The Universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. While the spatial size of the entire Universe is unknown, it is possible to measure the size of the observable universe, which is currently estimated to be 93 billion light years in diameter. In various multiverse hypotheses, a universe is one of many causally disconnected constituent parts of a larger multiverse, which itself comprises all of space and time and its contents. The earliest cosmological models of the Universe were developed by ancient Greek and Indian philosophers and were geocentric, placing Earth at the center. Over the centuries, more precise astronomical observations led Nicolaus Copernicus to develop the heliocentric model with the Sun at the center of the Solar System. In developing the law of universal gravitation, Isaac Newton built upon Copernicus' work as well as Johannes Kepler's laws of planetary motion and observations by Tyche Brahe. Further observational improvements led to the realization that the Sun is one of hundreds of billions of stars in the Milky Way, which is one of at least hundreds of billions of galaxies in the Universe. Many of the stars in our galaxy have planets. At the largest scale, galaxies are distributed uniformly and the same in all directions, meaning that the Universe has neither an edge nor a center. At smaller scales, galaxies are distributed in clusters and superclusters which form immense filaments and voids in space, creating a vast foam-like structure. The Big Bang theory is the prevailing cosmological description of the development of the Universe. Under this theory, space and time emerged together 13.799±0.021 billion years ago and the energy and matter initially present have become less dense as the Universe expanded. DO LIKE COMMENT AND FOLLOW

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2. The Universe is all of space and time and their
contents, including planets, stars, galaxies, and all
other forms of matter and energy. While the spatial
size of the entire Universe is unknown, it is possible
to measure the size of the observable universe,
which is currently estimated to be 93 billion light
years in diameter. In various multiverse
hypotheses, a universe is one of
many causally disconnected constituent parts of a
larger multiverse, which itself comprises all of space
and time and its contents. The earliest cosmological
models of the Universe were developed by ancient

3. Greek and Indian philosophers and were geocentric,
placing Earth at the center. Over the centuries, more
precise astronomical observations led Nicolaus
Copernicus to develop the heliocentric model with
the Sun at the center of the Solar System. In
developing the law of universal gravitation, Isaac
Newton built upon Copernicus' work as well
as Johannes Kepler's laws of planetary motion and
observations by Tyche Brahe. Further observational
improvements led to the realization that the Sun is
one of hundreds of billions of stars in the Milky Way,
which is one of at least hundreds of billions of
galaxies in the Universe. Many of the stars in our
galaxy have planets. At the largest scale, galaxies
are distributed uniformly and the same in all
directions, meaning that the Universe has neither an
edge nor a center. At smaller scales, galaxies are
distributed in clusters and superclusters which form
immense filaments and voids in space, creating a
vast foam-like structure. The Big Bang theory is the
prevailing cosmological description of the
development of the Universe. Under this theory,
space and time emerged
together 13.799±0.021 billion years ago and the
energy and matter initially present have become
less dense as the Universe expanded.

4. Space is the boundless three-dimensional extent
in which objects and events have relative position
and direction. Physical space is often conceived in
three linear dimensions, although
modern physicists usually consider it, with time, to
be part of a boundless four-
dimensional continuum known as space time. The
concept of space is considered to be of fundamental
importance to an understanding of the
physical universe However, disagreement continues
between philosophers over whether it is itself an
entity, a relationship between entities, or part of
a conceptual framework. Debates concerning the

5. nature, essence and the mode of existence of space
date back to antiquity; namely, to treatises like
the Timeous of Plato, or Socrates in his reflections
on what the Greeks called kora (i.e. "space"), or in
the Physics of Aristotle (Book IV, Delta) in the
definition of tops (i.e. place), or in the later
"geometrical conception of place" as
"space qua extension" in the Discourse on
Place (Qawl fi al-Makan) of the 11th-century Arab
polymath Alhazen. Many of these classical
philosophical questions were discussed in
the Renaissance and then reformulated in the 17th
century, particularly during the early development
of classical mechanics. In Isaac Newton's view,
space was absolute in the sense that it existed
permanently and independently of whether there
was any matter in the space. It includes living
things, planets, stars, galaxies, dust clouds, light,
and even time. Before the birth of the Universe,
time, space and matter did not exist. The Universe
contains billions of galaxies, each containing
millions or billions of stars. The space between the
stars and galaxies is largely empty. The universe
contains eight planets that are: Mercury, Venus,
Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Under this definition, the Solar System is
considered to have eight planets.

6. A planet is an astronomical
body orbiting a star or stellar remnant that is
massive enough to be rounded by its own gravity, is
not massive enough to cause thermonuclear fusion,
and has cleared its neighboring region of planet
esimals.
The term planet is ancient, with ties to
history, astrology, science, mythology, and religion.
Five planets in the Solar System are visible to
the naked eye. These were regarded by many early
cultures as divine, or as emissaries of deities. As
scientific knowledge advanced, human perception
of the planets changed, incorporating a number of
disparate objects. In 2006, the International
Astronomical Union (IAU) officially adopted a

7. resolution defining planets within the Solar System.
This definition is controversial because it excludes
many objects of planetary mass based on where or
what they orbit. Although eight of the planetary
bodies discovered before 1950 remain "planets"
under the current definition, some celestial bodies,
such as Ceres, Pallas, Juno and Vesta (each an
object in the solar asteroid belt), and Pluto (the
first trans-Neptunian object discovered), that were
once considered planets by the scientific
community, are no longer viewed as planets under
the current definition of planet.
Mercury is the smallest and innermost planet in
the Solar System. Its orbit around the Sun takes
only 87.97 days, the shortest of all the planets in the
Solar System. It is named after the Roman
deity Mercury, the messenger of the gods.
Like Venus, Mercury orbits the Sun within Earth's
orbit as an inferior planet, and its apparent
distance from the Sun as viewed from Earth never
exceeds 28°.

8. Venus is the second planet from the Sun. It is
named after the Roman goddess of love and beauty.
As the second-brightest natural object in the night
sky after the Moon, Venus can cast shadows and,
rarely, is visible to the naked eye in broad
daylight. Venus lies within Earth's orbit, and so
never appears to venture far from the Sun, setting in
the west just after dusk and rising in the east a bit
before dawn. Venus orbits the Sun every
224.7 Earth days.
Earth is the third planet from the Sun and the
only astronomical object known to harbor life.
According to radiometric dating and other sources
of evidence, Earth formed over 4.5 billion years
ago. Earth's gravity interacts with other objects in
space, especially the Sun and the Moon, Earth's
only natural satellite. Earth orbits around the Sun in
365.26 days, a period known as an Earth year.
During this time, Earth rotates about its axis about
366.26 times.

9. Mars is the fourth planet from the Sun and the
second-smallest planet in the Solar
System after Mercury. In English, Mars carries a
name of the Roman god of war and is often referred
to as the 'Red Planet'. The latter refers to the effect
of the iron oxide prevalent on Mars' surface, which
gives it a reddis appearance distinctive among the
astronomical bodies visible to the naked eye. Mars
is a terrestrial planet with a thin atmosphere, having
surface features reminiscent both of the impact
craters of the Moon and the valleys, deserts,
and polar ice caps of Earth.
Jupiter is the fifth planet from the Sun and the largest in
the Solar System. It is a gas giant with a mass one-
thousandth that of the Sun, but two-and-a-half times that
of all the other planets in the Solar System combined.
Jupiter has been known to astronomers since
antiquity. It is named after the Roman god Jupiter. When
viewed from Earth, Jupiter can be bright enough for
its reflected light to cast shadows, and is on average the

10. third-brightest natural object in the night sky after
the Moon and Venus.
Saturn is the sixth planet from the Sun and the second-
largest in the Solar System, after Jupiter. It is a gas
giant with an average radius about nine times that
of Earth. It has only one-eighth the average density of
Earth; however, with its larger volume, Saturn is over 95
times more massive. Saturn is named after
the Roman god of wealth and agriculture;
its astronomical symbol (♄) represents the god's sickle.
Uranus (from the Latin name Uranus for the Greek
god is the seventh planet from the Sun. It has the
third-largest planetary radius and fourth-largest
planetary mass in the Solar System. Uranus is
similar in composition to Neptune, and both have
bulk chemical compositions which differ from that
of the larger gas giants Jupiter and Saturn. For this
reason, scientists often classify Uranus and
Neptune as "ice giants" to distinguish them from the
gas giants.

11. Neptune is the eighth and farthest
known planet from the Sun in the Solar System. In
the Solar System, it is the fourth-largest planet by
diameter, the third-most-massive planet, and the
densest giant planet. Neptune is 17 times the mass
of Earth, slightly more massive than its near-
twin Uranus. Neptune is denser and physically
smaller than Uranus because its greater mass
causes more gravitational compression of its
atmosphere.

12. A star is an astronomical object consisting of a
luminous spheroid of plasma held together by its
own gravity. The nearest star to Earth is the Sun. Many
other stars are visible to the naked eye from Earth during
the night, appearing as a multitude of fixed luminous
points in the sky due to their immense distance from Earth.
Historically, the most prominent stars were grouped
into constellations and asterisms, the brightest of which
gained proper names. Astronomers have assembled star
catalogues that identify the known stars and provide
standardized stellar designations. However, most of the
estimated 300 sextillion (3×1023
)[1]
stars in the observable
universe are invisible to the naked eye from Earth,
including all stars outside our galaxy, the Milky Way.