1769 Transit of Venus observed from Tahiti
Encyclopedia
On June 3, 1769, British navigator, Captain James Cook
, British astronomer
Charles Green
and Swedish naturalist
Daniel Solander
observed and recorded the transit of Venus on the island of Tahiti
during Cook’s first voyage
around the world. During a transit, Venus appears as a small black disc travelling across the Sun. This unusual astronomical phenomenon takes place in a pattern that repeats itself every 243 years. It includes two transits that are eight years apart, separated by breaks of 121.5 and 105.5 years.
These men, along with a crew of scientists, were commissioned by the Royal Society of London for the primary purpose of viewing the transit of Venus. Not only would their findings help expand scientific knowledge, it would help with navigation
by accurately calculating the observer’s longitude. At this time, longitude
was difficult to determine and not always precise. A “secret” mission that followed the transit included the exploration of the South Pacific
to find the legendary Terra Australis Incognita or “unknown land of the South.”
or Mercury transits to determine astronomical unit
. In a 1716 issue of the Philosophical Transactions of the Royal Society
, Edmund Halley illustrated more fully Gregory’s theory and explained further how it could establish the distance between the Earth and the Sun. In his report, Halley suggested places that a full transit should be viewed due to a “cone of visibility.” Places he recommended for observing the phenomenon included the Hudson Bay
, Norway
and the Molucca Islands. The next transits would occur in 1761 and 1769. Halley died in 1742, almost twenty years before the transit.
The viewing of the 1761 transit involved the effort of 120 observers from nine nations. Thomas Hornsby
reported the observations as unsuccessful primarily due to poor weather conditions. He alerted the Royal Society in 1766 that preparations needed to begin for the 1769 transit. Hornsby’s publication in the Philosophical Transactions of the Royal Society in 1766 focused attention on the “cone of visibility” indicating, like Halley, some of the better places to observe the transit. The Royal Society boasted that the British “were inferior to no nation on earth, ancient or modern” and were eager to make another attempt.
When choosing a location for viewing the transit, The Royal Society basically chose the locations Halley suggested in his 1716 article. The committee recommended that the transit be observed from three points: the North Cape
at the Arctic tip of Norway, Fort Churchill
at Hudson Bay Canada and a suitable island in the South Pacific. They stated that two competent observers were to be sent to each location. King George III approved of the project and arranged for the Navy to provide ships. He allocated 4000 pounds for the society to help with the expenses.
, discovered Tahiti
. Wallis returned from his voyage in time to help the Royal Society decide that it would be an ideal location to observe the Transit of Venus. A big advantage was that Tahiti was one of the few islands in the South Pacific that they knew the longitude
and latitude
of. The Admiralty
was not really interested particularly where in the South Pacific that the Venus transit took place. They were more interested in the “secret” mission that would be revealed after the Venus transit observation: the search for the alleged southern continent.
HMS Bark Endeavour
was chosen to take the astronomers and other scientists to Tahiti. James Cook was commissioned as Lieutenant and appointed to command the vessel. Cook was the obvious choice as he was an outstanding seaman with navigational qualifications, a capable astronomer and had previously observed a transit in Canada for the Royal Society.
on shore. He required a completely stable platform which the ship could not provide and plenty of space to work with. The location of the observatory would be known as “Fort Venus.” A sandy spit on the northeast end of Matavai Bay was chosen for the site.
They began building Fort Venus two days after they arrived. They marked a perimeter and construction began. It had earthworks on three of its sides adjacent to deep channels. Wood was gathered to construct palisades that topped the earthworks. Casks from the ship were filled with wet sand and used for stability. The east side of the fort faced the river. Mounted guns were brought in from the ship. A gateway was assembled and within this fortification, fifty-four tents were pitched which housed the crew, scientists, and officers as well as the observatory, blacksmith equipment and a kitchen.
Cook sent a party led by Zachary Hickes
to a point on the east coast of the island for additional observations. John Gore led another group of thirty-eight more on a neighboring island of Eimeo (Moorea
). Both parties were briefed and supplied with the needed equipment.
On the day of the transit, the sky was clear. Independent observations were made by James Cook, Green and Solander with their own telescopes. Because of the rarity of the event, it was important to take accurate records. The next transit would not occur until 1874.
In his journal, Cook wrote:
“This day prov’d as favourable to our purpose as we could wish, not a Clowd was to be seen the whole day and the Air was perfectly clear, so that we had every advantage we could desire in Observing the whole of the passage of the Planet Venus over the Suns disk: we very distinctly saw an Atmosphere or dusky shade round the body of the Planet which very much disturbed the times of the Contacts particularly the two internal ones. Dr. Solander observed as well as Mr. Green and my self, and we differ’d from one another in observeing the times of the Contacts much more than could be expected. Mr Greens Telescope and mine were of the same Magnifying power but that of Dr was greater than ours.”
Recording the exact moment of the phases proved to be impossible due to a phenomenon called the “Black drop effect
.” Originally, it was believed that the effect came from the thick atmosphere on Venus, but the haziness was too extensive for this to be the reason. Recent studies now reveal that it is actually turbulence in the Earth’s atmosphere that leads to the smearing image of Venus.
For what they believed to be a failure in the observation, The Royal Society decided to blame Green who died on the voyage back to England. Cook’s rebuke was so sharp that it was taken from the official proceedings of the Society. Green was not given the opportunity to personally present his own data nor could he defend himself.
was astounding. There were at least 120 observers at sixty-two individual posts for the 1761 transit. Observations took place not only in Europe
, but also included Calcutta, Tobolsk
, Siberia
, the Cape of Good Hope
, and St. John’s
in Newfoundland. The 1769 viewing also proved to also be a vast international endeavor. Even though the Seven Years' War
was going on between Great Britain and France, the British Admiralty granted safe passage for French astronomer, Alexandre Guy Pingré
on his way to view the 1761 transit. During Cook’s journey to Tahiti, the French government instructed all its men-of-war to not to harm the Endeavour, since it was ‘out on enterprises that were service for all mankind’. With the Venus Transits, astronomers of the eighteenth century illustrated unity in the scientific community.
-based value used today for the astronomical unit is 92,955,000 miles. This is only a difference of eight-tenths of one percent. Considering what these astronomers had to work with, their results were “absolutely remarkable”.
James Cook
Captain James Cook, FRS, RN was a British explorer, navigator and cartographer who ultimately rose to the rank of captain in the Royal Navy...
, British astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
Charles Green
Charles Green (astronomer)
Charles Green was a British astronomer, noted for his assignment by the Royal Society in 1768 to the expedition sent to the Pacific Ocean in order to observe the transit of Venus and the transit of Mercury, aboard James Cook's Endeavour.A farmer's son, he became assistant to the Astronomer Royal...
and Swedish naturalist
Naturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
Daniel Solander
Daniel Solander
Daniel Carlsson Solander or Daniel Charles Solander was a Swedish naturalist and an apostle of Carl Linnaeus. Solander was the first university educated scientist to set foot on Australian soil.-Biography:...
observed and recorded the transit of Venus on the island of Tahiti
Tahiti
Tahiti is the largest island in the Windward group of French Polynesia, located in the archipelago of the Society Islands in the southern Pacific Ocean. It is the economic, cultural and political centre of French Polynesia. The island was formed from volcanic activity and is high and mountainous...
during Cook’s first voyage
First voyage of James Cook
The first voyage of James Cook was a combined Royal Navy and Royal Society expedition to the south Pacific ocean aboard HMS Endeavour, from 1768 to 1771...
around the world. During a transit, Venus appears as a small black disc travelling across the Sun. This unusual astronomical phenomenon takes place in a pattern that repeats itself every 243 years. It includes two transits that are eight years apart, separated by breaks of 121.5 and 105.5 years.
These men, along with a crew of scientists, were commissioned by the Royal Society of London for the primary purpose of viewing the transit of Venus. Not only would their findings help expand scientific knowledge, it would help with navigation
Navigation
Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...
by accurately calculating the observer’s longitude. At this time, longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....
was difficult to determine and not always precise. A “secret” mission that followed the transit included the exploration of the South Pacific
South Pacific Area
The South Pacific Area was a multinational U.S.-led military command active during World War II. It was a part of the U.S. Pacific Ocean Areas under Admiral Chester Nimitz.Instructions to the senior U.S...
to find the legendary Terra Australis Incognita or “unknown land of the South.”
Background
In 1663, Scottish mathematician James Gregory came up with the idea of solar parallax by using VenusVenus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
or Mercury transits to determine astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
. In a 1716 issue of the Philosophical Transactions of the Royal Society
Philosophical Transactions of the Royal Society
The Philosophical Transactions of the Royal Society is a scientific journal published by the Royal Society of London. It was established in 1665, making it the first journal in the world exclusively devoted to science, and it has remained in continuous publication ever since, making it the world's...
, Edmund Halley illustrated more fully Gregory’s theory and explained further how it could establish the distance between the Earth and the Sun. In his report, Halley suggested places that a full transit should be viewed due to a “cone of visibility.” Places he recommended for observing the phenomenon included the Hudson Bay
Hudson Bay
Hudson Bay , sometimes called Hudson's Bay, is a large body of saltwater in northeastern Canada. It drains a very large area, about , that includes parts of Ontario, Quebec, Saskatchewan, Alberta, most of Manitoba, southeastern Nunavut, as well as parts of North Dakota, South Dakota, Minnesota,...
, Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
and the Molucca Islands. The next transits would occur in 1761 and 1769. Halley died in 1742, almost twenty years before the transit.
The viewing of the 1761 transit involved the effort of 120 observers from nine nations. Thomas Hornsby
Thomas Hornsby
Thomas Hornsby FRS was a British astronomer and mathematician.Hornsby became a Fellow of Corpus Christi College, Oxford in 1760....
reported the observations as unsuccessful primarily due to poor weather conditions. He alerted the Royal Society in 1766 that preparations needed to begin for the 1769 transit. Hornsby’s publication in the Philosophical Transactions of the Royal Society in 1766 focused attention on the “cone of visibility” indicating, like Halley, some of the better places to observe the transit. The Royal Society boasted that the British “were inferior to no nation on earth, ancient or modern” and were eager to make another attempt.
When choosing a location for viewing the transit, The Royal Society basically chose the locations Halley suggested in his 1716 article. The committee recommended that the transit be observed from three points: the North Cape
North Cape, Norway
North Cape is a cape on the island of Magerøya in Northern Norway, in the municipality of Nordkapp. Its 307 m high, steep cliff is often referred to as the northernmost point of Europe, located at , 2102.3 km from the North Pole. However, the neighbouring point Knivskjellodden is actually...
at the Arctic tip of Norway, Fort Churchill
Churchill, Manitoba
Churchill is a town on the shore of Hudson Bay in Manitoba, Canada. It is most famous for the many polar bears that move toward the shore from inland in the autumn, leading to the nickname "Polar Bear Capital of the World" that has helped its growing tourism industry.-History:A variety of nomadic...
at Hudson Bay Canada and a suitable island in the South Pacific. They stated that two competent observers were to be sent to each location. King George III approved of the project and arranged for the Navy to provide ships. He allocated 4000 pounds for the society to help with the expenses.
Choosing an Island, a Ship and a Captain
In June 1767, British navigator, Samuel WallisSamuel Wallis
Samuel Wallis was a Cornish navigator who circumnavigated the world.Wallis was born near Camelford, Cornwall. In 1766 he was given the command of HMS Dolphin to circumnavigate the world, accompanied by the Swallow under the command of Philip Carteret...
, discovered Tahiti
Tahiti
Tahiti is the largest island in the Windward group of French Polynesia, located in the archipelago of the Society Islands in the southern Pacific Ocean. It is the economic, cultural and political centre of French Polynesia. The island was formed from volcanic activity and is high and mountainous...
. Wallis returned from his voyage in time to help the Royal Society decide that it would be an ideal location to observe the Transit of Venus. A big advantage was that Tahiti was one of the few islands in the South Pacific that they knew the longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....
and latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
of. The Admiralty
Admiralty
The Admiralty was formerly the authority in the Kingdom of England, and later in the United Kingdom, responsible for the command of the Royal Navy...
was not really interested particularly where in the South Pacific that the Venus transit took place. They were more interested in the “secret” mission that would be revealed after the Venus transit observation: the search for the alleged southern continent.
HMS Bark Endeavour
HMS Endeavour
HMS Endeavour may refer to one of the following ships:In the Royal Navy:, a 36-gun ship purchased in 1652 and sold in 1656, a 4-gun bomb vessel purchased in 1694 and sold in 1696, a fire ship purchased in 1694 and sold in 1696, a storeship hoy purchased in 1694 and sold in 1705, a storeship...
was chosen to take the astronomers and other scientists to Tahiti. James Cook was commissioned as Lieutenant and appointed to command the vessel. Cook was the obvious choice as he was an outstanding seaman with navigational qualifications, a capable astronomer and had previously observed a transit in Canada for the Royal Society.
Preparation for the Transit
Once the Endeavour arrived on the island, Cook decided to set up the Venus transit observatoryObservatory
An observatory is a location used for observing terrestrial or celestial events. Astronomy, climatology/meteorology, geology, oceanography and volcanology are examples of disciplines for which observatories have been constructed...
on shore. He required a completely stable platform which the ship could not provide and plenty of space to work with. The location of the observatory would be known as “Fort Venus.” A sandy spit on the northeast end of Matavai Bay was chosen for the site.
They began building Fort Venus two days after they arrived. They marked a perimeter and construction began. It had earthworks on three of its sides adjacent to deep channels. Wood was gathered to construct palisades that topped the earthworks. Casks from the ship were filled with wet sand and used for stability. The east side of the fort faced the river. Mounted guns were brought in from the ship. A gateway was assembled and within this fortification, fifty-four tents were pitched which housed the crew, scientists, and officers as well as the observatory, blacksmith equipment and a kitchen.
Cook sent a party led by Zachary Hickes
Zachary Hickes
Zachary Hickes was a Royal Navy officer, second-in-command on Lieutenant James Cook's voyage to the east coast of Australia. Hickes spelt his name with an "e", but it has often been written by others as Hicks without the "e".Hickes was 29 and held the rank of lieutenant when appointed to Cook's...
to a point on the east coast of the island for additional observations. John Gore led another group of thirty-eight more on a neighboring island of Eimeo (Moorea
Moorea
Moʻorea is a high island in French Polynesia, part of the Society Islands, 17 km northwest of Tahiti. Its position is . Moʻorea means "yellow lizard" in Tahitian...
). Both parties were briefed and supplied with the needed equipment.
The Day of the Transit
The observers were ordered to record the transit in four phases of Venus’ journey across of the sun. The first phase was when Venus began “touching” the outside rim of the sun. In the second phase, Venus was completely within the sun’s disc, but was still “touching” the outer rim. In the third phase, Venus has crossed the sun, was still completely within the disc, but was “touching” the opposite rim. Finally in the forth phase, Venus was completely off the sun, but was still “touching” its outer rim.On the day of the transit, the sky was clear. Independent observations were made by James Cook, Green and Solander with their own telescopes. Because of the rarity of the event, it was important to take accurate records. The next transit would not occur until 1874.
In his journal, Cook wrote:
“This day prov’d as favourable to our purpose as we could wish, not a Clowd was to be seen the whole day and the Air was perfectly clear, so that we had every advantage we could desire in Observing the whole of the passage of the Planet Venus over the Suns disk: we very distinctly saw an Atmosphere or dusky shade round the body of the Planet which very much disturbed the times of the Contacts particularly the two internal ones. Dr. Solander observed as well as Mr. Green and my self, and we differ’d from one another in observeing the times of the Contacts much more than could be expected. Mr Greens Telescope and mine were of the same Magnifying power but that of Dr was greater than ours.”
Recording the exact moment of the phases proved to be impossible due to a phenomenon called the “Black drop effect
Black drop effect
The black drop effect is an optical phenomenon visible during a transit of Venus and, to a lesser extent, a transit of Mercury.Just after second contact, and again just before third contact during the transit, a small black "teardrop" appears to connect Venus' disk to the limb of the Sun, making it...
.” Originally, it was believed that the effect came from the thick atmosphere on Venus, but the haziness was too extensive for this to be the reason. Recent studies now reveal that it is actually turbulence in the Earth’s atmosphere that leads to the smearing image of Venus.
Results of the 1769 Venus Transit Observations
The Royal Society was very disappointed in the results of data collected from the transit and Cook’s report. The Tahiti observers had trouble with the timing of the stages and their drawings were inconsistent. They later found out that this was also true with the observers at the other locations. Observers from all over noted a haze or “black drop” that seemed to follow Venus making it very difficult to record time entry point on the sun and the exit from the sun.For what they believed to be a failure in the observation, The Royal Society decided to blame Green who died on the voyage back to England. Cook’s rebuke was so sharp that it was taken from the official proceedings of the Society. Green was not given the opportunity to personally present his own data nor could he defend himself.
Scientific Community
Halley’s 1716 article called for observers to witness the transit at various places on the globe. The response from the scientific communityScientific community
The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...
was astounding. There were at least 120 observers at sixty-two individual posts for the 1761 transit. Observations took place not only in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, but also included Calcutta, Tobolsk
Tobolsk
Tobolsk is a town in Tyumen Oblast, Russia, located at the confluence of the Tobol and Irtysh Rivers. It is a historic capital of Siberia. Population: -History:...
, Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
, the Cape of Good Hope
Cape of Good Hope
The Cape of Good Hope is a rocky headland on the Atlantic coast of the Cape Peninsula, South Africa.There is a misconception that the Cape of Good Hope is the southern tip of Africa, because it was once believed to be the dividing point between the Atlantic and Indian Oceans. In fact, the...
, and St. John’s
St. John's, Newfoundland and Labrador
St. John's is the capital and largest city in Newfoundland and Labrador, and is the oldest English-founded city in North America. It is located on the eastern tip of the Avalon Peninsula on the island of Newfoundland. With a population of 192,326 as of July 1, 2010, the St...
in Newfoundland. The 1769 viewing also proved to also be a vast international endeavor. Even though the Seven Years' War
Seven Years' War
The Seven Years' War was a global military war between 1756 and 1763, involving most of the great powers of the time and affecting Europe, North America, Central America, the West African coast, India, and the Philippines...
was going on between Great Britain and France, the British Admiralty granted safe passage for French astronomer, Alexandre Guy Pingré
Alexandre Guy Pingré
Alexandre Guy Pingré was a French astronomer, priest, and naval geographer.He was born in Paris, France, and was educated at Senlis, where he became professor of theology in 1735. At an early age he had developed an interest in astronomy, and in 1749 he was appointed professor of astronomy at the...
on his way to view the 1761 transit. During Cook’s journey to Tahiti, the French government instructed all its men-of-war to not to harm the Endeavour, since it was ‘out on enterprises that were service for all mankind’. With the Venus Transits, astronomers of the eighteenth century illustrated unity in the scientific community.
Modern Results Compared to Results from the 1769 Venus Transit
Using the solar parallax values obtained from the 1769 transit, Hornsby wrote in Philosophical Transitions December 1771 that “the mean distance from the Earth to the Sun (is) 93,726,900 English miles.” The radarRadar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
-based value used today for the astronomical unit is 92,955,000 miles. This is only a difference of eight-tenths of one percent. Considering what these astronomers had to work with, their results were “absolutely remarkable”.