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243 Ida is an asteroid in the Koronis family of the main belt. It was discovered on 29 September 1884 by Johann Palisa and named after a nymph from Greek mythology. Later telescopic observations categorized Ida as an S-type asteroid, the most numerous type in the inner asteroid belt. On 28 August 1993, Ida was visited by the spacecraft Galileo, bound for Jupiter. It was the second asteroid to be visited by a spacecraft and the first found to possess a satellite. Like all main-belt asteroids, Ida's orbit lies between the planets Mars and Jupiter. Its orbital period is 4.84 years, and its rotation period is 4.63 hours. Ida has an average diameter of 31.4 km (19.5 mi). It is irregularly shaped and elongated, and apparently composed of two large objects connected together in a shape reminiscent of a croissant. Its surface is one of the most heavily cratered in the Solar System, featuring a wide variety of crater sizes and ages. Ida's moon, Dactyl, was discovered by mission member Ann Harch in images returned from Galileo. It was named after creatures which inhabited Mount Ida in Greek mythology. Data returned from the flyby pointed to S-type asteroids as the source for the ordinary chondrite meteorites, the most common type found on the Earth's surface. (more...)

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July 29: Ólavsøka in the Faroe Islands; National Anthem Day in Romania

• 1014 – Byzantine-Bulgarian Wars: Forces of the Byzantine Empire defeated troops of the Bulgarian Empire at the Battle of Kleidion in the Belasica Mountains near present-day Klyuch, Bulgaria.
• 1858 – Japan reluctantly signed the Treaty of Amity and Commerce, an Unequal Treaty giving the United States various commercial and diplomatic privileges.
• 1947 – ENIAC (pictured), the world's first general-purpose electronic digital computer, was turned on in its new home at the Ballistic Research Laboratory at Aberdeen Proving Grounds, remaining in continuous operation until October 2, 1955.
• 1958 – U.S. President Dwight D. Eisenhower signed the National Aeronautics and Space Act into law, establishing a new federal non-military space agency known as NASA.
• 1981 – A worldwide television audience of over 700 million people watched Charles, Prince of Wales, marry Diana Spencer at St Paul's Cathedral in London.

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