In this month: April
21st April 1702
Maria Kirch discovers a previously unknown comet becoming the first woman to make such a discovery. Dubbed the "Comet of 1702", it was the 10th-closest comet approach in history, missing Earth by 6,537,000 kilometres (0.0437 AU).
However, the comet was not named after her, as was the case with most newly discovered comets, due to her gender, her husband instead taking credit for its discovery. He admitted the truth regarding the discovery in 1710 but the comet was never named after her. Maria continued to pursue important work in astronomy, publishing under her own name, and with the proper recognition.
8th April 1980
Telesto, a moon of Saturn, is discovered using ground-based observations. It orbits Saturn at a distance of approximately 295,000 kilometres, taking 45.3 hours to make one trip around the planet. With a radius of 12.4 kilometres, it appears to have a smooth, icy surface and does not show signs of intense cratering seen on many of Saturn's other moons.
The image below is of the Moon taken in 2005 by Cassini, credit: NASA/JPL/Space Science Institute.
The name 'Telesto' is from Greek mythology. Telesto was one of the 3,000 daughters of the Titans, Oceanus and Tethys, and was the personification of the divine blessing or success.
7th April 2001
The NASA Mars Odyssey spacecraft is launched from Cape Canaveral arriving at Mars on the 24th October 2001. Its main mission was to investigate the Martian environment and to provide key information on the hazards future explorers might face. Early in the mission it determined that radiation in low-Mars orbit, an essential piece of information for eventual human exploration, is twice that in low-Earth orbit.
Mars Odyssey holds the record for the longest continually active spacecraft in orbit around a planet other than Earth. It has been in orbit since the 24th October 2001.
20th April 1859
Vincenzo Cerulli. Italian astronomer.
He observed Mars and developed the theory that the Martian canals were not real but an optical illusion, a theory that was later confirmed. During his career he discovered one asteroid, 704 Interamnia, notable for its relatively large diameter of approximately 350 kilometres, which makes it the fifth largest body in the traditional asteroid belt.
The Martian crater Cerulli, and the asteroids 366 Vincentina and 31028 Cerulli are named in his honour.
14th April 1868
Annie Scott Dill Maunder. Irish-British astronomer.
She was one of the leading astronomers of her time, but because of her gender, her contribution was often underplayed. She recorded the first evidence of the movement of sunspots from the poles toward the equator over the sun's 11-year cycle. In 1915 she became the first woman elected to the Royal Astronomical Society, 20 years after being refused membership because of her gender. Her husband was Walter Maunder, after whom the Maunder Minimum (an unexplained period of reduced sunspot activity that occurred between 1645 and 1715) is named.
In 2016 the Royal Astronomical Society established the Annie Maunder medal for an outstanding contribution to outreach and public engagement in astronomy or geophysics. The photograph right of Annie Maunder with her two cameras in the roof of an observatory in Algiers is by her sister-in-law Edith Maunder.
In June 2018 the Royal Observatory Greenwich installed a new telescope, the Annie Maunder Astrographic Telescope (AMAT), as part of a revival of telescopy in London.
The crater Maunder on the Moon is jointly named for Walter and Annie Maunder,
5th April 1935
Donald Lynden-Bell. British theoretical astrophysicist. He was the first astrophysicist to determine that galaxies contain supermassive black holes at their centres, and that such black holes power quasars. He worked at the University of Cambridge for his entire career, where he was the first director of its Institute of Astronomy. He was President of the Royal Astronomical Society from 1985–1987
The Asteroid 18235 Lynden-Bell is named in his honour.