Uploaded by Margie Roselle Opay

Our Sun

Our Sun (a star) and all the planets around it are part of a galaxy known as the Milky Way Galaxy. A
galaxy is a large group of stars, gas, and dust bound together by gravity. They come in a variety of
shapes and sizes. The Milky Way is a large barred spiral galaxy. All the stars we see in the night sky are in
our own Milky Way Galaxy. Our galaxy is called the Milky Way because it appears as a milky band of light
in the sky when you see it in a really dark area.
There are billions of other galaxies in the Universe. Only three galaxies outside our own Milky Way
Galaxy can be seen without a telescope, and appear as fuzzy patches in the sky with the naked eye. The
closest galaxies that we can see without a telescope are the Large and Small Magellanic Clouds. These
satellite galaxies of the Milky Way can be seen from the southern hemisphere. Even they are about
160,000 light years from us. The Andromeda Galaxy is a larger galaxy that can be seen from the northern
hemisphere (with good eyesight and a very dark sky). It is about 2.5 million light years away from us, but
its getting closer, and researchers predict that in about 4 billion years it will collide with the Milky Way. ,
i.e., it takes light 2.5 million years to reach us from one of our "nearby" galaxies. The other galaxies are
even further away from us and can only be seen through telescopes.
The band of the Milky Way galaxy can be seen at night in areas with dark skies. Here it is seen with
several Atacama Large Millimeter/submillimeter Array >Chile
Older cool stars-blue
Hot stars- red
The milky Way is a spiral galaxy of about 200,000,000,000 billion stars
The sun is located in the orion arm
A nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, the term
was used to describe any diffuse astronomical object, including galaxies beyond the Milky Way
Do you think any of these other planets outside our solar systems could support life like we know it on
Earth? We have not found any yet. For a planet to support life like on Earth, it would need to be very
similar to Earth. It would need to be solid for humans to stand on. It would also need to be the right
distance from its sun to have the right temperatures and pressure to support water for humans to drink!
So you’ve lived here all your life — in fact, everyone has — but what do you really know about the Milky
Way galaxy? Sure, you know it’s a spiral, and it’s 100,000 light years across.
Our solar system, with planets that orbit the Sun, is just a tiny part of the Milky Way galaxy, which is just
a tiny part of the entire universe. Of course, space is a rough neighborhood.
The ancient Greeks saw this band o­f light and called it "galaxies kuklos," for "milk circle." The Romans
called it the "Milky Way."
1. It’s a barred spiral. You might know that the Milky Way is a spiral galaxy, perhaps the most beautiful
galaxy type it will be later expounded later on just bear with us.
2. There’s a supermassive black hole at its heart. At the very center of the Galaxy, right at its very core,
lies a monster: a supermassive black hole.
In Avengers: Infinity War, Thanos begins his crusade to collect all six Infinity Stones and bring balance to
the universe by erasing half of all life from existence after his people on Titan wound up extinct. Thanos
sees the universe as a chaotic place because it’s overrun with too many beings, so he looks to bring
order to it by cutting life down to a manageable size he can rule over
3) It’s a cannibal. The Milky Way is pretty, but it’s savage, too. It’s currently eating several other galaxies
4) We live in a nice neighborhood…The Milky Way is not alone in space. We’re part of a small group of
nearby galaxies called — get ready to be shocked — the Local Group. We’re the heaviest guy on the
block, and the Andromeda galaxy is maybe a bit less massive, though it’s actually spread out more. The
Triangulum galaxy is also a spiral, but not terribly big, and there are other assorted galaxies dotted here
and there in the Group
6) You can only see 0.000003% percent of it. When you got out on a dark night, you can see thousands
of stars. But the Milky Way has two hundred billion stars in it. You’re only seeing a tiny tiny fraction of
the number of stars tooling around the galaxy. So the little bubble of stars we can see around us is just a
drop in the ocean of the Milky Way.
7) 90% of it is invisible. Whatever it is, it has mass, but doesn’t glow. So we call it Dark Matter, for lack of
a better term
8) Spiral arms are an illusion. We see the arms because the light is better there, not because that’s
where all the stars are. The arms are like cosmic traffic jams, regions where the local density is
enhanced. Like a traffic jam on a highway, cars enter and leave the jam, but the jam itself stays. The
arms have stars entering and leaving, but the arms themselves persist
9) It’s seriously warped.
The Milky Way is a flat disk roughly 100,000 light years across and a few thousand light years thick
(depending on how you measure it). It has the same proportion as a stack of four DVDs, if that helps.
The Milky Way is an island of hundreds of billions of stars, gas, and dust held together by gravity to form
a gigantic disk that is surrounded by a halo of globular clusters, which are smaller spherical groups of
Have you ever left a DVD out in the Sun? It can warp as it heats up, getting twisted (old vinyl LPs used to
be very prone to this). The Milky Way has a similar warp!
10.We’re going to get to know the Andromeda galaxy a lot better. The Andromeda Galaxy and the Milky
Way are approaching each other, two cosmic steam engines chugging down the tracks at each other at
200 kilometers per second. Eventually (it takes a few billion years), the two galaxies will merge, and will
become, what, Milkomeda? Andromeway? Well, whatever, they form a giant elliptical galaxy when they
finally settle down.
An interesting fact related to this is that the word galaxy actually comes from the Greek word, galactos
for milk! The Latin version of Milky Way is Via Lactea, with "Via" meaning "Way" or "Road" and "Lactea"
meaning "Milk"
As we mentioned, Galileo discovered that the Milky Way is made of dim stars, but what about its shape?
How can you tell the shape of something if you're inside it? In the late 1700s, astronomer Sir William
Herschel addressed this question. Herschel reasoned that if the Milky Way was a sphere, we should see
numerous stars in all directions. So, he and his sister Caroline counted the stars in more than 600 areas
of the sky. They found that there were more stars in the directions of the band of the Milky Way than
above and below. Herschel concluded that the Milky Way was a disk-shaped structure. And because he
found about the same numbers of stars in all directions along the disk, he concluded that the sun was
near the center of the disk.
Harlow Shapely was involved in a great debate about the nature of spiral nebulae (faint patches of light
visible in the night sky). He believed that they were "island universes," or galaxies outside the Milky
Way. Another astronomer, Heber Curtis, believed that spiral nebulae were part of the Milky Way. Edwin
Hubble's observations of Cepheid variables finally settled the debate -- the nebulae were indeed outside
the Milky Way.
Edwin Hubble studied galaxies and classified them into various types of elliptical and spiral galaxies.
According to Edwin Hubble's classification system, the Milky Way is a spiral galaxy, although more
recent mapping evidence indicates that it may be a barred spiral galaxy. The Milky Way has more than
200 billion stars. It's approximately 100,000 light years in diameter, and the sun is located about 28,000
light years from the center. If we look at the structure of the Milky Way as it would appear from the
outside, we can see the following parts:
How can we see the Milky Way if we are inside it?
1. Galactic disk: This is where most of the Milky Way's stars are located. The disk is made of old
and young stars, as well as vast amounts of gas and dust. Stars within the disk orbit the galactic
center in roughly circular orbits. (Gravitational interactions between the stars cause the circular
motions to have some up-and-down motion, like horses on a merry-go-round). The disk itself is
broken up into these parts: Nucleus:The center of the disk Bulge: This is the area around the
nucleus, including the immediate areas above and below the plane of the disk. Spiral
arms: These areas extend outward from the center. Our solar system is located in one of the
spiral arms of the Milky Way.
2. Globular clusters: A few hundred of these are scattered above and below the plane of the disk.
Globular clusters orbit the galactic center in elliptical orbits in which the directions are randomly
scattered. The stars in the globular clusters are much older stars than those in the galactic disk,
and there's little or no gas and dust.
3. Halo: This is a large, dim, region that surrounds the entire galaxy. The halo is made of hot gas
and possibly dark matter.
All of these components orbit the nucleus and are held together by gravity. Because gravity depends
upon mass, you might think that most of a galaxy's mass would lie in the galactic disk or near the center
of the disk. However, by studying the rotation curves of the Milky Way and other galaxies, astronomers
have concluded that most of the mass lies in the outer portions of the galaxy (like the halo), where there
is little light given off from stars or gases.
The Milky Way's gravity acts on two smaller satellite galaxies called the Large and Small Magellanic
Clouds (named after Ferdinand Magellan, the Portuguese explorer). They orbit below the plane of the
Milky Way and are visible in the Southern Hemisphere. The Large Magellanic Cloud is about 70,000 light
years in diameter and 160,000 light years away from the Milky Way. Astronomers think that the Milky
Way is actually siphoning off gas and dust from these satellite galaxies as they orbit.
The center of the Milky Way is in the constellation Sagittarius,