Tempel 1 (official designation: 9P/Tempel) is a periodic Jupiter-family comet discovered by Wilhelm Tempel in 1867. It completes an orbit of the Sun every 5.5 years. Tempel 1 was the target of the Deep Impact space mission, which photographed a deliberate high-speed impact upon the comet in 2005. It was re-visited by the Stardust spacecraft on February 14, 2011 and came back to perihelion in August 2016.
Composite of images of nucleus obtained by the Deep Impact impactor
|Discovered by||Wilhelm Tempel|
|Discovery date||April 3, 1867|
|Orbital characteristics A|
|Epoch||July 31, 2016|
|Perihelion||1.542 AU |
|Semi-major axis||3.145 AU|
|Orbital period||5.58 years (2,038 days)|
|Earth MOID||0.52 AU (78 million km)|
|Dimensions||7.6 km × 4.9 km (4.7 mi × 3.0 mi)  |
|Rotation period||40.7 hours |
|Last perihelion||August 2, 2016 |
|Next perihelion||March 4, 2022|
Halley's in history
The first known observation of Halley's took place in 239 B.C., according to the European Space Agency. Chinese astronomers recorded its passage in the Shih Chi and Wen Hsien Thung Khao chronicles. Another study (based on models of Halley's orbit) pushes that first observation back to 466 B.C., which would have made it visible by the Ancient Greeks.
When Halley's returned in 164 B.C. and 87 B.C., it probably was noted in Babylonian records now housed at the British Museum in London. "These texts have important bearing on the orbital motion of the comet in the ancient past," noted a Nature research paper about the tablets.
Another appearance of the comet in 1301 possibly inspired Italian painter Giotto's rendering of the Star of Bethlehem in "The Adoration of the Magi," according to the Britannica encyclopedia.Halley's most famous appearance occurred shortly before the 1066 invasion of England by William the Conqueror. It is said that William believed the comet heralded his success. In any case, the comet was put on the Bayeux Tapestry &mdash which chronicles the invasion &mdash in William's honor.
Astronomers in these times, however, saw each appearance of Halley's Comet as an isolated event. Comets were often foreseen as a sign of great disaster or change.
Even when Shakespeare wrote his play "Julius Caesar" around 1600, just 105 years before Edmond Halley calculated that the comet returns over and over again, one famous phrase spoke of comets as heralds: "When beggars die there are no comets seen The heavens themselves blaze forth the death of princes."
This Month in Physics History
Maria Mitchell, the first female professional astronomer in the United States, became instantly famous in October 1847, when she was the first to discover and chart the orbit of a new comet, which became known as "Miss Mitchell's Comet."
Maria Mitchell was born in 1818 in a large Quaker family on Nantucket. Her father was a schoolteacher, and later worked for a bank. The Mitchells encouraged education for all their children, even girls, which was unusual at the time.
Astronomy was Mr. Mitchell's favorite subject. The family owned a small telescope, and all the children assisted their father with his observations. Maria, a quiet child, worked hard at her studies, especially astronomy, and enjoyed helping her father. She also enjoyed reading, as there were always many books in the house.
As a young woman, Mitchell worked briefly as a schoolteacher, then as a librarian at the Nantucket Atheneum, while still continuing her astronomical observations. Her father encouraged her, and through him, Mitchell was fortunate to be able to meet some of the country's most prominent scientists, though generally as a young woman she was shy and avoided company.
At the time, some comets had been found, but the discovery of a new one was still considered a significant achievement. King Frederick VI of Denmark had offered a prize for the discovery of each new comet.
Every chance she got, even if the family had company, if the night was clear, Mitchell would go to the roof of the house to “sweep the heavens,” using the family's 2-inch reflecting telescope.
On the evening of October 1, 1847, Mitchell slipped out of a party and went to the roof to begin her observations. She noticed a small blurry streak, invisible to the naked eye, but clear in the telescope, and she guessed at once that it might be a comet. Excited, she ran to tell her father. He wanted to announce the discovery right away, but she was more cautious. She recorded the object's position, and continued to observe it to be sure it was a comet. On October 3, Mitchell's father sent off a letter to Cambridge announcing the discovery.
It turned out others had seen the comet at about the same time. Father de Vico at Rome observed the same comet on October 3, and several other people observed the same object shortly after that. However, Mitchell's priority was recognized, and she received the medal from the King of Denmark.
This brought Mitchell immediate international fame, and further honors. In 1848, she was the first woman elected to membership in the American Academy of Arts and Sciences. She was also a fellow of the American Association for the Advancement of Science.
Mitchell was often bemused by all the attention she received as a scientist. She wrote in her diary after one scientific meeting, “It is really amusing to find one's self lionized in a city where one has visited quietly for years to see the doors of fashionable mansions open wide to receive you, which never opened before. One does enjoy acting the part of greatness for a while! I was tired after three days of it, and glad to take the cars and run away.”
Mitchell made many other astronomical observations during her career, including observations of sunspots, comets, nebulae, stars, solar eclipses, and the moons of Saturn and Jupiter.
She always appreciated the night sky not just for the science but for its beauty, and she recorded this thought in her journal: “Feb. 12, 1855. I swept around for comets about an hour, and then I amused myself with noticing the varieties of color. I wonder that I have so long been insensible to this charm in the skies, the tints of the different stars are so delicate in their variety. What a pity that some of our manufacturers shouldn't be able to steal the secret of dyestuffs from the stars.”
In 1865 Mitchell became a faculty member at Vassar College, making her the first female astronomy professor in the United States. She was also appointed director of Vassar College Observatory.
With her students, Mitchell emphasized the importance of observation, and was known for asking them, “did you learn that from a book or did you observe it yourself?” Exemplifying this philosophy, she went to great lengths to observe things herself. In 1878, she and several students traveled two thousand miles to Colorado to witness a total solar eclipse.
In addition to her scientific work, Mitchell was also active in opposing slavery and in advocating for women's rights. She believed that women's minds were too often wasted when they were forced to spend their time sewing rather than pursuing intellectual activities.
Maria Mitchell died on June 28, 1889. Although she is relatively unknown today, perhaps because her scientific accomplishments may not seem as impressive to us as they did to her contemporaries, she was well-known and respected in her day. As the first American woman astronomer and an advocate for women, she paved the way for others. The Maria Mitchell Observatory on Nantucket is named after her, as is the Mitchell crater on the moon.
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Citizen Scientist Spots Never-Before-Seen Comet – The 4,000th Comet Discovery Using Solar and Heliospheric Observatory
The 4,000th comet discovered by ESA (European Space Agency) and NASA’s SOHO observatory is seen here in an image from the spacecraft alongside SOHO’s 3,999th comet discovery. The two comets are relatively close at approximately 1 million miles apart, suggesting that they could have been connected together as recently as a few years ago. Credit: ESA/NASA/SOHO/Karl Battams
On June 15, 2020, a citizen scientist spotted a never-before-seen comet in data from the Solar and Heliospheric Observatory, or SOHO — the 4,000 th comet discovery in the spacecraft’s 25-year history.
The comet is nicknamed SOHO-4000, pending its official designation from the Minor Planet Center. Like most other SOHO-discovered comets, SOHO-4000 is part of the Kreutz family of sungrazers. The Kreutz family of comets all follow the same general trajectory, one that carries them skimming through the outer atmosphere of the Sun. SOHO-4000 is on the small side, with a diameter in the range of 15-30 feet, and it was extremely faint and close to the Sun when discovered — meaning SOHO is the only observatory that has spotted the comet, as it’s impossible to see from Earth with or without a telescope.
ESA and NASA’s SOHO has discovered 4,000 comets in nearly 25 years. Karl Battams, who leads the mission’s comet-finding program, talks about four of his favorite comets first spotted by the Sun-watching observatory. Credit: NASA’s Goddard Space Flight Center
“I feel very fortunate to have found SOHO’s 4,000 th comet. Although I knew that SOHO was nearing its 4,000 th comet discovery, I did not initially think that this sungrazer would be it,” said Trygve Prestgard, who first spotted the comet in SOHO’s data. “It was only after discussing with other SOHO comet hunters, and counting through the most recent sungrazer discoveries, that the idea sunk in. I am honored to be part of such an amazing collaborative effort.”
SOHO is a joint mission of the European Space Agency (ESA) and NASA. Launched in 1995, SOHO studies the Sun from its interior to its outer atmosphere, with an uninterrupted view from its vantage point between the Sun and Earth, about a million miles from our planet. But over the past two and half decades, SOHO has also become the greatest comet finder in human history.
ESA and NASA’s SOHO observatory saw the 3,999th and 4,000th comets discovered by the spacecraft as they sped toward the Sun, seen close to the Sun by one of the spacecraft’s coronagraph instruments. Credit: ESA/NASA/SOHO/Karl Battams
SOHO’s comet-hunting prowess comes from a combination of its long lifespan, its sensitive instruments focused on the solar corona, and the tireless work of citizen scientists who scour SOHO’s data for previously-undiscovered comets, which are clumps of frozen gases, rock and dust that orbit the Sun.
“Not only has SOHO rewritten the history books in terms of solar physics, but, unexpectedly, it’s rewritten the books in terms of comets as well,” said Karl Battams, a space scientist at the U.S. Naval Research Lab in Washington, D.C., who works on SOHO and manages its comet-finding program.
The vast majority of comets found in SOHO’s data are from its coronagraph instrument, called LASCO, short for Large Angle and Spectrometric Coronagraph. Like other coronagraphs, LASCO uses a solid object — in this case, a metal disk — to block out the Sun’s bright face, allowing its cameras to focus on the relatively faint outer atmosphere, the corona. The corona is critical to understanding how the Sun’s changes propagate out into the solar system, making LASCO a key part of SOHO’s scientific quest to understand the Sun and its influence.
But focusing on this faint region also means LASCO can do something other telescopes can’t — it can see comets flying extremely close to the Sun, called sungrazers, which are otherwise blotted out by the Sun’s intense light and impossible to see. This is why nearly all of SOHO’s 4,000 comet discoveries have come from LASCO’s data.
Like most who have discovered comets in SOHO’s data, Prestgard is a citizen scientist, searching for comets in his free time with the Sungrazer Project. The Sungrazer Project is a NASA-funded citizen science project, managed by Battams, which grew out of comet discoveries by citizen scientists early into SOHO’s mission.
“I have been actively involved in the Sungrazer Project for about eight years. My work with sungrazers is what solidified my long-term interest in planetary science,” said Prestgard, who recently completed a master’s degree in geophysics from Université Grenoble Alpes in France. “I enjoy the feeling of discovering something previously unknown, whether this is a nice “real time” comet or a “long-gone” overlooked one in the archives.”
In total, Prestgard has discovered around 120 previously-unknown comets using data from SOHO and NASA’s STEREO mission.
This 4,000 th comet discovery came earlier than scientists initially expected — a byproduct of SOHO’s teamwork with the Parker Solar Probe mission. In coordination with Parker Solar Probe’s fifth flyby of the Sun, the SOHO team ran a special observation campaign in early June, increasing the frequency with which the LASCO instrument takes images of the Sun’s corona, as well as doubling the exposure time for each image. These changes in LASCO’s imaging were designed to help the instrument pick up faint structures that would later pass over Parker Solar Probe.
“Since Parker Solar Probe was crossing the plane of the sky as seen from Earth, the structures that we see from SOHO’s coronagraphs will be in the path of Parker Solar Probe,” said Angelos Vourlidas, an astrophysicist at the Johns Hopkins University Applied Physics Lab, in Laurel, Maryland, who works on the Parker Solar Probe and SOHO missions. “It’s the optimal configuration to do this type of imaging.”
These more-sensitive images also revealed a number of comets that, based on their brightness, would have been too faint to see in SOHO’s regular, shorter-exposure images. SOHO typically sees an uptick in comet discoveries each June, because Earth’s position in space places SOHO at a good angle to see sunlight reflecting off of comets following the Kreutz path, a family of comets that accounts for about 85% of the comets discovered by SOHO. But this June saw 17 comets discovered in the first nine days of the month, around double the normal rate of discoveries.
“Our exposure time is twice as long, so we’re gathering way more light, and seeing comets that are otherwise too faint for us to see — it’s just like any long-exposure photography,” said Battams. “It’s possible that if we doubled exposure time again, we’d see even more comets.”
Next visit is a long way off
Hale-Bopp represented an exciting time for astronomy. Scientists scrambled to examine the comet as much as possible during its brief cruise by Earth.The comet's last appearance in Earth's sky had been about 4,200 years before, and it won't return to the inner solar system for thousands of years.
Astronomers at the European Southern Observatory (ESO) released new images of the comet in 2001, four years after Hale-Bopp was closest to Earth. By that time, the comet had soared 1.2 billion miles (2 billion km) away from Earth, about halfway between the orbits of Saturn and Uranus.
"The large 'dirty snowball' nucleus of ice and dust (probably about 50 km (31 miles) diameter) continues to be active, despite the very low temperature where it is now. This is quite unusual for a comet," ESO stated, based on observations from the La Silla Telescope in Chile.
Studying comets is particularly challenging because of how difficult it is to predict a comet's brightness. Between 2014 and 2016, Europe's Rosetta spacecraft orbited Comet 67P/Churyumov&ndashGerasimenko to study what happens when a comet begins its closest approach to the sun. Rosetta's studies will help scientists better make predictions about how bright comets will be.
While amateurs still discover comets from time to time, the most prolific observers tend to be automated spacecraft. For example, the Solar and Heliospheric Observatory (SOHO) satellite is designed to study solar activity, and therefore, is perfectly positioned to capture sun-grazing comets. SOHO has captured images of more than 3,000 comets since launching into space in 1995.
Great January Comet of 1910
The first people to see this comet &mdash then already at first magnitude &mdash were workmen at the Transvaal Premier Diamond Mine in South Africa on Jan. 13, 1910. Two days later, three men at a railway station in nearby Kopjes casually watched the object for 20 minutes before sunrise, assuming that it was Halley's Comet.
Later that morning, the editor of the local Johannesburg newspaper telephoned the Transvaal Observatory for a comment. The observatory's director, Robert Innes, must have initially thought this sighting was a mistake, since Halley's Comet was not in that part of the sky and nowhere near as conspicuous. Innes looked for the comet the following morning, but clouds thwarted his view. However, on the morning of Jan. 17, he and an assistant saw the comet, shining sedately on the horizon just above where the sun was about to rise. Later, at midday, Innes viewed it as a snowy-white object, brighter than Venus, several degrees from the sun. He sent out a telegram alerting the world to expect "Drake's Comet" &mdash for so "Great Comet" sounded to the telegraph operator.
It was visible during the daytime for a couple more days, then moved northward and away from the sun, becoming a stupendous object in the evening sky for the rest of January in the Northern Hemisphere. Ironically, many people in 1910 who thought they had seen Halley's Comet instead likely saw the Great January Comet that appeared about three months before Halley. [Photos of Halley's Comet Through History]
NASA’s Stardust spacecraft flies by Comet Wild 2 on 2 January, gathering comet dust and taking close-up pictures
The highest number yet on the Torino Scale (see above) is reported in December 2004 – it is 4. The asteroid is now called Apophis and improved orbital calculations have reduced the threat level 1
NASA’s Deep Impact spacecraft becomes first object deliberately sent into collision with a comet, called Tempel 1, on 4 July
A method is proposed to move an asteroid from a collision course without touching it, using gravity alone
In antiquity, comets inspired both awe and alarm, "hairy stars" resembling fiery swords that appeared unpredictably in the sky. Often, comets seemed to be omens of doom &mdash the most ancient known mythology, the Babylonian "Epic of Gilgamesh," described fire, brimstone, and flood with the arrival of a comet, and the Roman emperor Nero saved himself from the "curse of the comet" by having all possible successors to his throne executed. This fear was not just limited to the distant past &mdash in 1910, people in Chicago sealed their windows to protect themselves from what they thought was the comet's poisonous tail.
For centuries, scientists thought comets traveled in the Earth's atmosphere, but in 1577, observations made by Danish astronomer Tycho Brahe revealed they actually traveled far beyond the moon. Isaac Newton later discovered that comets move in elliptical, oval-shaped orbits around the sun, and correctly predicted that they could return again and again.
Chinese astronomers kept extensive records on comets for centuries, including observations of Halley's Comet going back to at least 240 B.C., historic annals that have proven valuable resources for later astronomers.
A number of recent missions have ventured to comets. NASA's Deep Impact collided an impactor into Comet Tempel 1 in 2005 and recorded the dramatic explosion that revealed the interior composition and structure of the nucleus. In 2009, NASA announced samples the Stardust mission returned from Comet Wild 2 revealed a building block of life.
In 2014, the European Space Agency's Rosetta spacecraft entered orbit around Comet 67P/Churyumov-Gerasimenko. The Philae lander touched down on Nov 12, 2014. Among the Rosetta mission's many discoveries was the first detection of organic molecules on the surface of a comet a strange song from Comet 67P/Churyumov-Gerasimenko the possibilities that the comet's odd shape may be due to it spinning apart, or resulting from two comets fusing together and the fact that comets may possess hard, crispy outsides and cold but soft insides, just like fried ice cream. On Sept. 30, 2016, Rosetta intentionally crash-landed on the comet, ending its mission.
Comets have inspired dread, fear, and awe in many different cultures and societies around the world and throughout time. They have been branded with such titles as “the Harbinger of Doom” and “the Menace of the Universe.” They have been regarded both as omens of disaster and messengers of the gods.
A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and large enough to cause significant regional damage in the event of impact. Most of these objects are potentially hazardous asteroids (PHAs), and a few are comets.