when the 9 planets around the sun are discovered?

Answer 1

You are after a bit, so the link is here
http://www.johnstonsarchive.net/astro/wrjs103sp.html

there is also this
Planets

Most of the planets (including the Earth's moon) have been known to mankind since ancient times. The planets beyond Saturn were discovered in more recent times.
Uranus (1781)

The discovery of Uranus was unexpected. William Herschel in England thought he was looking at a strange comet in 1781. Through his telescope, the best in the world at that time, the object was seen to have a sharply defined disk and no tail. Subsequent positional measurements showed the orbit to be far away and virtually circular; and thus, a planet. The size of the known planetary solar system had instantly doubled.
Neptune (1846)

The discovery of Neptune is regarded as a triumph of celestial mechanics. Neptune's existence was inferred from its effect upon the orbit of Uranus. Using that effect, its position was predicted by Urbain Jean Joseph Le Verrier in France and by John Couch Adams in England. As a result of Le Verrier's prediction, Neptune was quickly found by Johann Galle of the Berlin Observatory in 1846.
Pluto (1930)

In contrast to the discoveries of Uranus and of Neptune, the discovery of Pluto was the result of a dedicated, diligent photographic search. In 1930, Clyde Tombaugh of the Lowell Observatory, detected the slight motion of the tiny planet among the greatly brighter background stars.

The stories of the planetary discoveries are described in "Planets Beyond" by Mark Littmann (1988, Wiley and Sons) and in "Planet Quest" by Ken Croswell (1997, Harcourt Brace & Company). The story of Neptune is preserved in the file of letters that were exchanged among the numerous participants. Synopses of these letters are available from a web-site by Nicholas Kollerstrom of University College London.

Answer 2

Mercury, Venus, Mars, Jupiter and Saturn can be seen without a telescope and have been known for thousands of years. In 1514 Copernicus developed a theory that the Earth is really one of the planets and not the center of the universe. His ideas were not accepted until many years later, but now we accept them and know that Earth is a planet too. Uranus was discovered in March 13, 1781 by William Herschel while he was systematically searching the sky with his telescope. Neptune was discovered Sept 23, 1846 based on calculations of unexplained perturbations of the orbit of Uranus. Pluto was discovered in 1930 after an exhaustive search for a 9th planet based on calculations similar to those used to discover Uranus, but those calculations were wrong and Pluto was actually discovered by accident.

Answer 3

There are only 8 planets. Pluto is not a planet anymore.

Answer 4

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