Guillaume Le Gentil facts for kids

Guillaume Joseph Hyacinthe Jean-Baptiste Le Gentil de la Galaisière (born September 12, 1725 – died October 22, 1792) was a French astronomer. He discovered several nebulae, which are giant clouds of gas and dust in space. He also became a member of the Royal Academy of Sciences. Le Gentil is most famous for his difficult and unsuccessful attempts to observe the transit of Venus from India in 1761 and 1769.

Early Life and Discoveries

Guillaume Le Gentil was born in Coutances, France. He first planned to join the church. However, he soon decided to study astronomy instead.

He made important discoveries in space. He found several objects that are now called Messier objects. These include M32, M36, and M38. He also found a cloudy area in the M8. Le Gentil was also the first to list a dark nebula. This dark cloud is sometimes known as Le Gentil 3. It is located in the constellation Cygnus.

Le Gentil's drawing of the Orion Nebula.

The Great Venus Transit Expeditions

Le Gentil was part of a big international science project. Scientists wanted to measure the exact distance to the Sun. To do this, they needed to watch the transit of Venus. A transit happens when a planet passes directly between a star and another planet. In this case, Venus passed in front of the Sun.

The idea for this project came from Edmond Halley. But it needed very careful measurements. These measurements had to be taken from many different places on Earth. So, over a hundred observers were sent around the world. Their goal was to watch the transit of Venus in 1761.

First Attempt: 1761 Transit

Le Gentil was part of the French team. He left Paris in March 1760. His destination was Pondicherry, a French area in India. He reached Isle de France (now Mauritius) in July.

However, the Seven Years' War had started. This war was between France and Britain. The war made it hard for him to travel further east. He finally found a ship heading to India's Coromandel Coast. He sailed in March 1761. He hoped to observe the transit from Pondicherry. The transit was on June 6, just a few months away. He was told they would arrive in time.

But the ship was blown off course by bad winds. It spent five weeks at sea. When it finally got near Pondicherry, the captain learned something bad. The British had taken over the city. So, the ship had to go back to Isle de France.

On June 6, the sky was clear. But Le Gentil was still on the ship at sea. He could not make proper observations because the ship was moving too much. He had traveled so far from Paris. So, he decided to stay and wait for the next transit of Venus. These transits happen in pairs, eight years apart. But each pair is separated by a very long time, either 105 or 121 years.

Second Attempt: 1769 Transit

After the first failed attempt, Le Gentil spent some time mapping the eastern coast of Madagascar. He then decided to try again for the 1769 transit. He planned to watch it from Manila in the Philippines.

But when he arrived, the Spanish authorities there were not friendly. So, he went back to Pondicherry. France had gotten Pondicherry back in 1763 after a peace treaty. He arrived there in March 1768. He built a small observatory to view the transit.

The day of the event was June 4, 1769. Sadly, the sky became completely cloudy. Le Gentil saw nothing at all. After all his efforts, he missed both transits.

Return Home and Later Life

Le Gentil's trip home was also full of problems. First, he got sick with dysentery. Then, his ship was caught in a storm. He was dropped off at Île Bourbon (Réunion). He had to wait there until a Spanish ship could take him home.

He finally arrived back in Paris in October 1771. He had been away for eleven years. He found out that he had been declared legally dead! He had been replaced in the Royal Academy of Sciences. His family had also taken his belongings.

Because of shipwrecks and wartime attacks, none of the letters he sent had reached his family or the Academy. It took a long legal fight and help from the king. Eventually, he got his place back in the Academy. He also remarried.

While in India, Le Gentil studied local astronomy. He wrote notes about it. He reported that a Tamil astronomer had predicted a lunar eclipse in 1765. The prediction was only off by 41 seconds. This was more accurate than some European charts at the time.

Guillaume Le Gentil died in Paris in 1792.

Tributes

Many things have been named in Le Gentil's honor:

• In 1866, Boulevard Legentil-de-la-Galaisière was named after him. This is one of the main streets in his hometown of Coutances.
• The Le Gentil crater on the Moon was named for him in 1935.
• In 2004, asteroid 12718 Le Gentil was named after him.