "the Cape."

The transfer of launch operations to the Cape coincided with the transfer of the Army's missile program from White Sands to a post just outside a north Alabama cotton town called Huntsville. Von Braun and his team arrived in April 1950. It was to remain his home for the next 20 years, a period in which the city's population increased ten fold.

The von Braun team worked to develop what was essentially a super-V2 rocket, named for the U.S. Army arsenal where it was being designed -- the Redstone.

In 1956, the Army Ballistic Missile Agency was established at Redstone Arsenal under von Braun's leadership to develop the Jupiter intermediate range ballistic missile. A version of the Redstone rocket, known as the Jupiter C, was used on January 31, 1958, to launch America's first satellite, Explorer I. Three years later, Mercury Redstones launched Alan Shepard and Virgil I. "Gus" Grissom on suborbital space flights, paving the way for John Glenn's first orbital flight.

In 1958, NASA was established, and, two years later, von Braun, his team, and the entire Army Ballistic Missile Agency were transferred to NASA to become the nucleus of the agency's space program.

The Army Missile Command, which owns Redstone Arsenal, continued its vital national defense mission after the transfer of ABMA to NASA, chalking up a remarkable number of successful programs to augment America's landpower. MICOM's successes include the Pershing II, the NIKE weapons systems, the HAWK system, Improved HAWK, Corporal, Sergeant, Lance and Chaparral, to name a few.

Pursuing a separate course -- that of developing rockets for space exploration -- the Marshall Space Flight Center's past quarter century has been a time of superlatives.

In 1961, almost as Alan Shepard was drying off from his landing in the Atlantic following his riding a Marshall-designed Redstone rocket on a sub-orbital flight which made him the first American in space, President Kennedy committed this nation to being first on the Moon. NASA's Marshall Center was charged with developing the family of giant rockets which would take us there.

The Saturn rockets developed at Marshall to support the Apollo program and to honor President Kennedy's pledge were, at the time, the most powerful space launch vehicles yet to have been invented.

Engineers, scientists, contractors, and other support personnel built well. On July 20, 1969, a transmission from the Moon's Sea of Tranquility reported: "The Eagle has landed."

Marshall's Saturn rockets first took us around the Moon, then to its cratered surface. Marshall-developed lunar excursion vehicles -- the ungainly Moon Buggies -- carried astronauts on far-ranging excursions in pursuit of samples of lunar soil and rock.

Closer to home, the team at Marshall developed America's first space station -- Skylab. Built to replace the upper stage of a Saturn V moon rocket, the Skylab module was successfully placed in orbit early on May 14, 1973.

Placing Skylab in orbit marked a major transition in the story of rocketry. Up until Skylab, the rocket had been the star -- the featured attraction. The focus had been on the up and down -- launch and recovery. Skylab, in essence stole the show. For the first time, space became a place in which to live and work. Flying aboard a rocket was about the Earthside equivalent of driving the family car to work. Just as having to drive to work is only incidental to work itself -- flying aboard a rocket became secondary to the work done once Skylab had been reached. The rocket, simply stated, became a means to an end -- the end in this case being the opportunity to learn to live and work in space.

A rash of malfunctions plagued Skylab's early days -- problems which tested the resourcefulness of the entire NASA team. The problems were overcome, however, and Skylab went on to become one of Marshall's proudest achievements.

A Marshall-developed Saturn I-B also carried aloft America's half of the first joint U.S.-Soviet space endeavor, the Apollo-Soyuz project.

After Apollo, the team at Marshall tackled designing a revolutionary national space transportation system, which came to be known simply as "The Space Shuttle."

It is anything but simple!

The space shuttle main engines are among the most powerful, most sophisticated devices ever invented. They represent a quantum leap in technology advancement over the engines which powered the Saturn V. Each of the three main engines in tail of the shuttle can provide almost a half-million pounds of thrust, a thrust equal to that produced by all eight of the Saturn I's first stage engines. Unlike most previous rocket engines, which were designed to be used only once -- and then for only a few minutes -- the space shuttle's main engines are designed to be used again and again, for up to 7.5 hours. The thrust to weight ratio for these engines is the best in the world -- each engine weighs less than 7,000 pounds but puts out the power equivalent of seven Hoover Dams!

Twenty-four successful flights of the space shuttle lulled America into a sense of complacency. Shuttle launches became routine -- a ho-hum event which had to scramble for an inch or two on page 2.

Then came the Challenger disaster....

The time since the loss of Challenger has been the busiest in the history of Marshall Space Flight Center. Teams of experts have been organized to find and fix the problems which led to the accident. Investigation quickly focused on a defective joint in the space shuttle's solid rocket motors. Rocket propulsion experts devised a number of modifications to the solid rocket motor design to remedy the fault.

A vigorous test program was undertaken to show that the problems had been solved.

The disaster-enforced hiatus in shuttle operations gave Marshall -- and other NASA installations -- an opportunity to address other shuttle-related concerns. Major steps were taken to enhance the reliability and safety of the turbine blades and turbo pumps in the shuttle's main engines. An escape system was created for the shuttle crew. Improvements were made to the orbiter's landing gear and brakes.

When America returned to manned spaceflight in 1988, it did so in a space vehicle which was vastly safer and more capable.

NASA also is examining using expendable launch vehicles on missions which do not require the shuttle's unique capabilities, and is looking into development of a new generation of heavy lift launch vehicles.

These will become the next chapter in the story of rocketry -- a story whose first chapters were written more than 2,400 years ago.

No one can say where our path will lead or when -- hopefully never -- the last chapter in this history will be written.



Milky Way Galaxy - our celestial backyard

On dark, clear nights we can sometimes see a faint, hazy band of light studded with many stars and stretching across the sky. This is the body of the Milky Way, the galaxy in which we live. Here in the southe rn part of Australia, the centre of the Milky Way passes almost directly overhead so we can obtain an excellent view of our galaxy.

Our understanding of the Universe has changed vastly over the last 400 years. The Earth is no longer regarded as the centre of the Universe. Now we know that we are like "suburban residents" of the Milky Way, situated well away from the centre of the galaxy. Our solar system is about 30,000 light years out from the galactic centre and orbits around it at a speed of 250 kilometres per second. The astronomer Harlow Shapley, in the 1920s, was the first to realise that we are not at the centre of the Milky Way.

Containing over 100 billion stars (some of which may have planets!), and different types of interstellar gas and dust, the "body" of our galaxy is shaped like a great disc 300 light years thick and 100,000 light years across. It is a spiral galaxy, and our Sun is about two thirds of the way out from the centre along one of the spiral arms. Humans like to think they are important; but in the vastness of the Milky Way, our Earth is like a grain of sand on the beach - and the Milky Way is only one of millions of galaxies wheeling through space!

The galaxy has four main parts:

Nuclear Bulge: The galaxy is shaped like a pancake with a bulge at the centre. This "nuclear bulge" is about 16,000 light years in radius, and contains mainly old stars and interstellar gas and dust.
Galactic Disc: The part of the pancake outside the bulge, extending about 50,000 light years out from the centre. The disc contains all the young stars, and more interstellar gas and dust.
Halo The spherical region surrounding the disc to a radius of about 65,000 light years. The halo contains old stars, globular star clusters, and thinly spread interstellar gas and dust.
Galactic Corona The galactic corona is an enormous sort of outer halo that may extend as far as 300,000 light years in radius. The corona is now believed to contain most of the mass of the galaxy.

The galaxy is slowly rotating: our Sun takes about 250 million years to do one orbit of the galactic centre. Hence our solar system must have made only 20 or so orbits.



Uranus was the first planet to be discovered in modern history. It was actually discovered by accident in 1781 by William Herschel.

Like the other gas giants, Uranus has a very thick cloud cover and an atmosphere made up mostly of hydrogen, helium, methane, and ammonia. The trace amount of methane is what gives Uranus and its twin, neptune, their blue color. Unlike Saturn and jupiter, Uranus has a different internal structure.

The core of Uranus is probably composed of liquid rock. Then, farther up, the liquid rock slowly gives way to an ocean made mostly of hydrogen, helium, and water, with small amounts of ammonia and methane. This "ocean" accounts for most of Uranus's bulk. Then, the water slowly thins out into the bland, almost featureless atmosphere.

Uranus also has a system of about 11 rings - not nearly as large as Saturn's. Nine were found when Uranus passed in front of a bright star in 1977, for the rings causing the star to temporarily disappear when they passed in front of it. This was the first time astronomers had detected rings around any planet other than Saturn. It was the first time, also, that astronomers had detected thin rings around any planet. The other two rings were found when voyager2 passed by.

Uranus also has 27 known moons most of which little is known about.


Composition of Uranus AtmosphereUranus is basically one big atmosphere - as far as we know, there is no real surface to the planet. Its composition is nearly all H2; the rest is approximately:

  • H2: 82.5±3.3%
  • He: 15.2±3.3%
  • CH4: 2.3%
  • HD: 0.0148%

Besides this, aerosols of ammonia ice, water ice, and ammonia hydrosulfide exist in the atmosphere. Methane ice may also be present.

The temperature at 1 bar is approximately 76 K, and at 0.1 bar it is 53 K. The density at 1 bar is 420 g/m3. Wind speeds range up to 200 m/s. The scale height of the Uranian atmosphere is about 27.7 km.

Unique Characteristicsz

Uranus has two main unique features:Uranus' Rings

  • First, there is absolutely no detail in the cloud cover. Only when pushed to the maximum level of color enhancement and contrast on computers do scientists start to see small swirls in the atmosphere.
  • Second, Uranus is the only planet rotates on its side. This produces the strangest seasons of any planet in the solar system. For 21 years, Uranus's moons are seen as one would view a dart board, with one pole facing the sun. The next 21 years Uranus has its side to the sun, and the moons move up and down across the equator. then the cycle repeats itself starting with the other pole. Scientists aren't sure why this is, but they think that a large body smashed into it with such force that it pushed the planet over.



Saturn is a gas giant. It's structure is very similar to jupiter's core is composed liquid rock. Next comes a layer of liquid hydrogen. It is under such high pressure that the nature of the hydrogen changes, and is able to conduct electricity like metal. This generates the planet's magnetic field.

The layer on top of this is ordinary liquid hydrogen. Next, the hydrogen thins out into the gaseous atmosphere. It is composed of mainly hydrogen and helium with trace amounts of methane, water, ammonia, and hydrogen sulfide.

Interestingly, Saturn creates some of its own heat, but in a much different way than Jupiter. Scientists believe that the hydrogen and helium are slowly separating out, like vinegar and oil when left to sit. In Saturn's case, the heavier helium is slowly making its way through the hydrogen, generating heat (from friction) as it goes.

Saturn has something like Jupiter's Great Red Spot, but it is a Great White Spot. Nothing is currently known about the phenomenon, but it is probably similar to the Great Red Spot in the way it has formed. Besides this, Saturn's outer atmosphere is not nearly as turbulent as Jupiter's. This is because, being about two times farther away from the sun, it receives approximately 1/4 as much as energy from it. Less energy means that there is less to power atmospheric phenomenon.


Composition of Saturn AtmosphereSaturn is basically one big atmosphere - as far as we know, there is no real surface to the planet. Its composition is nearly all H2; the rest is approximately:

  • H2: 96.3±2.4%
  • He: 3.25±2.4%
  • CH4: 0.45±0.2%
  • NH3: 0.0125±0.075%
  • HD: 0.011±0.0058%
  • C2H6: 0.0007±0.00015%

Besides this, aerosols of ammonia ice, water ice, and ammonia hydrosulfide exist in the atmosphere.

The temperature at 1 bar is approximately 134 K, and at 0.1 bar it is 84 K. The density at 1 bar is 190 g/m3. Below 30° latitude, wind speeds range up to 400 m/s, and above that only 150 m/s. The scale height of the Saturnian atmosphere is about 59.5 km.

Unique Characteristics

Saturn has a few unique features:

  • First, it is the least dense of all the planets. If there were a bathtub big enough to fit Saturn in, the planet would float.Saturn Ring Segment
  • Second is Saturn's magnificent ring system. This system has four sections. The farthest out, F, was discovered during the Voyager mission. Moving towards Saturn, next is the A section, and this section makes up about half the diameter of the entire system. Then comes the Cassini Division, between A and B, which is the large gap visible in most photographs. Next is the B ring, which has raised parts, caused by the planet's magnetism. These appear as spokes. In-between B and C, there is a small division called Enck's Division. The C ring is transparent. Farther in, there are very small ring particles which are slowly spiraling in towards the planet.

    The rings were probably formed relatively recently - several thousand years ago - when two of Saturn's satellites crashed together. The ring systems of the other gas giants probably formed the same way, only much earlier, which is why they are mostly gone; most of their rings have fallen into their planet's atmosphere. In about 100,000,000 years, Saturn's rings will probably be gone, too. See the table below for data on its rings.
  • Another interesting property of Saturn is how it generates heat. As seen in the table below, the average temperature of Saturn is approximately 130 K. However, due to the equation for thermal equilibrium (below), it should only be about 80 K. This extra heat is generated due to its gas slowly separating. Like an oily salad dressing, the gases in Saturn's atmosphere are very slowly separating, with the lighter gas rising up and the heavier gas falling down. As this happens, friction between the molecules heats the gas, accounting for the extra heat.


Neptune, like its twin, URANUS has an atmosphere composed of hydrogen, helium, methane, and ammonia. The methane creates the blue color. Neptune's internal structure is also the same as that of Uranus.

The core of Neptune is probably composed of liquid rock. Then, farther up, the liquid rock slowly gives way to an ocean, primarily containing hydrogen, helium, and water, but also ammonia and methane. This "ocean" accounts for most of Neptune's bulk. The ocean slowly thins out into the atmosphere.

This atmosphere contains much more detail than Uranus'. It has swirls of clouds and high-altitude cirrus clouds, as well as gigantic storms.

Neptune's High Cirrus CloudsNeptune also has a faint system of rings. The rings are made of pieces of material the size of a car or truck. There is about one thousandth of the matter in Neptune's rings as in Uranus'. If the rings were all rolled into a ball, the ball would be only a couple of miles across. That matter is spread across 125,000 km (77,500 miles).

In the outermost ring of Neptune, there are three anomalies called the "Three Arcs of Neptune." They are areas where the rings are relatively dense. Over the millions of years that these have existed, the particles in the arcs should have spread out until the ring was a uniform density. However, this has not happened. Scientists now believe that these arcs are shepherded by small moons.

Neptune has 13 known moons


Composition of Neptune AtmosphereNeptune is basically one big atmosphere - as far as we know, there is no real surface to the planet. Its composition is nearly all H2; the rest is approximately:

  • H2: 80.0±3.2%
  • He: 19.0±3.2%
  • CH4: 1.5±0.5%
  • HD: 0.0192%
  • C2H6: 0.00015%

Besides this, aerosols of ammonia ice, water ice, and ammonia hydrosulfide exist in the atmosphere. Methane ice may also be present.

The temperature at 1 bar is approximately 72 K, and at 0.1 bar it is 55 K. The density at 1 bar is 450 g/m3. Wind speeds range up to 200 m/s. The scale height of the Neptunian atmosphere is about 19.1-20.3 km.

Unique Characteristics

Neptune has a few features that no other planet has:

  • Neptune's Great Dark SpotFirst, it is the last non-controversial planet in the solar system, yet discovered (pluto is still under debate in some circles). Once Uranus had been discovered, perturbations in its orbit were seen. calculations were madeand it was predicted there should be a planet within a certain patch of sky. Within hours, Neptune was discovered in 1846.
  • The next feature that is unique to Neptune is the Great Dark Spot (right). It is a depression in the atmosphere surrounded by high cirrus clouds. Neptune's Great Dark Spot does not appear to be stable, though. A few years after the voyagers it, it had disappeared . Then, in 1995, it reappeared in Neptune's northern hemisphere.

    Neptune - No Great Dark Spot (HST)When the Great Dark Spot was first discovered, it was thought to be moving very slowly. However, when Neptune's rotation rate was finally determined, it showed that the Great Dark Spot wasn't moving slowly with the planet, but was actually moving in a direction opposite the planet's spin at almost supersonic speeds. These are ten times hurricane speeds on Earth.




Jupiter is the fifth planet from the Sun and is the largest planet in the solar system. If Jupiter were hollow, more than one thousand Earths could fit inside. It also contains two and a half times the mass of all the other planets combined. It has a mass of 1.9 x 1027 kg and is 142,800 kilometers (88,736 miles) across the equator. Jupiter possesses 62 known satellites. The four largest are
CALLISTO, EUROPA, GANYMEDE and IO, and were named after GALILEO GALILIE who observed them as long ago as 1610. The German astronomer Simon Marius claimed to have seen the moons around the same time, but he did not publish his observations and so Galileo is given the credit for their discovery.

Jupiter has a very faint ring system, but is totally invisible from the Earth. (The rings were discovered in 1979 by Voyager 1.) The atmosphere is very deep, perhaps comprising the whole planet, and is somewhat like the Sun. It is composed mainly of hydrogen and helium, with small amounts of methane, ammonia, water vapor and other compounds. At great depths within Jupiter, the pressure is so great that the hydrogen atoms are broken up and the electrons are freed so that the resulting atoms consist of bare protons. This produces a state in which the hydrogen becomes metallic.

Colorful latitudinal bands, atmospheric clouds and storms illustrate Jupiter's dynamic weather systems. The cloud patterns change within hours or days. The GREAT RED SPOT is a complex storm moving in a counter-clockwise direction. At the outer edge, material appears to rotate in four to six days; near the center, motions are small and nearly random in direction. An array of other smaller storms and eddies can be found through out the banded clouds.

AURORAL emissions, similar to Earth's NORTHENLIGHTS, were observed in the polar regions of Jupiter. The auroral emissions appear to be related to material from IO, that spirals along magnetic field lines to fall into Jupiter's atmosphere. Cloud-top lightning bolts, similar to superbolts in Earth's high atmosphere, were also observed.

Jupiter's Ring

Unlike Saturn's intricate and complex ring patterns, Jupiter has a simple ring system that is composed of an inner halo, a main ring and a Gossamer ring. To the Voyager spacecraft, the Gossamer ring appeared to be a single ring, but Galileo imagery provided the unexpected discovery that Gossamer is really two rings. One ring is embedded within the other. The rings are very tenuous and are composed of dust particles kicked up as interplanetary meteoroids smash into Jupiter's four small inner moons METIS, ADRASTEA,THEBE, and AMALTHEA. Many of the particles are microscopic in size.

The innermost halo ring is toroidal in shape and extends radially from about 92,000 kilometers (57,000 miles) to about 122,500 kilometers (76,000 miles) from Jupiter's center. It is formed as fine particles of dust from the main ring's inner boundary 'bloom' outward as they fall toward the planet. The main and brightest ring extends from the halo boundary out to about 128,940 kilometers (80,000 miles) or just inside the orbit of Adrastea. Close to the orbit of Metis, the main ring's brightness decreases.

The two faint Gossamer rings are fairly uniform in nature. The innermost Amalthea Gossamer ring extends from the orbit of Adrastea out to the orbit of Amalthea at 181,000 kilometers (112,000 miles) from Jupiter's center. The fainter Thebe Gossamer ring extends from Amalthea's orbit out to about Thebe's orbit at 221,000 kilometers (136,000 miles).

Jupiter's rings and moons exist within an intense radiation belt of electrons and ions trapped in the planet's magnetic field. These particles and fields comprise the jovian MAGNETOSPHERE, magnetic environment, which extends 3 to 7 million kilometers (1.9 to 4.3 million miles) toward the Sun, and stretches in a windsock shape at least as far as Saturn's orbit - a distance of 750 million kilometers (466 million miles).




From the perspective we get on Earth, our planet appears to be big and sturdy with an endless ocean of air. From space, astronauts often get the impression that the Earth is small with a thin, fragile layer of atmosphere. For a space traveler, the distinguishing Earth features are the blue waters, brown and green land masses and white clouds set against a black background.

Many dream of traveling in space and viewing the wonders of the universe. In reality all of us are space travelers. Our spaceship is the planet Earth, traveling at the speed of 108,000 kilometers (67,000 miles) an hour.

Earth is the 3rd planet from the Sun at a distance of about 150 million kilometers (93.2 million miles). It takes 365.256 days for the Earth to travel around the Sun and 23.9345 hours for the Earth rotate a complete revolution. It has a diameter of 12,756 kilometers (7,973 miles), only a few hundred kilometers larger than that of Venus. Our atmosphere is composed of 78 percent nitrogen, 21 percent oxygen and 1 percent other constituents.

Earth is the only planet in the solar system known to harbor life. Our planet's rapid spin and molten nickel-iron core give rise to an extensive magnetic field, which, along with the atmosphere, shields us from nearly all of the harmful radiation coming from the Sun and other stars. Earth's atmosphere protects us from meteors, most of which burn up before they can strike the surface.

From our journeys into space, we have learned much about our home planet. The first American satellite, Explorer 1, discovered an intense radiation zone, now called the Van Allen radiation belts. This layer is formed from rapidly moving charged particles that are trapped by the Earth's magnetic field in a doughnut-shaped region surrounding the equator. Other findings from satellites show that our planet's magnetic field is distorted into a tear-drop shape by the solarwind.. We also now know that our wispy upper atmosphere, once believed calm and uneventful, seethes with activity -- swelling by day and contracting by night. Affected by changes in solar activity, the upper atmosphere contributes to weather and climate on Earth.

Besides affecting Earth's weather, solar activity gives rise to a dramatic visual phenomenon in our atmosphere. When charged particles from the solar wind become trapped in Earth's magnetic field, they collide with air molecules above our planet's magnetic poles. These air molecules then begin to glow and are known as the auroras or the northern-southern lights.



the jewel of the sky, was once know by ancient astronomers as the morning star and evening star. Early astronomers once thought Venus to be two separate bodies. Venus, which is named after the Roman goddess of love and beauty, is veiled by thick swirling cloud cover.

Astronomers refer to Venus as Earth's sister planet. Both are similar in size, mass, density and volume. Both formed about the same time and condensed out of the same nebula. However, during the last few years scientists have found that the kinship ends here. Venus is very different from the Earth. It has no oceans and is surrounded by a heavy atmosphere composed mainly of carbon dioxide with virtually no water vapor. Its clouds are composed of sulfuric acid .droplets. At the surface, the atmospheric pressure is 92 times that of the Earth's at sea-level.

Venus is scorched with a surface temperature of about 482° C (900° F). This high temperature is primarily due to a runaway greenhouse effect. caused by the heavy atmosphere of carbon dioxide. Sunlight passes through the atmosphere to heat the surface of the planet. Heat is radiated out, but is trapped by the dense atmosphere and not allowed to escape into space. This makes Venus hotter than mercury.

A Venusian day is 243 Earth days and is longer than its year of 225 days. Oddly, Venus rotates from east to west. To an observer on Venus, the Sun would rise in the west and set in the east.

Until just recently, Venus' dense cloud cover has prevented scientists from uncovering the geological nature of the surface. Developments in radar telescopes and radar imaging systems orbiting the planet have made it possible to see through the cloud deck to the surface below. Four of the most successful missions in revealing the Venusian surface are NASA's Pioneer Venus mission (1978), the Soviet Union's Venera 15 and 16 missions (1983-1984), and NASA's Magellan radar mapping mission (1990-1994). As these spacecraft began mapping the planet a new picture of Venus emerged.

Venus' surface is relatively young geologically speaking. It appears to have been completely resurfaced 300 to 500 million years ago. Scientists debate how and why this occurred. The Venusian topography consists of vast plains covered by lava flows and mountain or highland regions deformed by geological activity. Maxwell Montes in Ishtar Terra is the highest peak on Venus. The Aphrodite Terra highlands extend almost half way around the equator. Magellan images of highland regions above 2.5 kilometers (1.5 miles) are unusually bright, characteristic of moist soil. However, liquid water does not exist on the surface and cannot account for the bright highlands. One theory suggests that the bright material might be composed of metallic compounds. Studies have shown the material might be iron pyrite (also know as "fools gold"). It is unstable on the plains but would be stable in the highlands. The material could also be some type of exotic material which would give the same results but at lower concentrations.




MESSENGER's Wide Angle Camera (WAC), part of the Mercury Dual Imaging System (MDIS), is equipped with 11 narrow-band color filters. As the spacecraft receded from Mercury after making its closest approach on January 14, 2008, the WAC recorded a 3x3 mosaic covering part of the planet not previously seen by spacecraft. The color image shown here was generated by combining the mosaics taken through the WAC filters that transmit light at wavelengths of 1000 nanometers (infrared), 700 nanometers (far red), and 430 nanometers (violet). These three images were placed in the red, green, and blue channels, respectively, to create the visualization presented here. The human eye is sensitive only across the wavelength range from about 400 to 700 nanometers. Creating a false-color image in this way accentuates color differences on Mercury's surface that cannot be seen in black-and-white (single-color) images. Color differences on Mercury are subtle, but they reveal important information about the nature of the planet's surface material. A number of bright spots with a bluish tinge are visible in this image. These are relatively recent impact craters. Some of the bright craters have bright streaks (called "rays" by planetary scientists) emanating from them. Bright features such as these are caused by the presence of freshly crushed rock material that was excavated and deposited during the highly energetic collision of a meteoroid with Mercury to form an impact crater. The large circular light-colored area in the upper right of the image is the interior of the Caloris basin. Mariner 10 viewed only the eastern (right) portion of this enormous impact basin, under lighting conditions that emphasized shadows and elevation differences rather than brightness and color differences. MESSENGER has revealed that Caloris is filled with smooth plains that are brighter than the surrounding terrain, hinting at a compositional contrast between these geologic units. The interior of Caloris also harbors several unusual dark-rimmed craters, which are visible in this image. The MESSENGER science team is working with the 11-color images in order to gain a better understanding of what minerals are present in these rocks of Mercury's crust. (Courtesy NASA/JHUAPL)