As mentioned before, there are several other candidates for the first written account which can probably be assigned to ancient Sumerian texts, but this one I find more along the lines of an unknown object in the sky. It was found on Egyptian papyrus during the reign of Thutmose III - 1504-1450 B.C.:
In the year 22, of the 3rd month of winter, sixth hour of the day...the scribes of the House of Life found it was a circle of fire that was coming in the sky.... It had no head, the breath of its mouth had a foul odor. Its body one rod long and one rod wide. It had no voice. Their hearts became confused through it; then they laid themselves on their bellies.... They went to the Pharaoh...to report it. His Majesty ordered...[an examination of] all which is written in the papyrus rolls of the House of Life. His Majesty was meditating upon what happened. Now after some days had passed, these things became more numerous in the skies than ever. They shone more in the sky than the brightness of the sun, and extended to the limits of the four supports of the heavens.... Powerful was the position of the fire circles. The army of the Pharaoh looked on with him in their midst. It was after supper. Thereupon, these fire circles ascended higher in the sky towards the south.... The Pharaoh caused incense to be brought to make peace on the hearth.... And what happened was ordered by the Pharaoh to be written in the annals of the House of Life...so that it be remembered for ever.
(Brinsley Le Poer Trench - The Flying Saucer Story, Reader's Digest - Mysteries of the Unexplained)

The First Official Investigation


The first official ufo investigation by a military can be attributed to Japan in the year 1235. On the night of September 24, General Yoritsume and his army observed some mysterious lights in the sky. The lights were seen for many hours - circling, swinging and moving in loops. The general ordered a "full-scale scientific investigation" of the lights. The report he received did nothing but explain away the phenomenon - "...the whole thing is completely natural, General. It is...only the wind making the stars sway."
(Jacques Valle - Passport to Magonia)
http://www.theastralworld.com/aliens_ufos/...-sightings.html

Many unusual celestial events were recorded in Japanese chronicles during the Middle Ages. As in Western society, such occurrences were usually considered "portents," often resulting in panics and other social disturbances. Here are some examples:

... on September 12, 1271, the famous priest Nichiren was about to be beheaded at Tatsunokuchi, Kamakura, when there appeared in the sky an object like a full moon, shiny and bright. Needless to say, the officials panicked and the execution was not carried out.

In 1361, a flying object described as being "shaped like a drum, about twenty feet in diameter" emerged from the inland sea off western Japan...

... on March 8, 1468, a dark object, which made a "sound like a wheel," flew from Mt. Kasuag toward the west at midnight. [Jacques Vallee, Passport to Magonia, pp.5-6]

The European record of possible UFO sightings continued throughout the 14th and 15th centuries:

1322 A.D. In the first hour of the night of Novr. 4... there was seen in the sky over Uxbridge, England, a pile (pillar) of fire the size of a small boat, pallid and livid in colour. It rose from the south, crossed the sky with a slow and grave motion, and went north. Out of the front of the pile, a fervent red flame burst forth with great beams of light. Its speed increased, and it flew thro' the air....

1387 A.D. In Novr. and Decr. of this year, a fire in the sky, like a burning and revolving wheel, or round barrel of flame, emitting fire from above, and others in the shape of a long fiery beam, were seen through a great deal of the winter, in the county of Leicester, Eng., and in Northamptonshire.

1461 A.D. On November 1, a fiery thing like an iron rod of good length and as large as one half of the moon was seen in the sky, over.... Arras, France for less than a quarter of an hour. This object was also described as being "shaped like a ship from which fire was seen flowing." [Jacques Vallee, UFO's in Space: Anatomy of a Phenomenon, p.9; Harold T. Wilkins, Flying Saucers on the Attack, pp.187, 188]

The Roman author Julius Obsequens, believed to have lived in the fourth century A.D., drew on Livy as well as other sources of his time to compile his book Prodigorium liber, which describes many peculiar phenomena, some of which could be interpreted as UFO sightings. Here are just a few examples:

216 B.C. Things like ships were seen in the sky over Italy... At Arpi (180 Roman miles, east of Rome, in Apulia) a round shield was seen in the sky. At Capua, the sky was all on fire, and one saw figures like ships...

99 B.C. When C. Murius and L. Valerius were consuls, in Tarquinia, there fell in different places.... a thing like a flaming torch, and it came suddenly from the sky. Towards sunset, a round object like a globe, or round or circular shield took its path in the sky, from west to east.

90 B.C. In the territory of Spoletium (65 Roman miles north of Rome, in Umbria) a globe of fire, of golden colour, fell to the earth, gyrating. It then seemed to increase in size, rose from the earth, and ascended into the sky, where it obscured the disc of the sun, with its brilliance. It revolved towards the eastern quadrant of the sky. [Harold T. Wilkins, Flying Saucers on the Attack, pp.164-69]

A later chronicler of inexplicable phenomena, one Conrad Wolffhart (a professor of grammar and dialectics who under the pen name of Lycosthenes wrote the compendium Prodigiorum ac Ostentorum Chronicon, published in 1567), mentions the following events:

393 A.D. Strange lights were seen in the sky in the days of the Emperor Theodosius. On a sudden, a bright globe appeared at midnight. It shone brilliantly near the day star (planet, Venus), about the circle of the Zodiac. This globe shone little less brilliantly than the planet, and little by little, a great number of other glowing orbs drew near the first globe. The spectacle was like a swarm of bees flying around the bee-keeper, and the light of these orbs was as if they were dashing violently against each other. Soon, they blended together into one awful flame, and bodied forth to the eye as a horrible two-edged sword. The strange globe which was first seen now appeared like the pommel to a handle, and all the little orbs, fused with the first, shone as brilliantly as the first globe. [This report is similar to modern accounts of UFO formations.] [Harold T. Wilkins, Flying Saucers on the Attack, pp.174, 177]

A rare typeset book from 1493, now preserved in a museum at Verdun, France, contains what may be the earliest pictorial representation of a UFO in Europe. Hartmann Schedel, author of the book Liber Chronicarum, describes a strange fiery sphere - seen in 1034 - soaring through the sky in a straight course from south to east and then veering toward the setting sun. The illustration accompanying the account shows a cigar-shaped form haloed by flames, sailing through a blue sky over a green, rolling countryside. (Jacques Vallee, UFO's in Space: Anatomy of a Phenomenon, p.9)

A term equivalent to our "flying saucer" was actually used by the Japanese approximately 700 years before it came into use in the West. Ancient documents describe an unusual shining object seen the night of October 27, 1180, as a flying "earthenware vessel." After a while the object, which had been heading northeast from a mountain in Kii province, changed its direction and vanished below the horizon, leaving a luminous trail. (Jacques Vallee, Passport to Magonia pp.4-5)

Here is a classical description from William of Newburgh's Chronicle of a flying saucer seen in England toward the end of the 12th century:

At Byland or Begland Abbey (the largest Cistercian abbey in England), in the North Yorkshire Riding, while the abbot and monks were in the refectorium, a flat, round, shining silvery object ["discus" is the word used in the Latin account] flew over the abbey and caused the utmost terror. [Harold T. Wilkins, Flying Saucers on the Attack, p.185]