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Annibale De Gasparis discovered asteroid #11 Parthenope, the second of his nine asteroid discoveries.
ref: en.wikipedia.org

Died, John Herschel, mathematician, astronomer

John Frederick William Herschel (7 March 1792 - 11 May 1871) was an English mathematician and astronomer, son of astronomer William Herschel.

John Herschel originated the use of the Julian day system in astronomy and made several important contributions to the improvement of photographic processes (Cyanotype). He coined the terms "photography", "negative", and "positive", and discovered sodium thiosulphite as a fixer of silver halides.

Julian days are important since astronomers, unlike historians, frequently need to do arithmetic with dates. Julian days simply enumerate the days and fraction which have elapsed since the start of the Julian era, defined as noon (GMT) on Monday, 1 January 4713 B.C.E. in the Julian calendar. This date is defined in terms of a cycle of years, but has the additional advantage that all known historical astronomical observations bear positive Julian day numbers, and periods can be determined and events extrapolated by simple addition and subtraction. Starting at noon, Julian dates are a bit eccentric, but astronomers who rise after the "crack of noon" and do most of their work when the Sun is down appreciate recording results in a calendar where the date doesn't change in the middle of the workday. Julian day notation is an ideal system for storing dates in computer programs, free of cultural bias and discontinuities, and can be readily transformed into other calendar systems.

While any event in recorded human history has a positive Julian day number, working with contemporary events with all those digits can be cumbersome. A Modified Julian Day (MJD) is created by subtracting 2,400,000.5 from a Julian day number, thus representing the number of days elapsed since midnight (00:00) Universal Time on 17 November 1858. Modified Julian Days are widely used to specify the epoch in tables of orbital elements of manmade artificial Earth satellites. Since no such objects existed prior to 4 October 1957, all satellite-related MJDs are positive.
ref: en.wikipedia.org

A. Borrelly discovered asteroid #233 Asterope.

L. Carnera discovered asteroid #486 Cremona.

G. H. Peters discovered asteroid #536 Merapi.

Died, Karl Schwarzschild, German physicist and astronomer, first exact solution to Einstein's field equations of general relativity (Schwarzschild radius, event horizon of a non-rotating black hole, 1915)
ref: www.physicsoftheuniverse.com

Born, Richard Feynman, physicist (quantum electrodynamics), Nobel 1965 with Tomonaga and Schwinger "for their fundamental work in quantum electrodynamics, with deep-ploughing consequences for the physics of elementary particles"
ref: www.nobelprize.org

Born, Antony Hewish, English radio astronomer, Nobel 1974 with Ryle "for their pioneering research in radio astrophysics: ..., Hewish for his decisive role in the discovery of pulsars"
ref: www.nobelprize.org

US President Truman signed a bill establishing a rocket test range at Cape Canaveral, Florida.
ref: history.nasa.gov

Jay Forrester filed a patent for core memory, the first type of random access memory used in computers. The patent was granted 28 February 1956.
ref: patents.google.com

Died, Walter S. Adams, US astronomer, director of Mount Wilson observatory 1923-1945, Bruce Medal 1928
ref: phys-astro.sonoma.edu

NASA's Lunar Orbiter 4 began photographing the Lunar surface from its orbit around the Moon.

Lunar Orbiter 4, launched 4 May 1967, was designed to take advantage of the fact the three previous Lunar Orbiters had completed the required needs for Apollo mapping and site selection. It was given a more general objective, to "perform a broad systematic photographic survey of Lunar surface features in order to increase the scientific knowledge of their nature, origin, and processes, and to serve as a basis for selecting sites for more detailed scientific study by subsequent orbital and landing missions." It was also equipped to collect selenodetic, radiation intensity, and micrometeoroid impact data. The spacecraft was placed in a cislunar trajectory and injected into an elliptical near polar high Lunar orbit on 7 May 1967 for data acquisition. The orbit was 2706 km x 6111 km with an inclination of 85.5 degrees and a period of 12 hours.

After initial photography on 11 May 1967, problems started occurring with the camera's thermal door, which was not responding well to commands to open and close. Fear that the door could become stuck in the closed position, covering the camera lenses, led to a decision to leave the door open. This required extra attitude control manuevers on each orbit to prevent light leakage into the camera which would ruin the film. On 13 May it was discovered that light leakage was damaging some of the film, and the door was tested and partially closed. Some fogging of the lens was then suspected due to condensation resulting from the lower temperatures. Changes in the spacecraft's attitude raised the temperature of the camera and generally eliminated the fogging. Continuing problems with the readout drive mechanism starting and stopping beginning on 20 May resulted in a decision to terminate the photographic portion of the mission on 26 May. Despite problems with the readout drive, the entire film was read and transmitted. The spacecraft acquired photographic data from 11 May to 26 May 1967, and readout occurred through 1 June 1967. The orbit was then lowered to gather orbital data for the upcoming Lunar Orbiter 5 mission.

A total of 419 high resolution and 127 medium resolution frames were acquired covering 99% of the Moon's near side at resolutions from 58 meters to 134 meters. Accurate data were acquired from all other experiments throughout the mission. Radiation data showed increased dosages due to solar particle events producing low energy protons. The spacecraft was used for tracking purposes until it impacted the Lunar surface due to the natural decay of the orbit on 31 October 1967, between 22 and 30 degrees W longitude.

Results of the Lunar Orbiter Program

NASA's Lunar Orbiter program consisted of 5 Lunar Orbiters which returned photographs of 99% of the surface of the Moon (both the near and far sides) with resolution down to 1 meter. Altogether the Orbiters returned 2180 high resolution and 882 medium resolution frames. The micrometeoroid experiments recorded 22 impacts showing the average micrometeoroid flux near the Moon was about two orders of magnitude greater than in interplanetary space but slightly less than the near Earth environment. The radiation experiments confirmed that the design of the Apollo hardware would protect the astronauts from average and greater-than-average short term exposure to solar particle events. The use of the Lunar Orbiters for tracking to evaluate the Manned Space Flight Network tracking stations and Apollo Orbit Determination Program was successful, with three Lunar Orbiters (2, 3, and 5) being tracked simultaneously from August to October 1967. The Lunar Orbiters were all eventually commanded to crash on the Moon before their attitude control gas ran out so they would not present navigational or communications hazards to the later Apollo flights.

See also Wikipedia, Lunar Orbiter 4
ref: nssdc.gsfc.nasa.gov

1973 00:20:00 GMT
USSR launched Cosmos 557, believed by observers to be an unmanned Soyuz-type vehicle. The USSR denied any relationship to manned programs.

Cosmos 557, launched 11 May 1973, was believed to be an unmanned Soyuz-type vehicle, although the USSR denied any relationship to a manned program. It may have been launched in an attempt to salvage part of the Salyut 2 mission, to serve as a substitute for the Salyut vehicle. It transmitted on a frequency of 922.75 mh, the same as used by Salyut spacecraft. The mission was apparently completed in 4 days; the craft subsequently reentered the Earth's atmosphere on 22 May 1973.
ref: nssdc.gsfc.nasa.gov

Comet C/1983 H1 (IRAS-Araki-Alcock) approached to within 0.0312 AUs (2.9 million miles/4.7 million km) of Earth, the closest comet approach in over 200 years.

Comet IRAS–Araki–Alcock (C/1983 H1, formerly 1983 VII) is a long-period comet that made the closest approach to Earth of any comet in 200 years, approaching to about 0.0312 AU (4,670,000 km; 2,900,000 mi) on 11 May 1983. The only recorded comets known to have come closer were Lexell's Comet (1770) and 55P/Tempel-Tuttle (1366).

As of 2019, three comets have come closer: comet P/1999 J6 (SOHO) passed about 0.01 AU (1,500,000 km; 930,000 mi) from Earth on 12 June 1999, 289P/Blanpain passed at 0.0248 AU (3,710,000 km; 2,305,000 mi) on 11 December 2003, and P/2016 BA14 (PANSTARRS) passed at 0.0237 AU (3,550,000 km; 2,200,000 mi) on 22 March 2016.

See also a photograph of C/1983 H1 taken at the time of its closest approach
See also What are the closest comet encounters with Earth?
ref: en.wikipedia.org

A transit of Earth across the Sun as seen from Mars took place; no humans were there to observe it.
ref: en.wikipedia.org

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