Guide to Space Archives

June 13, 2015December 23, 2015 by Matt Williams

Neil Armstrong: The First Man to Walk on the Moon

armstrong on the Moon — Neil Armstrong on the Moon in 1969. Credit: NASA

Neil Armstrong is considered one of the greatest heroes of the space age, earning renown within the United States and the world over for being the first person to land a spacecraft on the Moon and the first person to set foot on the Lunar surface. But what is the story behind the man? As with all heroes and inspiration figures, the road that led to his famous declaration “One small step for [a] man,” began early on in his life.

Early Life:
Neil was born on August 5, 1930, in Auglaize County near Wapakoneta, Ohio to Stephen Koenig Armstrong and Viola Louise Engel. His father worked as an auditor for the Ohio government, which meant that the family moved around quite a lot during Neil’s formative years. In fact, the Armstrong’s lived in a total of 20 towns for the first few years of Neil’s life.

From an early age, Neil demonstrated a deep passion for flying. When he was just two-years-old, his father took him to the Cleveland Air Races. On July 20, 1936, when he was five, he experienced his first airplane flight in Warren, Ohio, where he and his father took a ride in a Ford Trimotor airplane (also known as the “Tin Goose”).

The Experimental Aircraft Association is bringing a 1929 Ford Tri-Motor to the Purdue Airport on Wednesday (Sept 5). Purdue students, faculty and staff will be able to ride in the plane, which served as one of the worldÕs first airliners. (Photo provided by the Experimental Aircraft Association) — *The 1929 Ford Tri-Motor, which Armstrong flew in with his father on July 20th, 1936, on display at Purdue Airport. Credit: Experimental Aircraft Association*

As a child, Armstrong was also active in the Boy Scouts and obtained the rank of Eagle Scout. As a teenager, he began taking flying lessons and worked at the local airport and at other odd jobs in order to pay for it. At the age of 16, before he even had his driver’s license, Neil earned his pilot’s license and began down the path that would eventually take him into space.

At the age of 17, Armstrong went off to study aeronautical engineering. Although he had been accepted to the Massachusetts Institute of Technology, he decided instead to go to Purdue University in West Lafayette, Indiana, in order to be closer to home. His college tuition was paid for under the Holloway Plan, where applicants committed to two years of study, followed by three years of service in the U.S. Navy, before completed the final two years of their degree program.

Military Pilot:
In January of 1949, at the age of 18, Armstrong was called-up for military service and went off to the Naval Air Station in Pensacola, Florida, to begin his flight training. This lasted almost 18 months, during which time he qualified for carrier landing aboard the USS Cabot and USS Wright. On August 16th, 1950, two weeks after his 20th birthday, Armstrong was informed by letter that he was a fully qualified Naval Aviator.

*Two F9F-2 Panthers over Korea, with Armstrong piloting S-116 (left). Credit: U.S. Navy National Museum of Naval Aviation*

In June 1951, the carrier he had been assigned to – the USS Essex – set sail for Korea, where his unit (VF-51, an all-jet squadron) would act as a ground-attack squadron. In the course of the war, he flew 78 missions and accumulated approximately 121 hours of combat experience. His plane was shot down once, but Armstrong managed to eject and was rescued without incident or serious injury.

For his service to his country, he received several commendations, including the Air Medal for his first 20 combat missions, a Gold Star for the next 20, and the Korean Service Medal and Engagement Star. Armstrong left the Navy at age 22 on August 23rd, 1952, and became a Lieutenant, Junior Grade, in the U.S. Naval Reserve. He remained in the reserve for eight years, then resigned his commission on October 21st, 1960.

After his service in Korea, Armstrong returned to his studies at Purdue. In 1955, he was awarded a Bachelor of Science degree in Aeronautical Engineering, and a Master of Science degree in Aerospace Engineering from the University of Southern California in 1970. Armstrong would also be awarded honorary doctorates by several universities later on in life.

Armstrong, 30, and X-15 1 after a research flight in 1960. Credit: NASA — *Armstrong, at the age of 30, pictured in front of X-15 #1 after a research flight in 1960. Credit: NASA*

It was also during his time at Purdue that Armstrong met Janet Elizabeth Shearon, the woman he would go on to marry. After graduating, the two moved to Cleveland, Ohio, where Armstrong was working at the National Advisory Committee for Aeronautics’ (NACA) Lewis Flight Propulsion Laboratory as a research test pilot. The two married on January 28th, 1956, at the Congregational Church in Wilmette, Illinois.

After 18-months, the Armstrongs moved to Edwards Air Force Base in California where he began working for the NACA’s High-Speed Flight Station. While there, he flew multiple experimental aircraft, including the Bell X-1B, the T-33 Shooting Star, the Lockheed F-104, and the North American X-15. He also met legendary test pilot Chuck Yeager, and was involved in several incidents that went down in Andrew’s AFB folklore.

Gemini Program:
In September of 1962, Armstrong joined the NASA Astronaut Corps as part of what the press dubbed “the New Nine” – a group of nine astronauts that were selected for the Gemini and Apollo programs. These programs, which were the successor to the Mercury Program – which sought to place an astronaut in orbit (popularized by the movie The Right Stuff) – were designed with the intent of conducting long-term space flights and a manned mission to the Moon.

*The Agena Target Vehicle as seen from Gemini 8 during rendezvous. Credit: NASA*

Neil’s first mission to space would take place four years later, on March 16th, 1966, aboard a Titan II spacecraft, with Neil acting as Command Pilot and fellow astronaut David Scott as Pilot. Known as Gemini 8, this mission was the most complex mission to date, involving a rendezvous and docking with an unmanned Agena target vehicle, and some extra-vehicular activity (EVA) being performed.

The docking procedure was a success, but due to mechanical failure, the mission had to be cut short. On September 12th, 1966, Armstrong served as the Capsule Communicator (CAPCOM) for the Gemini 11 mission, remaining in communication with astronauts Pete Conrad and Dick Gordon as they conducted spacecraft rendezvous and EVA operations.

On April 5th, 1967, just three and half months after the Apollo 1 fire took place, Deke Slayton – one of the Mercury Seven astronauts and NASA’s first Chief of the Astronaut Office – brought Armstrong and many other veterans of project Gemini together and told that they would be flying the first Lunar missions.

Apollo 11 Crew Photo. Credit: NASA — *Apollo 11 Crew Photo, showing Neil Armstrong (left), Buzz Aldrin (right), and Michael Collins (middle). Credit: NASA*

Over the next six months, Armstrong and the other astronauts began training for a possible trip to the Moon, and Neil was named backup commander for the Apollo 8 mission. On December 23rd, 1968, as Apollo 8 orbited the Moon, Slayton informed Armstrong that he would be commander for the Apollo 11 mission, joined by Buzz Aldrin as lunar module pilot and Michael Collins as command module pilot.

Apollo 11:
On July 16th, 1969, the historic mission blasted off from the Kennedy Space Center in Florida at 13:32:00 UTC (9:32:00 a.m. EDT local time). Thousands of people crowded the highways and beaches near the launch site to watch the Saturn V rocket ascend into the sky. Millions more watched from home, and President Richard M. Nixon viewed the proceedings from the Oval Office at the White House.

The rocket entered the Earth’s orbit some twelve minutes later. After one and a half orbits, the S-IVB third-stage engine pushed the spacecraft onto its trajectory toward the Moon. After 30 minutes, the command/service module pair separated from this last remaining Saturn V stage, docked with the Lunar Module, and the combined spacecraft headed for the Moon.

*The Apollo 11 Command and Service Modules (CSM) are photographed from the Lunar Module (LM) in lunar orbit during the Apollo 11 lunar landing mission. Credit: NASA*

On July 19th at 17:21:50 UTC, Apollo 11 passed behind the Moon and fired its service propulsion engine to enter lunar orbit. On July 20th, the Lunar Module Eagle separated from the Command Module Columbia, and the crew commenced their Lunar descent. When Armstrong looked outside, he saw that the computer’s landing target was in a boulder-strewn area which he judged to be unsafe. As such, he took over manual control of the LM, and the craft landed at 20:17:40 UTC with only 25 seconds of fuel left.

Armstrong then radioed to Mission Control and announced their arrival by saying: “Houston, Tranquility Base here. The Eagle has landed.” Once the crew had gone through their checklist and depressurized the cabin, the Eagles’ hatch was opened and Armstrong began walking down the ladder to the Lunar surface first.

When he reached the bottom of the ladder, Armstrong said: “I’m going to step off the LEM now” (referring to the Lunar Excursion Module). He then turned and set his left boot on the surface of the Moon at 2:56 UTC July 21st, 1969, and spoke the famous words “That’s one small step for [a] man, one giant leap for mankind.”

About 20 minutes after the first step, Aldrin joined Armstrong on the surface and became the second human to set foot on the Moon. The duo then began their tasks of unveiling a plaque commemorating their flight, setting up the Early Apollo Scientific Experiment Package, and planting the flag of the United States. The crew then returned to the LM and blasted off, commencing their return trip to Earth.

A teensy-tiny Neil Armstrong is visible in the helmet of Buzz Aldrin during the Apollo 11 landing in July 1969. Credit: NASA — *Neil Armstrong is visible in the helmet of Buzz Aldrin during the Apollo 11 landing in July 1969. Credit: NASA*

Upon returning to Earth, the Apollo 11 crew went on a 45-day tour around the world called the “Giant Leap” tour. Armstrong also traveled to the Soviet Union to talk at the 13th annual conference of the International Committee on Space Research. While there, he met Valentina Tereshkova (the first female astronaut to go into space), Premier Alexei Kosygin, and was given a tour of the Yuri Gagarin Cosmonaut Training Center.

Shortly after the Apollo 11 mission, Armstrong announced that he did not intend to fly in space again; and in 1971, resigned from NASA. He then settled into a life of teaching, accepting a position in the Department of Aerospace Engineering at the University of Cincinnati. After eight years, he resigned. He also spent much of this time acting as a corporate spokesperson and serving on the board of directors of several companies.

Retirement and Death:
During his post-Apollo years, Armstrong also served on two spaceflight accident investigations. The first took place in 1970, where he served as part of the panel that investigated the Apollo 13 mission, presented a detailed chronology of the mission and made recommendations. In 1986, President Reagan appointed him as vice-chairman of the Rogers Commission to investigate the Space-shuttle Challenger disaster of that year.

Members of the U.S. Navy ceremonial guard hold an American flag over the ashes of Apollo 11 astronaut Neil Armstrong during a burial at sea service on board the USS Philippine Sea (CG-58), on Friday, September 14, 2012, in the Atlantic Ocean. Credit: NASA — *Neil Armstrong was buried at sea on Sept. 14th, 2012. The ceremony took place on board the USS Philippine Sea (CG-58) in the Atlantic Ocean. Credit: NASA*

In 2012, Armstrong underwent vascular bypass surgery to relieve blocked coronary arteries. Although he was reportedly recovering well, he died on August 25th, in Cincinnati, Ohio. In a ceremony that was held aboard the USS Philippine Sea (an American missile cruiser) Armstrong was buried with honors in a ceremony where a U.S. Navy ceremonial guard draped an American flag over his ashes before commended them to the sea.

For his years of service, Armstrong has received numerous medals including the Presidential Medal of Freedom, the Congressional Space Medal of Honor, the Congressional Gold Medal, the Robert J. Collier Trophy, and the Sylvanus Thayer Award.

Neil Armstrong has had over a dozen elementary, middle and high schools named in his honor, and many streets, buildings, schools, and other places around the world have been named in honor of Armstrong and/or the Apollo 11 mission. The lunar crater Armstrong, which sits approx. 50 km (31 miles) from the Apollo 11 landing site, and asteroid 6469 Armstrong are named in his honor.

Armstrong was also inducted into the Aerospace Walk of Honor, the National Aviation Hall of Fame, and the United States Astronaut Hall of Fame. Armstrong and his Apollo 11 crewmates were the 1999 recipients of the Langley Gold Medal from the Smithsonian Institution. His alma mater, Purdue University, also named a new engineering hall after him, which was completed in 2007.

Universe Today has articles on Neil Armstrong and first man on the Moon.

For more information, check out Neil Armstrong and NASA’s Human Spaceflight.

Astronomy Cast has an episode on the Moon.

Sources:
NASA: Who is Neil Armstrong
NASA: Biography of Neil Armstrong

June 13, 2015September 30, 2016 by Matt Williams

Who Was The First Man To Go Into Space?

Yuri Gagarin, posing for a photo op before the Vostok 1 mission on April 12th, 1961 Credit:

Picture if you will two titanic powers struggling to see who will be the first to conquer space. Between them, they have the best scientists in the world, many of whom they “borrowed” from Germany after the Second World War. They are sparing no expense, and that includes the cost in lives, in order to be the first to get a human being into space.

Sound scary? Well, if you were an American astronaut or a Soviet cosmonaut in the 1960’s, it sure would be! But for men like Yuri Gagarin, the first man to go into man in space (and also the first man to orbit the Earth) the rewards would last a lifetime.

Early Life:

Like most heroes of the space age, Gagarin’s story began in his infancy. Born to Alexey Ivanovich Gagarin and Anna Timofeyevna Gagarina in the village of Klushino, Russia (Smolensky Oblast) on March 9th, 1934, Yuri Alekseyevich Gagarin began his life on a collective farm and witnessed some terrible things in his early years.

In 1941, the village was occupied by the Nazis, and the Gagarin family was forced to relocate to a mud hut on their property as a German officer took possession of their house. His two older siblings were deported to Poland for slave labor in 1943, and did not return until after the war in 1945.

Gagarin pictured in a Yak-18 trainer plane. Credit: rian.ru — *Gagarin pictured in a Yak-18 plane, while training to become a pilot with the Soviet Air Force. Credit: rian.ru*

Another version of Gagarin’s biography suggests that the family relocated east of the Urals ahead of the Nazi advance, and returned to the region after the war. In either case, by 1946, the family moved to the nearby town of Gzhatsk, where Gagarin continued his secondary education.

At the age of 16, Gagarin entered into an apprenticeship as a foundryman at the Lyubertsy Steel Plant near Moscow, and also enrolled at a local “young workers” school for seventh grade evening classes. After graduating in 1951, he was selected for further training at the Saratov Industrial Technical School.

While there, Gagarin volunteered for weekend training as a Soviet air cadet at a local flying club, where he learned to fly biplanes and the Yak-18 trainer. He graduated from technical school in 1955, and was drafted into the Soviet Army.

Pilot:

In 1957, he was sent to the First Chkalov Air Force Pilot’s School in Orenburg, where he trained on Mig-15 jet fighters. While there, he met Valentina Ivanovna Goryacheva, a medical technician graduate of the Orenburg Medical School. The two were married on 7 November 1957, the same day Gagarin graduated from Orenburg.

launched into orbit on the Vostok 3KA-3 spacecraft (Vostok 1). Credit: space.com — *Gagarin pictured inside the cockpit of the Vostok 3KA-3 spacecraft (Vostok 1) before being launched into orbit. Credit: Getty Images*

By 1960, Gagarin had earned the rank of Senior Lieutenant and had come to the attention of the Soviet space program. After a rigorous selection process, he became one of 20 pilots selected to become a cosmonaut, and was further selected to be part of an elite training group known as the Sochi Six – from which the first cosmonauts of the Vostok program would be chosen.

Vostok Program:

Out of the twenty selected, Gagarin and fellow cosmonaut Gherman Titov were selected to be the first cosmonauts to go into space. This was due to a combination of factors, including their performance during training sessions, their height (since space was limited in the small Vostok cockpit), and by an anonymous vote by the members of the program.

Gagarin’s historic flight took place on April 12th, 1961, roughly one month before NASA was able to put a manned spacecraft of their own into space. His spaceship, the Vostok 1, weighing approximately 4700 kg (over 10,000 pounds), was quite primitive by modern standards. For starters, the craft wasn’t even piloted by Gagarin himself, mainly because the Russians had not yet tested the effects of weightlessness on any humans (only dogs!).

The actual flying was done by crews on the ground. It also had no maneuvering capabilities and consisted of a re-entry craft and service module. The cosmonaut was not even allowed to land in the re-entry craft because it was deemed too dangerous, and had to instead leave the craft and parachute to the ground.

Here the re-entry capsule of the Vostok 3KA-3 (also known as Vostok 1) spacecraft (Vostok 1) is seen with charring and its parachute on the ground after landing south west of Engels, in the Saratov region of southern Russia. Credit: space.com — *The re-entry capsule of the Vostok 3KA-3 (Vostok 1) is seen with charring and its parachute on the ground after landing south west of Engels, in southern Russia. Credit: space.com*

Gagarin’s flight began with his takeoff at the Baikonur Cosmodrome and ended with him parachuting safely to the ground in Kazakhstan one hour and forty-eight minutes later. During the flight, he was said to have been humming “The Motherland Hears, the Motherland Knows”, a patriotic song composed by Russian composer Dmitri Shostakovich.

According to western sources at the time, Gagarin was also rumored to have said “I don’t see any God up here” during his flight. However, the transcripts contradict this story, which appears to have been a reference to a remark Khrushchev had made after the flight and was falsely attributed to Gagarin. What he is known to have said during the flight was: “The Earth is blue… How wonderful. It is amazing.”

Retirement and Death:

Gagarin gained worldwide fame and recognition after the flight, touring Italy, Germany, the United Kingdom, Canada and Japan before returning home to Star City to continue his work with the Russian space program. He was no longer allowed into active service given his celebrity status, the government fearing that they might lose their poster boy in an accident.

*Soviet cosmonaut Yuri Gagarin, the first man to fly in space, as seen in 1968 before his death in a jet crash. Credit: RSC Energia*

This would prove to be an ironic decision, considering that seven years later, he died in an accident during a training flight. This occurred on March 27th, 1968, when Gagarin’s plane crashed and he and his instructor were killed. For many years, the circumstances surrounding the accident remained shrouded in mystery, and were the subject of much speculation and rumor.

In 2013, the truth about his death was finally revealed when the report detailing the incident was declassified. In an article that appeared on Russia Today, former cosmonaut Aleksey Leonov shared the details of the report, which indicated that the crash was the result of an unauthorized Su-15 fighter flying too close to Gagarin’s MiG, thus disrupting its flight and sending it into a spin.

Legacy:

In Russia, and around the world, Gagarin has gone down in history as one of the greatest astronauts/cosmonauts of all time and one of the biggest contributors to human space flight. For his accomplishments, he has been immortalized by numerous countries, and in countless ways.

*The statue of Yuri Gagarin, the first human to fly in space, looms over the town square in Karaganda, Kazakhstan March 9 as officials prepared to commemorate him on his 80th birthday. Credit: NASA*

In addition to commemorative coins, a hockey cup named in his honor and several commemorative stamps, he was given the title of “Hero of the Soviet Union” – a privilege reserved only for a select few. Numerous statues have also been erected in his honor, such as the one that towers over the town square in Karaganda, Kazakhstan (shown above).

Since 1962, April 12th has been celebrated in the USSR, and later in Russia and other post-Soviet states, as the Cosmonautics Day, in honor of his historic flight. In 2011, it was declared the International Day of Human Space Flight by the United Nations. Since 2001, Yuri’s Night, an international celebration, is held every April 12th to commemorate milestones in space exploration.

The Cosmonaut Training Center in Star City was renamed the Yuri Gagarin Cosmonaut Training Center in 1969, which was visited by Neil Armstrong during his tour of the Soviet Union.

The launch pad at Baikonur Cosmodrome from which Sputnik 1 and Vostok 1 were launched is now known as Gagarin’s Start. The village of Klushino where he was born was also renamed Gagarin in 1968 after his death, and his family’s house was converted into a museum.

*Yuri Gagarin, the first man in space, during his visit to France in 1963. Credit: Ria Novosti*

But perhaps the most notable thing about Gagarin, for which he is remembered most fondly, is his smile. As Sergei Korolev – one of the masterminds behind the early Soviet space program – once said, Gagarin possessed a smile “that lit up the darkness of the cold war”.

We have written many articles about Yuri Gagarin for Universe Today. Here’s Yuri Gagarin and Vostok 1, on the 50th Anniversary of Human Spaceflight. And here’s Who was the First Woman to go into Space?, Alan Shepard: Complicated, Conflicted and the Consummate Astronaut, Sally Ride, First American Woman in Space, Passes Away, and Who was the First Dog to go into Space?

If you’d like more info on the Yuri Gagarin, check out the History of Human Spaceflight, and here’s a link to Yuri Gagarin, The First Man in Space.

We’ve also recorded an entire episode of Astronomy Cast all about Space Capsules. Listen here, Episode 124: Space Capsules, Part 1: Vostok, Mercury and Gemini.

Sources:

June 12, 2015December 23, 2015 by Matt Williams

What is Halley’s Comet?

The Mawangdui silk, showing the shapes of comet tails and the different disasters associated with them, compiled in around 300 BC. Credit: NASA/JPL.

Halley’s Comet, also known as 1P/Halley, is the most well known comet in the Solar System. As a periodic (or short-term comet) it has orbital period that is less than 200 years, and has therefore been observed more than once by people here on Earth over the centuries.

It’s appearance in the skies above Earth has been noted since ancient times, and was associated with both bad and good omens by many cultures. But in truth, its behavior is no different than any short-term visitor that swings by from time to time. And its visits have become entirely predictable!

Discovery:
Halley’s Comet has been observed and recorded by astronomers since at least 240 BCE, with clear references to the comet being made by Chinese, Babylonian, and medieval European chroniclers. However, these records did not recognize that the comet was the same object reappearing over time. It was not until 1705 that English astronomer Edmond Halley, who used Newton’s Three Laws of Motion to determine that it was periodic.

Until the Renaissance, astronomers’ believed that comets – consistent with Aristotle’s views – were merely disturbances in the Earth’s atmosphere. This idea was disproved in 1577 by Tycho Brahe, who used parallax measurements to show that comets must lie beyond the Moon. However, for another century, astronomers would continue to believe that comets traveled in a straight line through the Solar System rather than orbiting the Sun.

In 1687, in his Philosophiæ Naturalis Principia Mathematica, Isaac Newton theorized that comets could travel in an orbit of some sort. Unfortunately, he was unable to develop a coherent model for explaining this at the time. As such, it was Edmond Halley – Newton’s friend and editor – who showed how Newton’s theories on motion and gravity could be applied to comets.

In his 1705 publication, Synopsis of the Astronomy of Comets, Halley calculated the effect that Jupiter and Saturn’s gravitational fields would have on the path of comets. Using these calculations and recorded observations made of comets, he was able to determine that a comet observed in 1682 followed the same path as a comet observed in 1607.

Pairing this with another observation made in 1531, he concluded that these observations were all of the same comet, and predicted that it would return in another 76 years. His prediction proved to be correct, as it was seen on Christmas Day, 1758, by a German farmer and amateur astronomer named Johann Georg Palitzsch.

His predictions not only constituted the first successful test of Newtonian physics, it was also the first time that an object besides the planets was shown to be orbiting the Sun. Unfortunately for Halley, he did not live to see the comet’s return (having died in 1742). But thanks to French astronomer Nicolas Louis de Lacaille, the comet was named in Halley’s honor in 1759.

The illustration shows a view of Augsburg, Germany with the comets of 1680, 1682, and 1683 in the sky. Click on image for larger view. Image credit: NASA/JPL — *The illustration shows a view of Augsburg, Germany with the comets of 1680, 1682 (Halley’s Comet), and 1683 in the sky. Credit: NASA/JPL*

Origin and Orbit:
Like all comets that take less than about 200 years to orbit the Sun, Halley’s Comet is believed to have originated from the Kuiper Belt. Periodically, some of these blocks of rock and ice – which are essentially leftover matter from the formation of the Solar System some 4.6 billion years ago – are pulled deeper into the Solar System and becomes active comets.

In 2008, another point of origin for the Halley-type comets had been proposed when a trans-Neptunian object with a retrograde orbit similar to Halley’s was discovered. Known as 2008 KV42, this comet’s orbit takes it from just outside the orbit of Uranus to twice the distance of Pluto. This suggests that Halley ‘s Comet could in fact be member of a new population of small Solar System bodies that is unrelated to the Kuiper Belt.

Halley is classified as a periodic or short-period comet, one with an orbit lasting 200 years or less. This contrasts with long-period comets, whose orbits last for thousands of years and which originate from the Oort Cloud – the sphere of cometary bodies that is 20,000 – 50,000 AU from the Sun at its inner edge. Other comets that resemble Halley’s orbit, with periods of between 20 to 200 years, are called Halley-type comets. To date, only 54 have been observed, compared with nearly 400 identified Jupiter-family comets.

Artists' impression of the Kuiper belt and Oort cloud, showing both the origin and path of Halley's Comet. Image credit: NASA/JPL. — *Artists’ impression of the Kuiper belt and Oort cloud, showing both the origin and path of Halley’s Comet. Credit: NASA/JPL*

Halley’s orbital period over the last 3 centuries has been between 75–76 years, although it has varied between 74–79 years since 240 BC. Its orbit around the Sun is highly elliptical. It has a perihelion (i.e. the point where it is nearest the Sun) of just 0.6 AU, which places it between the orbits of Mercury and Venus. Meanwhile, it’s aphelion – the farthest distance from the Sun – is 35 AU, the same distance as Pluto.

Unusual for an object in the Solar System, Halley’s orbit is retrograde – which means that it orbits the Sun in the opposite direction to the planets (or clockwise from above the Sun’s north pole). Due to the retrograde orbit, it has one of the highest velocities relative to the Earth of any object in the Solar System.

The orbits of the Halley-type comets suggest that they were originally long-period comets whose orbits were perturbed by the gravity of the gas giants and directed into the inner Solar System. If Halley was once a long-period comet, it is likely to have originated in the Oort Cloud. However, Halley is believed to have been a short-term comet for the past 16,000–200,000 years.

Because its orbit comes close to Earth’s in two places, Halley is the parent body of two meteor showers: the Eta Aquariids in early May, and the Orionids in late October. Observations conducted around the time of Halley’s appearance in 1986, however, suggest that the Eta Aquarid meteor shower might not originate from Halley’s Comet, although it might be perturbed by it.

Photo of Haley's Comet crossing the Milky Way, taken by the Kuiper Airborne Observatory in New Zealand on April 8th/9th, 1986. Credit: NASA — Photo of Haley’s Comet crossing the Milky Way, taken by the Kuiper Airborne Observatory in New Zealand on April 8th/9th, 1986. Credit: NASA

Structure and Composition:
As Halley approaches the Sun, it expels jets of sublimating gas from its surface, which knock it very slightly off its orbital path. This process causes the comet to form a bright tail of ionized gas (ion tail), and a faint one made up of dust particles. The ion tail is also known as a coma (a small atmosphere) which spans up to 100,000 km across and consists of violatiles such as water, methane, ammonia and carbon dioxide.

Despite the vast size of its coma, Halley’s nucleus is relatively small – barely 15 kilometers long, 8 kilometers wide and roughly 8 kilometers thick. Its mass is also relatively low (an estimated 2.2 × 10¹⁴ kg, or 242.5 billion tons) and its average density is about 0.6 g/cm³, indicating that it is made of a large number of small pieces held loosely together.

Spacecraft observations have shown that the gases ejected from the nucleus were 80% water vapor, 17% carbon monoxide and 3–4% carbon dioxide, with traces of hydrocarbons (although more-recent sources give a value of 10% for carbon monoxide and also include traces of methane and ammonia).

The dust particles have been found to be primarily a mixture of carbon–hydrogen–oxygen–nitrogen (CHON) compounds – which are common in the outer Solar System – and silicates, like those found in terrestrial rocks. At one time, it was thought that Halley could have delivered water to Earth in the distant past – based on the ratio of deuterium to hydrogen found in the comet’s water that showed it to be chemically similar to the Earth’s oceans. However, subsequent observations have indicated that this is unlikely.

This view of comet Halley's nucleus was obtained by the Halley Multicolour Camera (HMC) on board the Giotto spacecraft, as it passed within 600 km of the comet nucleus on March 13, 1986. Credit: ESA — *The nuclear of Halley’s Comet, obtained by the Halley Multicolour Camera (HMC) on board the Giotto spacecraft during its flyby on March 13, 1986. Credit: ESA*

The ESA’s Giotto (1985-1992) and Russia’s Vega missions (1986) gave planetary scientists their first view of Halley’s surface and structure. The images could only capture roughly 25% of the comet’s surface, but nevertheless revealed an extremely varied topography – with hills, mountains, ridges, depressions, and at least one crater.

Role in Myths and Superstitions:
As already noted, Halley’s Comet has a long and rich history when it comes to being observed by humans. Including its most recent visits, Halley’s Comet has been visible from Earth on 30 separate occasions. The earliest record of which were the Shih Chi and Wen Hsien Thung Khao chronicles, written in China ca. 240 BCE.

While it is believed that Babylonian scribes recorded the appearance of Halley’s Comet when it returned in 164 and 87 BCE, it’s most famous appearance occurred shortly before the 1066 invasion of England by William the Conqueror. Whereas King Harold of England saw the comet as a bad omen, William and his forces interpreted it as a sign of their impending victory (at least according to legend).

Throughout the Middle Ages, the appearances of comets in the night sky were seen as heralds of bad news, indicating that either a person of royal standing had died, or that dark days lay ahead. This is perhaps owing to what was seen as the erratic and unpredictable behavior of comets, when compared to the Sun, the Moon and the stars.

The Bayeux Tapestry, showing the appearance of Halley's Comet in the sky prior to William the Conqueror's invasion of England. Credit: Wikipedia Commons/Myrabella — *The Bayeux Tapestry, showing the appearance of Halley’s Comet in the sky in 1066. Credit: Wikipedia Commons/Myrabella*

With the development of modern astronomy, this view of comets has been largely dispelled. However, there are many who still hold to the “doom and gloom” view of Halley’s Comet, believing that it will strike the Earth at some point and trigger an Extinction Level Event, the likes of which has not been seen since the Dinosaurs.

Disappearance:
Halley’s overall lifespan is difficult to predict, and opinions do vary. In 1989, Russian astronomers Boris Chirikov and Vitaly Vecheslavov performed an analysis of 46 apparitions of Halley’s Comet taken from historical records and computer simulations. Their study showed that the comet’s dynamics were chaotic and unpredictable over long timescales, and indicated that its lifetime could be as long as 10 million years.

In 2002, David C. Jewitt conducted a study that indicated that Halley will likely evaporate, or split in two, within the next few tens of thousands of years. Alternately, Jewitt predicted that it could survive long enough to be ejected from the Solar System entirely within a few hundred thousand years.

Meanwhile, observations conducted by D.W. Hughes et al. suggests that Halley’s nucleus has been reduced in mass by 80–90% over the last 2000–3000 revolutions (i.e. 150,000 – 230,000 years). By their estimations, it would not be surprising at all if the comet evaporated entirely within the next 300 revolutions or so (approx. 25,000 years).

The last time Halley’s Comet was seen was in 1986, which means it will not reappear until 2061. As always, some are choosing to prepare for the worst – believing its next pass will signal the end of life as we know it – while others are contemplating if they will live long enough to witness it.

Universe Today has articles on famous comets and distant Halley’s Comet.

For more information, take a look at Comet Halley and Halley’s Comet.

Astronomy Cast has an episode on comets.

Sources: Wikipedia, NASA

June 11, 2015February 27, 2017 by Fraser Cain

How Low Can You Orbit?

The Earth’s atmosphere is a total drag, especially if you’re trying to orbit our planet. So how low can you go?

The Earth’s atmosphere is a total drag, especially if you’re trying to orbit our planet. It’s a drag. Get it? Atmospheric drag. Drag. Drag.

Hi, my name is Fraser Cain. I’m the publisher of Universe Today, and sometimes my team lets me write my own jokes.

I could have started off this episode with a reference to the “Adama Drop” in-atmosphere viper deployment from BSG, but instead I went with a Dad joke. My punishment is drawing attention to it.

So how low can you go? And if you go low enough, will Ludacris appear in the mirror?

We all appreciate the Earth’s atmosphere and everything it does for you. With all the breathing, and the staying warm and the not having horrible bruises all over your body from teeny space rocks pummeling us.

I’ve got an alternative view. The Earth’s atmosphere is your gilded pressurized oxygenated cage, and it’s the one thing keeping you from flying in space.And as we all know, this is your destiny.

Without the atmosphere, you could easily orbit the Earth, a few kilometers over its surface. Traveling around and around the planet like a person sized Moon. Wouldn’t that be great?

Well, it’s not going to happen. As you walk through the atmosphere, you bonk into all the air molecules. You don’t feel it when you’re moving at walking speed, but go faster, like an airplane, and it’ll rock you like a hurricane.

Without constant thrust pushing against the atmosphere, you’ll keep slowing down, and when you’re trying to orbit the planet, it’s a killer. Our atmosphere is like someone is constantly pushing the brakes on the fly in space party.

If you’ve played Kerbal Space Program, you know the faster you’re traveling, the higher you orbit. Conversely, the slower you travel, the lower you orbit. Travel slow enough and you’ll eat it, and by it, I meant as much planet as you can co-exist with after a high speed impact.

Being more massive means more momentum to push against the atmospheric drag. But with a large surface area, it acts like a parachute, slowing you down.

Hey, I know something that’s super massive with a huge surface area. The International Space Station orbits the planet at an altitude between 330 km and 435 km.

Why such a big range? The atmosphere is constantly pushing against the ISS as it orbits the planet. This slows down the space station’s speed and lowers its orbit. It wouldn’t last more than a couple of years if it wasn’t able to counteract the atmospheric drag.

The International Space Station, photographed by the crew of STS-132 as they disembarked. Credit: NASA

Fortunately, the station has rockets to increase its speed, and a faster speed means a higher orbit. It can even get assistance from docked spacecraft. If the space station were to go any lower, it would require higher and higher amounts of thrust to prevent re-entry into the Earth’s atmosphere.

So what are the limits? Anything below 160 km altitude will essentially re-enter almost immediately, as it’s buffeted by the thicker atmosphere. You really wouldn’t last more than a few hours at that altitude, but above 800 km you could orbit for more than 100 years.

Geosynchronous satellites that orbit the Earth and transmit our television signals are at an altitude of about 42,000 km. Satellites that high are never coming back down. Well, maybe not never.

Want to enjoy your orbital experience? Make sure you get yourself to an altitude of at least 300 km, 400 km just to be safe. You should shoot for more like 800 km if you just don’t want to worry about things for a while.

Knowing these risks, would you be willing to travel to orbit with current technology? Tell us in the comments below.

June 11, 2015April 26, 2016 by Matt Williams

What are the Galilean Moons?

Illustration of Jupiter and the Galilean satellites. Credit: NASA

It’s no accident that Jupiter shares its name with the king of the gods. In addition to being the largest planet in our Solar System – with two and a half times the mass of all the other planets combined – it is also home to some of the largest moons of any Solar planet. Jupiter’s largest moons are known as the Galileans, all of which were discovered by Galileo Galilei and named in his honor.

They include Io, Europa, Ganymede, and Callisto, and are the Solar System’s fourth, sixth, first and third largest satellites, respectively. Together, they contain almost 99.999% of the total mass in orbit around Jupiter, and range from being 400,000 and 2,000,000 km from the planet. Outside of the Sun and eight planets, they are also among the most massive objects in the Solar System, with radii larger than any of the dwarf planets.

Continue reading “What are the Galilean Moons?”

June 11, 2015December 30, 2016 by Matt Williams

What are the Different Types of Renewable Energy?

The Gemasolar solar power plant, situated near Seville in Spain. Credit: Torresol Energy

Renewable energy is becoming an increasingly important issue in today’s world. In addition to the rising cost of fossil fuels and the threat of Climate Change, there has also been positive developments in this field which include improvements in efficiency as well as diminishing prices.

All of this has increased the demand for alternative energy and accelerated the transition towards cleaner, more sustainable methods of electrical power. However, it is important to note that are many kinds – biomass, solar, wind, tidal, and geothermal power – and that each has its own share of advantages and drawbacks.

Biomass:

The most widely used form of renewable energy is biomass. Biomass simply refers to the use of organic materials and converting them into other forms of energy that can be used. Although some forms of biomass have been used for centuries – such as burning wood – other, newer methods, are focused on methods that don’t produce carbon dioxide.

For example, there are clean burning biofuels that are alternatives to oil and gas. Unlike fossil fuels, which are produced by geological processes, a biofuel is produced through biological processes – such as agriculture and anaerobic digestion. Common fuels associated with this process are bioethanol, which is created by fermenting carbohydrates derived from sugar or starch crops (such as corn, sugarcane, or sweet sorghum) to create alcohol.

Another common biofuel is known as biodiesel, which is produced from oils or fats using a process known as transesterification – where acid molecules are exchanged for alcohol with the help of a catalyst. These types of fuels are popular alternatives to gasoline, and can be burned in vehicles that have been converted to run on them.

Solar Power:

Solar power (aka. photovoltaics) is one of the most popular, and fastest-growing, sources of alternative energy. Here, the process involves solar cells (usually made from slices of crystalline silicon) that rely on the photovoltaic (PV) effect to absorb photons and convert them into electrons. Meanwhile, solar-thermal power (another form of solar power) relies on mirrors or lenses to concentrate a large area of sunlight, or solar thermal energy (STE), onto a small area (i.e. a solar cell).

Initially, photovoltaic power was only used for small to medium-sized operations, ranging from solar powered devices (like calculators) to household arrays. However, ever since the 1980s, commercial concentrated solar power plants have become much more common. Not only are they a relatively inexpensive source of energy where grid power is inconvenient, too expensive, or just plain unavailable; increases in solar cell efficiency and dropping prices are making solar power competitive with conventional sources of power (i.e. fossil fuels and coal).

*The Ivanpah Solar Power Facility in California, showing its three towers delivering concentrated solar power. Credit: Wikipedia commons/Sbharris*

Today, solar power is also being increasingly used in grid-connected situations as a way to feed low-carbon energy into the grid. By 2050, the International Energy Agency anticipates that solar power – including STE and PV operations – will constitute over 25% of the market, making it the world’s largest source of electricity (with most installations being deployed in China and India).

Wind Power:

Wind power has been used for thousands of years to push sails, power windmills, or to generate pressure for water pumps. Harnessing the wind to generate electricity has been the subject of research since the late 19th century. However, it was only with major efforts to find alternative sources of power in the 20th century that wind power has become the focal point of considerable research and development.

Compared to other forms of renewable energy, wind power is considered very reliable and steady, as wind is consistent from year to year and does not diminish during peak hours of demand. Initially, the construction of wind farms was a costly venture. But thanks to recent improvements, wind power has begun to set peak prices in wholesale energy markets worldwide and cut into the revenues and profits of the fossil fuel industry.

According to a report issued this past March by the Department of Energy, the growth of wind power in the United States could lead to even more highly skilled jobs in many categories. Titled “Wind Vision: A New Era for Wind Power in the United States”, the document indicates that by 2050, the industry could account for as much as 35% of the US’ electrical production.

In Denmark, wind power accounts for 28% of electrical production and is cheaper than coal power. Credit: denmark.dk — *In Denmark, wind power accounts for 28% of the country’s electrical production, and is now cheaper than coal power. Credit: denmark.dk*

In addition, last year, the Global Wind Energy Council and Greenpeace International came together to publish a report titled “Global Wind Energy Outlook 2014”. This report stated that worldwide, wind power could provide as much as 25 to 30% of global electricity by 2050. At the time of the report’s writing, commercial installations in more than 90 countries had a total capacity of 318 gigawatts (GW), providing about 3% of global supply.

Tidal Power:

Similar to wind power, tidal power is considered to be a potential source of renewable energy because tides are steady and predictable. Much like windmills, tide mills have been used since the days of Ancient Rome and the Middle Ages. Incoming water was stored in large ponds, and as the tides went out, they turned waterwheels that generated mechanical power to mill grain.

It was only in the 19th century that the process of using falling water and spinning turbines to create electricity was introduced in the U.S. and Europe. And it has only been since the 20th that these sorts of operations have been retooled for construction along coastlines and not just rivers.

Traditionally, tidal power has suffered from relatively high cost and limited availability of sites with sufficiently high tidal ranges or flow velocities. However, many recent technological developments and improvements, both in design and turbine technology, indicate that the total availability of tidal power may be much higher than previously assumed, and that economic and environmental costs may be brought down to competitive levels.

*Artist’ concept of a series of the Carnegie Wave Energy’s tidal system, where buoys anchored to the sea floor and use swells to move a series of pumps. Credit: Carnegie Wave Energy*

The world’s first large-scale tidal power plant is the Rance Tidal Power Station in France, which became operational in 1966. And in Orkney, Scotland, the world’s first marine energy test facility – the European Marine Energy Center (EMEC) – was established in 2003 to start the development of the wave and tidal energy industry in the UK.

In 2015, the world’s first grid-connected wave-power station (CETO, named after the Greek goddess of the sea) went online off the coast of Western Australia. Developed by Carnegie Wave Energy, this power station operates under water and uses undersea buoys to pump a series of seabed -anchored pumps, which in turn generates electricity.

Geothermal:

Geothermal electricity is another form of alternative energy that is considered to be sustainable and reliable. In this case, heat energy is derived from the Earth – usually from magma conduits, hot springs or hydrothermal circulation – to spin turbines or heat buildings. It is considered reliable because the Earth contains 10³¹ joules worth of heat energy, which naturally flows to the surface by conduction at a rate of 44.2 terawatts (TW) – more than double humanity’s current energy consumption.

One drawback is the fact that this energy is diffuse, and can only be cheaply harnessed in certain locations. However, in certain areas of the world, such as Iceland, Indonesia, and other regions with high levels of geothermal activity, it is an easily accessible and cost-effective way of reducing dependence on fossil fuels and coal to generate electricity. Countries generating more than 15 percent of their electricity from geothermal sources include El Salvador, Kenya, the Philippines, Iceland and Costa Rica.

The Krafla a geothermal power station located i0n Iceland. Credit: Wikipedia Commons/Ásgeir Eggertsson — *The Krafla a geothermal power station located in Iceland. Credit: Wikipedia Commons/Ásgeir Eggertsson*

As of 2015, worldwide geothermal power capacity amounts to 12.8 gigawatts (GW), which is expected to grow to 14.5 to 17.6 GW by 2020. What’s more, the Geothermal Energy Association (GEA) estimates that only 6.5 percent of total global potential has been tapped so far, while the IPCC reported geothermal power potential to be in the range of 35 GW to 2 TW.

Issues with Adoption:

One problem with many forms of renewable energy is that they depend on circumstances of nature – wind, water supply, and sufficient sunlight – which can impose limitations. Another issue has been the relative expense of many forms of alternate energy compared to traditional sources such as oil and natural gas. Until very recently, running coal-fired or oil-powered plants was cheaper than investing millions in the construction of large solar, wind, tidal or geothermal operations.

However, ongoing improvements made in the production of solar cells, wind turbines, and other equipment – not to mention improvements made in the amount of energy produced – has resulted in many forms of alternative energy becoming competitive with other methods. All over the world, nations and communities are stepping up to accelerate the transition towards cleaner, more sustainable, and more self-sufficient methods.

We have written many interesting articles on alternative energy on Universe Today. Here’s What is Alternative Energy?, What is Solar Energy? and Where does Geothermal Energy Come From?, Could the World Run on Solar and Wind Power?, and Harvesting Solar Power from Space.

You should also check out the National Renewable Energy Laboratory and Renewable Energy Policy Project.

Astronomy Cast also has an episode on the subject. Here’s Episode 51: Earth.

Sources:

June 8, 2015February 27, 2017 by Fraser Cain

What are Gravitational Waves?

When massive objects crash into each other, there should be a release of gravitational waves. So what are these things and how can we detect them?

Who wants to bet against Einstein? You? You? What about you?

Sure, there were a few bumps, but the guy’s track record on relativity is spotless. He explained the strange way that Mercury orbits the Sun. He guessed astronomers would see stars deflected by the Sun’s gravity during a solar eclipse. He predicted that gravity would redshift light, and it took physicists 50 years to finally come up with an experiment to verify it.

Based on his predictions, scientists confirmed galaxies warp light with their gravity, photons get time dilated when they pass near the Sun, and clocks that travel at high speeds experience less time than clocks on Earth.

They’ve even tested gravitational redshift, frame-dragging and the equivalence principle. Which is a word salad we’ll cover in the future, or for those of you who can’t wait, google.

Every time Bertie made a prediction about Relativity, physicists have been able to verify via experimentation. And so, according to this fuzzy man with the giant brain, when massive objects crash into each other, or when black holes form, there should be a release of gravitational waves.

So what are these things and how can we detect them?

First, a quick review. Mass causes a warp in space and time. The Sun’s “gravity” isn’t a pulling force, it’s really an indentation that the Sun causes in the space around itself.

Planets think they’re moving in a straight line, but they’re actually pulled into a circle while traveling through this warped spacetime. Go home planets, you’re drunk.

The idea is when mass moves or changes, Einstein said that there should be gravitational ripples produced in spacetime.

Our problem is that the size and effect of gravitational waves is incredibly small. We need to find the most catastrophic events in the Universe if we hope even detect them.

A supernova detonating asymmetrically, or two supermassive black holes orbiting each other, or a Galactus family reunion; are the magnitude of events we’re looking for.

The most serious attempt to detect gravitational waves is the Laser Interferometer Gravitational-Wave Observatory, or LIGO detector, in the United States. It has two facilities separated by 3000 km. Each detector carefully watches for any gravitational waves passing through by the length of time it takes for laser pulses to bounce within a 4km long sealed vacuum.

Laser Interferometer Gravitational-Wave Observatory Hanford installation - each arm extends for four kilometres. Credit: Caltech. — Laser Interferometer Gravitational-Wave Observatory Hanford installation – each arm extends for four kilometres. Credit: Caltech.

If a gravitational wave is detected, the two observatories use triangulation to determine its magnitude and direction. At least, that was the plan from 2002 to 2010. The problem was, it didn’t detect any gravitational waves for its entire run.

But hey, this is a job for science. Unbowed, the steely-eyed researchers rebuilt the equipment, improving its sensitivity by a factor of 10. This next round starts in 2015.

Scientists have proposed space-based instruments that could provide more sensitivity and increase the chances of detecting a gravitational wave.

Physicists assume this is a question of “when”, not “if” that gravitational waves will be detected, as only a fool bets against Einstein. Well, that and gravitational waves have already been detected… indirectly.

By watching the extremely regular energy blasts coming from pulsars, astronomers track exactly how quickly they’re radiating their energy away due to gravitational waves. So far, all the observations perfectly match the predictions of relativity. We just haven’t detected those gravitational waves directly… yet.

So, good news! Assuming the physicists and Einstein are right, we should see the detection of a gravitational wave in the next few decades, wrapping up a series of predictions about how insanely strange our Universe behaves.

Should we dig deeper into relativity, Einstein and his predictions? Tell us in the comments below.

June 6, 2015October 22, 2020 by Matt Williams

What Does NASA Stand For?

Chances are that if you have lived on this planet for the past half-century, you’ve heard of NASA. As the agency that is in charge of America’s space program, they put a man on the Moon, launched the Hubble Telescope, helped establish the International Space Station, and sent dozens of probes and shuttles into space.

But do you know what the acronym NASA actually stands for? Well, NASA stands for the National Aeronautics and Space Administration. As such, it oversees America’s spaceflight capabilities and conducts valuable research in space. NASA also has various programs on Earth dedicated to flight, hence why the term “Aeronautics” appears in the agency’s name.

June 5, 2015November 18, 2017 by Matt Williams

Uranus’ Moon Umbriel

Uranus and its five major moons. Credit:

The 19th century was an auspicious time for astronomers and planet hunters. In addition to the discovery of the Asteroid Belt that rests between Mars and Jupiter – as well as the many minor planets within – the outer solar planet of Uranus and its series of moons were also observed for the very first time.

Of these, Umbriel was certainly one of the most interesting finds. Aside from being Uranus’ third largest moon, it is also its darkest – a trait which contributed greatly to the selection of its name. And to this day, this large satellite of Uranus is shrouded in mystery…

Discovery and Naming:

Umbriel, along with its fellow moon Ariel, was discovered by English astronomer William Lassell on October 24th, 1851. Fellow English astronomer William Herschel, who had discovered Uranus’ moons of Titania and Oberon at the end of the 18th century, also claimed to have observed four additional moons around Uranus. However, his observations were not confirmed, leaving the confirmed discoveries of Ariel and Umbriel to Lassell, roughly half a century later.

Much like all of Uranus’ 27 moons, Umbriel was named after a character from Alexander Pope’s The Rape of the Lock, as well as plays by William Shakespeare. These names were suggested by John Herschel, the son of William Herschel, when he announced the discoveries of Titania and Oberon.

Size comparison of Earth, the Moon, and Umbriel. Credit: /Public Domain — *Size comparison of Earth, the Moon, and Umbriel. Credit: Tom Reding/Public Domain*

In keeping with the moon’s dark appearance, the name Umbriel – which was the name of the ‘dusky melancholy sprite’ in the The Rape of the Lock and is derived from the Latin Umbra (which means “shadow”) – seemed most appropriate for this satellite.

Size, Mass and Orbit:

Ariel and Umbriel are nearly the same size, with diameters of 1,158 kilometers and 1,170 kilometers respectively. Based on spectrograph analyses and estimates of the moon’s mass and density, astronomers believe that the majority of the planet consists of water ice, with a dense non-ice component constituting around 40% of its mass.

This could mean that Umbriel consists of an icy outer shell that surrounds a rocky core, or one made out of carbonaceous materials. It also means that though Umbriel is the third largest moon of Uranus, it is only the fourth largest in terms of mass. Furthermore, its dark appearance is believed to be the result of the interactions of surface water ice with energetic particles from Uranus’ magnetosphere.

These energetic particles would cause methane deposits (trapped in the ice as clathrate hydrate) to decompose and other organic molecules to darken, leaving behind a dark, carbon-rich residue. The satellite’s dark color is also due to its very low bond albedo – which is basically the amount of electromagnetic radiation (i.e. light) that gets reflected back from the surface.

So far, spectrographic analyses have only confirmed the existence of water and carbon dioxide. So the existence of organic particles or methane deposits in the ice remains theoretical. However, their presence would explain the prevalence of CO² and why it is concentrated mainly on the trailing hemisphere.

Umbriel’s orbital period – i.e. the time it takes the moon to orbit Uranus – is approximately 4.1 days, which is coincident with its rotational period. This means that the moon is a synchronous and tidally-locked satellite, with one face always pointing towards Uranus. The satellite is at an average distance of 266,000 kilometers from its planet, which makes it the third farthest from Uranus, behind Miranda and Ariel.

Voyager 2:

So far, the only close-up images of Umbriel have been provided by the Voyager 2 probe, which photographed the moon during its flyby of Uranus in January of 1986. During this flyby, the closest distance between Voyager 2 and Umbriel was 325,000 km (202,000 mi).

The images cover about 40% of the surface, but only 20% was photographed with the quality required for geological mapping. At the time of the flyby, the southern hemisphere of Umbriel was pointed towards the Sun – so the northern, darkened hemisphere could not be studied. At present, no future missions are planned to study the moon in greater detail.

US Geological Survey map of Umbriel. Credit: ISGS — *US Geological Survey map of Umbriel, showing its cratered surface and polygons. Credit: ISGS*

Interesting Facts:

The surface of Umbriel has far more and larger craters than do Ariel and Titania, ranging in diameter from a few kilometers to several hundred. The largest known crater on the surface is Wokolo, which is 210 km in diameter. Wunda, a crater with a diameter of about 131 kilometers, is the most noticeable surface feature, due to the ring of bright material on its floor (which scientists think are from the impact).

Other craters include Fin, Peri, and Zlyden which, like all of Umbriel’s surface features, are named after dark sprites from different cultures’ mythology. The only satellite of Uranus to have more craters is Oberon, and the planet is believed to be geologically stable.

It is further believes that surface has probably been stable since the Late Heavy Bombardment. The only signs of ancient internal activity are canyons and dark polygons – dark patches with complex shapes measuring from tens to hundreds of kilometers across. The polygons were identified from precise photometry of Voyager 2′s images and are distributed more or less uniformly on the surface of Umbriel, trending northeast – southwest.

Because Uranus orbits the Sun almost on its side, it is subject to an extreme seasonal cycle. Both northern and southern poles spend 42 years in complete darkness, and another 42 years in continuous sunlight, with the Sun rising close to the zenith over one of the poles at each solstice.

The southern hemisphere of Umbriel displays heavy cratering in this Voyager 2 image, taken Jan. 24, 1986, from a distance of 557,000 kilometers (346,000 miles). Credit: NASA/JPL — *The southern hemisphere of Umbriel displays heavy cratering in this Voyager 2 image, taken Jan. 24, 1986. The large impact crater of Wunda is visible at the top. Credit: NASA/JPL*

Because they are in the planet’s equatorial plane, Uranus’ satellites also experience these changes. This means that Umbriel’s north and south poles spend 42 years in light and then 42 years in darkness before repeating the cycle. In fact, the Voyager 2 flyby coincided with the southern hemisphere’s 1986 summer solstice, when nearly the entire northern hemisphere was in darkness.

Interesting little moon isn’t it? Even though no missions are currently planned to observe it in the coming years, one can only hope that future satellites happen to sneak a peek at it on their way to some other destination in the outer Solar System.

Universe Today has many interesting articles on the moons of Uranus, like how many moons does Uranus have?

You should also check out NASA’s page on Umbriel and Uranus’ moon Umbriel at Nine Planets.

Astronomy Cast has an episode on Uranus that you should check out.

Sources:

June 4, 2015February 27, 2017 by Fraser Cain

How Do Galaxies Die?

Everything eventually dies, even galaxies. So how does that happen? Time to come to grips with our galactic mortality. Not as puny flesh beings, or as a speck of rock, or even the relatively unassuming ball of plasma we orbit.

Today we’re going to ponder the lifespan of the galaxy we inhabit, the Milky Way. If we look at a galaxy as a collection of stars, some are like our Sun, and others aren’t.

The Sun consumes fuel, converting hydrogen into helium through fusion. It’s been around for 5 billion years, and will probably last for another 5 before it bloats up as a red giant, sheds its outer layers and compresses down into a white dwarf, cooling down until it’s the background temperature of the Universe.

So if a galaxy like the Milky Way is just a collection of stars, isn’t that it? Doesn’t a galaxy die when its last star dies?

But you already know a galaxy is more than just stars. There’s also vast clouds of gas and dust. Some of it is primordial hydrogen left from the formation of the Universe 13.8 billion years ago.

All stars in the Milky Way formed from this primordial hydrogen. It and other similar sized galaxies produce 7 bouncing baby stars every year. Sadly, ours has used up 90% of its hydrogen, and star formation will slow down until it both figuratively, and literally, runs out of gas.

The Milky Way will die after it’s used all its star-forming gas, when all of the stars we have, and all those stars yet to be born have died. Stars like our Sun can only last for 10 billion years or so, but the smallest, coolest red dwarfs can last for a few trillion years.

The Andromeda Galaxy will collide with the Milky Way in the future. Credit: Adam Evans — The Andromeda Galaxy. Credit: Adam Evans

That should be the end, all the gas burned up and every star burned out. And that’s how it would be if our Milky Way existed all alone in the cosmos.

Fortunately, we’re surrounded by dozens of dwarf galaxies, which get merged into our Milky Way. Each merger brings in a fresh crop of stars and more hydrogen to stoke the furnaces of star formation.

There are bigger galaxies out there too. Andromeda is bearing down on the Milky Way right now, and will collide with us in the next few billion years.

When that happens, the two will merge. Then there’ll be a whole new era of star formation as the unspent gas in both galaxies mix together and are used up.

Eventually, all galaxies gravitationally bound to each other in this vicinity will merge together into a giant elliptical galaxy.

We see examples of these fossil galaxies when we look out into the Universe. Here’s M49, a supermassive elliptical galaxy. Who knows how many grand spiral galaxies stoked the fires of that gigantic cosmic engine?

Eta Carinae shines brightly in X-rays in this image from the Chandra X-Ray Observatory.

Elliptical galaxies are dead galaxies walking. They’ve used up all their reserves of star forming gas, and all that’s left are the longer lasting stars. Eventually, over vast lengths of time, those stars will wink out one after the other, until the whole thing is the background temperature of the Universe.

As long as galaxies have gas for star formation, they’ll keep thriving. Once it’s gonzo, or a dramatic merger uses all the gas in one big party, they’re on their way out.

What could we do to prolong the life of our galaxy? Let’s hear some wild speculation in the comments below.