♥♥♥ . . .GALAXY. . .♥♥♥

The Universe within 50000 Light Years
The Milky Way Galaxy

About the Map

This map shows the full extent of the Milky Way galaxy - a spiral galaxy of at least two hundred billion stars. Our Sun is buried deep within the Orion Arm about 26 000 light years from the centre. Towards the centre of the Galaxy the stars are packed together much closer than they are where we live. Notice also the presence of small globular clusters of stars which lie well outside the plane of the Galaxy, and notice too the presence of a nearby dwarf galaxy - the Sagittarius dwarf - which is slowly being swallowed up by our own galaxy.

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Additional Maps
	A Map of the Milky Way Here is another map of the Milky Way viewed from above. This page also explains what scientific data there is for the spiral structure of our galaxy.
	A Galactic Sky Chart This is an all-sky plot of the 9000 brightest stars, plotted in galactic coordinates, and showing all of the constellations in the sky.

Data and Catalogs
	Globular Clusters Large galaxies are surrounded by a halo of tight spherical clusters of stars known as globular clusters. There are roughly 150 known globular clusters around our galaxy, and here is a list of them.

The Sagittarius Dwarf Galaxy

This dwarf galaxy is the nearest galaxy to our own. However, it was only discovered as recently as 1994. It lies on the far side of the galaxy from us and is heavily obscured by the intervening gas, dust and stars. It is approximately 78000 light years away and about 10000 light years in diameter. It is orbiting our galaxy in a period of about 1 billion years but it cannot be expected to last much longer, in a few hundred million years it will be ripped apart by our own galaxy. It contains about one hundred million stars. It also lies in roughly the same position as the globular cluster M54 but whether this globular cluster is actually part of the dwarf galaxy is unclear.

Galactic Cannibalism

The Sagittarius Dwarf Galaxy will probably not be the first galaxy that has been 'eaten' by our galaxy. The Sloan Digital Sky Survey for instance report that outside of the Galaxy there are huge clumps of stars that appear to be the remains of smaller galaxies that were ripped apart by the Milky Way more than a billion years ago. The distribution of these stars shows at least two clumps that are several thousand light years in size and more than 100 000 light years from the center of the Galaxy.

The Galactic Plane

Above - An all-sky plot of the 25000 brightest, whitest stars (B-V<0)>

Below - An infra-red view towards the centre of our Galaxy from the Two-Micron All Sky Survey. Our view of the Milky Way is much better in infra-red light. Visible in this image are the huge clouds of dust which block our view of the Galaxy in visible light. The Sagittarius Dwarf galaxy is also very dimly visible in this picture extending downwards from the left side of the bulge.

The earth's layers.

Image courtesy of
Lawrence Liverm

In 1970 Russian geologists started drilling into the Kola Peninsula, near Finland, hoping to learn more about Earth’s enigmatic insides. After 22 years of digging, work had to stop when the crust turned gooey under the drill bit; at 356 degrees Fahrenheit, the underground rock was much hotter than expected at that depth. The result of the scientists’ grand effort: a tunnel as wide as a cantaloupe extending all of 7.6 miles down.

The Kola borehole is by far the deepest one ever dug, yet it reaches a mere 0.2 percent of the way to the core. The rest of Earth’s interior remains as frustratingly out of reach as it was three centuries ago, when astronomer Edmond Halley suggested that our planet was hollow and filled with life. His ideas seem laughable today, but the truth is, when it comes to the inner Earth, no one knows anything for sure. Might a massive crystal sit at the center? What about a natural nuclear reactor? Are we so sure that the textbook diagram of the Earth sliced open, with nested layers of yellow, orange, and red, reflects reality?

The questions are so compelling that they inspired one geophysicist to draw up blueprints for a journey to the center of Earth. Nobody is doing it just yet; it would require cracking open the ground and pouring in thousands of tons of liquid metal. But that and other far-fetched ideas may inspire the ambitious projects necessary to catch a glimpse of the core—a place just 3,950 miles below our feet and yet, in many ways, less accessible than the edge of the visible universe, 13.8 billion light-years away.

ore National Labs

♥♥♥...layers of the lithosphere...♥♥♥

Another Diagram of the Inside Parts of Earth

If you could slice the Earth in half, you would see four layers: the crust, the mantle, the inner core, and the outer core. Each layer is made of different materials, has a different density, and has a different thickness. The Crust The crust is the top layer. Compared to the other layers, it is very thin. The crust varies from 5 to 70 kilometers in thickness. The crust includes rocks, minerals, and soil. There are two kinds of crust: continental and oceanic. The crust is made of many types of rocks and hundreds of minerals. These rocks and minerals are made from just 8 elements: Oxygen (46.6%), Silicon (27.72%), Aluminum (8.13%), Iron (5.00%), Calcium (3.63%), Sodium (2.83%), Potassium (2.70%) and Magnesium (2.09%). The oceanic crust has more Silicon, Oxygen, and Magnesium. The continental crust has more Silicon and Aluminum. The Mantle Directly below the crust is the mantle. The mantle makes up the largest volume of the Earth's interior. It is almost 2900 kilometers thick and comprises about 83 % of the Earth's volume. It has two parts, an upper layer and a lower layer. The crust and upper mantle form the brittle upper layers of the Earth's interior called the Lithosphere. The upper mantle is about 670 kilometers in depth. It is brittle and less dense. It is thought to be made of peridotite, a rock made from the minerals olivine and pyroxene. The rocks in the upper mantle are more rigid and brittle because of cooler temperatures and lower pressures. The Lower Mantle is much thicker and more dense. It is 670 to 2900 kilometers below the Earth's surface. This layer is hot and plastic. The higher pressure in this layer causes the formation of minerals that are different from those of the upper mantle. brittle - breaks easily plastic - can change shape without breaking The Outer and Inner Core The region beneath the mantle is called the core, and is made of two parts, a liquid outer core that is about 2250 km thick and a solid inner core which is 1220 km thick. The core is mostly made of iron, with a little bit of nickel. The outer core is at 1,800 - 3,200 miles (2,890-5,150 km) below the earth's surface. The temperature in the outer core is about 7200 - 9032 ºF (4000-5000ºC). The molten, liquid iron in the outer core is important because it helps create Earth's magnetic field. The inner core is 3,200 - 3,960 miles (5,150-6,370 km) below the earth's surface and mainly consists of iron, nickel and some lighter elements (probably sulphur, carbon, oxygen, silicon and potassium). The temperature in the inner core is about 9032 - 10832 ºF (5000-6000 ºC). Because of the high pressure, the inner core is solid. The outer core and the inner core together cause the earth's magnetism. Because the earth rotates, the molten outer core spins. The inner core does not spin because it's solid. This is what causes the earth's magnetism. Earth's magnetic north and magnetic south are NOT at the poles. Earth's "magnetic north" is in northern Canada and "magnetic south" is north of Antarctica and south of Australia. Another strange fact about Earth's magnetic poles is that they reverse every few million years. (North becomes south and south becomes north. This is called a "geomagnetic reversal." Scientists still do not fully understand why geomagnetic reversals happen.

Metamorphic Rocks

Pictures of Foliated and Non-Foliated Rock Types

Metamorphic rocks have been modified by heat, pressure and chemical process usually while buried deep below Earth's surface. Exposure to these extreme conditions has altered the mineralogy, texture and chemical composition of the rocks. There are two basic types of metamorphic rocks: 1) foliated metamorphic rocks such as gneiss, phyllite, schist and slate which have a layered or banded appearance that is produced by exposure to heat and directed pressure; and, 2) non-foliated metamorphic rocks such as marble and quartzite which do not have a layered or banded appearance. Pictures and brief descriptions of some common types of metamorphic rocks are provided below.

Metamorphic Rock Types Menu
Amphibolite	Gneiss	Hornfels	Marble
Phyllite	Quartzite	Schist	Slate

Sedimentary Rocks

Picture Gallery of the Most Common Rock Types

Sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks: 1) clastic sedimentary rocks such as breccia, conglomerate, sandstone and shale, that are formed from mechanical weathering debris; 2) chemical sedimentary rocks such as rock salt and some limestones, that form when dissolved materials precipitate from solution; and, 3) organic sedimentary rocks such as coal and some limestones which form from the accumulation of plant or animal debris. Pictures and brief descriptions of some common sedimentary rock types are shown below.

Sedimentary Rock Types Menu
Breccia	Chert	Coal	Conglomerate	Iron Ore
Limestone	Rock Salt	Sandstone	Shale	Siltstone

Igneous Rocks

Pictures of Intrusive and Extrusive Rock Types

Igneous rocks are formed from the solidification of molten rock material. There are two basic types: 1) intrusive igneous rocks such as diorite, gabbro, granite and pegmatite that solidify below Earth's surface; and 2) extrusive igneous rocks such as andesite, basalt, obsidian, pumice, rhyolite and scoria that solidify on or above Earth's surface. Pictures and brief descriptions of some common igneous rock types are shown below.

Igneous Rock Types Menu
Andesite	Basalt	Diorite	Gabbro	Granite	Obsidian
Pegmatite	Peridotite	Pumice	Rhyolite	Scoria	Tuff