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The Milky Way
By:
Padurariu Cristian
Danciu Serban
Padurariu Cristian & Danciu Serban
The Milky Way galaxy
• Milky
Way
Galaxy,
commonly referred to as
just the Milky Way, or
sometimes simply as the
Galaxy, is the galaxy in
which our Solar System is
located. The Milky Way is
a barred spiral galaxy that
is part of the Local Group
of galaxies.
Padurariu Cristian & Danciu Serban
Appearance from Earth
• All the stars that the eye can distinguish in the
night sky are part of the Milky Way Galaxy, but
aside from these relatively nearby stars, the
galaxy appears as a hazy band of white light
arching around the entire celestial sphere.
Padurariu Cristian & Danciu Serban
Size
• The stellar disk of the Milky
Way Galaxy is approximately
100,000
light-years
(30
kiloparsecs, 9×1017 km) in
diameter.
It is estimated to contain at least 200 billion
stars and possibly up to 400 billion stars, the
exact figure depending on the number of very
low-mass, or dwarf stars, which are hard to
detect.
Padurariu Cristian & Danciu Serban
Age
• In 2007, a star in the
Galactic
halo
was
estimated to be about
13.2 billion years old,
nearly as old as the
Universe. As the oldest
known object in the
Milky Way at that
time, it placed a lower
limit on the age of the
Milky Way.
Padurariu Cristian & Danciu Serban
Composition and structure
• The galaxy consists of
a
bar-shaped
core
region surrounded by a
disk of gas, dust and
stars forming four
distinct arm structures
spiralling outward in a
logarithmic
spiral
shape
(see
Spiral
arms).
Padurariu Cristian & Danciu Serban
Galactic Center
• The galactic disc, which
bulges outward at the
galactic center, has a
diameter of between
70,000 and 100,000
light-years. The exact
distance from the Sun
to the galactic center is
actively debated.
Padurariu Cristian & Danciu Serban
Sun's location and neighborhood
• The Sun (and therefore the Earth and the
Solar System) may be found close to the
inner rim of the galaxy's Orion Arm, in
the Local Fluff inside the Local Bubble,
and in the Gould Belt, at a distance of
7.62±0.32 kpc (~25,000±1,000 ly) from
the Galactic Center.
Padurariu Cristian & Danciu Serban
It takes the Solar System about 225–250
million years to complete one orbit of the galaxy
(a galactic year), so it is thought to have
completed 20–25 orbits during the lifetime of the
Sun and 1/1250 of a revolution since the origin
of humans.
Padurariu Cristian & Danciu Serban
Environment
• The Milky Way and
the
Andromeda
Galaxy are a binary
system of giant
spiral
galaxies
belonging to a group
of 50 closely bound
galaxies known as
the Local Group,
itself being part of
the
Virgo
Supercluster.
Padurariu Cristian & Danciu Serban
Velocity
• In the general sense, the absolute velocity of
any object through space is not a meaningful
question according to Einstein's special
theory of relativity,
which declares that
there is no "preferred"
inertial
frame
of
reference in space with
which to compare the
object's motion.
Padurariu Cristian & Danciu Serban
Discovery
• As Aristotle (384-322 BC) informs us in
Meteorologica (DK 59 A80), the Greek
philosophers Anaxagoras (ca. 500–428 BC)
and Democritus (450–370 BC) proposed the
Milky Way might consist of distant stars.
Padurariu Cristian & Danciu Serban
Milky Way vs. Andromeda
• Our galaxy, the Milky Way, will collide
with another galaxy, called Andromeda.
• Although they are close on the scale of the
galaxies they are yet far away as
even light takes two
million years to journey
between them.
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Padurariu Cristian & Danciu Serban