Known natural objects which can appear between the Earth and the Sun are the Moon (solar eclipse

Solar eclipse

As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially blocks the Sun as viewed from a location on Earth. This can happen only during a new moon, when the Sun and the Moon are in conjunction as seen from Earth. At least...

), Mercury (transit of Mercury

Transit of Mercury

A transit of Mercury across the Sun takes place when the planet Mercury comes between the Sun and the Earth, and Mercury is seen as a small black dot moving across the face of the Sun....

), Venus (transit of Venus

Transit of Venus

A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and Earth, becoming visible against the solar disk. During a transit, Venus can be seen from Earth as a small black disk moving across the face of the Sun...

), and some asteroids and comets. Transits of asteroids and comets can normally only be observed by very large telescopes. For example, all attempts to watch the transit of Comet Halley in front of the Sun in 1910 failed as result of its small diameter. All such transits can be calculated very well.

Nevertheless, there are different reports of solar transits of unknown objects, most of them from the 19th century. At that time, they were often attributed to an intramercurial planet, dubbed Vulcan

Vulcan (hypothetical planet)

Vulcan was a small planet proposed to exist in an orbit between Mercury and the Sun. In an attempt to explain peculiarities of Mercury's orbit, in the 19th-century French mathematician Urbain Jean Joseph Le Verrier hypothesized that they were the result of another planet, which he named Vulcan...

, but the existence of such a planet has since been ruled out, and these observations remain unexplained. Some may have been caused by dirt or other flaws in telescopes.

No known natural object, other than a few tiny asteroids, ever passes between the Earth and the Moon. As such an approach disturbs the orbit of such an asteroid in a manner that is sensitive to the exact separation and relative velocity, prediction of their future position can be a challenge.

Unexplained solar transits (incomplete)

Date	Event
	De Rostan in Basle and Croste in Sole observed the transit of an unknown object in front of the sun

} || Hoffmann saw a large round spot crossing the sun in north-south direction
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| || Prediger Fritsch saw in Quedlinburg a tiny spot crossing the sun in 6 hours.
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| || Prediger Fritsch saw in Quedlinburg a tiny spot crossing the sun in nortwestern-direction and accelerated thereby.
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| 1802 October 10 || Prediger Fritsch saw again an unknown object crossing the sun.
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| 1819 June 26 || Franz Gruithuisen observed two objects crossing the sun
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| 1822 October 23 || Sunspot observer J. W. Pastorff observed the transit of 2 objects
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| 1828 May 26 || Transit of unknown object in front of the sun observed telescopically
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| 1839 October 2 || Cupper saw transit of unidentified object in front of the sun.
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| 1845 May 11–13 || Erman saw the transit of several objects in front of the sun
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| 1847 || Benjamin Scott and his 5 year old son observed a solar transit of an unknown object similar in size to Venus.
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| 1849 March 12 || Sidebotham saw transit of tiny spot on the sun.
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| 1859 March 26 || Lescarbault saw transit of unknown body in front of the sun. Liais in Brasília did not see such thing. (Popular Science, Volume 13, pages 732-735, 1878)
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| 1862 March 20 || Lummis, ingenieur of Manchester, saw transit of unknown object in front of the sun.
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| 1865 March 8 || M. Coumbary observed in Constantinopele a 48 minutes long lasting transit of an unknown object.
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| 1867 October 17/18 || Lieutenant Herschel saw from noon October 17, 1867 until 6 am on October 18, 1869 multiple objects passing the sun
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| 1871 August 29 || Etienne Trouvelot saw a great number of obviously opaque objects crossing the disc of the sun
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| 1875 December – 1876 January 22 || Observation of multiple transits of unknown objects at Rio de Janeiro Observatory
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| 1880 November 30 || Solar astronomer Annibale Riccò

Annibale Ricco

Annibale Riccò was an Italian astronomer.He was born in Milan, Italy. In 1868 he was awarded a bachelors degree from the Università di Modena, then an engineering degree from the Politecnico di Milano...

 at Palermo Observatory saw a great number of objects crossing the sun
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| 1883 August 12 || Bonilla

José Bonilla Observation

On August 12, 1883, the astronomer José Bonilla reported that he saw more than 300 dark, unidentified objects crossing before the sun while observing sunspot activity at Zacatecas Observatory in Mexico. He was able to take several photographs, exposing wet plates at 1/100 second...

, director of Zacatecas Observatory, saw at least 283 objects crossing the sun. He took several photographs of them, which still exist and are claimed to be the oldest UFO photographs
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| 1888 November 30 || Annibale Riccò of Palermo Observatory saw several spindle-like objects crossing the sun (date uncertain)
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| 1989 May || Akira Oshiguru in Yokohama photographed several objects in front of the sun, which changed quickly their position
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Unexplained lunar transits (incomplete)

Date	Event
1874 April 24	Professor Schaffarik of Prague Observatory observed the transit of an unidentified object in front of the moon. He described it in its own words as a "flying machine"
1896 July 31	William R. Brooks William Robert Brooks William Robert Brooks was a British-born American astronomer, mainly noted as being one of the most prolific discoverers of new comets of all time, second only to Jean-Louis Pons... , director of Smith Observatory Smith Observatory for Smith Observatory at Geneva, New York, see Smith Observatory and Dr. William R. Brooks HouseSmith Observatory is an observatory at Beloit College in Beloit, Wisconsin. Completed in 1882, the observatory was a memorial to John F. Smith, and served the campus from 1882 until the 1950s. In 1967 it... , reported a dark circular disk-shaped object passing the moon in four seconds. Frank M. Chapman of the American Museum of Natural History American Museum of Natural History The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...  suggested that this may have been a bird.
1912 January 27–28	Frank B. Harris saw an object in front of the moon, which threw a shadow on the lunar surface. He described it as an "intensely black body about 250 miles long and fifty wide, allowing 2,000 miles from tip of cusp to cusp". He suggested it may have been the result of a volcanic eruption.
1947 May 3	An amateur astronomer in Boulder, Colorado observed a transit of an unknown object.
1950 May 6	Self-claimed alien contactee George Adamski George Adamski George Adamski was a Polish-born American citizen who became widely known in ufology circles, and to some degree in popular culture, after he claimed to have photographed ships from other planets, met with friendly Nordic alien "Space Brothers", and to have taken flights with them... saw and photographed the transit of a cigar-shaped object.
1954 December	Mr. Chloris Hamel of La Florida, Venezuela, observed several opaque objects crossing the moon.
1955 June 3	Eugene Metcalf of Paris, Illinois, reported, in a letter to Jessup, the observation of transits of objects in front of the moon which threw shadows on the lunar surface.
1965 December 1	Mutual transit of disk-like objects in front of the moon observed by Adhara Observatory in San Miguel, Argentina.

External links

• UFO Thinktank at Apex Research