ca 3.08 the milky way universe

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THE MILKY WAY UNIVERSE

Cosmic Adventure 3.08


The Place for the Stars

After the popularization of Copernicus heliocentric concept, the question naturally pop up was: “Where do the stars belong?”


The Milky Way!Photo by European Southern Observatory (ESO)


The Milky Way

If you look up the sky at night, far away from other lights such as bright cities, you’ll be able to see a beautiful streak of light across the sky. That’s the Milky Way. It is the groups of stars of which the sun is one.

There is no written record of how the Milky Way was noticed. But since it is there easily picked up by the naked eye, it must have also been familiar with our ancestors, long, long time ago.


The Name of the Milky Way

There were different names and accounts for the Milky Way in different cultures.

For example, Ancient Armenian mythology called the Milky Way the “Straw Thief’s Way”.

The Cherokee folktale called it the “Way the Dog Ran Away”.

Peoples in Eastern Asia named this hazy band of stars the "Silvery River" of Heaven.

Egyptian mythology described the Milky Way was as a pool of cow's milk.

Etc. etc.

You can find a great variety of these names in Wikipedia.

But perhaps the most popular explanation for the name was proposed by the ancient Greeks, although the original records were lost in history.


Hera’s Spilled Milk

The legend said that Zeus (Jupiter) wished to immortalize the infant Hercules (Heracles). He put the baby to his sleeping wife Hera's (Juno’s) breast so the baby could be nursed secretly. But Hera did not like the baby, probably because she knew that it was just another result of Zeus’ affairs. When Hera woke up and tried to pull away, her breast milk spurted into the night sky and created the Milky Way.


The Formation of Milky Way


According to Aristotle

According to great Greek philosopher Aristotle (384-322 BC), the Milky Way was the spot “where the celestial spheres came into contact with the terrestrial spheres.”

In ancient Greek time, there was no telescope. It was hard to say if it was right. It was only in the early 1600s, two thousand year later, the idea began to change


The Galilean Telescope

One of the greatest things Galileo had done that the other astronomers did not was the introduction of the telescope into astronomy.

The telescope was not invented by Galileo. It had long been in existence as early as the 13th century. In 1608, the Dutch spectacle maker Hans Lippershey began to make telescope that attracted attention. In 1909, Galileo heard of the invention. He constructed his own telescope and improved it to 30 time magnification.


First Powered Eyes on the Sky

Galileo Galilei began to use his telescope to observe the heavens in 1609. This was the first time in history when a human being set his eye on the universe through a telescope.

Many of the new things revealed by the invention were extremely disturbing. There were craters on a supposedly perfectly spherical moon; many moons circling Jupiter. With the ever improving power of his telescope, Galileo was able to see that the Milky Way was made up of countless stars.


The Milky Disk

In 1750 the English astronomer and mathematician Thomas Wright(1711-1786), speculated that the that the Milky Way was a large collection of stars held together by gravity. This huge number of stars rotate body around each other, working like the solar system, only on a much larger scale. The resulting flat disk of stars can be seen as a band on the sky from our point of view on earth.


Hypothesis of the Universe

In his book “An original theory or new hypothesis of the Universe published in 1750, Wright explained the appearance of the Milky Way as "an optical effect due to our immersion in what locally approximates to a flat layer of stars“, thus becoming the first man to define the shape of the Milky Way.


Measuring the Milky Way

From 1784 to 1785, the German-Anglo astronomer William Herschel (1738-1822) and his sister Caroline Herschel (1750-1848), were trying to survey the Milky Way for a full map of the stars.

William and his sister Caroline working on a mirror.


The Entire Universe

In 1785 the Herschels completed in making a complete map of the Milky Way. In size, this Milky Way is a huge universe. 100 - 180 kilo light-years in diameter. 2 kilo light-years in thickness. The sun is the bright dot near the middle.


Conelius Kapteyn

From 1901-1922, the Dutch astronomer, Jacobus ConeliusKapteyn (1851-1922), made extensive star counts from photographic plates.


~3 𝑘𝑝𝑐

~173 𝑘𝑝𝑐 ≈ 40,000 𝑙𝑖𝑔ℎ𝑡 𝑦𝑒𝑎𝑟𝑠

Kapteyn’s Universe Kapteyn succeeded in making a modern version of Herschel's Milky Way model with more accuracy and star counts. The sun is slightly off the center of the Milky Way.

1 𝑘𝑝𝑐= 1000 𝑝𝑐= 1 𝑘𝑖𝑙𝑜𝑝𝑎𝑟𝑠𝑒𝑐


The Size of our Universe

A light year is the distance covered by light in one year and light travels at a speed of 300,000,000 meters a second. So the resulted diameter is just huge beyond our imagination.

Within this confines, we may find 200 to 400 billion stars.


Harlow Shapley

In 1915, the American astronomer Harlow Shapley (1885-1972), was working with the then world’s most powerful 60 inch (1.5 meter) telescope at Mount Wilson.

Shapley, like most astronomers of the time, still thought that the Milky Way was all there was to the Universe. All other nebulae were relatively nearby objects and were merely patches of dust and gas in the sky.


Harlow Shapley’s Universe

Shapley succeeded in measuring and constructing an overall picture of the Milky Way galaxy, showing also the position of the solar system. This was supposed to be the first complete picture of what is believed to be our entire universe.

Our sun is about here!

About 27,000 light-years from the Galactic centre


Our Universe

Although familiar, it took thousands of years for human to understand what he was looking at. It was until 1750 that its shape was established by Thomas Wright. Since then up to the early 20th Century, people including scientists and astronomers believed that the Milky Way in which we lived, was the only galaxy in the Universe.


HUBBLE DISCOVERED A NEW UNIVERSE

To be continued in Cosmic Adventure 3.09

ca 3.08 the milky way universe

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