2. The Sun is the star at the center of
the Solar System. It is almost perfectly
spherical and consists of hot plasma
interwoven with magnetic fields.It has
a diameter of about1,392,684 km, about
109 times that of Earth, and its mass
accounts for about 99.86% of the total
mass of the Solar System. Chemically,
about three quarters of the Sun's mass
consists of hydrogen, while the rest is
mostly helium.The remainder (1.69%,
which nonetheless equals 5,628 times the
mass of Earth) consists of heavier
elements, including oxygen, carbon,
neon and iron, among others.
3.
4.
5. Mercury is the innermost planet in
the Solar System. It is also the smallest,
and its orbit is the most eccentric of the
eight planets. It orbits the Sun once in
about 88 Earth days, completing three
rotations about its axis for every two
orbits.The planet is named after
the Roman god Mercury, the messenger
to the gods. Mercury's surface is heavily
cratered and similar in appearance
to Earth's Moon, indicating that it has
been geologically inactive for billions of
years. Due to its near lack of an
atmosphere to retain heat, Mercury's
surface experiences the steepest
temperature gradient of all the planets,
ranging from a very cold 100 K at night to
a very hot 700 K during the day.
6.
7.
8.
9. Venus is the second planet from
the Sun, orbiting it every
224.7 Earth days.The planet is
named after the Roman goddess of
love and beauty.After the Moon, it
is the brightest natural object in the
night sky, reaching an apparent
magnitude of −4.6, bright enough
to cast shadows.BecauseVenus is
an inferior planet from Earth, it
never appears to venture far from
the Sun: its elongation reaches a
maximum of 47.8°.Venus reaches
its maximum brightness shortly
before sunrise or shortly after
sunset, for which reason it has been
referred to by ancient cultures as
the Morning Star or Evening Star.
10.
11. Earth is the third planet from the Sun, and
the densest and fifth-largest of the eight planets
in the Solar System. It is also the largest of the
Solar System's four terrestrial planets. Earth
formed approximately 4.54 billion years ago by
accretion from the solar nebula, and life
appeared on its surface within one billion
years.The planet is home to millions of species,
including humans.Earth's biosphere has
significantly altered the atmosphere and
other abiotic conditions on the planet, enabling
the proliferation of aerobic organisms as well as
the formation of the ozone layer, which together
with Earth's magnetic field blocks harmful solar
radiation, thus permitting formerly ocean-
confined life to move safely to land. Estimates on
how much longer the planet will to be able to
continue to support life range from 500
million years, to as long as 2.3 billion years.
12.
13.
14. The Moon is the only natural satellite of
the Earth, and the fifth largest satellite in
the Solar System. It is the largest natural
satellite of a planet in the Solar System
relative to the size of its primary,having
27% the diameter and 60% the density of
Earth, resulting in 1⁄81 its mass.The Moon
is the second densest satellite after Io, a
satellite of Jupiter.The Moon is thought
to have formed nearly 4.5 billion years
ago, not long after the Earth. Although
there have been several hypotheses for
its origin in the past, the current most
widely accepted explanation is that the
Moon formed from the debris left over
after a giant impact between Earth and
a Mars-sized body.The Moon is the
only celestial body other than Earth on
which humans have set foot.
15.
16. Mars is the fourth planet from the Sun and the
second smallest planet in the Solar System.
Named after the Roman god of war, it is often
described as the "Red Planet", as the iron
oxide prevalent on its surface gives it a reddish
appearance. Mars is a terrestrial planet with a
thin atmosphere, having surface features
reminiscent both of the impact craters of
the Moon and the volcanoes, valleys, deserts,
and polar ice caps of Earth.The rotational
period and seasonal cycles of Mars are likewise
similar to those of Earth, as is the tilt that
produces the seasons. Mars is the site of Olympus
Mons, the highest known mountain within the
Solar System, and ofValles Marineris, one of the
largest canyons. Mars has
two moons, Phobos and Deimos, which are small
and irregularly shaped.These may be
captured asteroids.
17.
18. Jupiter is the fifth planet from
the Sun and the largest planet in
the Solar System. It is a gas
giant with mass one-thousandth that of
the Sun but is two and a half times the
mass of all the other planets in our Solar
System combined. Jupiter is classified as
a gas giant along with Saturn , Uranus
and Neptune.Together, these four
planets are sometimes referred to as
the Jovian or outer planets.The planet
was known by astronomers of ancient
times, and was associated with the
mythology and religious beliefs of many
cultures.The Romans named the planet
after the Roman god Jupiter.When
viewed from Earth, Jupiter can reach
an apparent magnitude of −2.94, making
it on average the third-brightest object
in the night sky after the Moon
andVenus.
19.
20.
21.
22. Saturn is the sixth planet from
the Sun and the second largest
planet in the Solar System,
after Jupiter. Named after
the Roman god Saturn,
its astronomical symbol (♄)
represents the god's sickle. Saturn is
a gas giant with an average radius
about nine times that of Earth.While
only one-eighth the average density
of Earth, with its larger volume
Saturn is just over 95 times as
massive as Earth. Saturn's interior is
probably composed of a core of iron,
nickel and rock (silicon and oxygen
compounds), surrounded by a deep
layer of metallic hydrogen, an
intermediate layer of liquid
hydrogen and liquid helium and an
outer gaseous layer.
23.
24.
25. Uranus is the seventh planet from the Sun.
It has the third-largest planetary radius
and fourth-largest planetary mass in
the Solar System. It is named after the
ancient Greek deity of the sky Uranus,
the father of Cronus (Saturn) and
grandfather of Zeus (Jupiter).Though it is
visible to the naked eye like the
five classical planets, it was never
recognized as a planet by ancient
observers because of its dimness and
slow orbit. SirWilliam
Herschel announced its discovery on
March 13, 1781, expanding the known
boundaries of the Solar System for the
first time in modern history. Uranus was
also the first planet discovered with
a telescope. Uranus is similar in
composition to Neptune, and both are of
different chemical composition than the
larger gas giants, Jupiter and Saturn.
26.
27.
28.
29. Neptune is the eighth and
farthest planet from the Sun in the Solar
System. It is the fourth-largest planet by
diameter and the third-largest by mass.
Neptune is 17 times the mass
of Earth and is somewhat more massive
than its near-twin Uranus, which is 15
times the mass of Earth but not as
dense. On average, Neptune orbits the
Sun at a distance of 30.1 AU,
approximately 30 times the Earth–Sun
distance.With a mass of
1.0243×1026 kg, Neptune is an
intermediate body between Earth and
the larger gas giants: its mass is
seventeen times that of the Earth but
just 1/19th that of Jupiter.The
planet's surface gravity is only surpassed
by Jupiter. Neptune's equatorial radius
of 24764 km is nearly four times that of
the Earth. Neptune and Uranus are
often considered a sub-class of gas giant
termed "ice giants“.
30.
31. Pluto, formal designation 134340 Pluto, is
the second-most-massive known dwarf
planet in the Solar System (after Eris) and
the tenth-most-massive body observed
directly orbiting the Sun. Originally
classified as the ninth planet from the Sun,
Pluto was recategorized as a dwarf planet
and plutoid owing to the discovery that it
is only one of several large bodies within
the Kuiper belt. Like other members of the
Kuiper belt, Pluto is composed primarily of
rock and ice and is relatively small,
approximately one-sixth the mass of
the Earth's Moon and one-third its volume.
It has an eccentric and highly inclined orbit
that takes it from 30 to 49 AU (4.4–7.4
billion km) from the Sun.This causes Pluto
to periodically come closer to the Sun than
Neptune. As of 2011, it is 32.1 AU from the
Sun.
32.
33.
34. Eris, formal designation 136199 Eris,
is the most massive known dwarf
planet in the Solar System and the
ninth most massive body known to
orbit the Sun directly. It is estimated
to be 2326 (±12) km in diameter, and
27% more massive than Pluto, or
about 0.27% of the Earth's mass.Eris
was discovered in January 2005 by
a Palomar Observatory-based team
led by Mike Brown, and its identity
was verified later that year. It is
a trans-Neptunian object (TNO) and
a member of a high-eccentricity
population known as the scattered
disc. It has one known moon,
Dysnomia.As of 2011, its distance
from the Sun is 96.6AU, roughly
three times that of Pluto.With the
exception of some comets, Eris and
Dysnomia are currently the most
distant known natural objects in the
Solar System.
35. Ceres, formally 1 Ceres, is the
only dwarf planet in the inner Solar
System, and the largest asteroid. It is
a rock–ice body 950 km (590 mi) in
diameter, and though the smallest
identified dwarf planet, it constitutes
a third of the mass of the asteroid
belt. Discovered on 1 January 1801
by Giuseppe Piazzi, it was the first
asteroid to be identified, though it
was classified as a planet at the
time. It is named after Ceres,
the Roman goddess of growing
plants, the harvest, and motherly
love.The Cererian surface is probably
a mixture of water ice and
various hydrated minerals such
as carbonates and clays. It appears to
be differentiated into
a rocky core and icy mantle, and may
harbour an ocean of liquid water
under its surface.
36. Kuiper belt, is a region of the Solar
System beyond the planets,
extending from the orbit of Neptune
(at 30 AU) to approximately 50AU
from the Sun. It is similar to
the asteroid belt, although it is far
larger—20 times as wide and 20 to
200 times as massive. Like the
asteroid belt, it consists mainly
of small bodies, or remnants from
the Solar System's formation.While
most asteroids are composed
primarily of rock and metal, Kuiper
belt objects are composed largely of
frozen volatiles (termed "ices"), such
as methane, ammonia and water.
The classical belt is home to at least
three dwarf planets: Pluto, Haumea,
and Makemake.
37. Asteroids are a class of small Solar
System bodies in orbit around the Sun.
They have also been called planetoids,
especially the larger ones.These terms
have historically been applied to any
astronomical object orbiting the Sun that
did not show the disk of a planet and was
not observed to have the characteristics
of an active comet, but as small objects
in the outer Solar System were
discovered, their volatile-based surfaces
were found to more closely resemble
comets, and so were often distinguished
from traditional asteroids.Thus the
term asteroid has come increasingly to
refer specifically to the small bodies of
the inner Solar System out to the orbit
of Jupiter, which are usually rocky or
metallic.
38.
39. A comet is an icy small Solar
System body (SSSB) that, when
close enough to the Sun, displays
a visible coma (a thin, fuzzy,
temporary atmosphere) and
sometimes also a tail.
These phenomena are both due
to the effects of solar
radiation and the solar wind upon
the nucleus of the comet. Comet
nuclei range from a few hundred
meters to tens of kilometers
across and are composed of loose
collections of ice, dust, and small
rocky particles. Comets have
been observed since ancient
times and have traditionally been
considered bad omens.
40.
41. A star is a massive, luminous sphere
of plasma held together by gravity.The
nearest star to Earth is the Sun, which is
the source of most of the energy on the
planet. Other stars are visible from Earth
during the night when they are not
obscured by atmospheric phenomena,
appearing as a multitude of fixed
luminous points because of their
immense distance. Historically, the most
prominent stars on the celestial
sphere were grouped together into
constellations and asterisms, and the
brightest stars gained proper names.
Extensive catalogues of stars have been
assembled by astronomers, which
provide standardized star designations.
42.
43.
44. A galaxy is a massive, gravitationally bound system consisting
of stars, stellar remnants, an interstellar medium of gas and dust,
and an important but poorly understood component called dark
matter.The word galaxy is derived from the Greek galaxias, literally
"milky", a reference to the Milky Way. Examples of galaxies range
from dwarfs with as few as ten million (107) stars to giants with a
hundred trillion (1014) stars, each orbiting their galaxy's own center
of mass.
Galaxies contain varying amounts of star systems, star clusters and
types of interstellar clouds. In between these objects is a
sparse interstellar medium of gas, dust, and cosmic rays. Dark
matter appears to account for around 90% of the mass of most
galaxies. Observational data suggests that super massive black
holes may exist at the center of many, if not all, galaxies.They are
thought to be the primary driver of active galactic nuclei found at
the core of some galaxies.The Milky Way galaxy appears to harbor
at least one such object.
45.
46. A black hole is a region of space
time where gravity prevents
anything, including light, from
escaping.The theory of general
relativity predicts that a sufficiently
compact mass will deform space
time to form a black hole.Around a
black hole there is a mathematically
defined surface called an event
horizon that marks the point of no
return. It is called "black" because it
absorbs all the light that hits the
horizon, reflecting nothing, just like a
perfect black body in
thermodynamics.Quantum
mechanics predicts that black holes
emit radiation like a black body with
a finite temperature.This
temperature is inversely proportional
to the mass of the black hole,
making it difficult to observe this
radiation for black holes of stellar
mass or greater.
47. A meteorite is a natural object
originating in outer space that
survives impact with the Earth's
surface. A meteorite's size can range
from small to extremely large. Most
meteorites derive from small
astronomical objects called
meteoroids, but they are also
sometimes produced by impacts
of asteroids.When a meteoroid
enters the atmosphere, frictional,
pressure, and chemical interactions
with the atmospheric gasses cause
the body to heat up and emit light,
thus forming a fireball, also known as
a meteor or shooting/falling star.
The term bolide refers to either an
extraterrestrial body that collides
with the Earth, or to an exceptionally
bright, fireball-like meteor
regardless of whether it ultimately
impacts the surface.
48. The MilkyWay is the galaxy that
contains the Earth.This name
derives from its appearance as a dim
"milky" glowing band arching across
the night sky, in which the naked eye
cannot distinguish individual stars.
The term "MilkyWay" is a translation
of the Classical Latin via lactea, from
the HellenisticGreek γαλαξίας
κύκλος (pr. galaxías kýklos, "milky
circle").The MilkyWay appears like a
band because it is a disk-shaped
structure being viewed from inside.
The fact that this faint band of light
is made up of stars was proven in
1610 when GalileoGalilei used his
telescope to resolve it into individual
stars. In the 1920s, observations by
astronomer Edwin Hubble showed
that the MilkyWay is just one of
many galaxies.
49. In the context of spaceflight, a satellite is
an object which has been placed
into orbit by human endeavour. Such
objects are sometimes called artificial
satellites to distinguish them from natural
satellites such as the Moon.The world's
first artificial satellite, the Sputnik 1, was
launched by the Soviet Union in 1957.
Since then, thousands of satellites have
been launched into orbit around
the Earth. Some satellites, notably space
stations, have been launched in parts and
assembled in orbit. Artificial satellites
originate from more than 50 countries and
have used the satellite launching
capabilities of ten nations.A few hundred
satellites are currently operational,
whereas thousands of unused satellites
and satellite fragments orbit the Earth
as space debris. A few space probes have
been placed into orbit around other
bodies and become artificial satellites to
the Moon, Mercury,
Venus, Mars, Jupiter, Saturn, and the Sun.
50.
51. As seen from the Earth, a solar
eclipse occurs when the Moon
passes between the Sun and Earth,
and the Moon fully or partially blocks
the Sun.This can happen only at new
moon, when the Sun and the Moon
are in conjunction as seen from
Earth. In a total eclipse, the disk of
the Sun is fully obscured by the
Moon. In partial and annular
eclipses only part of the Sun is
obscured.
52. A lunar eclipse occurs when the Moon
passes directly behind the Earth into
its umbra.This can occur only when the
Sun, Earth, and Moon are aligned
exactly, or very closely so, with the Earth
in the middle. Hence, a lunar eclipse can
only occur the night of a full moon.The
type and length of an eclipse depend
upon the Moon's location relative to
its orbital nodes. Unlike a solar eclipse,
which can only be viewed from a certain
relatively small area of the world, a lunar
eclipse may be viewed from anywhere
on the night side of the Earth. A lunar
eclipse lasts for a few hours, whereas a
total solar eclipse lasts for only a few
minutes at any given place, due to the
smaller size of the moon's shadow.Also
unlike solar eclipses, lunar eclipses are
safe to view without any eye protection
or special precautions, as they are no
brighter than the full moon itself.
53. In modern astronomy, a
constellation is an internationally
defined area of the celestial
sphere.These areas are grouped
around asterisms (which
themselves are generally referred
to in non-technical language as
"constellations"), which are
patterns formed by prominent
stars within apparent proximity
to one another on Earth's night
sky.There are also numerous
historical constellations not
recognized by the IAU, or
constellations recognized in
regional traditions of astronomy
or astrology, such asChinese,
Hindu andAustralian Aboriginal.
54. The universe is commonly defined as
the totality of existence, including
planets, stars, galaxies, the contents
of intergalactic space, and all
matter and energy. Definitions and
usage vary and similar terms include
the cosmos, the world and nature.
Scientific observation of earlier
stages in the development of the
universe, which can be seen at great
distances, suggests that the universe
has been governed by the same
physical laws and constants
throughout most of its extent and
history.
55. The Big Bang theory is the prevailing cosmological model that describes
the early development of the Universe. According to the Big Bang theory,
the Universe was once in an extremely hot and dense state which
expanded rapidly.This rapid expansion caused the Universe to cool and
resulted in its present continuously expanding state. According to the
most recent measurements and observations, the Big Bang occurred
approximately 13.75 billion years ago, which is thus considered the age of
the Universe.After its initial expansion from a singularity, the Universe
cooled sufficiently to allow energy to be converted into various
subatomic particles, including protons, neutrons, and electrons.While
protons and neutrons combined to form the first atomic nuclei only a few
minutes after the Big Bang, it would take thousands of years for
electrons to combine with them and create electrically neutral atoms.
The first element produced was hydrogen, along with traces of helium
and lithium. Giant clouds of these primordial elements would coalesce
through gravity to form stars and galaxies, and the heavier elements
would be synthesized either within stars or during supernovae.