Side view of the Milky Way Galaxy:
Top view of the Milky Way Galaxy:
The Milky Way is a barred spiral galaxy, with four main arms
spiraling outwards from a center bar structure. These arms are formed of
several components, including stars, gas, and dust.
a) Location of the
Sun
The Sun (and therefore the Earth as well) is located
approximately 8 kpc from the galactic center on what is known as the Orion Arm,
a smaller section of the galaxy located between two of the main spiral arms
(the Carina-Sagittarius Arm and the Perseus Arm, not labeled).
b) Thin disk
This is a relatively thin disk structure surrounding the
center of the galaxy that contains stars as well as gas and dust. The stars
within the thin disk make up the majority of stars within the galaxy, and are
relatively young compared to stars in the thick disk.
c) Thick disk
A much larger disk of stars surrounding the center of the
galaxy containing significantly older stars than the thin disk.
d) Bulge
This “bulge” at the center of the Milky Way is tightly packed
with stars, gas, and dust, and is roughly 3 kpc across.
e) Halo
The halo of the Milky Way contains sparsely distributed old
stars and globular clusters (see below). The halo is thought to be as wide as 40 kpc across.
f) Globular clusters
Globular clusters are dense clusters of old stars located
within the galaxy’s halo. They are much older and denser than open clusters,
which are located within the disk(s).
g) Small Magellanic
Cloud (SMC)
The Small Magellanic Cloud, or SMC, is a dwarf galaxy with a
central bar structure similar to the Milky Way, but with an irregular shape. It
is located approximately 61 kpc from the Milky Way. The SMC and LMC (see below)
are thought to possibly be orbiting the Milky Way due to the gravitational attraction.
The SMC is much smaller than the Milky
Way, with a mass of approximately 7 billion \( M_{\odot}\) (as compared to the
Milky Way’s 1012 \( M_{\odot}\)), and has a diameter of around 2.1
kpc (as compared to the Milky Way’s diameter of roughtly 30.5 kpc).
h) Large Magellanic
Cloud (LMC)
i) Sgr A*
Sagittarius A* is a small and very bright source of
radiation that is believed to be a supermassive black hole at the very center
of the Milky Way. When viewed from telescopes on Earth, it appears as part of
the Sagittarius constellation, and is surrounded by a spiral structure known as
Sagittarius A West.
j) Location of Orion
star forming region
The Orion Nebula is a region in which stars are formed by a
gravitational collapse of clouds containing clouds of gas and dust. This star
forming region is located approximately 412 pc from the Earth, and has a mass
of approximately 2000 \( M_{\odot}\).
k) Nearest known open
cluster to the Sun
Open clusters are groups of relatively young stars that
formed from the same star-forming cloud, and due to their proximity are still
loosely bound by gravity. They are generally found in the galactic disk(s), as
opposed to globular clusters, which are found in the halo. The nearest known
open cluster to the Sun is known as Hyades, at a distance of approximately 47
pc from the Sun.
l) Furthest known
open cluster to the Sun
The furthest known open cluster from the Sun is known as
Berkeley 29, at a distance of about 15 kpc away from the Sun. This is roughly
twice the distance from the Sun to the galactic center.
m) Scale length
The scale length of a galaxy is the length over which the
number density of stars drops by a factor of e, or approximately 2.7. The Milky Way Galaxy has a scale length of
3.5 kpc. The distance from the galactic center to the Sun is approximately
twice the scale length of the galaxy.
n) Scale height
The scale height of a galaxy is the perpendicular height
over which the density of stars drops by a factor of e, or approximately 2.7. The Milky Way has a scale height of
approximately 330 pc.
Beautiful!
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