Question: What was the first planet identified in our solar system?

Timeline of discovery of Solar System planets and their moons




Solar System
Objects

by orbit
by size
by discovery date
models

Lists
Gravitationally-rounded
(equilibrium) objects
Possible dwarf planets
Moons (natural satellites)
Planetary-mass moons
Minor planets

Comets
Asteroids

Planets
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
 Solar Systemportal
 Starportalvt

The timeline of discovery of Solar System planets and their natural satellites charts the progress of the discovery of new bodies over history. Each object is listed in chronological order of its discovery (multiple dates occur when the moments of imaging, observation, and publication differ), identified through its various designations (including temporary and permanent schemes), and the discoverer(s) listed.
Historically the naming of moons did not always match the times of their discovery. Traditionally, the discoverer enjoys the privilege of naming the new object; however, some neglected to do so (E. E. Barnard stated he would "defer any suggestions as to a name" [for Amalthea] "until a later paper"[1] but never got around to picking one from the numerous suggestions he received) or actively declined (S. B. Nicholson stated "Many have asked what the new satellites" [Lysithea and Carme] "are to be named. They will be known only by the numbers X and XI, written in Roman numerals, and usually prefixed by the letter J to identify them with Jupiter."[2]). The issue arose nearly as soon as planetary satellites were discovered: Galileo referred to the four main satellites of Jupiter using numbers while the names suggested by his rival Simon Marius gradually gained universal acceptance. The International Astronomical Union (IAU) eventually started officially approving names in the late 1970s.

Key
In the following tables, planetary satellites are indicated in bold type (e.g. Moon) while planets and not planets, which directly circle the Sun, are in italic type (e.g. Earth). The Sun itself is indicated in roman type. The tables are sorted by publication/announcement date. Dates are annotated with the following symbols:
i: for date of first imaging (photography, etc.);
o: for date of first human visual observation, either through telescope or on photographic plate;
p: for date of announcement or publication.
In a few cases, the date is uncertain and is then marked "(?)".
* Note: Moons marked by an asterisk (*) had complicated discoveries. Some took years to be confirmed, and in several cases were actually lost and rediscovered. Others were found in Voyager photographs years after they were taken.
Color legend
The planets and their natural satellites are marked in the following colors:





Planets
Mercury
Venus
Earth and satellite
Mars and satellites
Jupiter and satellites
Saturn and satellites
Uranus and satellites
Neptune and satellites

Dwarf planets
Ceres
Pluto and satellites
Haumea and satellites
Makemake and satellite
Eris and satellite

Designations
Other designations are synonyms or periphrases sometimes encountered for the object.
Permanent designations (of planetary satellites) are explained here.
Temporary designations are explained here.
Prehistory


17th century

18th century

19th century

20th century
1901–1950

1951–2000

21st century
2000s

2010s

See also
Timeline of Solar System astronomy
Timeline of Solar System exploration
Solar System






James L. Hilton,